Polar cycloaddition of 9-thiaphenanthrenium salt with 1,3-dienes

Treatment of 9-thiaphenanthrenium salt 1 with conjugated dienes underwent regio- and stereospecific [2(+)+4]-type polar cycloaddition to afford the corresponding sulfonium salt adducts 2 in good yields. Nucleophilic attack of some alcohols to the cycloadduct 2a led to the two kinds of ring-opened compounds 3 and 4. Reactions of compound 2a with a variety of bases yielded the vinylcyclopropane derivative 5 and the ring-opened product 6. Treatment of compound 2a with LDA in the presence of methyl acrylate afforded the compound 7 which is believed to derive from Michael-addition of a reactive ylide intermediate to an alpha,beta-unsaturated ester. Reductive cleavage of compound 2a with NaBH4 or SmI2 afforded the ring-opened product 8. (C) 1997 Elsevier Science Ltd.