Toward an Enantioselective Total Synthesis of Sarain A: Construction of an Advanced Intermediate and Rearrangement of the Sarain A Core under Mild Conditions

A high-yielding N-sulfonyliminium ion-enoxysilane cyclization and a ring-closing metathesis are key steps in the enantioselective synthesis of late-stage intermediates en route to sarain A. Also revealed is an unprecedented rearrangement of the tetracyclic sarain A core under mildly acidic conditions. [structure: see text]