Substrate-controlled stereoselectivity in the Yamamoto aldol reaction.

The Yamamoto aldol reaction is a vinylogous aldol reaction that relies on bulky aluminium-based Lewis acids. These activate both the aldehyde as well as become part of the enolate moiety. The report discloses the first detailed study on the substrate-controlled Yamamoto aldol reaction in which 2,3-syn and 2,3-anti disubstituted aldehydes serve as the stereodirecting elements. The "size" of the substituent in the β-position strongly determines the facial selectivity of enolate addition to the aldehyde. Large substituents favour formation of 1,3-syn diols while slim alkynyl groups preferentially lead to 1,3-anti products.