Direct Dichlorovinylation of Some Carbonyl Compounds by Trichloroethylene Under Conditions of Phase-Transfer Catalysis

Reaction of ketones 1 and 3 with trichloroethylene (TRI) carried out in the presence of 50% aq. NaOH and TBAHS as a catalyst, in ethyl ether (phase-transfer catalysis, PTC) afford 1,2-dichlorovinylated ketones 2 and 4, respectively in good yields, usually as mixtures of Z and E isomers. PTC reaction of aldehydes 5 with TRI, carried out with DMSO instead of TBAHS, yields O-dichlorovinylated products 6, as mixtures of isomers in the case of 6a. These products are formed via C- or O-addition of ambident enolate anions to dichloroacetylene (generated from TRI by a base) and fast protonation of highly basic dichlorovinyl anions thus formed.