HETEROCYCLES

Communication | Special issue | Vol. 80, No. 2, 2010, pp. 787-797
Received, 28th July, 2009, Accepted, 31st August, 2009, Published online, 2nd September, 2009.
DOI: 10.3987/COM-09-S(S)81

■ Allylic Alkylation of Indoles with Butadiene Promoted by Palladium Catalyst and Triethylborane

Masanari Kimura,* Katsumi Tohyama, Yumi Yamaguchi, and Tomohiko Kohno

Department of Applied Chemistry, Faculty of Engineering, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

Triethylborane promotes the Pd-catalyzed allylic alkylation of a wide variety of indoles with 1,3-butadiene to provide C3-octadienylindoles and C3-bis(octadienyl)indolenines in good to excellent yields under mild conditions.

Pd-catalyzed allylic alkylation is one of the most attractive strategies for constructing important fundamental constituents of complicated molecules and fine chemicals.1 Allylation of indoles is a particularly efficient and successful method for the construction of vital elements found in a diverse range of biologically and physiologically active molecules.2
Recently, we have demonstrated that a Pd(0) species in the presence of Et3B catalytically activates allylic alcohols to undergo electrophilic C-allylation of active methylene compounds3 and N-allylation of primary and secondary aromatic and aliphatic amines.4 Furthermore, the Pd/Et3B catalytic system worked effectively for the C3 selective allylation of indoles by direct use of allylic alcohols and provided 3-allylindoles in excellent yields (Scheme 1).5 The same procedure was applied to the diastereofacial selective alkylative cyclic amination on the C2-C3 double bond of tryptophan methyl ester and furnished hexahydropyrrolo[2,3-b]indole skeletons, found widely in many alkaloids such as physostigmine and amauromine. We have also found that the combination of Et3B and Pd catalyst effectively activates a wide variety of allylic alcohols to undergo either selective monoallylic alkylation of pyrroles at the C2 position with disubstituted allylic alcohols or diallylic alkylation at the C2 and C5 positions with monosubstituted allylic alcohols.6 It is possible to shift the selectivity in favor of monoallylation under conditions employing an excess amount of pyrrole and triethylamine as promoters. Moreover, we have also reported the Pd/Et3B system promoted the amphiphilic allylation of aldimines, which are prepared from a wide variety of amines and aldehydes with 2-methylenepropane-1,3-diol to construct nitrogen heterocyclic compounds such as pyrrolidines (Scheme 2).7 Thus, the combination of Pd(0) catalyst and Et3B works for the generation of both allyl cationic and anionic species directly from allylic alcohols to achieve amphiphilic allylation.

Since the development of η3-bis-π-allylpalladium species from Pd catalysts and conjugated dienes,8 the transition-metal catalyzed telomerization of conjugated dienes with nucleophiles has become an efficient method of C-C bond and C-hetero atom bond formation.9 Conjugated dienes are important building blocks for cosmetic chemicals and industrial polymers as well as physiologically active molecules such as terpenoids.10
Herein we report that the combination of Et3B and Pd catalyst promoted the dimerization of butadiene followed by electrophilic allylation at the C3 position of indole to provide 3-(2,7-octadienyl)indole 1, and the further allylated product, 3,3-bis(2,7-octadienyl)indolenine 2, in good to excellent yields (eq 1).

The reaction was performed simply by combining a homogeneous mixture of indole, Pd(PPh3)4 catalyst, 1,3-butadiene, and Et3B (30–240 mol %) in dry THF at room temperature under nitrogen atmosphere.11 Both Pd(PPh3)4 and Et3B are indispensable for the reaction; in the absence of either, no reaction takes place. The reactions of indole with 4 equivalents of 1,3-butadiene with various amounts of Et3B are summarized in Table 1. A catalytic amount of Et3B accelerated the dimerization of butadiene and the subsequent electrophilic allylation of indole gave rise to 3-(2,7-octadienyl)indole 1a in moderate yield (run 2, Table 1). Increasing the amount of Et3B generated a higher yield of the further octadienylated product, bis(2,7-octadienyl)indolenine 2a (runs 2-4, Table 1).
In the presence of excess butadiene (6 equivalents) and Et3B (2.4 equivalents), indolenine 2a was obtained as the sole product (run 5, Table 1). Next, we examined a wide variety of substituted indoles under similar catalytic systems. These results are summarized in Table 2. 3-Methylindole (skatole) was found to be an efficient substrate for the allylic alkylation (run 1, Table 2).

Treatment of skatole with 2.0 equivalents of 1,3-butadiene provided 3-methyl-3-(2,7-octadienyl)indolenine 1b in reasonable yield within 2 hours. Thus, the electrophilic alkylation reaction occurs smoothly with 3-alkyl substituted indoles with their enhanced nucleophilicity on the C3 carbon.5 4-Methylindole underwent a similar reaction to give octadienylindole 1c as a major product along with a trace amount of bis(octadienyl)indolenine 2c (run 2, Table 2). Nitro, methoxy, and bromo substituted indoles also participated in the reaction and the desired products were obtained in good to reasonable yields irrespective of the steric and electronic nature of the substituents (runs 3-6, Table 2). The indole NH group is required for the reaction to proceed; N-methyl substituted indole did not undergo the reaction at all under this catalytic system and was recovered quantitatively (run 7, Table 2). These results imply that Et3B coordinates to the nitrogen atom of indole, increasing its acidity, and thus activating the C3 enamine carbon atom towards electrophilic alkylation.

The present reaction was applied to the diastereoselective alkylation of tryptamine derivatives to afford pyrroloindoles. Under this catalytic system, 1,3-butadiene underwent the dimerization with concomitant electrophilic allylation at the C3 carbon atom of tryptamine and the subsequent intramolecular amination toward the electrophilic imine carbon atom furnished the pyrroloindole skeleton (eq 2). Tryptophol also underwent the consecutive allylic alkylation and amination processes involving dimerization of butadiene to give 2H-furo[2,3-b]indole in excellent yield (eq 3). This transformation has the potential for the efficient construction of vital indole alkaloid frameworks.

On the basis of these results, a plausible reaction mechanism via dimerization of butadiene promoted by Pd catalyst and Et3B is illustrated in Scheme 3. The Pd(0)-catalyzed dimerization of butadiene affords an η1,η3-octadienylpalladium species, which subsequently undergoes protonation at the C6 position to give the η3-allylpalladium indolyltriethylborate intermediate. Since indole is a heterocyclic compound containing a weakly Lewis basic nitrogen, Et3B is capable of serving as a Lewis acid to enhance the nucleophilicity of the C3 position by abstraction of a hydrogen atom from the NH bond. The activated indole readily undergoes Friedel-Crafts alkylation with the η3-octadienylpalladium species to provide 3-(2,7-octadienyl)indole, along with regeneration of the Pd(0) active species.

In summary, we have shown that a combination of Pd(0) catalyst and Et3B effectively activates butadiene to undergo the C-allylation of indole via oligomerization of the diene. The C3 carbon atom of the parent indole moiety serves as a good nucleophile to undergo exhaustive allylations to furnish the C3 bis(octadienyl)indolenine in high yield. Tryptamine and tryptophol also underwent similar allylic alkylations followed by intramolecular cyclization to afford pyrrolo[2,3-b]indole and 2H-furo[2,3-b]indole frameworks, respectively.

ACKNOWLEDGEMENTS
Financial support from the Ministry of Education, Culture, Sports, Science, and Technology, Japanese Government (Grant-in-Aid for Scientific Research (B) 21350055) is gratefully acknowledged. This work was partially supported by the Asahi Glass Foundation.

References

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11. Typical reaction procedure (run 4, Table 1): Into a N2 purged flask containing indole (117 mg, 1 mmol), Pd(PPh3)4 (55.6 mg, 0.05 mmol) purged with nitrogen were successively added THF (5 mL), 1,3-butadiene (400 µL, 4 mmol; liquefied by cooling at -78 ˚C prior to use under argon atmosphere) and triethylborane (2.4 mL, 1 M hexane; Aldrich) were introduced successively via a syringe. The reaction mixture was stirred at room temperature for 24 h, during which the reaction was monitored by means of TLC. After dilution with ethyl acetate (30 mL), the mixture was washed with sat. NaCl (30 mL). The organic layer was dried (MgSO4) and the solvent was removed in vacuo. The residue was subjected to the column chromatography over silica gel (Fujisirisia NH; eluent: hexane/EtOAc = 32:1) and 3-[(E)-octa-2,7-dienyl]-1H-indole (1a): and 3,3-bis[(E)-octa-2,7-dienyl]-3H-indole (2a) were obtained in 65% and 32% yields, respectively. 3-[(E)-Octa-2,7-dienyl]-1H-indole (1a): IR (neat) 3418 (s), 2926 (s), 1639 (s), 968 (s), 741 (s) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.48 (quint, J = 7.0 Hz, 2 H), 1.98 – 2.07 (m, 4 H), 3.48 (d, J = 7.0 Hz, 2 H), 4.93 (dd, J = 3.4, 10.1 Hz, 1 H), 4.99 (dd, J = 3.4, 17.1 Hz, 1 H), 5.57 (dt, J = 14.2, 7.0 Hz, 1 H), 5.67 (dt, J = 14.2, 7.0 Hz, 1 H), 5.80 (ddt, J = 10.1, 17.1, 7.0 Hz, 1 H), 6.96 (br s, 1 H), 7.09 (t, J = 7.4 Hz, 1 H), 7.20 (t, J = 7.4 Hz, 1 H), 7.34 (d, J = 7.4 Hz, 1 H), 7.59 (d, J = 7.4 Hz, 1 H), 7.90 (br s, 1 H); 13C NMR (CDCl3, 100 MHz): δ 28.6, 28.8, 31.2, 110.9, 114.2, 115.5, 119.0, 121.2, 121.8, 127.4, 128.8, 130.8, 136.3, 138.7, 141.9. High-resolution MS, calcd for C16H19N: 225.3288, Found m/z (relative intensity): 225.1490 (M+, 100), 225 (10), 182 (20).
3,3-Di[(E)-octa-2,7-dienyl]-3H-indole (2a): IR (neat) 2926 (s), 1639 (s), 970 (s), 910 (s), 742 (s) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.30 (quint, J = 7.0 Hz, 4 H), 1.82 – 1.98 (m, 8 H), 2.39 – 2.54 (m, 4 H), 4.91 (dd, J = 3.4, 10.1 Hz, 2 H), 4.93 (dd, J = 3.4, 17.5 Hz, 2 H), 5.09 (dt, J = 13.9, 7.0 Hz, 2 H), 5.34 (dt, J = 13.9, 7.0 Hz, 2 H), 5.72 (ddt, J = 10.1, 17.5, 7.0 Hz, 2 H), 7.19 – 7.33 (m, 3 H), 7.59 (d, J = 7.8 Hz, 1 H), 8.00 (br s, 1 H); 13C NMR (CDCl3, 100 MHz): δ 28.4, 31.7, 32.9, 37.4, 61.5, 114.3, 121.2, 122.1, 123.9, 125.6, 127.5, 134.3, 138.5, 141.7, 155.5, 177.9. High-resolution MS, calcd for C24H31N: 333.5096, Found m/z (relative intensity): 333.2451 (M+, 100), 265 (15).
Other new compound’s data are as follows.
3-Methyl-3-[(E)-octa-2,7-dienyl]-3H-indole (1b): IR (neat) 2925 (s), 1639 (s), 1603 (s), 972 (s), 910 (s), 743 (s) cm-1; 1H NMR (CDCl3, 400 MHz): δ 1.22 – 1.42 (m, 2 H), 1.34 (s, 3 H), 1.80 – 1.98 (m, 4 H), 2.39 (dd, J = 7.4, 13.7 Hz, 1 H), 2.44 (dd, J = 7.4, 13.7 Hz, 1 H), 4.92 (br d, J = 10.0 Hz, 1 H), 4.60 (br d, J = 17.6 Hz, 1 H), 5.15 (dt, J = 15.1, 7.4 Hz, 1 H), 5.40 (dt, J = 15.1, 7.4 Hz, 1 H), 5.75 (ddt, J = 10.0, 17.6, 7.4 Hz, 1 H), 7.22 – 7.38 (m, 3 H), 7.62 (d, J = 7.8 Hz, 1 H), 8.03 (s, 1 H); 13C NMR (CDCl3, 100 MHz): δ 20.0, 29.0, 32.2, 33.4, 39.6, 57.9, 114.8, 121.5, 122.0, 124.7, 126.3, 128.0, 134.9, 139.0, 143.8, 155.2, 179.4. High-resolution MS, calcd for C17H21N: 239.1674, Found m/z (relative intensity): 239.1666 (M+, 94), 224 (7), 170 (100).
4-Methyl-3-[(E)-octa-2,7-dienyl-1H-indole (1c): IR (neat) 3411 (s), 3321 (s), 2925 (m), 2856 (s), 1963 (m), 1618 (m), 1504 (s), 1436 (m), 1342 (m), 1155 (m), 970 (m), 910 (m), 746 (m) cm-1; 1H NMR (CDCl3, 400 MHz): δ 1.46 (quint, J = 7.4, 2 H), 2.04 (dtd, J = 7.4, 6.8, 1.2 Hz, 4 H), 2.68 (s, 3 H), 3.62 (dd, J = 6.1, 1.2 Hz, 2 H), 4.93 (dd, J = 10.2, 2.2 Hz, 1 H), 4.98 (dd, J = 17.1, 2.2 Hz, 1 H), 5.46 (dtt, J = 17.1, 6.7, 1.2 Hz, 1 H), 5.73 (dtt, J = 17.1, 6.1, 1.2 Hz, 1 H), 5.80 (ddt, J = 17.1, 10.2, 6.8 Hz, 1 H), 6. 81 (d, J = 7.2 Hz, 1 H), 6.91 (s, 1 H), 7.03 (dd, J = 7.9, 7.4 Hz, 1 H), 7.17 (d, J = 7.9, 1 H), 7.89 (br s, 1 H); 13C NMR (CDCl3, 100 MHz): δ 20.1, 28.8, 30.4, 31.9, 33.3, 108.8, 114.3, 116.3, 120.7, 121.7, 121.9 125.9, 123.0, 130.8, 136.8, 130.9, 136.8, 138.7. High-resolution MS, calcd for C17H21N: 239.1674, Found m/z (relative intensity): 239.1680 (M+, 100).
4-Methyl-3,3-di[(E)-octa-2,7-dienyl]-3H-indole (2c): IR (neat) 3076 (w), 2926 (m), 2854 (w), 1639 (w), 1529 (s), 1441 (w), 1354 (s), 1331 (w), 968 (m), 912 (m), 741 (m) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.22 (quint, J = 7.3 Hz, 4 H), 1.80 (dt, J = 13.7, 7.3 Hz, 8 H), 2.41 (s, 3 H), 2.60 (dd, J = 13.7, 7.1 Hz, 2 H), 2.72 (dd, J = 13.7, 7.1 Hz, 2 H), 4.84 - 4.91 (m, 6 H), 5.33 (dt, J = 15.1, 7.1 Hz, 2 H), 5.68 (ddt, J = 17.8, 9.5, 6.6 Hz, 2 H), 6.96 (d, J = 7.6 Hz, 1 H), 7.19 (t, J = 7.6 Hz, 1 H), 7.38 (d, J = 7.6 Hz, 1 H), 7.91 (s, 1 H); 13C NMR (CDCl3, 100 MHz) δ 18.4, 28.3, 31.5, 32.7, 36.0, 62.9, 114.2, 118.6, 124.0, 127.7, 127.8, 132.8, 133.4, 138.4, 138.6, 156.1, 177.8. HRMS calcd for C25H33N: 347.2613. Found m/z (relative intensity): 347.2608 (M+, 100).
4-Nitro-3-[(E)-octa-2,7-dienyl]-1H-indole (1d): IR (neat) 3385 (m), 2926 (m), 2853 (w), 1514 (s), 1443 (m), 1325 (s), 1290 (m), 1250 (m), 1111 (m), 972 (m), 912 (m), 787 (m), 732 (s) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.42 (quint, J = 7.6 Hz, 2 H), 2.00 (dt, J = 7.6, 6.6 Hz, 4 H), 3.55 (d, J = 6.3 Hz, 2 H), 4.92 (ddt, J = 10.3, 2.2, 1.2 Hz, 1 H), 4.97 (ddt, J = 17.1, 2.2, 1.7 Hz, 1 H), 5.39 (dtt, J = 15.1, 6.6, 1.3 Hz, 1 H), 5.56 (dtt, J = 15.1, 6.3, 1.3 Hz, 1 H), 5.78 (ddt, J = 17.1, 10.3, 6.6 Hz, 1 H), 7.20 (s, 1 H), 7.60 (dd, J = 8.0, 0.9 Hz, 1 H), 7.76 (dd, J = 8.0, 0.9 Hz, 1 H), 8.30 - 8.46 (br s, 1 H); 13C NMR (CDCl3, 100 MHz) δ 28.7, 30.3, 31.9, 33.2, 114.2, 115.5, 116.5, 117.1, 119.0, 120.6, 126.3, 127.9, 128.9, 131.2, 138.7, 138.9. HRMS calcd for C16H18N2O2: 270.1368. Found m/z (relative intensity): 270.1369 (M+, 100).
4-Nitro-3,3-di[(E)-octa-2,7-dienyl]-3H-indole (2d): IR (neat) 3074 (m), 2926 (s), 2853 (s), 1639 (s), 1593 (w), 1562 (m), 1440 (s), 1416 (m), 964 (s), 910 (s), 789 (s), 748 (s) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.13 (quint, J = 6.8 Hz, 4 H), 1.71 (dt, J = 7.3, 6.8 Hz, 8 H), 2.77 (dd, J = 13.9, 6.8 Hz, 2 H), 2.98 (dd, J = 13.9, 6.8 Hz, 2 H), 4.77 (dt, J = 14.3, 6.8 Hz, 2 H), 4.89 (dd, J = 16.3, 2.2 Hz, 2 H), 4.86 (dd, J = 10.7, 2.2 Hz, 2 H), 5.30 (dt, J = 14.3, 7.3 Hz, 2 H), 5.63 (ddt, J = 16.3, 10.7, 6.8 Hz, 2 H), 7.48 (dd, J = 8.3, 7.6 Hz, 1 H), 7.86 (d, J = 7.6 Hz, 1 H), 8.00 (d, J = 8.3 Hz, 1 H), 8.08 (s, 1 H); 13C NMR (CDCl3, 100 MHz) δ 28.2, 31.4, 32.6, 35.1, 66.4, 114.3, 121.5, 123.2, 126.7, 128.9, 134.4, 135.6, 138.4, 146.1, 159.2, 180.6. HRMS calcd for C24H30N2O2: 378.2307. Found m/z (relative intensity): 378.2297 (M+, 100).
5-Nitro-3-[(E)-octa-2,7-dienyl]-1H-indole (1e): IR (neat) 3375 (s), 2926 (m), 2839 (w), 1624 (w), 1510 (m), 1470 (m), 1319 (s), 1221 (m), 1101 (m), 968 (w), 912 (w), 738 (w) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.49 (quint, J = 7.4 Hz, 2 H), 2.03 - 2.09 (m, 4 H), 3.49 (dd, J = 5.1, 0.7 Hz, 2 H), 4.93 (ddt, J = 10.3, 2.2, 1.2 Hz, 1 H), 4.99 (d, J = 17.1, 2.2, 1.7 Hz, 1 H), 5.56 - 5.69 (m, 2 H), 5.80 (ddt, J = 17.1, 10.3, 6.8 Hz, 1 H), 7.11 (s, 1 H), 7.36 (d, J = 9.0 Hz, 1 H), 8.10 (dd, J = 9.0, 2.2 Hz, 1 H), 8.27 - 8.38 (br s, 1 H), 8.57 (d, J = 2.2 Hz, 1 H); 13C NMR (CDCl3, 100 MHz) δ 28.3, 28.7, 28.3, 31.8, 33.2, 110.8, 114.4, 116.5, 117.6, 117.7, 118.2, 126.8, 127.7, 131.8, 138.6, 139.3, 141.4. HRMS calcd for C16H18N2O2: 270.1368. Found m/z (relative intensity): 270.1369 (M+, 100), 269 (7).
5-Methoxy-3-[(E)-octa-2,7-dienyl]-1H-indole (1f): IR (neat) 3417 (s), 2927 (s), 2831(m), 1624(s), 1585(m), 1485 (m), 1454 (s), 1215 (m), 1172 (m), 968 (m), 914 (m), 831 (m) cm-1; 1H NMR (CDCl3, 400 MHz): δ 1.49 (quint, J = 7.3, 2 H), 2.05 (dt, J = 6.6, 7.3 Hz, 4 H), 3.41 (d, J = 6.1 Hz, 2 H), 3.84 (s, 3 H), 4.92 (dd, J = 10.2, 2.0 Hz, 1 H), 4.98 (dd, J = 17.1, 2.0 Hz, 1 H), 5.58 (dd, J = 15.2, 6.6 Hz, 1 H), 5.66 (dd, J = 15.3, 6.1 Hz, 1 H), 5.79 (ddt, J = 17.1, 10.2, 6.6 Hz, 1 H), 6.83 (dd, J = 8.8, 2.4 Hz, 1 H), 6.93 (s, 3 H), 7.03 (d, J = 2.4 Hz, 1 H), 7.22 (d, J = 8.8 Hz, 1 H), 7.88 (br s, 1 H); 13C NMR (CDCl3, 100 MHz): δ 28.7, 28.8, 31.9, 33.2, 55.9, 111.6, 112.0, 114.3, 115.1, 122.1, 127.8, 128.7, 130.8 131.5, 138.7, 153.7. High-resolution MS, calcd for C17H21NO: 255.1623, Found m/z (relative intensity): 255.1620 (M+, 100).
5-Methoxy-3-bis[(E)-octa-2,7-dienyl]-3H-indole (2f): IR (neat) 3074 (s), 2925 (s), 2837(m), 1963(s), 1591(m), 1554 (m), 1469 (s), 1336 (m), 1228 (m), 1176 (m), 966 (m), 910 (m), 810 (m) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.31 (quint, J = 7.3 Hz, 4 H), 1.89 - 1.93 (m, 8 H), 2.39 (dd, J = 13.4, 6.8 Hz, 2 H), 2.46 (dd, J = 13.3, 7.4 Hz, 2 H), 3.82 (s, 3 H), 4.90 (dd, J = 10.2, 3.2 Hz, 1 H), 4.91 (dd, J = 10.2, 3.2 Hz, 1 H), 4.92 (dd, J = 17.1, 3.2 Hz, 1 H), 4.93 (dd, J = 17.1, 3.2 Hz, 1 H), 5.10 (dd, J = 15.1, 6.8 Hz, 2 H), 5.37 (dt, J = 15.1, 7.4 Hz, 2 H), 5.72 (ddt, J = 17.1, 10.2, 6.6 Hz, 2 H), 6. 80 - 6.84 (m, 2 H), 7.74 - 7.50 (m, 1 H), 7.88 (br s, 1 H); 13C NMR (CDCl3, 100 MHz): δ 28.5, 31.7, 32.9, 37.5, 55.7, 62.6, 109.0, 112.1, 114.3, 121.1, 124.0, 134.3, 138.5 143.5, 149.3, 158.2, 175.9. High-resolution MS, calcd for C25H33NO: 363.2562, Found m/z (relative intensity): 363.2568 (M+, 66), 309 (100).
6-Bromo-3-[(E)-octa-2,7-dienyl]-1H-indole (1g): IR (neat): 3425 (s), 2925 (s), 2854 (m), 1640 (m), 1614 (m), 1454 (m), 1332 (m), 1089 (m), 968 (m), 802 (m) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.46 (quint, J = 7.4 Hz, 2 H), 2.04 (dt, J = 7.4, 6.3 Hz, 1 H), 2.04 (dt, J = 7.4, 6.7, 1.8 Hz, 1 H), 3.42 (dd, J = 6.1, 1.1Hz, 1 H), 4.93 (dd, J = 10.1, 1.8 Hz, 1 H), 4.98 (dq, J = 17.1, 1.8 Hz, 1 H), 5.59 (dt, J = 16.3, 6.3 Hz, 1 H), 5.63 (dt, J = 16.3, 6.1 Hz, 1 H), 5.79 (ddt, J = 17.1, 10.1, 6.7 Hz, 1 H), 6.93 (t, J = 1.1 Hz, 1 H), 7.18 (dd, J = 8.4, 1.7 Hz, 1 H), 7.44 (d, J = 8.4 Hz, 1 H), 7.49 (d, J = 1.7 Hz, 1 H), 7.90 (br s, 1 H); 13C NMR (CDCl3, 100 MHz) δ 28.5, 28.7, 31.8, 33.2, 113.8, 114.3, 115.4, 115.7, 120.3, 121.9, 122.4, 126.3, 128.4, 131.1, 138.6. High-resolution MS, calcd for C16H18BrN: 303.0623, Found m/z (relative intensity): 303.0629 (M+, 49), 249 (100).
6-Bromo-3,3-bis[(E)-octa-2,7-dienyl]-3H-indole (2g): IR (neat) 3074 (m), 2925 (s), 2825 (m), 1639 (s), 1593 (s), 1471 (s), 970 (s), 910 (s), 802 (m) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.31 (quint, J = 7.5 Hz, 4 H), 1.82 - 1.95 (m, 8 H), 2.41 (dd, J = 13.9, 7.8 Hz, 2 H), 2.47 (dd, J = 13.9, 7.8 Hz, 2 H), 4.92 (dd, J = 10.4, 1.6 Hz, 2 H), 4.94 (dq, J = 17.0, 1.6 Hz, 2 H), 5.03 (dt, J = 14.9, 7.8 Hz, 2 H), 5.36 (dt, J = 14.9, 6.9 Hz, 2 H), 5.73 (ddt, J = 17.0, 10.2, 6.7 Hz, 2 H), 7.12 (dd, J = 8.0 Hz, 1 H), 7.36 (dd, J = 8.0, 1.8 Hz, 1 H), 7.73 (d, J = 1.8 Hz, 1 H); 13C NMR (CDCl3, 100 MHz) δ 28.4 (2C), 32.9 (4C), 37.2 (2C), 61.7, 114.4 (2C), 120.9, 123.3, 123.5 (4C), 124.4, 128.5, 134.7 138.4 (2C), 140.6, 157.0. High-resolution MS, calcd for C24H30BrN: 411.1562, Found m/z (relative intensity): 411.1556 (M+, 100).
1,2,3,3a,8,8a-Hexahydro-1-methoxycarbonyl-3a-(2,7-octadienyl)-pyrrolo[2,3-b]indole (3): IR (neat) 2925 (s), 2856 (s), 1705 (s), 1639 (s), 1606 (s), 1490 (s), 1448 (s), 1386 (s), 1211 (s), 968 (s), 740 (s); 1H NMR (CDCl3, 400 MHz) δ 1.43 (quint, J = 7.4 Hz, 2 H), 2.01 - 2.14 (m, 4 H), 2.37 (d, J = 6.3 Hz, 2 H), 3.03 (d, J = 3.2 Hz, 1 H), 3.57 (dt, J = 2.7, 7.3 Hz, 1 H), 3.58 (dd, J = 2.7, 10.0 Hz, 1 H), 3.64 (s, 3 H), 4.97 (dd, J = 2.0, 17.1 Hz, 1 H), 4.93 (dd, J = 1.9, 10.2 Hz, 1 H), 5.12 (s, 1 H), 5.44 (dt, J = 6.3, 14.9 Hz, 2 H), 5.77 (ddt, J = 6.7, 10.2, 17.1 Hz, 1 H), 6.53 - 6.58 (m, 2 H), 6.75 - 6.70 (m, 2 H), 7.00 - 7.05 (m, 2 H); 13C NMR (CDCl3, 100 MHz) δ 28.6, 31.9, 33.1, 34.9, 41.0, 45.8, 52.4, 57.3, 80.1, 109.1, 114.3, 118.5, 123.0, 125.0, 128.1, 131.8, 134.1, 138.5, 155.4. Anal. Calcd for C20H26N2O2: C, 73.59; H, 8.03; N, 8.58; O, 9.80. Found: C, 73.42; H, 8.40; N, 8.38.
3,3a,8,8a-Tetrahydro-3a-(2,7-octadienyl)-2H-furo[2,3-b]indole (4): IR (neat) 3352 (s), 2858 (s), 1639 (s), 1611 (s), 910 (s), 742 (s) cm-1; 1H NMR (CDCl3, 400 MHz) δ 1.40 (quint, J = 7.4 Hz, 2 H), 1.90 – 2.02 (m, 6 H), 2.41 (dd, J = 7.8, 14.1 Hz, 1 H), 2.51 (dd, J = 6.3, 14.1 Hz, 1 H), 3.54 (m, 1 H), 3.94 (m, 1 H), 4.54 (br s, 1 H), 4.93 (br d, J = 10.3 Hz, 1 H), 4.96 (br d, J = 14.3 Hz, 1 H), 5.33 (m, 1 H), 5.35 (br s, 1 H), 5.46 (m, 1 H), 5.76 (dddd, J = 6.3, 7.8, 10.3, 14.3 Hz, 1 H), 6.57 (d, J = 7.6 Hz, 1 H), 6.74 (t, J = 7.6 Hz, 1 H), 7.03 – 7.07 (m, 2 H); 13C NMR (CDCl3, 100 MHz) δ 28.6, 31.9, 33.0, 39.5, 41.2, 57.9, 67.1, 97.4, 108.1, 114.3, 118.6, 123.5, 125.6, 127.9, 132.4, 133.8, 138.6, 149.4. High-resolution MS, calcd for C18H23NO: 269.1780, Found m/z (relative intensity): 269.1780 (M+, 100), 215 (11).