STUDIES ON THE STEREOSELECTIVITY OF OSMYLATION OF CIS-BICYCLO[3.3,0]OCT-6-ENES

Treatment of cis-2-oxabicyclo [3.3.0]oct-6-en-3-one 1 with osmium tetr aoxide under a variety of conditions led predominantly to attack from the more hindered face of the alkene to give, after protection of the diol, the ende-acetonide 8 as the major product, It is apparent that t he stereochemical outcome of this reaction is due to a directing effec t from the lactone carbonyl at C-3 since osmylation of the analogous l actols 3, acetals 4 and cyclic ethers 5 gave attack mainly from the le ss hindered exo-face, The exo-acetonide 7 was prepared in a 3-stage pr ocedure from cis-bicyclo[3.2.0]heptenone 6 in 54% yield, In this case the stereoselectivity of the osmylation reaction was governed, as expe cted, by the conformation of the bicyclic skeleton, no directing effec t from the ketone carbonyl was apparent.