Regiospecific Ring Opening of Some Methyl- and Phenyl-Substituted 1,1,2-Trihalocyclopropanes to Acetylenic Acetals or Ketals by Variation of Reaction Conditions.
摘要:
Regiospecific ring opening of six title compounds has been achieved under various reaction conditions. With dry sodium ethoxide in dry THF as reagent acetylenic diethyl ketals are obtained in 66-81% isolated yield. With DBU in dry ethanol, the corresponding acetylenic diethyl acetals are formed and isolated in 50-67% yield. Finally, treatment of the substrates with 50% aqueous sodium hydroxide in the presence of 2-propanol, triethylbenzylammonium chloride and dichloromethane gave acetylenic diisopropyl acetals, in 82% yield at the best. By-product formation was negligible in most cases.
Formation of Acetylenic Acetals by Ring Opening of 1,1,2-Trihalocyclopropanes under Phase-Transfer Conditions.
摘要:
A number of substituted 1,1-dibromo- and 1,1-dichlorocyclopropanes with an additional chlorine or bromine atom attached to C-2 were synthesized in reasonable to good yields by dihalocarbene addition to the corresponding alkenes under phase-transfer conditions. When the trihalides were treated with 50% aqueous sodium hydroxide in the presence of ethanol, triethylbenzylammonium chloride and dichloromethane, most of the compounds underwent ring opening and afforded mixtures of acetylenic acetals, usually in good yields. The reaction most likely involves cyclopropene intermediates, which in some cases also rearrange to a minor extent to the corresponding vinylcarbenes and afford alpha,beta-unsaturated aldehydes.