Chiral bifunctional sulfide-catalyzed asymmetric bromoaminocyclizations
Takumi Nakamura, Ken Okuno, Kazuma Kaneko, Masahiro Yamanaka, Seiji Shirakawa
Abstract
A BINOL-derived chiral bifunctional sulfide catalyst bearing a phenylurea moiety was applied to enantioselective bromoaminocyclization reactions of 2-allylaniline derivatives, which provide optically active 2-substituted indoline products as important motifs for biologically active compounds. A protecting group on the nitrogen of the 2-allylaniline substrate was carefully optimized, and highly enantioselective reactions were achieved by employing the p-biphenylsulfonyl-protected substrates. The origin of the good level of enantioselectivity for the present bromoaminocyclization was also investigated on the basis of DFT calculations. The resultant optically active 2-(bromomethyl)indoline products could be transformed to various 2-substituted indolines with no loss of the optical purity.