MECHANISM OF HETEROCYCLIC RING EXPANSIONS .4. REACTION OF AN IMIDAZOLE, PYRAZOLE, AND 1,2,4-TRIAZOLE WITH DICHLOROCARBENE

On reaction with dichlorocarbene in basic or neutral conditions, 2,4,5-trimethylimidazole gave 5-chloro-2,4,6-trimethylpyrimidine, and 3,5-dimethyl-1,2,4-triazole gave tris-3,5-dimetnyl-1,2,4-triazol-1-ylmetnane. In basic conditions 3,4,5-trimethylpyrazole gave 4-dichloromethyl-3,4,5- trimethylpyrazolenine but in neutral conditions it gave four minor products: 4-chloro-3,5,6-trimethylpyridazine, 2-chloro-4,5,6-trimethylpyrimidine, 1-trichlorovinyl-3,4,5-trimethylpyrazole, and tris-3,4,5-trimethylpyrazol-1 -ylmethane. Thus the known reactions of dichlorocarbene with 1H-pyrroles are paralleled and several new reactions are observed. Reasons for the observed product distribution, and possible reaction mechanisms, are proposed.