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Angewandte
Communications
P. M. Pihko), Wiley-VCH, Weinheim, 2009, chap. 6; d) Y. Xi, X.
Keywords: asymmetric catalysis · cyclizations · lactams ·
organocatalysis · reaction mechanisms
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How to cite: Angew. Chem. Int. Ed. 2015, 54, 12102–12106
Angew. Chem. 2015, 127, 12270–12274
[1] For reviews on halocyclization, see: a) A. Castellanos, S. P.
2012, 7, 456; d) S. E. Denmark, W. E. Kuester, M. T. Burk,
f) K. Murai, H. Fujioka, Heterocycles 2013, 87, 763; g) C. K. Tan,
[10] a) See Ref. [4b]; b) Y. Zhao, X. Jiang, Y.-Y. Yeung, Angew.
c) L. Zhou, D. W. Tay, J. Chen, G. Y. C. Leung, Y.-Y. Yeung,
Chem. Commun. 2013, 49, 4412; d) X. Jiang, C. K. Tan, L. Zhou,
[11] The details appear in the Supporting Information.
[12] The ee value of the bromolactamization product was highly
dependent on the size of the alcohol additive, and much lower
conversion was observed when a sterically bulky alcohol was
used. In addition, the use of Et2O in place of EtOH as the
additive led to a significant reduction in ee value, thus suggesting
that the hydroxy group of EtOH might play a crucial role in the
reaction. Thus, we speculate that the ethanol might involve in the
enantiodetermining step with the involvement of hydrogen
bonding. For details, see the Supporting Information.
[13] CCDC 1063550 (2h) and 1063551 (5b) contain the supplemen-
tary crystallographic data for this paper. These data can be
[15] S. M. Ahmad, D. C. Braddock, G. Cansell, S. A. Hermitage, J. M.
[16] Since carbamate can undergo tautomerization, we cannot rule
out the possibility that 3d-Br might exist as the form of O-Br
species instead of N-Br species.
[2] For selected recent efforts on the development of catalytic
enantioselective halolactonization, see: a) K. Murai, J. Naka-
Synlett 2014, 1701; e) T. Arai, N. Sugiyama, H. Masu, S. Kado, S.
[3] For selected recent efforts on the development of catalytic
enantioselective haloaminocyclization, see: a) C. B. Tripathi, S.
G. Jiang, H. Liu, J. Hu, X. Pan, H. Zhang, X. Wan, Y. Lai, D. Ma,
[4] For selected recent efforts on the development of catalytic
enantioselective haloetherification, see: a) C. H. Müller, C.
Tay, G. Y. C. Leung, Y.-Y. Yeung, Angew. Chem. Int. Ed. 2014,
[5] For elegant reports of enantioselective bromo-N-cyclization of
olefinic carbamate substrates using a metal catalysts, see: a) D.
Harding, T. H. Tiner in Comprehensive Organic Synthesis, Vol. 4
(Ed.: B. M. Trost), Pergamon, New York, 1991, p. 363.
[7] a) A. Jaganathan, A. Garzan, D. C. Whitehead, R. J. Staples, B.
M. Wang, J. Wu, C. Hoong, V. Rauniyar, F. D. Toste, J. Am.
Kawato, A. Kubota, H. Ono, H. Egami, Y. Hamashima, Org.
[17] Although the reaction rate between 3d and NBS was slow, the
reaction rate between 3d and bromine source could be greatly
enhanced by replacing NBS with TBCO.
[8] Organocatalysts such as thioureas have been widely utilized in
various asymmetric reactions. In contrast, carbamates have not
been used as catalysts in organic transformations. For references
on thiourea organocatalysts, see: a) M. S. Sigman, E. N. Jacob-
C. E. Song, Cinchona Alkaloids in Synthesis and Catalysis:
Ligands, Immobilization and Organocatalysis (Ed.: C. E. Song),
Wiley-VCH, Weinheim, 2009, chap. 8; c) M. Kotke, P. R.
Schreiner in Hydrogen Bonding in Organic Synthesis (Ed.:
[18] We also attempted to cyclize an olefinic amide with a benzene
core instead of an indole. The corresponding bromolactam could
be obtained in good yield and appreciable enantioselectivity. For
details, see the Supporting Information.
Received: May 25, 2015
Revised: July 5, 2015
Published online: August 28, 2015
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 12102 –12106