Rhodium carbonyl-catalyzed carbonylation of unsaturated compounds: III. Synthesis of α,β-unsaturated ethyl ketones by cross-hydrocarbonylation of acetylenes and ethylene with carbon monoxide and hydrogen

Abstract

Rhodium carbonyl-catalyzed cross-hydrocarbonylation of acetylenes and ethylene with carbon monoxide and hydrogen gives α,β-unsaturated ethyl ketones. Under CO (10 kg cm −2) and H 2 (50 kg cm −2) at 90°C the reaction of diphenylacetylene with ethylene in the presence of Rh 4(CO) 12 catalyst gave ( E)-1,2-diphenyl-1-penten-3-one ( 3a) in 91% yield. Under similar conditions phenylacetylene ( 1d), 1-hexyne ( 1e), 3,3-dimethyl-1-butyne ( 1f), and trimethylsilylacetylene ( 1g) gave ( E)-1-phenyl-1-penten-3-one ( 3d), ( E)-4-nonen-3-one ( 3e), ( E)-6,6-dimethyl-4-hepten-3-one ( 3f), and ( E)-1-trimethylsilyl-1-pentene-3-one ( 3g) in 76, 68, 93, and 62% yields, respectively. Thus, the reaction of terminal acetylenes proceeds with high stereo- and regioselectivity: the propionyl group is introduced to the less-sterically hindered acetylenic carbon atom. By comparison of the regioselectivity with that in the formation of 5-ethyl-2(5 H)-furanone ( 2), which is obtained in the presence of a hydrogen donor such as alcohol, these reactions are assumed to include a β-acylvinylrhodium complex as the common key intermediate.