Catalytic hydrogenation of 3,4-epoxybut-1-ene with cationic rhodium complexes

Abstract

Catalytic hydrogenation of 3,4-epoxybut-1-ene with cationic rhodium complexes has been investigated under 1 atmosphere of hydrogen at 30 °C. But-2-enal, the main product, but-2-en-1-ol, and but-3-en-1-ol were produced by isomerization via selective abnormal fission of the epoxide ring.

The catalytic activity for hydrogenation of the epoxide depended on the nature of the phosphorus ligands of the catalyst. The order of activity of the ligands for the formation of alcohols (PEt₃≳ diphos PPh₃ > PMe₃)[diphos = 1,2-bis(diphenylphosphino)ethane] was different from that observed for hydrogenation of 1,2-epoxy-1-phenylethane. It should be noted that the diphos- and PPh₃-catalysts, which showed quite limited activity for both carbonyl compounds and 1,2-epoxy-1-phenylethane, exhibited considerable activity for the title compound. The epoxide ring may be activated by the adjacent olefinic bond to a considerable extent. A mechanism is proposed to explain the high reactivity of the epoxide and the ligand effects on the catalytic activity which differed in the hydrogenation of 1,2-epoxy-1-phenylethane and 1,2-epoxybutane.