Ring opening of alkynyl sugars by Nicholas reaction—application to enantioselective synthesis of oxepane subunits of marine trans-fused polyether Toxins

Abstract

Pyranose ring of cobalt-complexed alkynyl sugars was cleaved by Nicholas reaction. The reaction of 22 was diastereoselective and this selectivity was presumably due to steric interaction between cobalt acetylene moiety and tert-butyldiphenylsilyloxy function. The resulting linear cobalt complex 23 was modified and converted into dehydrooxepane unit of ciguatoxin by Nicholas reaction.