NEW REGIOSELECTIVE PREPARATION OF CYCLOPE NTANES USING A TANDEM SEQUENCE OF STEREOSELECTIVE CLEAVAGE AND [3+2]CYCLOADDITION BETWEEN METHYLENECYCLOPROPYL KETONES AND ALLYTRIMETHYLSILANE

The TiCL1-mediated reactivity of five complementary substituted methyl enecyclopropyl ketones with allyltrimethylsilane has been studied. The regioselectivity of the reaction, which affords functionalized methyl ene and/or alkylidenecyclopentanes in good yields, depends on the subs titution of the cyclopropanic carbon a to the carbonyl function. The r eaction occurs via a stereoselective cleavage of the carbocycle follow ed by a tandem [3+2] cycloaddition of the resultant (Z)-1,3-zwitterion with allyltrimethylsilane that acts as the 1,2-partner in a synclinal approach. (C) 1998 Elsevier Science Ltd. All rights reserved.