NEW REARRANGEMENT OF AN ASPIDOSPERMA ALKALOID - THE FIRST BIOMIMETIC ENTRY IN THE GONIOMITINE SKELETON

The first biomimetic approach to the skeleton of goniomitine (12) from an Aspidosperma alkaloid is described. With 16-chloro-1-dehydro-5-met hoxyvincadifforme (4) (easily available from vincadifformine (1) as st arting material, the rearrangement is performed in two steps: (a) Oxid ation of 4 by m-CPBA followed by methanolysis affords the hemiketal 10 with a tetrahydro-1,2-oxazine structure for ring C, and (b) acid-cata lyzed reaction on 10 provides either a mixture of both rearranged comp ounds 15 and 16 or 15 alone according to reaction time. Mechanisms of formation of 10, 15, and 16 are discussed.