Room-Temperature Coupling/Decarboxylation Reaction of α‑Oxocarboxylates with α‑Bromoketones: Solvent-Controlled Regioselectivity for 1,2- and 1,3-Diketones

A transition-metal-free
and room-temperature coupling/decarboxylation
reaction between α-oxocarboxylates and α-bromoketones
is reported herein. It represents the first mild and regioselective
synthesis of either 1,2- or 1,3-diketones from the same starting materials.
Notably, the regioselectivity is simply controlled by solvents. The
preliminary experimental data and DFT calculations suggest sequential
Darzens-type coupling, alkaline hydrolysis, KOH-promoted oxirane opening
and decarboxylation in one pot. This method is efficient for the synthesis
of α,β-epoxy-γ-butyrolactone and curcuminoids.