An asymmetric synthesis of a key intermediate 16 to (+)-lactacystin 1 has been established starting from epoxide 2 via intramolecular mercurioamidation of allylic trichloroacetimidate 4 and concomitant addition-reduction of ester 13 by Prⁱ MgBr, in which reduction of the intermediate ketone proceeded with complete stereoselectivity.