Organocatalytic Cleavage of Fatty 1,2-Diketones to Esters

Abstract

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 K 2 CO 3 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 2 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.

Synthesis of Imidazoles from Fatty 1,2‐Diketones

“…Within the frame of a research programme aiming at the valorization of vegetable oil derivatives, [33] we have recently reported a clean access to fatty α‐hydroxyketones from the corresponding 1,2‐diols by either palladium‐catalyzed selective oxidation using oxygen as a clean oxidant or by ruthenium‐catalyzed dehydrogenation [33b] . Moreover, the corresponding fatty 1,2‐diketones were also prepared by oxidation of α‐hydroxyketones, using oxygen [33f] . With a clean access to fatty 1,2‐diketones in hands, we now report the synthesis of imidazoles from these starting materials through Debus–Radziszewski reaction (Scheme 2).…”

Mechanistic study of NHC-catalyzed oxidative N vs. O chemoselective acylation of aldehydes with alkanolamines

“…[23][24][25] In recent years, a large number of synthetically important transformations have been developed in the presence of NHCbased organocatalysts. 26,27 Unlike phosphine ligands, NHCs are found to be very stable under oxidative conditions, 28 and has thus been employed for several transformations: oxidation of aldehydes to esters, 29,30 amidation and azidation of aldehydes, 31,32 b-activation of saturated aldehydes, 33 a-functionalization of simple aldehydes, 34 oxidative cleavages of cyclic 1,2-diketones, 35 among others. [36][37][38] Of note, Maheswari and coworkers 39 reported the oxidative amidation of aryl aldehydes with amines catalyzed by an imidazolium-based NHC in the presence of NBS as the terminal oxidant (Scheme 1).…”