2,5-Bis(methoxycarbonyl)-4-hydroxycyclopent-2-en-1-one as an Intermediate in Weiss' Glyoxal Reaction. Analogous Chemistry of Malondialdehyde

Article abstract of DOI:10.1021/jo00326a057

Glyoxal and dimethyl 3-oxoglutarate condense at pH <6 to form a reactive intermediate, 2,5-bis(methoxycarbonyl)-4-hydroxycyclopent-2-en-1-one, part of which dimerizes to yield 3 after hydrolysis-decarboxylation.Its structure was proved by single-crystal X-ray crystallography performed on the dimethyl ester.Support for this mechanism comes from studying the analogous reaction of malondialdehyde, which gives 2,6-bis(methoxycarbonyl)phenol at pH 5 but not at pH 8 where phenol formation is usually more rapid.The product at pH 8 is tetramethyl 3,7-dioxobicyclo<3.3.1>nonane-2,4,6,8-tetracarboxylate.