A regio- and stereo-selective route to 1,1,3- and 1,2,3-trihalogenobutadienes by dehydrohalogenation of alkyl-substituted 1,1,2,3-tetrahalogenocyclopropanes

Abstract

Non-terminal alkenes vicinally substituted with chlorine are converted into 2,3-dialkyl-1,1,2,3-tetrahalogenocyclopropanes on reaction with dichlorocarbene generated under phase-transfer conditions, or dibromocarbene generated either by phase transfer or from the thermolysis of phenyl-(tribromomethyl)mercury. 1,1,2,3-Tetrahalogenocyclopropanes are also obtained by reaction of the corresponding vicinal bromochloro- and dibromo-alkenes with dichlorocarbene under phase-transfer conditions or of the latter alkenes with phenyl(tribromomethyl)mercury. The tetrahalides produced undergo ring-opening when heated in the presence of quinoline, overall elimination of hydrogen halide leading to specifically substituted trihalogenobutadienes.