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.