Highly diastereoselective Michael addition of lithiated camphor imines of glycine esters to .alpha.,.beta.-unsaturated esters. Synthesis of optically pure 5-oxo-2,4-pyrrolidinedicarboxylates of unnatural stereochemistry

Abstract

The lithium enolates of camphor imines of glycine esters underwent highly diastereoselective Michael additions to α,β-unsaturated esters. The tightly chelated structure of the Z,E enolates and the selective approach of the α,β-unsaturated esters to the re face of the enolates were responsible for the high diastereoselectivity observed. The use of alkylidenemalonate acceptors led to the diastereospecific formation of Michael adducts. Removal of the camphor auxiliary of the adducts and concomitant cyclization led to optically pure enantiomeric 5-oxo-2,4-pyrrolidinedicarboxylates of unnatural stereochemistry