Achieving high selectivity and facile displacement with a new thiol auxiliary for boron-mediated aldol reactions.

Synthesis of a new thiol auxiliary (1) is readily achieved (in five or six steps, >74% overall yield from norephedrine) and is shown to give high diastereoselectivity in boron-mediated anti-aldol reactions with a range of aldehydes. This new thiol auxiliary may be directly displaced by a range of nucleophiles under very mild conditions, to give the corresponding phosphonate esters, alcohols, acids, SNAC thiolesters, and methyl esters.