Vh. Rawal et al., PHOTOCYCLIZATION-FRAGMENTATION ROUTE TO DIQUINANES AND TRIQUINANES - STEREOCONTROLLED ASYMMETRIC-SYNTHESIS OF (-)-ISOCOMENE, Pure and applied chemistry, 68(3), 1996, pp. 675-678
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.