Reaction of dimethyl sodio-3-ketoglutarate with glyoxal and substituted glyoxals: First expeditious preparation of bicyclo[3.3.0]octane-3,7-dione; synthesis and crystal structure of 5,7-dihydroxy-4-methoxycarbonyl-3-phenyl-1-indanone

A simple and efficient two-step preparation of bicyclo3.3.0]octane-3,7-dione starting from the sodium enolate of dimethyl 3-ketoglutarate and glyoxal is described. This is an unprecedented case in which a condensation reaction of glyoxal is more successful under vigorous conditions (refluxing methanol) than under much milder ones (buffered water at ambient temperature). The major product (after hydrolysis-decarboxylation) from the analogous sequence with phenylglyoxal is 5,7-dihydroxy-4-methoxycarbonyl-3-phenyl-1-indanone, the result of a Dieckmann reaction in addition to the Michael and aldol reactions. Only the latter two occur in aqueous buffers, where the product after hydrolysis-decarboxylation is 1-phenylbicyclo3.3.0]octane-3,7-dione. The X-ray crystal structure of the indanone reveals a novel hydrogen bonding phenomenon.