Addition of free radicals to unsaturated systems. Part XIX. The direction of radical addition ot 1,1,1-trifluorobut-2-ene

Abstract

The photochemical reactions of trifluoroiodomethane or hydrogen bromide with 1,1,1-trifluorobut-2-ene have been studied. Trifluoroiodomethane gives the 1 : 1 adducts 1,1,1-trifluoro-2-iodo-3-trifluoromethylbutane and 1,1,1-trifluoro-3-iodo-2-trifluoromethylbutane in high yield in the ratio 80 : 20, and the major adduct is a mixture of the erythro- and threo-isomers in the approximate ratio 1 : 2. Treatment of the 1,1,1-trifluoro-2-iodo-3-trifluoromethylbutane isomers separately with potassium hydroxide gives predominantly trans-1,1,1-trifluoro-3-trifluoromethylbut-2-ene from the threo-isomer and the corresponding cis-olefin from the erythro-isomer. 1,1,1-Trifluoro-3-iodo-2-trifluoromethylbutane similarly gives 1,1,1-trifluoro-2-trifluoromethylbut-2-ene in high yield. The 1 : 1 adducts 2-bromo- and 3-bromo-1,1,1-trifluorobutane are formed in the approximate ratio 65 : 35 in the reaction with hydrogen bromide, but trans-4-bromo-1,1,1-trifluorobut-2-ene is also a major product.