Condensation of ketones with dimethyl dimethylmaleate. A synthesis of calythrone

Condensation of 4-methylpentan-2-one with dimethyl dimethylmaleate by use of sodium hydride gives calythrone (2-isovaleryl-4,5-dimethylcyclopentene-1,3-dione)(. 5%) but the main product is an ester, shown to be methyl 4-isovaleryl-2-methyl-3-oxocyclopentanecarboxylate and not as previously suggested. Reactions with acetone and acetophenone give only the corresponding cyclopentanone derivatives.