Nickel-Catalyzed Reductive Deoxygenation of Diverse C–O Bond-Bearing Functional Groups

Abstract

We report a catalytic method for the direct deoxygenation of various C–O bond-containing functional groups. Using a Ni­(II) pre-catalyst and silane reducing agent, alcohols, epoxides, and ethers are reduced to the corresponding alkane. Unsaturated species including aldehydes and ketones are also deoxygenated via initial formation of an intermediate silylated alcohol. The reaction is chemoselective for C­(sp3)–O bonds, leaving amines, anilines, aryl ethers, alkenes, and nitrogen-containing heterocycles untouched. Applications toward catalytic deuteration, benzyl ether deprotection, and the valorization of biomass-derived feedstocks demonstrate some of the practical aspects of this methodology.

Nickel-catalyzed reductive decarboxylation of fatty acids for drop-in biofuel production

“…Replacing PMHS with different hydrogen sources commonly reported for this type of transformation 39,40 signicantly decreased the formation of the desired product under this set of conditions (Table 1, entries 7 and 8). Notably, other reductive agents such as Mn (Table 1, entry 10) completely inhibited the decarboxylation.…”

Selective Biocatalytic Defunctionalization of Raw Materials

“…Catalytic transformations of oxygen-containing starting materials to specifically deoxygenated products are of great synthetic interest not only for the defunctionalization of biobased raw materials, but also in late-stage defunctionalization. [122] Highly selective and straightforward biocatalytic deoxygenations provide a sustainable and viable strategy for meeting these synthetic objectives (see Scheme 8). The selective sugar deoxygenation can be catalyzed in a one-step reaction by ribonucleotide reductases in a 1,2-radical migration mechanism.…”

Acidic Ionic Liquids as Metal-Free and Recyclable Catalysts for Direct Reduction of Aromatic Allylic Alcohol in Dimethyl Carbonate via Hydrogen Transfer

“…Therefore, direct reduction of alcohols has drawn more and more attention, and most activated alcohols, such as benzyl alcohols, allylic alcohols, , or propargyl alcohols, , have been successfully deoxidized. Transition metal complexes such as Ir, Mn, Ru, and so on with specific ligands were used as the catalysts to achieve direct reduction of alcohols by employing hydrosilane, silane, or hydrazine as the reducing agent (Scheme a). − In addition, Lewis acids were also favorable for the reaction by enhancing C–O bond cleavage and prolonging the existence of benzyl cation intermediates (Scheme b), thus creating an opportunity for effective hydrogen transfer . However, the transition metal complexes or Lewis acids were the main catalysts to achieve the C–O bond dissociation and further reduction of alcohols, easily leading to metal contamination. − …”