Alpha-hydroxy esters via enantioselective hydrogen-mediated C-C coupling: regiocontrolled reactions of silyl-substituted 1,3-diynes.
[reaction: see text] Catalytic hydrogenation of ethyl glyoxalate in the presence of 1,3-diynes 4a-9a using chirally modified rhodium catalysts enables formation of alpha-hydroxy esters 4c-9c in highly optically enriched form. Notably, for such trialkylsilyl-substituted 1,3-diynes, C-C coupling occurs exclusively at the carbon atom bearing silicon. Pi-back-bonding from low valent rhodium as described by the Dewar-Chatt-Duncanson model appears to direct the regiochemistry of C-C coupling, as corroborated by calculations of the diyne LUMO coefficients.
Cho
Chang-Woo
CW
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
Krische
Michael J
MJ
D002384:Catalysis; D053280:Diynes / Q000737:chemistry*; D004952:Esters; D006865:Hydrogenation; D015394:Molecular Structure; D012238:Rhodium / Q000737:chemistry; D012821:Silanes / Q000737:chemistry*; D013237:Stereoisomerism
D053280:Diynes; D004952:Esters; D012821:Silanes; D012238:Rhodium