Stereospecific Synthesis of cis and trans 1-Oxabicyclo[4,4,0]decanes and 9-Methoxycarbonyl-1-oxabicyclo[4,3,0]nonanes

2-(2'-Phenylsulphinylprop-2'-enyl)cyclohexanone (3) and 2-ethoxycarbonyl-2-(2'-phenylsulphinylprop-2'-enyl) cyclopentanone(12) derived from 2-phenylsulphinyl-3--toluenesulphonyloxyprop-1-ene (1) and 2-phenylsulphinyl-3-methanesulphonyloxyprop-1-ene (10) by reaction with 1-pyrroridinylcyclohexene (2) and 2-ethoxycarbonyl cyclopentanone (11) respectively, were reduced with sodium borohydride to afford in each case a racemic mixture of four isomeric hydroxy alkenyl sulphoxides that on oxidation produced in each case two hydroxy alkenyl sulphones cis (4),(13) and trans (5),(14) which separated by column chromatography. Treatment of the hydroxy alkenyl sulphones (4),(5),(13) and (14) with a molar equivalent of base yielded the corresponding 3-phenylsulphonyl cyclic adducts (6),(7),(15) and (16) respectively that were reduced with Raney nickel to afford the requisite cis and trans 1-oxabicyclo4,4,0decanes (8) and (9) and 9-methoxycarbonyl-1-oxabicyclo4,3,0nonanes (17) and (18) in good yields.