Catalytic asymmetric hydrogenation of indoles using a rhodium complex with a chiral bisphosphine ligand PhTRAP

Highly enantioselective hydrogenation of N-protceted indoles was successfully developed by use of the rhodium catalyst generated in situ from [Rh(nbd)(2)]SbF6 and the chiral bisphosphine PhTRAP, which can form a trans-chelate complex with a transition metal atom. The PhTRAP-rhodium catalyst required a base (e.g., Cs2CO3) for the achievement of high enantioselectivity. Various 2-substituted N-acetylindoles were converted into the corresponding chiral indolines with up to 95% ee. The hydrogenations of 3-substituted N-tosylindoles yielded indolines possessing a stereogenic center at the 3-position with high enantiomeric excesses (Lip to 98% ee). (c) 2006 Elsevier Ltd. All rights reserved.