SYNTHESIS OF FUNCTIONALIZED CYCLOPENTANES, CYCLOHEXANES AND CYCLOHEPTANES BY A SILICON-INDUCED DOMINO REACTION

1,3-Functionalized cyclopentanes, -hexanes and -heptanes are obtained by addition of Lithiated silyldithioacetals 7 to epoxyhomoallyl tosyla tes 4-6. The reaction involves a cascade of epoxide ring opening, of B rook 1,4-rearrangement and tosylate substitution. The method is partic ularly suitable for the preparation of cyclopentanes, whereas cyclohex anes and -heptanes are formed in yields only up to 49%. Use of enantio merically pure epoxides provides optically active cyclopentanes (S)-10 b, d, 11a as well as oxetanes (S)-14a, b. Hydrolysis of the dithioacet al function leads to the corresponding ketones 12. Cyclization of epox ide 24b gives an anellated cyclopentane 26, the configuration of which was established by X-ray structural analysis of dinitrobenzoate 27. U se of epoxide 29b provides the anellated tetrahydrofuran 30.