Study of the formation and thermal decomposition of an azo-bridged tricyclic ring system

1-Amino-2-methyl-1,3-pentadienes were treated with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate to give diazatricyclo[2.2.2.0]octenes and dimethyl 4-methylpyridazine-3,6-dicarboxylate, the product distribution being largely dependent on the nature of the amino substituent. Under similar conditions the analogous 1-morpholino-1,3-butadiene afforded dimethyl pyridazine-3,6-dicarboxylate as the major product. The tricyclic products underwent selective thermal decomposition to give dimethyl 4-methylpyridazine-3,6-dicarboxylate in excellent yield. The proposed mechanism of the formation as well as of the decomposition was supported by quantum chemical calculations and experimental evidence. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheirn, Germany, 2006)