4- or 5-Chloro- or cyanoisoxazoles, 5-chloromethylisoxazoles, and 5-methylisoxazoles were made by the 1,3-dipolar cycloaddition of nitrile oxides to α-halogeno- or α-alkoxyolefins. In the case of cis- and trans-1,2-dichloroethylene, (5a and b) the intermediate cis- and trans-4,5-dichloroisoxalines (6a and b) were isolated. Both 6a and b were dehydrochlorinated with base to give the 4-chloroisoxazole (7a) exclusively. The cis-isomer 6a reacted faster than the trans-somer 6b. The reactions were found to be specific in every reaction since only one isomer was isolated. The structures of the products were established from n.m.r. spectral analysis.