Enantioselective Michael addition of 2-nitropropane to chalcone analogues catalyzed by chiral azacrown ethers based on α-D-glucose and D-mannitol

The chiral monoaza-15-crown-5 type lariat ethers 1 and 2 derived from alpha-(D)-glucose and from (D)-mannitol, respectively, have been applied as phase transfer catalysts in the enantioselective Michael addition of 2-nitropropane to aromatic 3b-c and heteroaromatic 3d-h chalcone analogues. Among the catalysts, the glucose-based le with a phosphinoxidobutyl side arm proved to be the most effective, it inducing 34% e.e. for 4b, 59% e.e. for 4c, 80% e.e. for 4d, 64% e.e. for 4e, 17% e.e. for 4f. Catalyst la having 3-hydroxypropyl substituent resulted in 81% e.e. for compound 4g. The formation of the (+)-(S)-enantiomer of 4 was preferred using crown ethers 1a-c, while the (-)-(R)-enantiomer was in excess with catalyst 2. The absolute configuration of the Michael adduct 4d was determined by single-crystal X-ray analysis. (C) 2003 Elsevier Science Ltd. All rights reserved.