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tetrahydroindole-3-carboxylate methyl ester, THI-3-CO2Me, C10H13NO2 extending the reaction time (48 hours) the conversion never exceeded
(2a).7 The window of activity for PHI-3-CO2Me was similar to all other 91% (GCMS) and was isolated by alumina filtration (87%). 1H NMR
indolic molecules described above, and only deviated by requiring an (300 MHz, CDCl3): 7.31–7.20 (m, 3H), 6.99 (m, 2H), 4.90 (s, 2H), 2.44
extra 24 hours (72 hours total) for completion. The reaction is quanti- (m, 8H), 1.82–1.71 (m, 8H). 13C NMR (126 MHz, CDCl3): 139.05, 128.57,
tative by GCMS and 89% isolated by distillation. Perhydrocarbazole, PHC 126.85, 126.22, 126.18, 114.73, 46.19, 23.62, 23.55, 21.83, 21.36.
(3) to octahydrocarbazole, OHC, C12H17N (3a).13 PHC deviated from the
1 Y. Ye, G. W. Qin and R. S. Xu, Phytochemistry, 1994, 37, 1201–1203.
2 F. Schroder, S. Franke, W. Francke, H. Baumann, M. Kaib, J. M.
Pasteels and D. Daloze, Tetrahedron, 1996, 52, 13539–13546.
3 C. C. McComas and D. L. Van Vranken, Tetrahedron Lett., 1999, 40,
8039–8043.
4 D. O’Hagan, Nat. Prod. Rep., 2000, 17, 435–446.
5 M. Bergauer, H. Hubner and P. Gmeiner, Tetrahedron, 2004, 60,
1197–1204.
6 D. F. Brayton, C. M. Jensen and S. Jorgensen, Proceedings of the
2012 US Department of Energy Annual Merit Review Meeting, 2012,
Crystal City, VA.
7 D. Clarisse, B. Fenet and F. Fache, Org. Biomol. Chem., 2012, 10,
6587–6594.
8 D. H. Mei, M. Neurock and C. M. Smith, J. Catal., 2009, 268,
181–195.
9 V. A. Mamedov, T. N. Beschastnova, N. A. Zhukova, A. T. Gubaidullin,
R. A. Isanov and I. K. Rizvanov, Tetrahedron Lett., 2008, 49,
4658–4660.
10 L. Piras, C. Ghiron, G. Minetto and M. Taddei, Tetrahedron Lett.,
2008, 49, 459–462.
11 I. Gottker-Schnetmann, P. White and M. Brookhart, J. Am. Chem.
Soc., 2004, 126, 1804–1811.
standard dehydrogenation techniques by requiring an extra 24 hours
(72 hours total) for completion and quadrupling the catalyst loading
(4%). The reaction was found to be quantitative by GCMS and was
isolated by alumina filtration (92%). Methyl perhydrocarbazole, MePHC
(4) to methyl octahydrocarbazole, MeOHC, C13H19N (4a). MePHC deviated
from the standard dehydrogenation techniques by requiring an
increase the catalyst loading (2.5%). The reaction was found to be
quantitative by GCMS and was isolated by alumina filtration (91%).
1H NMR (300 MHz, CDCl3): 3.31 (s, 3H), 2.52 (m, 4H), 2.41 (m, 4H), 1.84
(m, 4H) 1.74 (m, 4H). 13C NMR (126 MHz, CDCl3): 126.16, 114.35, 29.70,
23.58, 23.50, 21.69, 21.23. Ethyl perhydrocarbazole, EPHC (5) to ethyl
octahydrocarbazole, EOHC, C14H21N (5a). EPHC’s selective dehydrogena-
tion window is much narrower, activity starts at 172 1C, but the outer
rings begin to undergo dehydrogenation at 180 1C. The optimum
temperature was found to be 178 1C and two days for complete
conversion (EPHC completely consumed, GCMS). At some point prior
to isolation the ethyl group is cleaved, giving 86% ethyloctahydro-
carbazole (EOHC) and 9% octahydrocarbazole (OHC). The same pro-
duct distribution is observed whether isolated via distillation or by
alumina plug filtration. 1H NMR (300 MHz, CDCl3): 3.72 (q, J = 7 Hz,
2H), 2.55 (m, 4H), 2.41 (m, 4H), 1.85–1.74 (m, 8H), 1.24 (t, J = 7 Hz, 3H).
13C NMR (126 MHz, CDCl3): 125.21, 114.27, 37.24, 23.49, 23.47, 21.59,
21.16, 16.41. Benzyl perhydroindole, BPHI (6) to benzyl tetrahydroindole,
BTHI, C15H17N (6a).14 BPHI deviated from the standard indolic dehydro-
genation techniques as regardless of ramping up mol% of catalyst or
extending the reaction time (48 hours) the conversion never exceeded
89% (GCMS) and was isolated by alumina filtration (86%). Benzyl per-
12 J. Illesinghe, R. Ebeling, B. Ferguson, J. Patel, E. M. Campi,
W. R. Jackson and A. J. Robinson, Aust. J. Chem., 2004, 57, 167–176.
13 R. S. Alekseyev, A. V. Kurkin and M. A. Yurovskaya, Chem. Heterocycl.
Compd., 2011, 47, 584–596.
14 I. A. Andreev, D. S. Belov, A. V. Kurkin and M. A. Yurovskaya,
Eur. J. Org. Chem., 2013, 649–652.
hydrocarbazole, BPHC (7) to benzyl octahydrocarbazole BOHC, C19H23
N
(7a).15 (7a). BPHC deviated from the standard carbazolic dehydro- 15 B. K. Banik, S. Samajdar and I. Banik, J. Org. Chem., 2004, 69,
genation techniques as regardless of ramping up mol% of catalyst or
213–216.
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Chem. Commun., 2014, 50, 5987--5989 | 5989