Ethyl 7-Acetyl-8a-methyl-3-(1-phenyl-1H-tetrazol-5-yl)-1,4,4a,5,6,8a-hexahydro-7H-pyrano[2,3-c]pyridazine-1-carboxylate

Abstract

The Diels–Alder reaction of ethyl 3-(1-phenyl-1H-tetrazol-5-yl-1,2-diaza-1,3-butadiene-1-carboxylate with 2-acetyl-6-methyl-2,3-dihydro-4H-pyran (methyl vinyl ketone dimer) regioselectively afforded the corresponding 3-(tetrazol-5-yl)-hexahydro-7H-pyrano[2,3-c]pyridazine in quantitative yield. An X-ray crystal structure of this cycloadduct is reported.

Diaza-1,3-butadienes as Useful Intermediate in Heterocycles Synthesis

“…The aza-Diels–Alder reaction of methyl vinyl ketone 117 with 116 , generated in situ under basic conditions from hydrazone 118 , was recently reported; however, the expected cycloadduct was not formed; instead, 116 reacts with the methyl vinyl ketone dimer 119 present in the reaction medium to afford 3-(tetrazol-5-yl)-hexahydro-7 H -pyrano[2,3-c]pyridazine 120 in low yield. Nevertheless, directly reacting hydrazone 118 with 119 in the presence of sodium carbonate at room temperature for 30 h afford pyrano[2,3-c] pyridazine 120 in very high yield as a single regioisomer ( Scheme 24 ) [ 52 ].…”