Highly Diastereoselective Aldol Additions of a Chiral Ethyl Ketone Enolate under Lewis Base Catalysis

The aldol addition of a chiral ethyl ketone enolate bearing an oxygen substituent (OTBS) at the α-position proceeds with high internal and relative diastereoselectivities with various achiral aldehydes in good yields. The profound influence of the resident stereogenic center allows for the use of an achiral catalyst, such as HMPA, with minor attenuation in internal stereoselectivity.