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

Abstract

Abstract 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% 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.