Abstract
Some potentially useful chiral building blocks bearing bicyclo[2.2.1]heptane framework utilizable enantiodivergently have been prepared in optically pure forms from D-mannitol by chemically and from dicyclopentadiene by enzymatically. Owing to their rigid framework and high functionality, chemical transformations could be carried out efficiently in highly stereo-controlled manners. Moreover, their latent symmetric structures allowed enantiodivergent synthesis of the target molecules. Potentiality of the chiral synthons thus prepared has been demonstrated by establishing enantiocontrolled routes to the following compounds: α-yohimbane indole alkaloids, (-)-nitraraine, (-)-dihydronitraraine, a key prostaglandin intermediate, (4S,5S)-4,5-dihydroxy-4,5-O-isopropylidene-2-cyclopenten-1-one, sandal oil sesquiterpenes, (+)- and (-)-β-santalene, (+)- and (-)-epi-β-santalene, a cuparene type sesquiterpene, (+)- and ()-α-cuparenone, the first simple benzomorphane type alkaloid, (+)- and (-)-aphanorphine, and a calabar bean alkaloid, (+)- and (-)-physostigmine. The present synthesis did not support the proposed structures for nitraraine and dihydronitraraine. Proposed relative structure of (-)-aphanorphine was first confirmed by the present synthesis which also established the absolute structure of the first simple benzomorphane natural product which remained undetermined.
