Synthetic studies on fusicoccin A: Alternative synthetic approach to the C-ring fragment

An enantioselective synthetic method for the C-ring fragment of fusicoccin A, starting from the CBS reduction, is described. The key steps in this synthesis involve the regioselective formation of p-methoxybenzylidene acetal, the construction of the C15 asymmetric carbon of fusicoccin A by a highly stereoselective Michael reaction, and the regioselective reduction of p-methoxybenzylidene acetal. This synthesis of the C-ring fragment was performed in 16 steps. In contrast, the synthesis starting from the baker's yeast reduction, which was developed simultaneously, involved 11 steps. While the baker's yeast-mediated approach is shorter, the baker's yeast reduction suffers from variable conversion efficiency. Therefore, the synthesis via CBS reduction could be an efficient alternative synthetic method for the C-ring fragment.