tert-Butyldimethylsilyltriflate (TBSOTf)/NEt(3) 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/NEt(3) dual activation, with key intermediates of silylalkynylketene acetals. This novel methodology was illustrated by a formal total synthesis of (+/-)-hamigeran B.
The combination of a modular assembly of enantiopure triynes and a powerful rhodium-catalyzed [2 + 2 + 2] alkyne cyclotrimerization reaction opens new and efficient entries to a set of alcyopterosins, including the first total synthesis of the alcyopterosins L, M, and C.
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