Hydrogen Borrowing Catalysis with Secondary Alcohols: A New Route for the Generation of β‑Branched Carbonyl Compounds

A hydrogen
borrowing reaction employing secondary alcohols and
Ph* (Me5C6) ketones to give β-branched
carbonyl products is described (21 examples). This new C–C
bond forming process requires low loadings of [Cp*IrCl2]2, relatively low temperatures, and up to 2.0 equiv of
the secondary alcohol. Substrate-induced diastereoselectivity was
observed, and this represents the first example of a diastereoselective
enolate hydrogen borrowing alkylation. By utilizing the Ph* group,
the β-branched products could be straightforwardly cleaved to
the corresponding esters or amides using a retro-Friedel–Crafts
reaction. Finally, this protocol was applied to the synthesis of fragrance
compound (±)-3-methyl-5-phenylpentanol.