Hydrogen-mediated C-C bond formation: catalytic regio- and stereoselective reductive condensation of alpha-keto aldehydes and 1,3-enynes.
Hydrogenation of 1,3-enynes in the presence of alpha-keto aldehydes using cationic Rh(I) catalysts enables regio- and stereoselective reductive coupling to the acetylenic terminus of the enyne to afford (E)-2-hydroxy-3,5-dien-1-one products. Reductive condensation of 1-phenyl but-3-en-1-yne 1a with phenyl glyoxal 2a performed under an atmosphere of D(2) provides the product of mono-deuteration, (E)-2-hydroxy-3-deuterio-3,5-dien-1-one deuterio-3a, in 85% yield. Competition experiments involving catalytic hydrogenation of phenyl glyoxal in the presence of equimolar quantities of 1,4-diphenylbutadiene and 1,4-diphenylbut-3-en-1-yne 10a, as well as 1,4-diphenylbut-3-en-1-yne 10a and 1,4-diphenylbutadiyne, are chemoselective for coupling to the more highly unsaturated partner, suggesting a preequilibrium involving precoordination and exchange of the pi-unsaturated pronucleophiles with the catalyst prior to C-C bond formation, as well as a preference for coordination of the most pi-acidic reacting partner, as explained by the Dewar-Chatt-Duncanson model for alkyne coordination.
Jang
Hye-Young
HY
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
Huddleston
Ryan R
RR
Krische
Michael J
MJ
D000447:Aldehydes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D010084:Oxidation-Reduction; D013237:Stereoisomerism
D000447:Aldehydes; D000480:Alkynes; D007659:Ketones; D006859:Hydrogen