Highly enantioselective synthesis of α-methylene-δ-valerolactones by an asymmetric Michael reaction
摘要:
The synthesis of alpha-methylene-6-valerolactones 7, 13, and 19 with enantiomeric excesses of 90-97% was achieved by the asymmetric Michael reaction of chiral imines 3, 9, and 15 with the acrylate 1. Reduction of the carbonyl group of the resulting adducts followed by lactonization and HWE reaction with formaldehyde yielded the lactones as mixtures of diastereoisomers. (c) 2006 Elsevier Ltd. All rights reserved.
The enantioselective Michael-type reaction of chiral 2-substituted cyclic imines, reacting as their secondary enamine tautomers, has been extended to a linear ketimine possessing an oxo group on one of the substituents. A single secondary enamine tautomer is observed due to H-bonding of the NH group, thus allowing the reaction to proceed with a high degree of stereoselectivity.