Addition of Diphenyldiazomethane to Unsubstituted and Chloro-Substituted 1,4-Benzoquinones. Effects of Chloro Substituents on the Addition Modes

Article abstract of DOI:10.1246/bcsj.61.2507

Unsubstituted 1,4-benzoquinone (1a) reacted with diphenyldiazomethane (DDM) at the C=C double bonds to give dihydroxy-3H-indazole (2a) and its benzhydryl ether (3a) together with benzodipyrazole derivative (4a).Similarly, reactions of 2-chloro- and 2,3-dichloro-1,4-benzoquinones (1b and 1c) with DDM yielded the corresponding dihydroxy-3H-indazoles (2b, 2b', and 2c) and their benzhydryl ethers (3b, 3b', and 3c) along with 5-13 percent benzophenone (6).On the other hand, reaction of 2,6-dichloro-1,4-benzoquinone (1e) with DDM gave bicyclic 5e and tricyclic diones (7e), together with benzophenone dimethyl acetal (9) in the presence of added methanol.In the same conditions, 2,3,5-trichloro-1,4-benzoquinone (1f) provided bicyclic dione (5f) and 9.Formation of 6 and 9 was interpreted as arising from the hydrolysis and methanolysis of the 1:1 betaine intermediates given by the addition of DDM to the quinonoid C=O double bonds.The C=O addition increased with increasing chlorine substituents.