Total Synthesis of Illudinine, Illudalic Acid, and Illudacetalic Acid

Illudinine, illudalic acid, and illudacetalic acid—originally assigned structures I, II, and III, respectively—have each been synthesized from indan in 15 steps. During the course of the work, the structure of natural illudacetalic acid was revised from the simple acetal III to the mixed acetal 29, and this change was verified by establishing the identity of synthetic 29 with the natural material. Salient features of the synthesis include the preparation of the hydrocarbon VIII, functionalization of the aromatic ring to give VII, selective oxidation of VII to the C-7 ketone VI, elaboration of the cyclopentanone ring into the dialdehyde IV, and conversion of IV to the natural products I, II, and 29.