Catalytic carbonyl Z-dienylation via multicomponent reductive coupling of acetylene to aldehydes and alpha-ketoesters mediated by hydrogen: Carbonyl insertion into cationic rhodacyclopentadienes.
Exposure of aldehydes or alpha-ketoesters to equal volumes of acetylene and hydrogen gas at ambient temperature and pressure in the presence of cationic rhodium catalysts provides products of carbonyl Z-butadienylation, which arise via multicomponent coupling of four molecules: two molecules of acetylene, a molecule of vicinal dicarbonyl compound, and a molecule of elemental hydrogen. The collective data suggest a catalytic mechanism involving carbonyl insertion into a cationic rhodacyclopentadiene intermediate derived via oxidative dimerization of acetylene. Hydrogenolytic cleavage of the resulting oxarhodacycloheptadiene via formal sigma-bond metathesis provides the product of carbonyl addition and cationic rhodium(I) to close the catalytic cycle. Studies involving the hydrogenation of 1,6-diyne 14a in the presence of alpha-ketoester 6a corroborate the proposed catalytic mechanism. These multicomponent couplings represent the first use of acetylene gas, a basic chemical feedstock, in metal-catalyzed reductive C-C bond formation.
Kong
Jong Rock
JR
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
Krische
Michael J
MJ
D000114:Acetylene / Q000737:chemistry*; D000447:Aldehydes / Q000737:chemistry*; D002384:Catalysis; D002412:Cations / Q000737:chemistry; D003517:Cyclopentanes / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D010084:Oxidation-Reduction; D013237:Stereoisomerism
D000447:Aldehydes; D002412:Cations; D003517:Cyclopentanes; D007659:Ketones; D006859:Hydrogen; D000114:Acetylene