Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan.
J Am Chem Soc. 2010 Sep 8;132(35):12194-6. doi: 10.1021/ja105096r.
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.
硅基硼酸酯与末端炔烃的加成反应的区域选择性可以通过选择钯催化剂上的磷配体来切换。在（η(3)-C(3)H(5))Pd(PPh(3))Cl（1.0 mol %）存在下，硅烷化反应以正常的区域选择性进行，以高产率得到 1-硼基-2-硅基-1-烯烃。相比之下，当反应使用带有 P(t-Bu)(2)(联苯-2-基)的钯催化剂进行时，选择性地形成了相反的区域异构体，2-硼基-1-硅基-1-烯烃。提出了一种涉及可逆插入/β-硼基消除步骤的区域选择性变化的反应机制。
