Ruthenium-catalyzed cyclization of alkyne-epoxide functionalities through alternation of the substituent and structural skeleton of epoxides

Abstract

Treatment of 1-(o-ethynylphenyl)-2-alkyl-2-aryl epoxides with TpRuPPh 3(CH3CN)2PF6 catalyst (10 mol %) in hot toluene (100 °C, 12 h) led to an atypical cyclization and gave 1-aryl-2-alkyl-1H-indene derivatives and carbon monoxide efficiently. The cyclization of 1-cis-enynyl-2-alkyl epoxides with this catalyst in hot toluene (10 mol %, 100 °C, 12 h) gave 2,5-disubstituted phenols in 45-72% yields. Under the same conditions, 1-cis-enynyl- 2,2-dialkyl epoxides and 1-cis-enynyl- 2-alkyl-2-aryl epoxides gave the corresponding 6,6-disubstituted cyclohexa-2,4-dien-1-ones in good yields (85-91%). Mechanisms for these new cyclization reactions are proposed on the basis of trapping experiments and isotope labeling experiments. The formation of 1H-indene products likely involves ruthenium-acyl intermediates whereas cyclohexa-2,4-dien-1-ones are thought to derive from ruthenium-ketene intermediates.