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.
Halogenocycloprop anation des dioxolannes ethyleniques et des enones correspondantes par les monohalogenocarbenoides
作者:R. Barlet、M. Vincens
DOI:10.1016/0040-4020(77)84076-3
日期:1977.1
of conjugated enones and their dioxolanes has been achieved by monohalocarbenoîds generated from methylene chloride and gem-dichloroethane. In both cases, besides expected chloro-adducts, corresponding bromo-adducts are obtained. Formation of these adducts involves halogen exchange by the primary chlorocarbenoid with lithium bromide associated with methyllithium. Conjugated enones give trans α-halocyclopropanic