Titanium enolates and “ate” complexes of N,N-disubstituted amides and thioamides in the Michael reaction.

Abstract The synthetic potential, regio- and stereoselectivity of titanium dialkylamide and dialkylthioamide enolates and “ate” complexes in reaction with some conjugate carbonyl compounds are investigated. Titanium enolates react preferentially in 1,2-position while “ate” complexes afford 1,4-regiocontrol. The stereochemical behaviour of the latter follows in general the lithium and potassium precursors. Marked influence of solvent and of electrophile geometry on 1,4-stereoselectivity was found with the amides but not with the thioanalogs. The stereochemistry of the amide titanium “ate” complexes is correlated with a cyclic transition state. The solvent effect is explained by involvement into the transition structure. Some advantages of the titanium “ate” complexes are discussed.