tert‐Butyldimethylsilyl‐Directed Highly Enantioselective Approach to Axially Chiral α‐Allenols

A highly efficient and enantioselective synthesis of axially chiral α-allenols was realized in practical yields with 96-99% ee or de from TBS-protected propargylic alcohols, aldehydes, and a commercially available, inexpensive, chiral, secondary amine (S)-α,α-diphenylprolinol or its enantiomer followed by desilylation. The easily removable TBS group not only acts as a protecting group, but also as a possible sterically directing group for the excellent enantioselectivity and in situ prevention of possible allene racemization.