Unusual formation of tetrahydropyridazine-3,4,5,6-tetracarboxylic and pyrroletetracarboxylic esters upon decomposition of methyl diazoacetate in the presence of pyridine

Thermal, photolytic, and thermocatalytic decomposition of methyl diazoacetate (MDA) in the presence of Rh-2(OAc)(4) or Cu(acac)(2) in refluxing pyridine afforded isomeric trans,cis- and cis, trans- 3,4,5,6 -tetra(methoxycarbonyl) - 1,4,5,6-tetrahydropyridazines (- 1 : 1) in a total yield of 30-70%. Decomposition of MDA in refluxing o-xylene in the presence of Rh-2(OAc)(4) and pyridine (20 mol.%) gave rise to 2,3,4,5 -tetra (methoxycarbonyl)pyrrole in a yield of up to 40%. In these transformations of MDA, neither dimethyl fumarate (or dimethyl maleate) nor the corresponding 2-pyrazolines were generated as intermediates.