The conjugateaddition of Ti “ate” complexes of ketone enolates to α,β-unsaturated ketones can be accelerated by activating the substrate via complexation with t-BuMe2SiCl or trityl triflate.
The conjugate addition of Ti “ate” complexes of ketone and ester enolates to α,β-unsaturated carbonyl compounds was studied. The reaction was found to be highly regio- and stereoselective. Compared to the lithium enolates, ketone enolate Ti complexes showed an improved 1,4-regioselectivity. t-Butyl propionate enolate Ti complex gave the opposite stereochemical results compared to the parent lithium
Michael reactionbetween silyl enolates and 0',/3-unsaturated carbonyl compounds by using a catalytic amount of Lewis base such as lithium alkoxide in DMF proceeds smoothly to afford the corresponding Michael-adducts in good yields with moderate to high diastereoselectivities. This reaction can be reasonably explained by considering an alkoxide anion-initiated autocatalytic process.