PHOTOCYCLIZATION-FRAGMENTATION ROUTE TO DIQUINANES AND TRIQUINANES - STEREOCONTROLLED ASYMMETRIC-SYNTHESIS OF (-)-ISOCOMENE

We recently reported a general approach to the di- and triquinane fram eworks. The strategy takes advantage of two powerful reactions to buil d the molecular complexity, a Diels-Alder reaction to construct a norb ornane, and a Paterno-Buchi reaction to form a latent diquinane. The k ey step in the strategy is a reductive fragmentation reaction which li berates the quinane skeleton. This presentation will focus on the succ essful implementation of this strategy to the first controlled asymmet ric synthesis of (-)-isocomene. The chirality of the natural product i s derived from a highly scalemic norbornene ester that is readily avai lable via the Helmchen Diels-Alder reaction. Subsequent elaboration pr ovides a strained ketoalkene. Selective fragmentation of strategic bon ds and further transformations afford the natural product in optically pure form, in good overall yield. Recent results aimed at altering th e ''normal'' course of the reductive fragmentation will also be descri bed.