Switch of regioselectivity in palladium-catalyzed silaboration of terminal alkynes by ligand-dependent control of reductive elimination.
The regioselectivity in the addition of silylboronic esters to terminal alkynes can be switched by the choice of phosphorus ligands on the palladium catalysts. The silaboration proceeds with normal regioselectivity in the presence of (eta(3)-C(3)H(5))Pd(PPh(3))Cl (1.0 mol %) to give 1-boryl-2-silyl-1-alkenes in high yields. In sharp contrast, selective formation of the inverse regioisomers, 2-boryl-1-silyl-1-alkenes, takes place when the reaction is carried out with a palladium catalyst bearing P(t-Bu)(2)(biphenyl-2-yl). A reaction mechanism for the change of regioselectivity that involves reversible insertion/beta-boryl elimination steps is proposed.
Ohmura
Toshimichi
T
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan. ohmura@sbchem.kyoto-u.ac.jp
Oshima
Kazuyuki
K
Taniguchi
Hiroki
H
Suginome
Michinori
M
D000480:Alkynes / Q000737:chemistry*; D001880:Boranes / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D008024:Ligands; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry*; D012821:Silanes / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D000480:Alkynes; D001880:Boranes; D008024:Ligands; D009942:Organometallic Compounds; D012821:Silanes; D010165:Palladium