STEREOCONTROL IN ORGANIC-SYNTHESIS USING SILICON-CONTAINING COMPOUNDS- A FORMAL SYNTHESIS OF PROSTAGLANDINS CONTROLLING THE STEREOCHEMISTRY AT C-15 USING A SILYL-TO-HYDROXY CONVERSION FOLLOWING A STEREOCHEMICALLY CONVERGENT SYNTHESIS OF AN ALLYLSILANE

Hydrosilylation of isoprene with chloro(diphenyl)silane gave (Z)-chlor o(2-methylbut-2-enyl)-diphenylsilane 7. The cuprate reagent derived fr om this chloride underwent conjugate addition to methyl cinnamate 11, 1,2-silylcupration with hex-1-yne 16 and allene 18, and allylic displa cement reactions with 1-vinylcyclohexyl acetate 20 and (Z)-1-cyclopent yloct-2-en-1-yl acetate 22. The silyl group in each of the products wa s converted into a hydroxy, with the removal of the 2-methylbut-2-enyl group taking place under much milder acidic conditions than those nee ded to remove the phenyl group from the dimethyl(phenyl)silyl group, a nd making this group suitable for the conversion of an allylsilane int o an allyl alcohol. A stereospecifically anti conjugate displacement o f the allylic benzoate group in zoyloxyoct-2'-enyl)-2-oxabicyclo[3.3.0 ]octan-3-one 52, and a stereospecifically syn conjugate displacement o f the carbamate group in moyloxyoct-2'-enyl)-2-oxabicyclo[3.3.0]octan- 3-one 51, gave stereoconvergently the same allylsilane (1'E,2 '' Z)-(1 S,5R,6R,7R,3'S)-7-benzoyloxy-6-[3'-(2 ''-methylbut-2 ylsilyloct-1'-eny l]-2-oxabicyclo[3.3.0]octan-3-one 53. Silyl-to-hydroxy conversion gave the allyl alcohol hydroxyoct-1'-enyl)-2-oxabicyclo[3.3.0]octan-3-one 54, having the relative and absolute stereochemistry at C-15 of the pr ostaglandins.