Department of Chemistry, McGill University, Montreal, QC, Canada.
FRQNT Centre for Green Chemistry and Catalysis, Montreal, QC, Canada.
Nat Commun. 2021 Aug 17;12(1):4970. doi: 10.1038/s41467-021-25229-8.
Carboxylic acids are readily available, structurally diverse and shelf-stable; therefore, converting them to the isoelectronic boronic acids, which play pivotal roles in different settings, would be highly enabling. In contrast to the well-recognised decarboxylative borylation, the chemical space of carboxylic-to-boronic acid transformation via deoxygenation remains underexplored due to the thermodynamic and kinetic inertness of carboxylic C-O bonds. Herein, we report a deoxygenative borylation reaction of free carboxylic acids or their sodium salts to synthesise alkylboronates under metal-free conditions. Promoted by a uniquely Lewis acidic and strongly reducing diboron reagent, bis(catecholato)diboron (Bcat), a library of aromatic carboxylic acids are converted to the benzylboronates. By leveraging the same borylative manifold, a facile triboration process with aliphatic carboxylic acids is also realised, diversifying the pool of available 1,1,2-alkyl(trisboronates) that were otherwise difficult to access. Detailed mechanistic studies reveal a stepwise C-O cleavage profile, which could inspire and encourage future endeavours on more appealing reductive functionalisation of oxygenated feedstocks.
羧酸易得、结构多样且稳定，因此将其转化为具有重要作用的等电子硼酸，将非常有意义。与人们熟知的脱羧硼酸化反应不同，由于羧酸 C-O 键热力学和动力学惰性，通过脱氧转化羧酸为硼酸的化学空间尚未得到充分探索。在此，我们在无金属条件下，通过一种独特的路易斯酸性和强还原二硼试剂双（邻苯二酚）二硼（Bcat），报告了游离羧酸或其钠盐的脱氧硼化反应，以合成烷基硼酸酯。在这种路易斯酸性和强还原二硼试剂的促进下，一系列芳香羧酸被转化为苄基硼酸酯。通过利用相同的硼化反应途径，还实现了脂肪族羧酸的简便三硼化过程，使原本难以获得的 1,1,2-烷基（三硼酸酯）的种类多样化。详细的机理研究揭示了分步 C-O 断裂的过程，这可能为未来更具吸引力的含氧原料的还原官能化提供灵感和鼓励。
