Electrophilic alkylation and some stereochemical consequences

CONDENSATION OF TRICHLOROMETHYL PERCHLOROAROMATIC COMPOUNDS WITH TRICHLOROETHYLENE 

Attempts to synthesize perchloropropenylbenzenes, such as a,p-dichloro-propenylbenzene, with reagent BMC had been unsuccessful (Ballester and Riera, 1960). An alternative way was devised, consisting in the condensation of perchlorotoluene with trichloroethylene in methylene chloride by means of aluminium chloride. Such a process had to surmount significant steric hindrance, particularly the formation of a sterically strained intermediate adduct, and therefore the reaction had to be conducted at moderate temperature. It was nevertheless expected that steric strain would assist the subsequent hydrogen chloride elimination to form the ethylene bond (72). 

C6Cl5CCl2+CHCI=CCl2 — C6CI5CCI2-CHCI-CCI2 

Presumably, the role of calcium or lithium chloride is to temper the 

This condensation with trichloroethylene has also been performed with perchloro-p-xylene and with perchlorobi-p-tolyl (Ballester et al., 1967). From the first chlorocarbon, four isomers were isolated instead of the expected three (cis,cis cis,trans trans,trans) (see p. 322). 

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