Novel Catalytic Performance of Ruthenium Catalysts Toward the Characteristic Carbonylation Reactions

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A novel ruthenium catalyst system of[PPN][Ru_3H(CO)_<11>]/PCy_3[PPN=bis(triphenylphosphine)-iminium, Cy=cyclohexyl]for the direct hydroamidation and hydroesterification of alkenes with formamides and alkyl formates has been developed. These addition reactions proceeded smoothly under an argon atmosphere, and carbon monoxide is not needed to suppress decarbonylation of formyl compounds or to maintain the catalytic activity.On the other hand, during our effort to extend the previously reported ruthenium-catalyzed intermolecular Pauson-Khand reaction of 1, 6-enynes, we have found novel(η^3-C_3H_5)RuBr(CO)_3/Et_3N-catalyzed carbonylative cyclization of allylic carbonates with alkenes to give the corresponding cyclopentenones in high yields. In addition, cyclopentenones were prepared by a novel rutheniumcatalyzed coupling of cyclobutenediones with alkenes via C-C bond cleavage. For example, treatment of 4-butyl-3-isopropoxycyclobut-3-ene-1, 2-dione with 2-norbornene in the presence of a catalytic amount of Ru_3(CO)_<12> and PEt_3 in THF under 3 atm of carbon monoxide at 160℃ for 20 h gave the corresponding cyclopentenone, 4-butyl-5-isopropoxytricyclo[5.2.1.0^<2,6>]dec-4-en-3-one, in 75% yield(exo 100%). The reaction proceeds via a ruthenacyclopentenedione and/or ruthenacyclobutenone intermediate, which would be obtained by unsymmetrical ring-opening of cyclobutenediones with an active ruthenium catalyst.In coclusion, both reactions will open up new chemistry in the field of ruthenium-catalyzed carbonylation reactions, and offer the novel and practical methods for preparation of cyclopentenones which are quite attractive and important due to the wide abundance of this structural unit in a large number of natural products and biologically active compounds. These cyclopentenone syntheses may be the complement of the catalytic intermolecular Pauson-Khand reaction.