Substrate-Controlled Michael Additions of Chiral Ketones to Enones
摘要:
Substrate-controlled Michael additions of the titanium(IV) enolate of lactate-derived ketone 1 to acyclic alpha,beta-unsaturated ketones in the presence of a Lewis acid (TiCl4 or SnCl4) provide the corresponding 2,4-anti-4,5-anti dicarbonyl compounds in good yields and excellent diastereomeric ratios. Likely, the nucleophilic species involved in such additions are bimetallic enolates that may add to enones through cyclic transition states. Finally, further studies indicate that a structurally related beta-benzyloxy chiral ketone can also participate in such stereocontrolled conjugate additions.
Titanium chloride-mediated reactions of the silyl ketene acetals derived from N-methylephedrine esters: an asymmetric variant of the Mukaiyama reaction