Selective Nickel‐Catalyzed Hydrodeacetoxylation of Aryl Acetates

• Published in: Angewandte Chemie 2022-09, Vol.134 (38), p.n/a
• Main Authors: De Smet, Gilles, Bai, Xingfeng, Mensch, Carl, Sergeyev, Sergey, Evano, Gwilherm, Maes, Bert U. W.
• Format: Article
• Language: English
• Subjects: Acetates; Acetic acid; Aromatic compounds; Aryl Acetates; Catalysis; Chemistry; C−O Bond Activation; Deoxygenation; Hydrodeacetoxylation; Nickel; Nickel Catalysis; Phenols; Reduction; Renewable Resources
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202201751

Acetate serves as a renewable and easily installed leaving group for selective deoxygenation of phenolics (ArOH). Ni‐catalyzed hydrodeacetoxylation of aryl acetates (Ar−OAc) with HBpin in a green carbonate solvent selectively delivers the corresponding deoxygenated arenes (ArH). The method is also applicable to highly challenging guaiacyl and syringyl acetates, leaving −OMe groups intact without arene reduction. Renewable 4‐propylguaiacol obtained from pine can also be transformed without significant loss in yield versus oil derived feedstock. The observed chemoselectivity for Ar−OAc versus ArO−Ac bond cleavage was rationalized based on mechanistic experiments and DFT calculations. ArOH side‐product formation is attributed to direct competitive Ni‐catalyzed reduction of the C=O bond. Hydrodeacyloxylation of a set of aryl alkanoates featured interesting chemoselectivity with a dramatic influence of the length and structure of the alkyl chain on catalysis. Electron‐rich aryl acetates derived from (renewable) phenolics were selectively reduced to the corresponding arenes using pinacolborane (HBpin) and a nickel‐N‐heterocyclic carbene (NHC) catalytic system in the green solvent dimethylcarbonate (DMC). The method is applicable to 4‐propylguaiacyl acetate derived from pine wood.