Regiospecific ring opening of some methyl- and phenyl-substituted 1,1,2-trihalocyclopropanes to acetylenic acetals or ketals by variation of reaction conditions

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.