THERMOLYSIS OF N-ALLYLIC 1,2,4-TRIAZOLES

A number of 4-allylic substituted 3,5-diphenyl-4H-1,2,4-triazoles were thermolyzed at 315-320 degrees in evacuated glass ampoules. The main reaction in the melt was rearrangement to the corresponding 1-substitu ted triazoles, which appeared to proceed via competing S(N)2 and S(N)2 ' mechanisms. The allylic systems were observed to undergo [2,3]-allyl walk reactions between the 1- and 2-ring positions. Allyl to vinyl is omerization also took place. Substitution of the allylic moiety increa sed the rate of reaction but decreased the rate of isomerization of al lylic to the vinylic substituted triazoles. The 4-vinyl substituted tr iazoles were inert under the reaction conditions. Some triazoles were converted into substituted pyridines. This was proposed to proceed via nitrogen extrusion and formation of a 1,3-dipolar intermediate (nitri le ylide) which added intramolecularly to the allyl moiety and subsequ ently aromatized to the pyridine.