Vitamin D: Enantioselective synthesis of (3aR,4R, 7aS)-4-hydroxy-7a-methylperhydro-1-indenone, a suitable CD-ring fragment

A practical synthesis of trans-hydrindanone 5a from (+)-Wieland-Miescher ke tone 8 is described. The target molecule 5a is a suitable precursor for the synthesis of analogues of 1 alpha ,25-dihydroxyvitamin D-3 modified at C-1 6, C-17 or C-20. During the total synthesis it was found that hydroboration of (1,1)-ethylenedioxy-8a-methyl-1,2,3,4,6,7,8,8a-octahydronaphthalene (11 ) leads to a cis-decalin 13 instead of the literature reported trans-fusion .