Asymmetric Michael addition of silyl nitronates to cyclic α,β-unsaturated ketones catalyzed by chiral quaternary ammonium bifluorides:: isolation and selective functionalization of enol silyl ethers of optically active γ-nitro ketones

Highly enantio selective Michael addition of silyl nitronates to cyclic alpha,beta-unsaturated ketones has been accomplished by the utilization of N-spiro C-2-symmetric chiral quaternary ammonium bifluoride 1 as an efficient catalyst, offering a new route to the enol silyl ethers of optically active gamma-nitro ketones. The synthetic utility of this transformation has been demonstrated by the diastereoselective derivatizations of the optically active enol silyl ethers to the corresponding alpha-substituted cyclic ketones having three consecutive stereochemically defined stercocenters. (c) 2005 Elsevier Ltd. All rights reserved.