Addition of tetrachloromethane to cis-cycloalkenes in the presence of transition metal complexes

Abstract

Reactivity, regioselectivity and stereoselectivity of the addition reaction between tetrachloromethane and C₅ to C₁₀ cycloalkenes in the presence of copper, ruthenium, molybdenum, cobalt and iron complexes as catalysts and dibenzoyl peroxide as an initiator have been examined in the temperature range 22 to 80°C. Relative reactivities of the cycloalkenes decreased in sequence C₈>C₅>C₇>C₆>C₁₀. These rates were not strongly affected by the catalysts indicating that the reactivities of cycloalkenes are mainly controlled by I-strain in the cycloalkene molecule. Transannular addition was observed in the reactions of cis-cyclooctene and cis-cyclodecene. The ratio of transannular to vicinal addition was significantly lowered by [RuCl₂(PPh₃)₃] and [CuCl(NHEt₂)₂], in comparison with dibenzoyl peroxide. A strong catalyst effect on the stereoselectivity of the addition reaction of cyclohexene was also recorded. The trans:cis isomer ratio of the adduct was significantly affected by ruthenium catalysts and, to lesser extent, by copper, molybdenum, cobalt and iron catalysts. The catalyst effect on regioselectivity and stereoselectivity strongly support a non-chain mechanism involving coordination of reactants and product formation at the metal centre in contrast to the classical initiation of chain reactions by organic peroxides.