HETEROCYCLES

Paper | Regular issue | Vol. 78, No. 2, 2009, pp. 369-387
Received, 29th July, 2008, Accepted, 19th September, 2008, Published online, 25th September, 2008.
DOI: 10.3987/COM-08-11508

■ Studies on the Amino-Heck Reactions of Unsaturated Ketones O-Phosphinyloximes for the Preparation of Substituted Pyridines

Jia-Liang Zhu,* Yi-Lin Su, Yu-Hui Chan, I-Chia Chen, and Chuan-Chen Liao

Department of Chemistry, National Dong-Hwa University, Hualien 974, Taiwan, R.O.C.

Abstract

The amino-Heck cyclization process has been applied into a range of γ,δ-unsaturated ketone O-diethylphosphinyloximes 1 and δ,ε-unsaturated ketone O-diethylphosphinyloximes 7. Under the specific catalytic conditions developed by us, these substrates were found to preferentially undergo the 6-endo cyclization to give the formation of 2-substituted pyridines 3 and substituted methylpyridines 8, respectively, in moderate to good yields. Besides, several interesting aspects on the effects of phosphinyl groups, solvents, bases and molecular sieves on the regioselectivity of the cyclization of 1 have also been realized.

INTRODUCTION
The palladium-catalyzed intramolecular Heck-type cyclization of unsaturated ketone oxime derivatives provides a conceptually powerful means for the preparation of aza-heterocycles.1 According to literatures, a great variety of heterocyclic compounds such as pyrroles,2-5 pyridines,6 isoquinolines,6b azaazulenes,7 and imidazoles,8 has been achieved via this approach. For instance, there are several types oxime derivatives including γ,δ-unsaturated ketone O-pentafluorobenzoyloximes1,2 and O-methylsulfonyloximes,2 3-butynyl 4-(methoxycarbonyl)-3-butynyl phenyl ketone O-pentafluorobenzoyloximes5 and 3,3-difluoroallyl ketone O-pentafluorobenzoyloximes3 were reported to undergo the cyclization under the catalysis of Pd(0) complexes to afford substituted pyrroles. As a complement to these existing methods, we have recently developed a novel amino-Heck protocol for the synthesis of substituted pyrroles by utilizing the readily prepared γ,δ-unsaturated ketone O-diethylphosphinyloximes 1 as the substrates.9 In addition to their pronounced stability and the efficiency for the cyclization, these precursors also exhibited the interesting regioselective tendency. For example, during the initial model studies with phenyl-4-penten-1-one O-diethylphosphinyloxime (1a), we discovered that under the reaction conditions of Pd(PPh3)4/Et3N/DMF, which were commonly employed for other types oxime derivatives,1,2,8 the reaction occurred preferentially in a 6-endo fashion to give the formation of 2-phenylpyridine (3a) in 46% yield. The desired product 2a arising from the 5-exo cyclization was only formed in 16% yield (Scheme 1). After screening several reaction conditions, we found that 2a could be achieved in almost quantitative yield (90%) by treating 1a with Pd(PPh3)4 and 1,8-diaza-bicyclo[5.4.0]undec-7-ene (DBU) in CH3CN. These results suggest that with this type of oxime derivatives, the control of the regioselectivity of the cyclization can be attended to some extent with the adjustment of the catalytic conditions. We then applied the reaction conditions favouring the 5-exo cyclization [Pd(PPh3)4/DBU/CH3CN] into a number of γ,δ-unsaturated O-diethylphosphinyloximes, to allow the generation of a series of 2-substituted 5-methylpyrroles and several indoles in good to high yields with no trace of by-products resulting from Beckmann rearrangement, a competing side process being frequently encountered by other types oxime derivatives.1a

Similarly to other types of oxime derivatives, the cyclization of γ,δ-unsaturated ketone O-phosphinyloximes 1 should be initiated by the oxidative addition of 1 to Pd(0) to generate an alkylideneaminopalladium(II) intermediate A (Scheme 2). The subsequent 5-exo or 6-endo cyclization affords the σ-complex species B or C, respectively. From which, the substituted pyrroles 2 or pyridines 3 can be released through β-elimination followed by isomerization or oxidative dehydrogenation.10
In the previous studies we did not further pursue the more favorable catalytic conditions for the 6-endo cyclization. Nevertheless, it should be noted that the formation of 3a observed in our cases is quite unusual, because all of the γ,δ-unsaturated ketone oxime derivatives previously documented, differing from 1a only by the functional groups on the nitrogen atom, were revealed to undergo the 5-exo

cyclization exclusively under the same reaction conditions to afford 2a as the sole cyclization products.1,2 On the other hand, for the substrates including O-pentafluorobenzoyloximes6 and O-acetyloximes10,11 used for preparing pyridines, a β- acetoxy, a β-methoxy or an α,β-unsaturated functionality was shown to be indispensable for the 6-endo cyclization in addition to the γ,δ-double bond. These substrates, as outlined in Figure 1 (4-6) are obviously more difficult to be accessed compared with 1, and for some of them, the yields of the cyclization reactions are extremely low. For these reasons and due to the broad synthetic and biological utilities of the pyridinyl compounds,12 we envisaged that it would be valuable if we could turn 1 into the useful precursors for the generation of pyridines. To this end, an extensive investigation was carried out, which eventually allowed us to find a catalytic system to further promote the 6-endo cyclization of 1 on the basis of what we had already accomplished in the previous studies. With its application, the synthesis of a range of 2-substituted pyridines was achieved mostly in good yields. In addition, we also applies the hitherto unexplored δ,ε-unsaturated ketone O-diethylphosphinyloximes to the cyclization process for the preparation of substituted methyl pyridines. Herein, we wish to report the details of these studies.

RESULTS AND DISCUSSION
We speculated that the unusual regioselectivity observed for 1a under the conditions of Pd(PPh3)4/Et3N/DMF (Scheme 1) might be attributed to the unique coordination nature and/or the steric effect of the phosphinyl group. With true reason(s) being obscure for us, we began our investigation by surveying the substitution effect of phosphinyl groups on the regioselectivity. Accordingly, substrates 1b and 1c, with a bulkier diphenylphosphinyl and a smaller dimethylphosphinyl groups to replace the diethylphosphinyl moeity of 1a, were prepared following the procedure previously developed for the preparation of 1a.9 As shown in Scheme 3, treatment of the O-hydroxyoxime intermediate derived from benzaldehyde in three synthetic steps with diphenyl chlorophosphate [ClPO(OPh)2] and dimethyl chlorophosphate [ClPO(OMe)2], respectively, in the presence of NaH readily led to the formation of 1b and 1c in high yields. Since the stereogeometry of 1a had been proven to have no influence on the regioselectivity of the cyclization,9 both 1b (E/Z = 78:22) and 1c (E/Z = 90:10) were used as the unseparated isomeric mixtures13 for the subsequent investigation. The results of the cyclization reactions of 1a-c under the same catalytic conditions are given in Table 1.

Among three substrates, 1b was shown to be mostly in favour of the 5-exo cyclization to give the highest ratio between 2a and 3a (64:36) (Table 1, entry 2). This result can presumably be rationalized in term of a steric effect, i.e. a bulky diphenylphosphinyl group being prone to adopt the exo position in a cyclic transition state (Scheme 2, intermediate B) in order to minimize the conformational strain. However, what was not clear from these experiments was the same 3a/2a ratios obtained from 1a and 1c (74:26) (Table 1, entries 1 and 3). The assumption that the steric difference between the diethylphosphinyl and the dimethylphosphinyl groups was not sufficiently large enough to make the difference in regioselectivity may somewhat account for this observation. Given the similar regioselectivity, reactivity and the preparative manner, the unsaturated O-diethylphosphinyl oximes should be more appropriate to be used as substrates than the corresponding O-dimethylphosphinyl oximes with regard to the much higher cost of ClPO(OMe)2 than that of ClPO(OEt)2. Consequently, we used O-diethylphosphinyl oximes as the substrates for the following experiments.
After the aforementioned investigation, we then turned our attention to identifying reaction conditions that would enhance the desired 6-endo cyclization. The previous experiments had already demonstrated that when accompanied with Pd(PPh3)4 and Et3N, DMF was superior to CH3CN as a solvent in respect of offering higher yield of 3a.9 On the basis of these results, several other solvent systems including tetrahydrofurane (THF), 1,4-dioxane, dimethyl sulfoxide (DMSO) and N,N-dimethyl acetamide (DMA) were investigated with 1a. As shown in Table 2, the reactions carried out with THF and 1,4-dioxane proceeded sluggishly to afford only trace amounts of 3a (5% and 6%) and 2a (8%), along with recovered 1a in 40% and 52% yields even after prolonged reaction times (Table 2, entries 1 and 2). Moreover, the use of DMSO also turned out to be unsuccessful in giving no detectable formation of 3a and 2a, and 80% of intact 1a (entry 3). The reaction in DMA gave a comparable 3a/2a ratio (70:30) with that obtained from DMF (Table 1, entry 1), but a much lower yield of 3a (Table 2, entry 4). These disappointing results led us to look for other variants to modify reaction conditions.

Having proved DMF to be not displaceable for the 6-endo cyclization, we next evaluated a range of bases by using 1a as the substrate and Pd(PPh3)4 as the catalyst. As illustrated in Table 3, when potassium carbonate and acetate were employed, the reactions displayed some preference for the 6-endo cyclization to give 3a and 2a in the ratios of 55:45 and 64:36, respectively, but the yields of 3a were only modest (Table 3, entries 1, 2). Furthermore, we observed that the reaction performed with potassium t-butoxide only afforded a trace amount of 3a (5%) as the only detectable cyclization product (entry 3), and the starting material easily decomposed within a short period of time (＜10 min) to yield a complex mixture under such strong basic conditions. The use of DBU produced only 9% of 3a as the minor regioisomeric product together with 27% of 2a (entry 4). In the case of 1,4-diazabicylo[2,2,2]octane (Dabco) (entry 5), the desired 3a was also formed in low yield (19%) but as the major cyclization product (3a:2a 59:41). The use of pyridine resulted in the relative higher 3a/2a ratio in comparison with that given in entry 5, but the yield of 3a was still only moderate (29%) (entry 6). Finally, we were gratified to discover that with the employment of diisopropylethyl amine (DIPEA) as the base, the yield of 3a could be significantly improved to 71% (entry 7), higher than those obtained from the other types of oxime derivatives.6,11 Meanwhile, the competing 5-exo cyclization was also suppressed to a large extend as reflected by the ratio between 3a and 2a (83:17). Thus, the results given in entry 7 represented the best ones obtained from 1a in terms of both yield of 3a and 3a/2a ratio.

In most cases listed in Table 3, we also noted the formation of 1-phenyl-pent-4-en-1-one (10-47% and 10% for entry 7) arising from the hydrolysis of 1a. According to the literature reports,9,14 such type of side reactions can be minimized in the presence of molecular sieves. To our surprise, the addition of molecular sieves (MS) 4 Å to the reaction under the conditions of Pd(PPh3)4/DIPEA/DMF caused no apparent reduction of the ketone but a dramatic change in regioselectivity to give 2a in 29% yield and a trace amount of 3a (~ 3%) (3a:2a 9:91). To verify if this 5-exo promoting effect of MS was common, we combined a few above-described catalytic conditions [Pd(PPh3)4/Et3N/DMF (Table 1, entry 1), Pd(PPh3)4/K2CO3/DMF (Table 3, entry 1) and Pd(PPh3)4/DBU/DMF (Table 3, entry 4) ] with the use of MS and applied to 1a. In contrast to the examples given in Table 1 and 3, these reactions were all overwhelmingly dominated by the 5-exo cyclization with MS, resulting in the drastically decreased ratios between 3a and 2a (Table 4, entries 2-4). The underlying causes of the above-mentioned base and MS effects on the regiochemistry are still not fully understood for us and will be subjected to our further exploration.

The reaction conditions indicated in entry 7 of Table 3 were subsequently applied into a range of γ,δ-unsaturated ketone O-diethylphosphinyloximes with various substitutions (1d-i), which were all readily prepared from the corresponding aldehydes following the procedure given in Scheme 3. Among which, 1d-f and 1h-i were previously used for the preparation of the pyrroles,9 while 1g were synthesized for the first time.13 As shown in Table 5, under the reaction conditions, the substrates possessing the aromatic (1d, 1f-g) and heteroaromatic (1e) substituents cyclized preferentially in a 6-endo pathway to give rise to the 2-substituted pyridines 3d-g as the major products in good yields (50-61%) (entries 1-4). These compounds could be easily separated from pyrrole byproducts (5-16%) by flash chromatography on basic aluminium oxide. We additionally observed that the electronic natures of the 4-substituents on the phenyl moiety seemed to have no effect on the 6-endo cyclization as illustrated by the almost equal yields of 3f and 3g (entries 3 and 4). However, the current catalytic system appeared to be less applicable to the cycloalkyl or alkyl substituted substrates. The cyclization reactions of 1h and 1i did not show strong regioselective bias to furnish pyridines 3h and 3i in 26% and 20% yield, respectively (entries 5 and 6), together with the corresponding pyrroles in almost equal yields (23% and 18%, respectively).
To further extend the utility of the cyclization process, we also investigated the possibility of using the homologated δ,ε-unsaturated ketone O-diethylphosphinyloxime precursors for the generation of substituted methylpyridines. It was expected that by using these hitherto unexplored substrates, the complete control of the regioselectivity of the cyclization could be achieved. At first, several δ,ε-unsaturated ketone O-diethylphosphinyloximes 7a-e were prepared in the analogous manner as for synthesizing 1, except using pent-4-enylmagnesium bromide for the first addition step (Scheme 4).13

We then explored the suitable cyclization conditions by using 7a as the substrate. However, with the extension of one carbon unit, 7a was found to be more difficult to cyclize than 1a under most of the reaction conditions given in Table 3 (entries 1 and 2, 4-7) and Table 1, to provide only small amounts of 2-methyl 6-phenylpyridine (8a) (< 10%) plus 60-86% of 1-phenyl-hex-5-en-1-one resulting from the hydrolysis. After several unsuccessful attempts, we discovered that the addition of 5 equivalents of tetrabutylammonium chloride [(n-Bu)4NCl] to the reaction under the catalytic system of Pd(PPh3)4 (0.2 eq)/Et3N (5 eq)/MS 4 Å/DMF could result in the generation of 8a in 50 % yield. Based on this, it was further found that the yield of 8a could be improved to 63% when (n-Bu)4NCl was replaced by tetrabutylammonium bromide [(n-Bu)4NBr]. The reaction conditions of Pd(PPh3)4 (0.2 eq)/Et3N (5 eq)/MS 4 Å/DMF/(n-Bu)4NBr (5eq) were then applied to 7b-e and the results are compiled in Table 6. For 7b-d bearing the aryl and heteroaryl substituents, the reactions offered the desired pyridines 8b-d in modest to good yields (36-50%), as well as the ketone byproducts in 26-54% yields (entries 2-4). The relatively low-yielding formation of the pyridine was observed for 7e substituted with an alkyl group. The reaction of which afforded 8e in 21% yield, along with a large amount of the ketone (74%) (entry 5).
The cyclization products 3a, 3d-i and 8a-e were all purified by flash chromatography on basic aluminium oxide and satisfactory spectra (1H, 13C-NMR, IR and HRMS) were obtained for them. For those known compounds (3a, 3d-h, 8a-c), the NMR data were found to agree well with those reported in the literature.15

In conclusion, we have demonstrated that the regioselectivity of the amino-Heck reactions of γ,δ-unsaturated ketone O-diethylphosphinyloximes, particularly for those bearing aromatic or heteroaromatic substituents, could be deliberately controlled to a large extend with the adjustment of catalytic conditions. Thus, these compounds can serve as the versatile and useful precursors for the preparation of either substituted methylpyrroles or 2-substituted pyridines. Under the catalytic conditions of Pd(PPh3)4/DIPEA/DMF, they were shown to preferentially undergo the 6-endo cyclization to afford 2-substituted pyridines in moderate to good yields. During the course of the studies, several interesting aspects regarding the effects of phosphinyl groups, solvents, bases and molecular sieves on the regioselectivity have also been observed, and the further investigation to disclose the true reasons behind these observations should be necessary. The synthetic scope of the protocol has been further expanded to the synthesis of substituted methylpyridines form δ,ε-unsaturated ketone O-diethylphosphinyloximes, thereby providing a new entry into this type of heterocyclic compounds.

EXPERIMENTAL
All of starting materials were obtained from commercial suppliers and used without further purification. Reactions were performed under an atmosphere of Nitrogen. Tetrahydrofuran was distilled from sodium-benzophenone, and dichloromethane, triethylamine, dimethylformamide, 1,4-dioxane, dimethyl sulfoxide and N,N-dimethylacetamide were distilled from calcium hydride before use. TLC analysis was carried out on Merck 25 DC-Alufolien Kieselgel 60F254 aluminum-backed plates visualised by using UV light, or by means of ethanolic solution of vanillin (5%) with sulphuric acid (5%). All of the compounds were purified by flash chromatography on Merck Art.9385 Kiesegel 60 silica gel (230-400 mesh) or Brockmann I basic aluminum oxide (~150 mesh). NMR spectra (1H, 13C) were recorded on a Bruker 400 spectrometer using deuteriochloroform (CDCl3) as solvent. Chemical shifts measurements are reported in delta (δ) units. Splitting patterns are described as singlet (s), doublet (d), triplet (t), quartet (q) or multiplet (m). Coupling constants (J) are reported in Hertz (Hz). Infrared (IR) spectra were recorded on an IR-FT JASCO 410 spectrophotometer (neat) and resonances are reported in wave numbers (cm-1). High resolution mass spectra (HRMS) were determined by using a A. E. I. model MS-50 mass spectrometer in fast atom bombardment (FAB) or electron impact (EI) mode. Elemental analyses were performed on Perkin Elmer 240C apparatus.
General Procedure for the Preparation of γ,δ- and δ,ε-Unsaturated Phosphinyl Oxime Substrates from the Corresponding Ketones; 1-Phenyl-4-penten-1-one O-diethylphosphinyloxime (1a): To a solution of 1-phenyl-4-penten-1-one (317 mg, 1.98 mmol) in MeOH (8 mL), NaOAc (179 mg, 2.18 mmol) and NH2OH·HCl (152 mg, 2.18 mmol) were successively added. The reaction mixture was stirred at 20 °C for 6 h, then diluted with CH2Cl2 (30 mL) and washed sequentially with H2O (2 x 10 mL) and saturated NaCl aq soln (10 mL). After dried over anhydrous Na2SO4 and concentrated at ambient temperature, the crude hydroxyoxime was dissolved in anhyd THF (13 mL). The solution was cooled to 0 °C and added with NaH (60%, 95 mg, 2.38 mmol). Stirring was continued at 0 °C for another 20 min under N2, before (EtO)2POCl (0.61 ml, 3.96mmol) was added dropwise in 3 min. The reaction mixture was allowed to warm to rt and continued to stir for 12 h. After concentration, the crude residue was subjected to chromatographic purification on silica gel (hexane-EtOAc 5:1, 1:1) to afford 1a as a mixture of two isomers (E/Z = 87:13) (513 mg, 83%).
IR (neat): 2983 , 1276 , 1034 , 919 cm-1; 1H NMR (400 MHz, CDCl3): Z-isomer : δ 1.30 (td, J1 = 7.1 Hz, J2 = 0.7 Hz , 6H), 2.24 (dt, J1 = 7.4 Hz, J2 = 7.2 Hz , 2H), 2.74 (broad t, J = 7.6 Hz, 2H), 4.10-4.19 (m, 4H), 4.96-5.09 (m, 2H), 5.70-5.83 (m, 1H), 7.31-7.37 (m, 2H), 7.37-7.48 (m, 3H) ppm; E-isomer: δ 1.38 (td, J1 = 7.1 Hz, J2 = 0.7 Hz , 6H), 2.32 (dt, J1 = 7.8 Hz, J2 = 7.3 Hz , 2H), 2.95 (broad t, J = 7.9 Hz, 2H), 4.21-4.34 (m, 4H), 5.00 (broad d, J = 11.5 Hz, 1H), 5.04 (broad d, J = 17.1 Hz, 1H), 5.82 (dm, J = 17.1 Hz, 1H), 7.37-7.45 (m, 3H), 7.65 (broad d, J = 7.8 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3): Z-isomer: δ 16.1 (d, J = 6.1 Hz), 30.2, 34.7, 64.5 (d, J = 5.5 Hz), 115.8, 127.5, 128.3, 129.6, 132.1, 136.5, 166.9 (d, J = 13.0 Hz) ppm; E-isomer: δ 16.2 (d, J = 6.3 Hz), 27.0, 30.5, 64.6 (d, J = 6.0 Hz), 115.8, 127.1, 128.7, 130.5, 133.6, 136.6, 166.7 (d, J = 13.4 Hz) ppm; HRMS-FAB: m/z [M + H]+ calcd. for C15H23O4NP: 312.1365; found: 312.1357.
1-Phenyl-4-penten-1-one O-diphenylphosphinyloxime (1b):The typical procedure for the preparation of 1a was followed by using ClPO(OPh)2 instead of ClPO(OEt)2. From 210 mg (1.31 mmol) of 1-phenyl-4-penten-1-one, 1b was obtained as a pale yellow oil after flash chromatography on silica gel (hexane-EtOAc 3:1, 1:1, 1:2) (422 mg, E/Z = 78:22, 79%).
IR (neat): 3074, 1687, 1591, 1489, 1442, 1298, 1188, 766, 688 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 2.21 (td, J1 = 7.8 Hz, J2 = 7.3 Hz, 2H), 2.90 (broad t, J = 7.9 Hz, 2H), 4.96 (broad d, J = 9.0 Hz, 1H), 4.99 (broad d, J = 17.3 Hz, 1H), 5.72 (dm, J = 17.3 Hz, 1H) 7.17-7.24 (m, 3H), 7.27-7.53 (m, 10H), 7.63 (broad d, J = 8.1 Hz, 2H) ppm; Z-isomer: δ 2.18-2.26 (m, 2H), 2.76 (broad t, J = 7.5 Hz, 2H), 5.01-5.13 (m, 2H), 5.79-5.93 (m, 1H), 7.15-7.22 (m, 3H), 7.27-7.53 (m, 10H), 7.52 (broad d, J = 8.0Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 27.3, 30.4, 115.9, 120.4 (d, J = 4.7 Hz), 125.5, 127.3, 128.7, 129.8, 130.8, 133.0, 136.3, 150.6 (d, J = 7.3 Hz), 168.0 (d, J = 13.6 Hz) ppm; Z-isomer: δ 30.0, 34.7, 115.7, 119.8 (d, J = 4.1 Hz), 125.4, 127.3, 128.9, 129.6, 129.7, 131.9, 137.0, 150.5 (d, J = 7.3 Hz), 168.2 (d, J = 12.5 Hz) ppm; HRMS-FAB: m/z [M + H]+ calcd. for C23H23O4NP: 408.1365; found: 408.1367.
1-Phenyl-4-penten-1-one O-dimethylphosphinyloxime (1c): The typical procedure for the preparation of 1a was followed by using ClPO(OMe)2 instead of ClPO(OEt)2. From 157 mg (0.98 mmol) of 1-phenyl-4-penten-1-one, 1c was obtained as a yellow oil after flash chromatography on silica gel (hexane-EtOAc 4:1, 2:1) (236 mg, E/Z = 90:10, 85%).
IR (neat): 2954, 1641, 1572, 1444, 1281, 1043, 764, 694 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 2.30 (td, J1 = 7.7 Hz, J2 = 7.2 Hz, 2H), 2.95 (broad t, J = 7.9 Hz, 2H), 3.88 (d, J = 11.1 Hz, 6H), 4.99 (broad d, J = 9.8 Hz, 1H), 5.02 (broad d, J = 17.0 Hz, 1H), 5.80 (dm, J = 17.0 Hz, 1H), 7.35-7.46 (m, 3H), 7.59-7.68 (m, 2H) ppm; Z-isomer: δ 2.21 (td, J1 = 7.6 Hz, J2 = 6.8 Hz, 2H), 2.73 (broad t, J = 7.6 Hz, 2H), 3.78 (d, J = 11.2 Hz, 6H), 4.95-5.06 (m, 2H), 5.70-5.81 (m, 1H), 7.30-7.34 (m, 2H) 7.35-7.46 (m, 3H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 27.0, 30.5, 55.1 (d, J = 6.1 Hz), 115.9, 127.2, 128.7, 130.6, 133.4, 136.5, 167.2 (d, J = 13.2 Hz) ppm; Z-isomer: δ = 30.2, 34.7, 54.9 (d, 6.0 Hz), 127.5, 128.3, 129.7, 131.9, 136.4, 167.3 (d, 12.5 Hz) ppm; HRMS-EI: m/z [M]+ calcd. for C13H18O4NP: 283.0973; found: 283.0979.
1-(2-Naphthalyl)-4-penten-1-one O-diethylphosphinyloxime (1d):The typical procedure for the preparation of 1a was followed; 1-(2-naphthalyl)-4-penten-1-one (120 mg, 0.57 mmol) was used as starting material. Flash chromatography on silica gel (hexane-EtOAc 5:1, 1:1) gave 1d as a yellow oil. Yield: 200 mg (97%) (E/Z = 93:7).
IR (neat): 2982, 1443, 1275, 1165, 1033, 917 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 1.41 (td, J1 = 7.1 Hz, J2 = 0.9 Hz, 6H), 2.39 (td, J1 = 7.8 Hz, J2 = 7.8 Hz, 2H), 3.08 (broad t, J = 7.9 Hz, 2H), 4.23-4.38 (m, 4H), 5.02 (broad d, J = 10.1 Hz, 1H), 5.07 (broad d, J = 17.1 Hz, 1H), 5.87 (dm, J = 17.1 Hz, 1H), 7.50-7.58 (m, 2H), 7.82-7.92 (m, 4H), 8.08 (s, 1H) ppm; Z-isomer: δ 1.30 (td, J1 = 7.0 Hz, J2 = 0.7 Hz, 6H), 2.27 (td, J1 = 7.7 Hz, J2 = 7.5 Hz, 2H), 2.85 (broad t, J = 7.6 Hz, 2H), 4.08-4.24 (m, 4H), 4.98-5.11 (m, 2H), 5.69-5.82 (m, 1H), 7.42-7.52 (m, 2H), 7.79-7.89 (m, 4H), 8.08 (s, 1H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 16.2 (d, J = 6.4 Hz), 26.8, 30.7, 64.7 (d, J = 5.8 Hz), 115.8, 123.9, 126.6, 127.3, 127.5, 127.7, 128.4, 128.7, 131.0, 132.9, 134.3, 136.6, 166.6 (d, J = 13.5 Hz) ppm; HRMS-EI: m/z [M]+ calcd. for C19H24O4NP: 361.1443; found: 361.1446.
1-(4-Pyridinyl)-4-penten-1-one O-diethyl phosphinyloxime (1e): The typical procedure for the preparation of 1a was followed; 1-(4-pyridinyl)-4-penten-1-one (171 mg, 1.06 mmol) was used as starting material. Flash chromatography on silica gel (hexane-EtOAc 1:1, EtOAc) gave 1e as a viscous oil. Yield: 262 mg (79%) (E/Z = 83:17).
IR (neat): 2984, 1595, 1544, 1410, 1274, 1032, 916 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 1.38 (t, J = 7.1 Hz, 6H), 2.31 (td, J1 = 7.8 Hz, J2 = 7.0 Hz, 2H), 2.94 (broad t, J = 7.8 Hz, 2H), 4.19-4.35 (m, 4H), 5.00 (broad d, J = 9.2 Hz, 1H), 5.03 (broad d, J = 17.3 Hz, 1H), 5.78 (dm, J = 17.3 Hz, 1H), 7.53 (d, J = 6.1 Hz, 2H), 8.67 (broad d, J = 6.1 Hz, 2H) ppm; Z-isomer: δ 1.29 (t, J = 7.1 Hz, 6H), 2.18-2.29 (m, 2H), 2.73 (broad t, J = 7.5 Hz, 2H), 4.08-4.19 (m, 4H), 4.92-5.08 (m, 2H), 5.70-5.90 (m, 1H), 7.21 (d, J = 6.1 Hz, 2H), 8.62-8.72 (m, 2H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 16.2 (d, J = 6.3 Hz), 26.4, 30.3, 64.9 (d, J = 5.9 Hz), 116.3, 121.2, 136.0, 141.3, 150.3, 164.9 (d, J = 13.9 Hz) ppm; Z-isomer: δ 16.1 (d, J = 6.0 Hz), 29.8, 34.2, 64.8 (d, J = 6.0 Hz), 116.2, 121.8, 135.9, 140.3, 150.0, 164.8 (d, J = 13.5 Hz) ppm; HRMS-FAB: m/z [M + H]+ calcd. for C14H22O4N2P: 313.1317; found: 313.1318.
1-(4-Methoxyphenyl)-4-penten-1-one O-diethylphosphinyloxime (1f): The typical procedure for the preparation of 1a was followed; 1-(4-methoxyphenyl)-4-penten-1-one (177 mg, 0.93 mmol) was used as starting material. Flash chromatography on silica gel (hexane-EtOAc 5:1, 1:1) gave 1f as a pale yellow
oil. Yield: 257 mg (81%) (E/Z = 70:30).
IR (neat): 2974, 2929, 1606, 1514, 1255, 1032, 922 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 1.37 (td, J1 = 7.1 Hz, J2 = 0.7 Hz, 6H), 2.31 (td, J1 = 7.4 Hz, J2 = 7.2 Hz, 2H), 2.91 (broad t, J = 7.9 Hz, 2H), 3.83 (s, 3H), 4.20-4.31 (m, 4H), 4.99 (broad d, J = 10.0 Hz, 1H), 5.03 (broad d, J = 17.2 Hz, 1H), 5.82 (dm, J = 17.2 Hz, 1H), 6.90 (d, J = 8.9 Hz, 2H), 7.62 (d, J = 8.9 Hz, 2H) ppm; Z-isomer: δ 1.31 (td, J1 = 7.0 Hz, J2 = 0.6 Hz, 6H), 2.22 (td, J1 = 7.6 Hz, J2 = 7.4 Hz, 2H), 2.73 (broad t, J = 7.6 Hz, 2H), 3.83 (s, 3H), 4.11-4.20 (m, 4H), 4.95-5.05 (m, 2H), 5.72-5.89 (m, 1H), 6.91 (d, J = 8.9 Hz, 2H), 7.38 (d, J = 8.9 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 16.2 (d, J = 6.5 Hz), 26.8, 30.7, 55.3, 64.5 (d, J = 5.9 Hz), 114.0, 115.7, 125.9, 128.6, 136.7, 161.5, 166.1 (d, J = 13.2 Hz) ppm; Z-isomer: δ 16.1 (d, J = 6.4 Hz), 30.5, 34.5, 55.3, 64.4 (d, J = 6.0 Hz), 113.6, 124.0, 129.7, 136.6, 160.5, 165.8 (d, J = 12.1 Hz) ppm; HRMS-EI: m/z [M + H]+ calcd. for C16H25O5NP: 342.1470; found: 342.1473.
1-(4-Fluorophenyl)-4-penten-1-one O-diethylphosphinyloxime (1g): The typical procedure for the preparation of 1a was followed; 1-(4-fluorophenyl)-4-penten-1-one (160 mg, 0.90 mmol) was used as starting material. Flash chromatography on silica gel (hexane-EtOAc 6:1, EtOAc) gave 1g as a yellow oil. Yield: 216 mg (73%) (E/Z = 84:16); IR (neat): 3078, 2983, 1641, 1603, 1510, 1277, 1034, 843 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 1.37 (t, J = 7.1 Hz, 6H), 2.28 (td, J1 = 7.8 Hz, J2 = 7.6 Hz, 2H), 2.91 (broad t, J = 7.9 Hz, 2H), 4.18-4.31 (m, 4H), 4.97 (broad d, J = 9.7 Hz, 1H), 5.01 (broad d, J = 17.4 Hz, 1H), 5.78 (dm, J = 17.4 Hz, 1H), 7.06 (tm, J = 8.5 Hz, 2H), 7.64 (dd, J1 = 8.8 Hz, J2 = 5.4 Hz, 2H) ppm; Z-isomer: δ 1.29 (t, J = 7.1 Hz, 6H), 2.19 (td, J1 = 7.6 Hz, J2 = 7.4 Hz, 2H), 2.71 (broad t, J = 7.6 Hz, 2H), 4.08-4.18 (m, 4H), 4.93-5.02 (m, 2H), 5.69-5.81 (m, 1H), 7.04-7.11 (m, 2H), 7.35 (dm, J = 8.7 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 16.2 (d, J = 6.4 Hz), 26.9, 30.5, 64.7 (d, J = 6.0 Hz), 115.8 (d, J = 21.8 Hz), 116.0, 129.2 (d, J = 8.5 Hz), 129.6 (d, J = 3.1 Hz), 136.4, 164.1 (d, J = 251.0 Hz), 165.8 (d, J = 13.4 Hz) ppm; Z-isomer: δ 16.1 (d, J = 6.5 Hz), 30.2, 34.6, 64.6 (d, J = 6.0 Hz), 115.5 (d, J = 21.9 Hz), 115.9, 127.9 (d, J = 3.4 Hz), 129.8 (d, J = 8.5 Hz), 136.3, 163.1 (d, J = 250.1 Hz), 165.7 (d, J = 12.8 Hz) ppm; HRMS-FAB: m/z [M]+ calcd. for C15H21FO4NP: 329.1192; found: 329.1189.
1-Cyclohexyl-4-penten-1-one O-diethylphosphinyloxime (1h): The typical procedure for the preparation of 1a was followed; 1-cyclohexyl-4-penten-1-one (97 mg, 0.58 mmol) was used as starting material. Flash chromatography on silica gel (hexane-EtOAc 10:1, 3:1) gave 1h as a colourless oil. Yield: 128 mg (69%) (E/Z = 68:32).
IR (neat): 2981, 2931, 1666, 1641, 1450, 1275 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 1.16-1.35 (m, 5H), 1.32 (td, J1 = 7.0 Hz, J2 = 0.8 Hz, 6H), 1.63-1.82 (m, 5H), 2.18-2.43 (m, 5H), 4.09-4.25 (m, 4H), 4.97 (broad d, J = 10.2 Hz, 1H), 5.02 (broad d, J = 17.0 Hz, 1H), 5.78 (dm, J = 17.0 Hz, 1H) ppm; Z-isomer: δ 1.16-1.35 (m, 5H), 1.32 (td, J1 = 7.0 Hz, J2 = 0.8 Hz, 6H), 1.63-1.82 (m, 5H), 2.18-2.43 (m, 5H), 4.09-4.25 (m, 4H), 4.93-5.06 (m, 2H), 5.73-5.83 (m, 1H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 16.2 (d, J = 6.3 Hz), 25.7, 25.8, 25.9, 27.3, 30.0, 43.8, 64.4 (d, J = 5.9 Hz), 115.4, 137.0, 172.8 (d, J = 12.2 Hz) ppm; Z-isomer: δ 16.2 (d, J = 6.3 Hz), 28.9, 29.8, 30.2, 30.4, 38.2, 64.4 (d, J = 5.9 Hz), 115.3, 137.4, 172.0 (d, J = 12.5 Hz) ppm; HRMS-FAB: m/z [M + H]+ calcd. for C15H29O4NP: 318.1834; found: 318.1829.
Dodec-1-en-5-one O-diethylphosphinyloxime (1i): The typical procedure for the preparation of 1a was followed; dodec-1-en-5-one (136 mg, 0.75 mmol) was used as starting material. Flash chromatography on silica gel (hexane-EtOAc 10:1, 3:1) gave 1i as a viscous oil. Yield: 162 mg (65%) (E/Z = 50:50).
IR (neat): 2929, 1277, 1036, 918 cm-1; 1H NMR of isomeric mixture (400 MHz, CDCl3): δ 0.88 (t, J = 6.4 Hz, 3H), 1.21-1.32 (m, 8H), 1.35 (t, J = 7.1 Hz, 6H), 1.45-1.58 (m, 2H), 2.25-2.35 (m, 3H), 2.35-2.42 (m, 2H), 2.48 (broad t, J = 7.8 Hz, 1H) 4.12-4.29 (m, 4H), 5.00 (broad d, J = 10.2 Hz, 1H), 5.05 (broad d, J = 17.1 Hz, 1H), 5.80 (dm, J = 17.1 Hz, 1H) ppm; 13C NMR of isomeric mixture (100 MHz, CDCl3): δ 14.0, 16.1 (d, J = 6.3 Hz), 22.6, 25.8, 26.0, 28.1, 28.9, 29.2, 29.6, 29.8, 30.0, 31.6, 31.7, 33.2, 33.9, 64.3 (d, J = 5.8 Hz), 115.6, 115.7, 136.7, 136.9, 169.7 (d, J = 12.6 Hz), 169.8 (d, J = 11.9 Hz) ppm; HRMS-EI: m/z [M - CH3]+ calcd. for C15H29O4NP: 318.1834; found: 318.1837.
1-Phenyl-5-hexen-1-one O-diethylphosphinyloxime (7a): The typical procedure for the preparation of 1a was followed; 1-phenyl-5-hexen-1-one (160 mg, 0.92 mmol) was used as the starting material. Flash chromatography on silica gel (hexane-EtOAc 8:1, 3:1) gave 7a as a viscous oil. Yield: 239 mg (80%) (E/Z = 86:14).
IR (neat): 2981, 1641, 1444, 1275, 916 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 1.38 (td, J1 = 7.0 Hz, J2 = 0.8Hz, 6H), 1.63 (m, 2H), 2.14 (td, J1 = 7.2 Hz, J2 = 7.0 Hz, 2H ), 2.86 (broad t, J = 8.0 Hz, 2H), 4.21-4.38 (m, 4H), 4.99 (broad d, J = 10.1 Hz, 1H), 5.02 (broad d, J = 17.1 Hz, 1H), 5.79 (dm, J = 17.1 Hz, 1H), 7.37-7.47 (m, 3H), 7.66 (dd, J1 = 7.8 Hz, J2 = 1.2 Hz, 2H) ppm; Z-isomer: δ 1.30 (td, J1 = 7.0 Hz, J2 = 0.9 Hz, 6H ), 1.54 (m, 2H), 2.05-2.13 (m, 2H), 2.65 (broad t, J = 7.7 Hz, 2H), 4.19-4.21 (m, 4H), 4.93-5.04 (m, 2H), 5.66-5.78 (m, 1H), 7.32-7.37 (m, 2H), 7.37-7.47 (m, 3H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 16.2 (d, J = 6.3 Hz), 25.7, 27.0, 33.6, 64.6 (d, J = 5.9 Hz), 115.5, 127.1, 128.6, 130.5, 133.6, 137.5, 167.3 (d, J = 13.2 Hz) ppm; Z-isomer: δ 16.1 (d, J = 6.3 Hz), 25.4, 33.0, 34.7, 64.4 (d, J = 5.8 Hz), 115.4, 127.4, 128.3, 129.5, 132.3, 137.6, 167.4 (d, J = 13.4 Hz) ppm; HRMS-FAB: m/z [M + H]+ calcd. for C16H25O4NP: 326.1521; found: 326.1514.
1-(4-Pyridinyl)-5-hexen-1-one O-diethylphosphinyloxime (7b): The typical procedure for the preparation of 1a was followed; 1-(4-pyridinyl)-5-hexen-1-one (173 mg, 0.99 mmol) was used as the starting material. Flash chromatography on silica gel (hexane-EtOAc 5:1, EtOAc) gave 7b as a yellow oil. Yield: 254 mg (79%) (E/Z = 75:25).
IR (neat): 3078, 2983, 1641, 1595, 1545, 1275, 1032, 916 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 1.38 (t, J = 7.1 Hz, 6H), 1.65 (m, 2H), 2.13 (td, J1 = 7.2 Hz, J2 = 7.1 Hz, 2H), 2.83 (broad t, J = 8.0 Hz, 2H), 4.20-4.34 (m, 4H), 5.00 (broad d, J = 10.1 Hz, 1H), 5.02 (broad d, J = 17.5 Hz, 1H), 5.77 (dm, J = 17.5 Hz, 1H), 7.57 (d, J = 6.2 Hz, 2H), 8.67 (broad d, J = 6.2 Hz, 2H) ppm; Z-isomer: δ 1.29 (t, J = 7.0 Hz, 6H), 1.54-1.62 (m, 2H), 2.06-2.14 (m, 2H), 2.62 (broad t, J = 7.7 Hz, 2H), 4.09-4.20 (m, 4H), 4.95-5.01 (m, 2H), 5.66-5.76 (m, 1H), 7.21 (broad d, J = 6.2 Hz, 2H), 8.67-8.70 (m, 2H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 16.2 (d, J = 6.3 Hz), 25.5, 26.4, 33.5, 64.9 (d, J = 5.9 Hz), 115.9, 121.1, 137.1, 141.2, 150.4, 165.5 (d, J = 13.8 Hz) ppm; Z-isomer: δ 16.1 (d, J = 6.3 Hz), 25.1, 32.9, 34.3, 64.8 (d, J = 5.9 Hz), 115.8, 121.7, 137.2, 140.4, 150.1, 165.4 (d, J = 13.4 Hz) ppm; HRMS-FAB: m/z [M + H]+ calcd. for C15H24O4N2P: 327.1483; found: 327.1474.
1-(4-Methoxyphenyl)-5-hexen-1-one O-diethylphosphinyloxime (7c): The typical procedure for the preparation of 1a was followed; 1-(4-methoxyphenyl)-5-hexen-1-one (210 mg, 1.03 mmol) was used as the starting material. Flash chromatography on silica gel (hexane-EtOAc 10:1, 2:1) gave 7c as a yellow oil. Yield: 296 mg (81%) (E/Z = 88:12).
IR (neat): 2981, 1608, 1514, 1255, 1032, 918, 837 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 1.36 (t, J = 7.1 Hz, 6H), 1.65 (m, 2H), 2.12 (td, J1 = 7.1 Hz, J2 = 7.1 Hz, 2H), 2.81 (broad t, J = 8.0 Hz, 2H), 3.81 (s, 3H), 4.19-4.31 (m, 4H), 4.97 (broad d, J = 10.2 Hz, 1H), 5.01 (broad d, J = 17.1 Hz, 1H), 5.77 (dm, J = 17.1 Hz, 1H), 6.89 (d, J = 8.8 Hz, 2H), 7.61 (d, J = 8.8 Hz, 2H) ppm; Z-isomer: δ 1.30 (t, J = 7.1 Hz, 6H), 1.55 (m, 2H), 2.03-2.10 (m ,2H), 2.63 (broad t, J = 7.6 Hz,, 2H), 3.81 (s, 3H), 4.09-4.21 (m, 4H), 5.01-5.10 (m, 2H), 5.66-5.79 (m, 1H), 6.86-6.93 (m, 2H), 7.37 (d, J = 8.7 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 16.2 (d, J = 6.4 Hz), 25.9, 26.8, 33.6, 55.3, 64.5 (d, J = 5.9 Hz), 114.0, 115.5, 125.9, 128.6, 137.6, 161.5, 166.6 (d, J = 13.3 Hz) ppm; Z-isomer: δ 16.1 (d, J = 6.4 Hz), 25.8, 33.0, 34.5, 55.2, 64.4 (d, J = 6.1 Hz), 113.6, 115.3, 124.1, 129.7, 137.7, 160.5, 166.3 (d , J = 13.3 Hz) ppm; HRMS-FAB: m/z [M]+ calcd. for C17H26O5NP: 355.1549; found: 355.1539.
1-(4-Fluorophenyl)-5-hexen-1-one O-diethylphosphinyloxime (7d): The typical procedure for the preparation of 1a was followed; 1-(4-fluorophenyl)-5-hexen-1-one (101 mg, 0.53 mmol) was used as the starting material. Flash chromatography on silica gel (hexane-EtOAc 6:1, 1:1) gave 7d as a yellow oil. Yield: 132 mg (73%) (E/Z = 85:15).
IR (neat): 3076, 2983, 1641, 1602, 1512, 1275, 1063, 918, 842 cm-1; 1H NMR (400 MHz, CDCl3): E-isomer: δ 1.37 (td, J1 = 7.1 Hz, J2 = 0.7 Hz, 6H), 1.64 (m, 2H), 2.12 (td, J1 = 7.2 Hz, J2 = 7.0 Hz, 2H), 2.82 (broad t, J = 8.0 Hz, 2H), 4.19-4.31 (m, 4H), 4.98 (broad d, J = 10.1 Hz, 1H), 5.01 (broad d, J = 17.1 Hz, 1H), 5.76 (dm, J = 17.1 Hz, 1H), 7.07 (t, J = 8.8 Hz, 2H), 7.65 (dm, J = 8.8 Hz, 2H) ppm; Z-isomer: δ 1.30 (td, J1 = 7.0 Hz, J2 = 0.7 Hz, 6H), 1.55 (m, 2H), 2.03-2.10 (m, 2H), 2.63 (broad t, J = 7.7 Hz, 2H), 4.08-4.19 (m, 4H), 4.91-5.01 (m, 2H), 5.65-5.78 (m, 1H), 7.05-7.12 (m, 2H), 7.36 (dm, J = 8.8 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3): E-isomer: δ 16.2 (d, J = 6.4 Hz), 25.7, 26.9, 33.5, 64.6 (d, J = 6.0 Hz), 115.6, 115.7 (d, J = 22.4 Hz), 129.1 (d, J = 8.5 Hz), 129.7 (d, J = 3.5 Hz), 137.4, 164.2 (d, J = 251.0 Hz), 166.3 (d, J = 13.5 Hz) ppm; Z-isomer: δ 16.1 (d, J = 5.9 Hz), 25.5, 32.9, 34.7, 64.5 (d, J = 6.2 Hz), 115.5, 115.5 (d, J = 22.1 Hz), 128.1 (d, J = 3.8 Hz), 129.8 (d, J = 8.4 Hz), 137.5, 163.1 (d, J = 250.1 Hz), 166.2 (d, J = 13.0 Hz) ppm; HRMS-FAB: m/z [M + H]+ calcd. for C16H24FO4NP: 344.1427; found: 344.1433.
Tridec-1-en-6-one O-diethylphosphinyloxime (7e): The typical procedure for the preparation of 1a was followed; tridec-1-en-6-one (87 mg, 0.44 mmol) was used as the starting material. Flash chromatography on silica gel (hexane-EtOAc 10:1, 5:1) gave 7e as a colourless oil. Yield: 97 mg (63%) (E/Z = 50:50).
IR (neat):2979, 1641, 1277, 1066, 920 cm-1; 1H NMR of the isomeric mixture (400 MHz, CDCl3): δ 0.85 (t, J = 6.5 Hz, 3H), 1.22-1.30 (m, 8H), 1.33 (td, J1 =7.1 Hz, J2 = 0.8 Hz, 6H), 1.44-1.53 (m, 2H), 1.55-1.65 (m, 2H), 2.03-2.10 (m, 2H), 2.22-2.29 (m, 2H), 2.32-2.39 (m, 2H), 4.12-4.23 (m, 4H), 4.96 (broad d, J = 11.6 Hz, 1H), 4.99 (broad d, J = 17.2 Hz, 1H), 5.75 (dm, J = 17.2 Hz, 1H) ppm; 13C NMR of the isomeric mixture (100 MHz, CDCl3): δ = 14.0, 16.2 (d, J = 6.4 Hz), 22.6, 25.0, 25.2, 25.8, 26.1, 28.2, 28.8, 28.9, 29.2, 29.7, 31.6, 31.7, 33.1, 33.2, 33.6, 33.8, 64.3 (d, J = 5.7 Hz), 115.3, 115.4, 137.5, 137.7, 170.3 (d, J = 12.6 Hz), 170.4 (d, J = 12.4 Hz) ppm; HRMS-FAB: m/z [M + H]+ calcd. for C17H35O4NP: 348.2304; found: 348.2297.
Typical Experimental Procedure for the Amino-Heck Reactions of γ,δ-Unsaturated O-Diethylphosphinyloximes for the Generation of 2-Substituted Pyridines; 2-Phenylpyridine (3a): Under a nitrogen atmosphere, Pd(PPh3)4 (37.5 mg, 0.032 mmol) and DIPEA (210 mg, 1.62 mmol) were sequentially added to a solution of 1a (101 mg, 0.32 mmol) in anhyd DMF (16.2 mL, 0.02 M) at r.t. The resulting yellow suspension was quickly warmed to 80 °C and continued to stir for 12 h. The reaction mixture was then cooled to r.t., filtrated through a Celite pad and washed with EtOAc (80 mL). The filtrate was successively washed with H2O (2 × 10 mL) and saturated NaCl aq soln (10 mL). After concentration, the crude products were subjected to chromatographic purification on aluminum oxide (hexane-EtOAc 5:1, 3:1) to afford 3a in 71% yield (35.7 mg).
IR (neat): 1735, 1266, 739 cm-1; 1H NMR (400 MHz, CDCl3): δ 7.19-7.26 (m, 1H), 7.40-7.52 (m, 3H), 7.70-7.79 (m, 2H), 8.00 (d, J = 7.3 Hz, 2H), 8.70 (d, J = 4.7 Hz, 1H) ppm; 13C NMR (100 MHz, CDCl3): δ 120.6, 122.1, 126.9, 128.8, 129.0, 136.7, 139.4, 149.7, 157.5 ppm; HRMS-FAB: m/z [M]+ calcd. for C11H9N: 155.0735; found: 155.0733.
2-Heptylpyridine (3i): The typical procedure for the preparation of 3a was followed; 1i (158 mg, 0.47 mmol) was used as the starting material. Flash chromatography on aluminum oxide (hexane-EtOAc 15:1, 7:1) gave 3i in 20% yield (16.8 mg).
IR (neat): 2954, 2925, 1591, 1570, 1473, 1435, 758 cm-1; 1H NMR (400 MHz, CDCl3): δ 0.87 (t, J = 6.9 Hz, 3H), 1.22-1.40 (m, 7H), 1.64-1.76 (m, 3H), 2.77 (t, J = 7.8 Hz, 2H), 7.09 (ddd, J1 = 7.6 Hz, J2 = 4.9 Hz, J3 = 0.6 Hz, 1H), 7.14 (d, J = 7.6 Hz, 1H), 7.58 (td, J1 = 7.6 Hz, J2 = 1.8 Hz, 1H ), 8.52 (broad d, J = 4.9 Hz, 1H) ppm; 13C NMR (100 MHz, CDCl3): δ 14.1, 22.7, 29.2, 29.4, 30.0, 31.8, 38.5, 120.8, 122.7,
136.2, 149.2, 162.6 ppm; HRMS-EI: m/z [M – Et]+ calcd. for C10H14N: 148.1126; found: 148.1127.
Typical Experimental Procedure for the Amino-Heck Reactions of δ,ε-unsaturated ketone O-diethylphosphinyloximes for the Generation of Substituted Methylpyridines; 2-Methyl-6-phenylpyridine (8a): Under a nitrogen atmosphere, Pd(PPh3)4 (79.6 mg, 0.069 mmol) and molecular sieves (MS) 4 Å (34 mg) were added to a solution of 7a (112 mg, 0.34 mmol) in anhyd DMF (17.2 mL, 0.02 M) at rt. The reaction mixture was stirred at r.t. for 10 min, then Et3N (174 mg, 1.72 mmol) and (n-Bu)4NBr (555 mg, 1.72 mmol) were successively added. The mixture was quickly warmed to 80 °C and continued to stir for 12 h. The reaction mixture was then cooled to rt, filtrated through a Celite pad and washed with EtOAc (100 mL). The filtrate was successively washed with H2O (2 × 15 mL) and saturated NaCl aq soln (15 mL). After concentration, the crude products were subjected to chromatographic purification on aluminum oxide (hexane-EtOAc 5:1, 3:1) to afford 8a in 63% yield (36.7 mg).
IR (neat): 2954, 1589, 1448, 1444, 758, 694 cm-1; 1H NMR (400 MHz, CDCl3): δ 2.63 (s, 3H), 7.10 (d, J = 7.5 Hz, 1H), 7.39 (t, J = 7.2 Hz, 1H), 7.46 (t, J = 7.4 Hz, 2H), 7.52 (d, J = 7.7 Hz, 1H), 7.64 (t, J = 7.7 Hz, 1H), 7.97 (d, J = 7.6 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3): δ 24.8, 117.6, 121.6, 127.0, 128.6, 128.7, 136.9, 139.8, 157.0, 158.4 ppm; HRMS-EI: m/z [M]+ calcd. for C12H11N: 169.0891; found: 169.0889.
2-(4-Fluorophenyl)-6-methylpyridine (8d):
The typical procedure for the preparation of 8a was followed; 7d (97 mg, 0.28 mmol) was used as the starting material. Flash chromatography on aluminum oxide (hexane-EtOAc 10:1, 1:1) gave 8d in 42% yield (22.2 mg).
IR (neat): 3062, 2925, 1601, 1456, 845 cm-1; 1H NMR (400 MHz, CDCl3): δ 2.62 (s, 3H), 7.09 (d, J = 7.6 Hz, 1H), 7.14 (tm, J = 8.8 Hz, 2H), 7.46 (d, J = 7.8 Hz, 1H), 7.63 (t, J = 7.7 Hz, 1H), 7.96 (dm, J = 8.8 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3): δ 24.7, 115.5 (d, J = 21.5 Hz), 117.3, 121.5, 128.8 (d, J = 8.2 Hz), 135.9 (d, J = 2.9 Hz), 136.9, 155.9, 158.4, 163.4 (d, J = 247.8 Hz) ppm; HRMS-EI: m/z [M]+ calcd. for C12H10FN: 187.0797; found: 187.0797; Anal. Calcd for C12H10FN: C, 76.99; H, 5.38; N, 7.48. Found: C, 76.63; H, 5.34; N, 7.51.
2-Heptyl-6-methylpyridine (8e): The typical procedure for the preparation of 8a was followed; 7e (95 mg, 0.27 mmol) was used as the starting material. Flash chromatography on aluminum oxide (hexane-EtOAc 15:1, 10:1) gave 8e in 20% yield (10.5 mg).
IR (neat):2954, 1593, 1456, 789 cm-1; 1H NMR (400 MHz, CDCl3): δ 0.87 (t, J = 6.8 Hz, 3H), 1.23-1.29 (m, 4H), 1.31-1.37 (m, 3H), 1.66-1.72 (m, 3H), 2.52 (s, 3H), 2.73 (broad t, J = 7.9 Hz, 2H), 6.94 (d, J = 7.6 Hz, 1H), 6.95 (d, J = 7.6 Hz, 1H), 7.46 (t, J = 7.6 Hz, 1H) ppm; 13C NMR (100 MHz, CDCl3): δ 14.1, 22.7, 24.6, 29.2, 29.5, 30.3, 31.8, 38.6, 119.4, 120.3, 136.4, 157.6, 162.0 ppm; HRMS-FAB: m/z [M + H]+ calcd. for C13H22N: 192.1752; found: 192.1757; Anal. Calcd for C13H21N: C, 81.61; H, 11.06; N, 7.32. Found: C, 81.64; H, 11.06; N, 7.30.

ACKNOWLEDGEMENTS
We are grateful to the National Science Council of Republic of China (Taiwan) and National Dong-Hwa University for financial support.

References

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