Epoxide 2 was prepared from 3,4-dichloro-1-butene (1) by epoxidation with m-CPBA and subsequent dehydrohalogenation of the intermediate dichloroepoxide with molten KOH, affording 2 in 64% overall yield (2 steps). Catalytic CuBr/SMe(2)-mediated S(N)2' addition of sp(2)- or sp(3)-hybridized Grignard reagents to 2-chloro-3,4-epoxy-1-butene (2) afforded (Z)-3-chloroallylic alcohols such as 3 in good yields and with high regio- and stereoselectivity.