Catalytic cross-coupling of ketones and secondary alcohols with primary alcohols is reported. An abundant manganese-based pincer catalyst catalyzes the reactions. Low loading of catalyst (2 mol %) and catalytic use of a mild base (5–10 mol %) are sufficient for efficient cross-coupling. Various aryl and heteroaryl ketones are catalytically cross-coupled with primary alcohols to provide the selective α-alkylated products. Challenging α-ethylation of ketones is also attained using ethanol as an alkylating reagent. Further, direct use of secondary alcohols in the reaction results in in situ oxidation to provide the ketone intermediates, which undergo selective α-alkylation. The reaction proceeds via the borrowing hydrogen pathway. The catalyst oxidizes the primary alcohols to aldehydes, which undergo subsequent aldol condensation with ketones, promoted by catalytic amount of Cs2CO3, to provide the α,β-unsaturated ketone intermediates. The hydrogen liberated from oxidation of alcohols is used for hydrogenation of α,β-unsaturated ketone intermediates. Notably either water or water and dihydrogen are the only byproductsin these environmentally benign catalytic processes. Mechanistic studiesallowed inferring all of the intermediates involved. Dearomatization–aromatizationmetal–ligand cooperation in the catalyst facilitates the facileO–H bond activation of both primary and secondary alcohols,and the resultant manganese alkoxide complexes produce correspondingcarbonyl compounds, perhaps via β-hydride elimination. The manganese(I)hydride intermediate plays dual role as it hydrogenates α,β-unsaturatedketones and liberates molecular hydrogen to regenerate the catalyticallyactive dearomatized intermediate. Metal–ligand cooperationallows all of the manganese intermediates to exist in same oxidationstate (+1) and plays an important role in these catalytic cross-couplingreactions.
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