Formation of 2-bromo-4-t-butyl-7-methoxy-2H-azepine and 4-t-butyl-7-methoxy-2-succinimidyl-2H-azepine by the respective reactions of 5-t-butyl-2-methoxy-3H-azepine with bromine and NBS suggests a plausible mechanism for the conversion of 3H-azepine to 2H-azepine as 1,4-addition of an electrophile and a consequent 1,2-dehydrobromination. Different from the case of cycloheptatriene, reaction of 3H-azepine with bromine did not give any delocalized ionic species.