Nouvelle cyclopentannélation regiosélective par une séquence tandem ouverture electrophile/cycloaddition [3+2] entre cétones méthylènecyclopropaniques et l'allyltriméthylsilane
摘要:
The TiCL1-mediated reactivity of five complementary substituted methylenecyclopropyl ketones with allyltrimethylsilane has been studied. The regioselectivity of the reaction, which affords functionalized methylene and/or alkylidenecyclopentanes in good yields, depends on the substitution of the cyclopropanic carbon a to the carbonyl function. The reaction occurs via a stereoselective cleavage of the carbocycle followed 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.