Specific Two-Step Decarboxylation of Copper(I,II) β-Keto Carboxylates. A Novel Type of Regulation of the Decarboxylation of β-Keto Acids

Article abstract of DOI:10.1021/jo00337a032

Copper(I,II) β-keto carboxylates undergo a specific two-step decarboxylation.For example, the decarboxylation of copper(I) 1-oxocyclohexane-2-carboxylate (1) evolves CO2 in a 50percent yield in dimethylformamide (DMF) at 70 deg C.No further CO2 evolution beyond this 50percent decarboxylation occurs at 70 deg C.At a higher temperature of 120 deg C., the remaining 50percent of the CO2 is released.This specific two-step decarboxylation of 1 results from the intermediate formation of a dicopper(I) salt of the enol of 1-oxocyclohexane-2-carboxylic acid (10) which is stable to decarboxylation at 70 deg C.Compound 10 is isolated from the reaction mixture after the 50percent decarboxylation.Decarboxylations of copper(I,II) benzoylacetates, copper(I) oxaloacetate, copper(II) 1-oxo-cyclohexane-2-carboxylate, and copper(II) chloride 1-oxocyclohexane-2-carboxylate also proceed stepwise in DMF.On the other hand, copper(I,II) benzoylcyclopropane-1-carboxylates without an enolizable α-hydrogen atom evolve CO2 in a usual one-step manner.The present specific two-step decarboxylation of copper(I,II) β-keto carboxylates provides a novel type of regulation of the decarboxylation of β-keto acids and also a method of generating copper(I,II) enolate.The bearing of the two-step decarboxylation of copper(I) β-keto carboxylates on both the Cu(I)-mediated carboxylation of ketones and organic synthesis is also described.