Fleming-Tamao oxidation and masked hydroxyl functionality: Total synthesis of (+)-pramanicin and structural elucidation of the antifungal natural product (-)-pramanicin

The total synthesis of (+)-pramanicin (41b) is reported, thereby establishing the relative and absolute stereochemistry of the naturally occurring antifungal agent. The key steps involve (i) conjugate addition of the diethyl((diethylamino)diphenylsilyl)zincate to a suitably protected gamma-lactam 3 and quenching of the resultant enolate with the alpha,beta-unsaturated gamma,delta-epoxy aldehyde 2 (X = H), (ii) Ni(acac)(2)-catalyzed hydroxylation of a beta-dicarbonyl array, and (iii) Fleming-Tamao oxidation to reveal the masked C-3 hydroxyl group.