Thermal Rearrangement of Allyl Substituted Unsymmetric 4H-1,2,4-Triazoles to the Corresponding 1H-1,2,4-triazoles

A series of neat 4-(2-alkenyl) substituted 5-methyl-3-phenyl-4H-1,2,4-triazoles were thermolyzed at 320 oC producing a rearrangement products, of which the regioisomeric 1- and 2-substituted triazoles were the main products. The group migrations were rationalized in terms of consecutive SN2-type reactions. This mechanism was supported by a study of the alkylations of the triazoles which gave similar product mixtures. 4-(2-alkenyl) substituted 3-phenyl-4H-1,2,4-triazoles, on the other hand, gave predominantly elimination products.