Brønsted acid-catalyzed asymmetric allylation and propargylation of aldehydes

Abstract

A method synthesizing homoallylic or homopropargylic alcohols was developed to react aldehydes with allyl boronates, such as allylboronic acid pinacol ester, or allenylborates in the presence of a catalytic amount of a chiral binaphthyl-derived chiral phosphoric acid. The method showed enhanced enantiocontrol and chemical yield, which increased with lower temperatures. A large series of aldehydes were tested under these catalytic conditions and wide successful substrate scope was found, including aryl, heteroaryl, aromatic aldehydes, heteroaryl aldehydes, α,β-unsaturated aldehydes and aliphatic aldehydes, and alkyl aldehydes. Likewise, the use of crotyl boronates (E and Z) were successfully reacted with aryl aldehydes under the conditions to allow for highly enantio- and diasteo-selective crotylation.