Reduction of phenylacetylenes using Raney Ni-Al alloy, Al powder in the presence of noble metal catalysts in water

Abstract

The chemoselective reduction is based on the reaction between Al either as powder or from the alloy and water which generates in situ hydrogen to effect the reduction of the targeted functional groups. Raney Ni-Al alloy with Al powder can reduce phenylacetylenes to the corresponding ethylbenzene (3) in water in excellent yield at 120 °C for 6 h in a sealed tube. In addition, the complete reduction of the aromatic ring to ethylcyclohexane required 60 °C for 12 h with Raney Ni-Al alloy, Al powder in the presence of Pt/C. Appropriate selection of reaction conditions allowed the selective preparation of ethylbenzene as well as ethylcyclohexane from phenylacetylene.