HETEROCYCLES

Paper | Special issue | Vol. 90, No. 2, 2015, pp. 1205-1213
Received, 31st July, 2014, Accepted, 25th August, 2014, Published online, 5th September, 2014.
DOI: 10.3987/COM-14-S(K)100

■ Thiazole/Thiazolone-Fused Cycloheptatrienyl Phosphonates: Reactions of 2H-Cyclohepta[d]thiazole-2-thione and -2-one with Phosphites

Ohki Sato* and Ikumi Suzuki

Department of Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570 , Japan

Abstract

2H-Cyclohepta[d]thiazole-2-thione reacted with either trimethyl or dimethyl phosphite to furnish dimethyl 2-methylthio-4H-cyclohepta[d]thiazole-4-phosphonate and the regioisomers, 6- and 8-phosphonates. In the reaction with triphenyl phosphite, the successive S-methylation by methyl iodide and hydrolysis afforded an isomeric mixture of diphenyl 4-, 6- and 8-phosponates. Treatment of the oxygen analogue, 2H-cyclohepta[d]thiazol-2-one and triphenyl/diphenyl phosphite with/without hydrolysis gave diphenyl 3,4-dihydro-2H-cyclohepta[d]thiazol-2-one-4-phosphonate and the isomeric 6- and 8-phosphonates.

INTRODUCTION
2H-Cyclohepta[d]thiazole-2-thione (1) and the oxygen analogue, -2-one (2), which have polarized structures similar to that of azulenes, are classified as non-benzenoid aromatics. Although some preparation methods1-3 and reactions3-5 of 1 and/or 2 had been reported, our previous work with dimethyl malonate/sodium hydride3 was the only example in the reaction with nucleophiles. For further investigation of their reactivities, we focused on the reagents of phosphites. It is well known that trialkyl phosphites as a nucleophile are used in Michaelis-Arbuzov reaction6-8 and Perkow reaction.8,9 Reagents for Horner-Wadsworth-Emmons reaction10 are prepared by the former reaction with alkyl halides. Trialkyl phosphites are also used to construct tetrathiafulvalene (TTF) derivatives by the condensation of trithio- and/or dithiocarbonates.11 Therefore, whether phosphites act as a nucleophile or a condensation reagent toward 1 and 2 is of interest.
In this manuscript, we report the reactions of 1 and 2 with several phosphites, which attack to a seven-membered ring moiety of the substrates as a nucleophile, producing three kinds of regioisomeric cycloheptatrienyl phosphonates fused with a thiazole/thiazolone ring.

RESULTS AND DISCUSSION
The reaction of 1 and an excess amount of trimethyl phosphite without a solvent would generate an intermediate mixture of 3a, 3b and 3c, phosphite-adducts at 4-, 6- and 8-positions of 1, respectively (Scheme 1). The intermediates (3a-c) would be S-methylated by surplus trimethyl phosphite and/or the other molecules of 3a-c acting as a trimethoxy phosphonium salt to form a 2-(methylthio)thiazole moiety, and would be also demethylated by the other molecules of 3a-c acting as a thiolate to form a dimethyl phosphonate moiety. The final products were dimethyl 2-methylthio-4H-cyclohepta[d]thiazole-4- phosphonate (4a, 34%) and its 6- and 8-regioisomers (4b and 4c, 6 and 24%). These products are classified both as cycloheptatrienyl phosphonates and thiazoles, and their chemical and physical properties attract much attention. Non-substituted dimethyl cycloheptatrienyl phosphonate had been synthesized by the reaction of tropylium tetrafluoroborate with sodium dimethyl phosphite.12

Dimethyl phosphite has equilibrium between five-coordinated and three-coordinated structures. The intermediates (5a-c) are 4-, 6- and 8-adducts of 1 with the three-coordinated one (Scheme 2), and a phosphonate moiety would be formed smoothly by the deprotonation instead of demethylation as mentioned in Scheme 1. Indeed, treatment with dimethyl phosphite afforded the same products (4a-c) as described above in 25, 7 and 25% yields, respectively. In this case, S-methylation of the intermediates would be caused by surplus dimethyl phosphite.

Prepared dimethyl phosphonates (4a-c) were all yellowish brown oil. The H-H and C-H relationship was determined by their H-H COSY and HMQC NMR spectra. From these results, the peaks of their quaternary carbons were revealed. As shown in the following figure, C-2 peaks of 4a-c were assigned at δ 167.5, 165.6 and 164.6, respectively, by comparison with the peak of 2-(methylthio)benzothiazole (δ 167.9).13 These results indicate that 4a-c have a S-methyl thiazole framework instead of a N-methyl thiazole-2-thione one. In the same way, peaks of C-3a and C-8a were assigned at δ 142.9, 130.8 (for 4a), 152.6, 134.0 (for 4b) and 151.2, 122.4 (for 4c) by comparison with corresponding peaks of the benzothiazole (δ 153.4, 135.2).13 The longest-wavelength peaks in the UV-VIS absorption spectra of 4a-c appeared at 331, 306 and 296 nm, respectively, on the basis of each expanded π-conjugated system. That is, 4-phosphonate (4a) has longer conjugated one than that of 6- and 8-isomers (4b and 4c). 31P NMR, IR and MS spectra of 4a-c were also consistent with their proposed structures, respectively.

The reaction of 1 with triphenyl phosphite and the successive S-methylation by methyl iodide would generate 2-methylthio-4-, 6- and 8-phosphite-adducts (6a-c, Scheme 3), which were hydrolyzed to furnish diphenyl 4-phosphonate (7a, 17%) and an inseparable mixture of 6- and 8-phosphonates (7b and 7c, 8 and 11%). In the case with diphenyl phosphite as shown by square brackets in Scheme 3, the same products (7a, 7b and 7c, 31, 11 and 23%) were obtained by formal deprotonation of the intermediates (8a-c). The deprotonation process might occur before the S-methylation one by methyl iodide. Isolated compound (7a) was yellow oil, and its 1H, 13C and 31P NMR and MS spectra were consistent with the proposed structure. In the case of 7b and 7c, their structures were presumed by comparison with 1H NMR spectra of dimethyl 6- and 8-phosphonates (4b and 4c). That is, the coupling pattern at a seven-membered ring moiety of 7b and 7c was very close to that of 4b and 4c, respectively. The reaction of 1 and triphenyl/diphenyl phosphite without methyl iodide gave a complex mixture.

2H-Cyclohepta[d]thiazol-2-one (2), the oxygen analogue of 1, reacted with trimethyl or dimethyl phosphite to give a complex mixture, and no product could be determined in either case. Treatment of 2 with triphenyl or diphenyl phosphite would form corresponding intermediates (9a-c) or (10a-c), which were hydrolyzed or deprotonated to afford diphenyl 3,4-dihydro-2H-cyclohepta[d]thiazol-2-one-4- phosphornate (11a: colorless needles) and the regioisomeric 6- and 8-phosphonates (11b: yellow oil and 11c: colorless powder). Those yields were 26, 6 and 16% with triphenyl phosphite or 40, 8 and 41% with diphenyl phosphite, respectively (Scheme 4). In the case of the reaction with methyl iodide, N- and/or O-methylation of 9/10 did not occurred, and the same products (11a-c) as described above were confirmed in the reaction mixture.

The H-H and C-H relationship was determined by their H-H COSY and HMQC NMR spectra. As shown in the following figure, C-2 peaks of 11a-c were assigned at δ 172.8, 172.3 and 173.2, respectively, as a carbonyl carbon by comparison with the peaks of 4- and 6-adducts of malonate [12a (δ 174.0) and 12b (δ 172.2)] derived from 2 with dimethyl malonate/sodium hydride.3 The 8-regioisomer of malonate-adduct had not been formed by the reaction. In the same way, peaks of C-3a and C-8a were assigned at δ 118.8, 115.1 (for 11a), 132.9, 119.8 (for 11b) and 131.1, 105.1 (for 11c) by comparison with the peaks of 12a (δ 124.8, 113.3) and 12b (δ 132.6, 119.8).3 The NOE correlation appeared between NH and H-4 of 4-phosphonate (11a). Other data such as 31P NMR, IR, UV-VIS and MS spectra and elemental analysis results (for 11a and 11c) also supported proposed structures of 11a-c.

In conclusion, we have succeeded in the preparation of thiazole/thiazolone-fused cycloheptatrienyl phosphonates (4a-c, 7a-c and 11a-c) by the reactions of 2H-cyclohepta[d]thiazole-2-thione (1) and -2-one (2) with several phosphites. Further work, aimed at Horner-Wadsworth-Emmons reaction10 of the prepared phosphonates with carbonyl compounds for construction of various thiazole/thiazolone-fused heptafulvenes, is in progress.

EXPERIMENTAL
Mps were determined with a Laboratory Devices MEL-TEMP apparatus and are uncorrected. 1H, 13C and 31P NMR spectra were obtained with Bruker AV500, AV400 and/or AV300 spectrometers. IR spectra were obtained with a Perkin Elmer System 2000 FT instrument and electronic spectra (UV-VIS) with a JASCO V-560 spectrophotometer. MS spectra were obtained with a Bruker AutoflexIII spectrometer. Unless otherwise stated the spectra were taken in the following solvents/media: IR, neat and/or KBr; UV-VIS, MeOH and/or CH2Cl2; 1H, 13C and 31P NMR, CDCl3 and/or MeOH-d4; MS spectra were taken at a MALDI-TOF method. The progress of reactions was followed by TLC method using Merck Silica gel 60F254.
The reaction of 2H-cyclohepta[d]thiazole-2-thione (1) with trimethyl phosphite: A mixture of 1 (50 mg, 2.8 x 10-1 mmol) and trimethyl phosphite (15 mol eq.) was heated without a solvent at 100-110 °C for 3 h under Ar. THF (0.5 mL) and H2O (0.5 mL) were added to the reaction mixture, and the solution was heated at 50 °C for 3 h to hydrolyze surplus trimethyl phosphite. The resulting mixture was extracted with sat. aq. NaHCO3/CH2Cl2. The organic layer was dried over MgSO4 and the solvent was removed under reduced pressure to give a crude mixture of 4a, 4b and 4c. The mixture was purified by SiO2 column chromatography and HPLC (SiO2, EtOAc/EtOH) to give 4a (29 mg, 34%), 4b (5.3 mg, 6%) and 4c (20 mg, 24%).
Dimethyl 4-phosphonate (4a): yellowish brown oil; 1H NMR (CDCl3) δ 2.66 (s, 3H), 3.68 (d, J = 10.5 Hz, 3H), 3.75 (d, J = 10.5 Hz, 3H), 4.38 (dd, J = 25.8, 8.3 Hz, 1H), 5.54 (ddd, J = 10.7, 9.0, 8.3 Hz, 1H), 6.21 (ddd, J = 10.7, 6.3, 4.5 Hz, 1H), 6.30 (dd, J = 11.3, 6.3 Hz, 1H), 6.63 (d, J = 11.3 Hz, 1H); 13C NMR (CDCl3) δ 16.7, 41.9 (d, J = 144.6 Hz), 53.2 (d, J = 7.5 Hz), 53.4 (d, J = 6.3 Hz), 120.8, 121.0 (d, J = 7.5 Hz), 127.0, 129.1 (d, J = 10.1 Hz), 130.8 (d, J = 7.5 Hz), 142.9 (d, J = 6.3 Hz), 167.5; 31P NMR (CDCl3) δ 27.95; IR (neat) ν 1248, 1035, 831; UV-VIS (MeOH, log ε) λmax 264 (3.64), 331 (3.91); MS (MALDI-TOF, dithranol): m/z 302 ([M-H]+), 303 (M+), 304 ([M+H]+); HRMS (MALDI-TOF, dithranol) Calcd for C11H13NO3PS2: 302.0075. Found: 302.0079.
Dimethyl 6-phosphonate (4b): yellowish brown oil; 1H NMR (CDCl3) δ 2.63 (dtt, J = 20.5, 6.5, 1.0 Hz, 1H), 2.71 (s, 3H), 3.79 (d, J = 10.5 Hz, 3H), 3.81 (d, J = 10.5 Hz, 3H), 5.51 (ddd, J = 12.5, 9.5, 6.5 Hz, 1H), 5.61 (ddd, J = 12.5, 9.5, 6.5 Hz, 1H), 6.77 (dt, J = 9.5, 1.0 Hz, 1H), 6.95 (dt, J = 9.5, 1.0 Hz, 1H); 13C NMR (CDCl3) δ 16.4, 36.7 (d, J = 152.2 Hz), 53.1 (d, J = 6.3 Hz, 2C), 116.8 (d, J = 3.8 Hz), 118.5 (d, J = 5.0 Hz), 121.7 (d, J = 16.3 Hz), 126.4 (d, J = 16.3 Hz), 134.0, 152.6, 165.6; 31P NMR (CDCl3) δ 32.79; IR (neat) ν 1256, 1030, 827; UV-VIS (MeOH, log ε) λmax 233 (4.07), 252 (3.85), 306 (3.72); MS (MALDI-TOF, dithranol): m/z 302 ([M-H]+), 303 (M+), 304 ([M+H]+); HRMS (MALDI-TOF, dithranol) Calcd for C11H13NO3PS2: 302.0075. Found: 302.0086.
Dimethyl 8-phosphonate (4c): yellowish brown oil; 1H NMR (CDCl3) δ 2.67 (s, 3H), 3.75 (d, J = 10.5 Hz, 3H), 3.76 (d, J = 10.5 Hz, 3H), 3.93 (dd, J = 25.8, 8.1 Hz, 1H), 5.50 (ddd, J = 10.0, 8.5, 8.1 Hz, 1H), 6.18 (ddd, J = 10.0, 6.3, 3.3 Hz, 1H), 6.37 (dd, J = 11.6, 6.3 Hz, 1H), 6.99 (d, J = 11.6 Hz, 1H); 13C NMR (CDCl3) δ 16.5, 36.5 (d, J = 150.9 Hz), 53.4 (d, J = 6.3 Hz), 53.5 (d, J = 7.5 Hz), 120.2 (d, J = 6.3 Hz), 122.4 (d, J = 7.5 Hz), 127.1, 127.7, 129.3 (d, J = 11.3 Hz), 151.2 (d, J = 10.1 Hz), 164.6 (d, J = 2.5 Hz); 31P NMR (CDCl3) δ 27.51; IR (neat) ν 1252, 1029, 826; UV-VIS (MeOH, log ε) λmax 267 (4.03), 296 (3.62); MS (MALDI-TOF, dithranol): m/z 302 ([M-H]+), 303 (M+), 304 ([M+H]+); HRMS (MALDI-TOF, dithranol) Calcd for C11H13NO3PS2: 302.0075. Found: 302.0094.
The reaction of 1 with dimethyl phosphite: A mixture of 1 (152 mg, 8.5 x 10-1 mmol) and dimethyl phosphite (20 mol eq.) was heated without a solvent at 100-110 °C for 3 h under Ar. THF (1.5 mL) and H2O (1.5 mL) were added to the reaction mixture, and the solution was heated at 50 °C for 3 h to hydrolyze surplus dimethyl phosphite. The resulting mixture was extracted with sat. aq. NaHCO3/CH2Cl2. The organic layer was dried over MgSO4 and the solvent was removed under reduced pressure to give a crude mixture of 4a, 4b and 4c. The mixture was purified by SiO2 column chromatography and HPLC (SiO2, EtOAc/EtOH) to give 4a (65 mg, 25%), 4b (18 mg, 7%) and 4c (65 mg, 25%).
The reaction of 1 with triphenyl or diphenyl phosphite: A mixture of 1 and triphenyl or diphenyl phosphite (6.1 or 9.3 mol eq.) was heated without a solvent at 100-110 °C for 3 h under Ar. Methyl iodide (10 mol eq.) was added at room temperature, and the mixture was stirred for 2 h to form methylthio ethers. THF (1.5 mL) and H2O (1.5 mL) were added to the reaction mixture, and the solution was heated at 50 °C for 3 h to hydrolyze surplus triphenyl/diphenyl phosphite and triphenoxy phosphonium salts (in the only case with triphenyl phosphite). The resulting mixture was extracted with sat. aq. NaHCO3/CH2Cl2. The organic layer was dried over MgSO4 and the solvent was removed under reduced pressure to give a crude mixture of 7a, 7b and 7c. The mixture was purified by SiO2 column chromatography and HPLC (SiO2, EtOAc/EtOH) to give 7a (17 or 31%) and an inseparable mixture of 7b (8 or 11%) and 7c (11 or 23%). The yields of 7b and 7c were determined by 1H NMR spectra of their mixture.
Diphenyl 4-phosphonate (7a): yellow oil; 1H NMR (CDCl3) δ 2.61 (s, 3H), 4.75 (dd, J = 22.5, 8.5 Hz, 1H), 5.66 (dt, J = 11.5, 8.5 Hz, 1H), 6.29-6.33 (m, 2H), 6.63 (d, J = 11.5 Hz, 1H), 7.05 (d like, J = 8.0 Hz, 2H), 7.10 (t like, J = 8.0 Hz, 1H), 7.15 (t like, J = 8.0 Hz, 1H), 7.19 (d like, J = 8.0 Hz, 2H), 7.25 (t like, J = 8.0 Hz, 2H), 7.30 (t like, J = 8.0 Hz, 2H); 13C NMR (CDCl3) δ 16.4, 42.7 (d, J = 147.1 Hz), 120.0 (d, J = 7.5 Hz), 120.3 (d, J = 3.8 Hz, 2C), 120.7 (d, J = 5.0 Hz, 2C), 121.0, 124.8, 125.0, 127.2 (d, J = 1.3 Hz), 129.5 (2C), 129.6 (2C), 129.8 (d, J = 11.3 Hz), 131.5 (d, J = 7.5 Hz), 141.7 (d, J = 6.3 Hz), 150.5 (d, J = 10.0 Hz, 2C), 167.5; 31P NMR (CDCl3) δ 14.99; MS (MALDI-TOF, dithranol): m/z 426 ([M-H]+), 427 (M+), 428 ([M+H]+); HRMS (MALDI-TOF, dithranol) Calcd for C21H17NO3PS2: 426.0388. Found: 426.0398.
An inseparable mixture of diphenyl 6- and 8-phosphonates (7b and 7c): Selected 1H NMR (CDCl3) of 7b δ 2.71 (s, 3H), 2.94 (dtt, J = 21.0, 6.5, 1.5 Hz, 1H), 5.68 (ddd, J = 13.0, 9.5, 6.5 Hz, 1H), 5.80 (ddd, J = 13.0, 9.5, 6.5 Hz, 1H), 6.83 (dt, J = 9.5, 1.5 Hz, 1H), 7.03 (dt, J = 9.5, 1.5 Hz, 1H), 7.16-7.20 (m, 6H), 7.29-7.33 (m, 4H); Selected 31P NMR (CDCl3) of 7b δ 20.37; Selected 1H NMR (CDCl3) of 7c δ 2.67 (s, 3H), 4.26 (dd, J = 25.5, 8.0 Hz, 1H), 5.65 (ddd, J = 10.5, 8.5, 8.0 Hz, 1H), 6.28 (ddd, J = 10.5, 6.5, 3.5 Hz, 1H), 6.38 (dd, J = 11.5, 6.5 Hz, 1H), 7.01 (d, J = 11.5 Hz, 1H), 7.09-7.11 (m, 4H), 7.13-7.17 (m, 2H), 7.27-7.31 (m, 4H); Selected 31P NMR (CDCl3) of 7c δ 14.86.
The reaction of 2H-cyclohepta[d]thiazol-2-one (2) with triphenyl or diphenyl phosphite: A mixture of 2 and triphenyl or diphenyl phosphite (6.2 or 8.4 mol eq.) was heated without a solvent at 100-110 °C for 3 h under Ar. THF (1.5 mL) and H2O (1.5 mL) were added to the reaction mixture, and the solution was heated at 50 °C for 3 h to hydrolyze surplus triphenyl/diphenyl phosphite and triphenoxy phosphonium salts (in the only case with triphenyl phosphite). The resulting mixture was extracted with sat. aq. NaHCO3/ CH2Cl2. The organic layer was dried over MgSO4 and the solvent was removed under reduced pressure to give a mixture of crude 11a, 11b and 11c. The mixture was purified by SiO2 column chromatography and HPLC (SiO2, EtOAc/EtOH) to give 11a (26 or 40%), 11b (6 or 8%) and 11c (16 or 41%), respectively.
Diphenyl 4-phosphonate (11a): colorless needles; mp 192-193 °C (dec.); 1H NMR (CDCl3) δ 4.15 (dd, J = 25.5, 8.5 Hz, 1H), 5.45 (dt, J = 10.5, 8.5 Hz, 1H), 6.22-6.27 (m, 2H), 6.30-6.34 (m, 1H), 7.05-7.08 (m, 4H), 7.15 (t like, J = 7.5 Hz, 2H), 7.27-7.30 (m, 4H), 9.62 (brs, 1H); 1H NMR (MeOH-d4) δ 4.62 (dd, J = 26.5, 8.5 Hz, 1H), 5.54 (ddd, J = 11.5, 8.5, 8.0 Hz, 1H), 6.23 (dd, J = 11.5, 6.5 Hz, 1H), 6.28 (d, J = 11.5 Hz, 1H), 6.38 (dt, J = 11.0, 6.5 Hz, 1H), 7.02 (d like, J = 7.5 Hz, 2H), 7.07 (d like, J = 7.5 Hz, 2H), 7.17-7.22 (m, 2H), 7.32 (t like, J = 7.5 Hz, 2H), 7.34 (t like, J = 7.5 Hz, 2H); 13C NMR (CDCl3) δ 39.5 (d, J = 150.9 Hz), 115.1 (d, J = 11.3 Hz), 116.5 (d, J = 6.3 Hz), 118.8 (d, J = 6.3 Hz), 120.27 (d, J = 5.0 Hz, 2C), 120.33 (d, J = 3.8 Hz, 2C), 123.6, 125.5, 125.6, 126.7, 129.87 (2C), 129.89 (2C), 130.5 (d, J = 6.3 Hz), 150.0 (d, J = 7.5 Hz), 150.1 (d, J = 10.1 Hz), 172.8; 31P NMR (CDCl3) δ 13.34; IR (KBr) ν 3157, 1670, 1487, 1249, 1211, 1185, 1162, 949, 765; UV-VIS (MeOH, log ε) λmax 336 (3.51); UV-VIS (CH2Cl2, log ε) λmax 329 (3.52); MS (MALDI-TOF, dithranol): m/z 396 ([M-H]+), 397 (M+), 398 ([M+H]+). Anal. Calcd for C20H16NO4PS: C, 60.45; H, 4.06. Found: C, 60.38; H, 3.98.
Diphenyl 6-phosphonate (11b): yellow oil; 1H NMR (CDCl3) δ 2.84 (dt, J = 20.5, 6.5 Hz, 1H), 5.53 (ddd, J = 13.3, 9.5, 6.5 Hz, 1H), 5.66 (ddd, J = 13.3, 9.5, 6.5 Hz, 1H), 6.45 (dd, J = 9.5, 1.0 Hz, 1H), 6.51 (dd, J = 9.5, 1.0 Hz, 1H), 7.17-7.20 (m, 6H), 7.32 (t like, J = 8.0 Hz, 4H), 9.91 (brs, 1H); 13C NMR (CDCl3) δ 38.0 (d, J = 155.9 Hz), 113.6 (d, J = 3.8 Hz), 117.5 (d, J = 3.8 Hz), 119.6 (d, J = 17.6 Hz), 119.8, 120.49 (d, J = 2.5 Hz, 2C), 120.53 (d, J = 2.5 Hz, 2C), 123.1 (d, J = 17.6 Hz), 125.5 (2C), 129.9 (4C), 132.9, 150.06 (d, J = 7.5 Hz), 150.12 (d, J = 7.5 Hz), 172.3; 31P NMR (CDCl3) δ 19.95; IR (neat) ν 3168, 1685, 1488, 1263, 1186, 1162, 942, 765; UV-VIS (MeOH, log ε) λmax 261 (3.62), 268 (3.60), 303 (3.51); UV-VIS (CH2Cl2, log ε) λmax 262 (3.76), 269 (3.73), 310 (3.52); MS (MALDI-TOF, dithranol): m/z 396 ([M-H]+), 397 (M+), 398 ([M+H]+); HRMS (MALDI-TOF, dithranol) Calcd for C20H15NO4PS: 396.0459. Found: 396.0461.
Diphenyl 8-phosphonate (11c): colorless powder; mp 67 °C (dec.); 1H NMR (CDCl3) δ 4.05 (dd, J = 26.0, 9.0 Hz, 1H), 5.63 (dt, J = 10.5, 9.0 Hz, 1H), 6.24-6.31 (m, 3H), 7.08 (d like, J = 8.5 Hz, 2H), 7.11-7.17 (m, 4H), 7.25-7.31 (m, 4H), 10.10 (brs, 1H); 13C NMR (CDCl3) δ 38.6 (d, J = 152.2 Hz), 105.1 (d, J = 6.3 Hz), 119.6 (d, J = 6.3 Hz), 120.3 (d, J = 5.0 Hz, 2C), 120.4 (d, J = 5.0 Hz, 2C), 120.8, 125.25, 125.32, 129.72 (2C), 129.75 (d, J = 7.5 Hz), 129.78 (2C), 130.1, 131.1 (d, J = 10.1 Hz), 150.15 (d, J = 8.8 Hz), 150.23 (d, J = 8.8 Hz), 173.2; 31P NMR (CDCl3) δ 14.44; IR (KBr) ν 3136, 1666, 1488, 1263, 1211, 1188, 1160, 929, 768; UV-VIS (MeOH, log ε) λmax 324 (3.35); UV-VIS (CH2Cl2, log ε) λmax 330 (3.37); MS (MALDI-TOF, dithranol): m/z 396 ([M-H]+), 397 (M+), 398 ([M+H]+). Anal. Calcd for C20H16NO4PS: C, 60.45; H, 4.06. Found: C, 60.24; H, 3.88.

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