Solution pyrolysis (240) of dimethyl 1, 2-dibromocyclobutane-1, 2-dicarboxylate gives COz and methyl bromide (2 mol) in good yield in lieu of cracking or geometrical isomerization. According to their behavior under pyrolysis conditions, methyl 3-bromocyclobutene-2- carboxylate and methyl 3-bromobutadiene-2-carboxylate are permissible intermediates in the cyclobutane decomposition. Elimination-debromocarbomethoxylation of 0-halo esters ...