BICYCLO[2.2.1]HEPTANES IN ORGANIC-SYNTHESIS - STEREOCONTROLLED APPROACH TO STEROL SIDE-CHAIN CONSTRUCTION - SYNTHESIS OF DE-AB-CHOLEST-11-EN-9-ONE

The vast majority of sterols, including insect and crustacean moulting hormones, and the active metabolites of vitamin D possess the R configuration at C(20) (cf. cholesterol (1)). The[formula ommitted] problems associated with generating and controlling chirality in acyclic systems have primarily been responsible for the limited success recorded to date for elaborating the stereochemistry at C(17) and at C(20) of sterol side chains.1,2 A potential solution to this problem is embodied in the bicyclo[2.2.1]heptane derivative 2 whose conformational rigidity allows for elaboration of not only the chirality at C(20), but also that encountered at C( 13), C(14), and C(17). We detail below the conversion of (-)-2 into (+)-de-AB-cholest-l 1-en-9-one (3), a known precursor to tachysterol and precalciferol. © 1979, American Chemical Society. All rights reserved.