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Abstract

2,19-Dioxo[3.3](3,3´)azobenzolophane (5) has been obtained in a total yield of 18% by way of CO insertion and cyclization of 1,2-bis[3-(bromomethyl)phenyl]-4,4-dimethyl-3,5-pyrazoli-dinedione (1) using CO 2(CO) 8 in acetonitrile followed by the removal of the N-protecting 4,4-dimethylmalonyl groups. 5 is obtained predominantly as the trans / trans isomer 5a and can be isomerized by irradiation with [lambda]=369 nm to a mixture of nearly equal amounts of the trans / trans, cis / trans, and cis / cis isomers 5a, 5b and 5c. The thermal isomerization back to 5a is slow but fast upon irradiation with [lambda]=443 nm.