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

Abstract

Several types of 2-diazo-1,3-dicarbonyl compounds (3), including α-diazo-β-ketoesters, 2-diazo-1,3-diketones and diazomalonates, are converted into the corresponding vicinal tricarbonyls (VTCs) (4) upon exposure to Rh2(OAc)4 catalyst and oxygen gas. The transformation is proposed to occur through the aerobic oxygenation of the rhodium carbenoid intermediate, facilitated by the suppression of a Wolff rearrangement via weak interaction with the substrate carbonyl group (ROC=O or RC=O). The reactions of α-diazo-β-ketoesters and 2-diazo-1,3-diketones give the desirable α,β-diketoesters and vic-triketones in 27-78% isolated 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).