Rhodium-catalyzed aerobic conversion of 2-diazo-1,3-dicarbonyls to vicinal tricarbonyl compounds and their in-situ stability toward oxidative degradation

Several types of 2-diazo-1,3-dicarbonyls, including α -diazo- β -ketoesters, 2-diazo-1,3-diketones and diazomalonates, are converted into the corresponding vicinal tricarbonyl compounds (VTCs) upon exposure to Rh 2 (OAc) 4 catalyst and oxygen gas. The transformation is proposed to occur through the aerobic oxygenation of the rhodium carbenoid, which is facilitated by the suppression of a Wolff rearrangement via weak interaction with the substrate carbonyl group (ROC=O or RC=O). From α -diazo-β-ketoesters and 2-diazo-1,3-diketones, the desirable α,β -diketoesters and vic -triketones are obtained in 27-78% yields, along with carboxylic acids and/or 2-oxoacids generated by in-situ oxidative C-C single bond cleavage of the former products. Moreover, the bond cleavage process is completely inhibited when the reactions are performed with diazomalonates, leading to the good to excellent formation of oxomalonates (up to 92% yield).