Enantioselective Alkylations of Tributyltin Enolates Catalyzed by Cr(salen)Cl:  Access to Enantiomerically Enriched All-Carbon Quaternary Centers

The catalytic asymmetric alpha-alkylation of tributyltin enolates with a range of primary alkyl halides is catalyzed by a chiral Cr(salen) complex. The reaction constitutes the first transition-metal-catalyzed system for alpha-alkylation of carbonyl substrates with this important class of electrophiles, providing access to five-, six-, and seven-membered ring ketone products bearing alpha-quaternary stereocenters in high enantioselectivity and synthetically useful yields.