Microwave-irradiated transition-metal catalysis: Rapid and efficient dehydrative carbon-carbon coupling of alcohols with active methylenes

A rapid and highly productive synthetic microwave-irradiation protocol for transition-metal-catalyzed carbon-carbon coupling of a wide range of benzylic/allylic alcohols with beta-diones, beta-keto esters, and dialkyl malonates is reported. In a representative screening of transition-metal catalysts, salts of Zn, Cu, Fe, Sc, Ru, Pt, Ta, and Mo were found to furnish the coupling products. In light of the results obtained, among all of these catalysts copper(II) triflate was found to be relatively more effective compared to other catalysts even in the case of a less reactive benzyl alcohol or diester. Interestingly, these MW-irradiated reactions are performed in a more or less MW-transparent medium, such as toluene, having a very low tan delta, or under neat conditions.