Iridium-Catalyzed Regioselective Silylation of Secondary Alkyl C–H Bonds for the Synthesis of 1,3-Diols

We
report Ir-catalyzed intra­molecular silyl­ation of
secondary alkyl C–H bonds. (Hydrido)­silyl ethers, generated in situ by de­hydro­gen­ative coupling of
a tertiary or conformationally restricted secondary alcohol with diethyl­silane,
undergo regio­selective silyl­ation at a secondary C–H
bond γ to the hydroxyl group. Oxidation of the resulting oxa­silol­anes
in the same vessel generates 1,3-diols. This method provides a strategy
to synthesize 1,3-diols through a hydroxyl-directed, functionalization
of secondary alkyl C–H bonds. Mechanistic studies suggest that
the C–H bond cleavage is the turnover-limiting step of the
catalytic cycle. This silyl­ation of secondary C–H bonds
is only 40–50 times slower than the analogous silyl­ation
of primary C–H bonds.

本工作报道了铱（Ir）催化的二级烷基C-H键分子内硅基化反应。通过叔醇或构象受限的二级醇与二乙基硅烷经脱氢偶联原位生成的氢硅醚，可在相对于羟基的γ位二级C-H键处发生区域选择性硅基化。在同一反应容器中对生成的氧硅杂环戊烷（oxasilolane）进行氧化，即可得到1,3-二醇。该方法通过羟基导向的二级烷基C-H键官能团化策略，实现了1,3-二醇的合成。机理研究表明，C-H键断裂是该催化循环的决速步。该二级C-H键硅基化反应的速率仅比一级C-H键的同类硅基化反应慢40~50倍。