Oxidative decarboxylation as a route to ketene acetals: assignment of relative and absolute stereochemistry to the fungal metabolite benesudon by total synthesis.

The unusual ketene acetal benesudon, which is a bioactive fungal metabolite, was synthesized from d-glucose by a route involving radical cyclization to form the five-membered ring and oxidative decarboxylation to generate the key central double bond. The originally suggested stereochemistry for the quaternary center C(5) must be revised, as both possibilities were prepared and a comparison with an authentic sample was made. The absolute configuration of benesudon is 4S,5R,6S.