Organocatalytic Cleavage of Fatty 1,2-Diketones to Esters

The cleavage of a fatty 1,2-diketone derived from methyl oleate into the corresponding esters, i.e., methyl nonanoate and dimethyl azelate, was studied by organocatalysis using oxygen as a clean oxidant. Only carbene generated from thiazolium salts and K2CO3 could efficiently catalyze this transformation. It was found that, under the optimized conditions, the oxidative cleavage leads to the formation of a 1:1 mixture of esters and potassium carboxylates. An acidic treatment of the mixture, followed by esterification with methanol, led to the desired esters with 75 and 77% yield. This protocol was extended to a range of symmetrical and unsymmetrical fatty 1,2-diketones and the corresponding esters were isolated with 61-84% yield.