Intramolecular Alkynylogous Mukaiyama Aldol Reaction Starting from Bicyclic Alkanones Tethered to Alkynyl Esters: Formal Total Synthesis of (+/-)-Hamigeran B

tert-Butyldimethylsilyltriflate (TBSOTf)/NEt3 treatment of alkynyl esters tethered to bicycloalkanones led to tricyclic allenoates with total diastereoselectivity for the ring junction. The allenoates result from an intramolecular alkynylogous Mukaiyama aldol reaction promoted by a TBSOTf/NEt3 dual activation, with key intermediates of silylalkynylketene acetals. This novel methodology was illustrated by a formal total synthesis of (+/-)-hamigeran B