Heard David M, Lessard Martin C, Hall Dennis G
Department of Chemistry, 4-010 Centennial Centre for Interdisciplinary Science, University of Alberta, 11335 Saskatchewan Dr NW, Edmonton, AB, T6G2G2, Canada.
Angew Chem Int Ed Engl. 2025 Jul 7;64(28):e202507571. doi: 10.1002/anie.202507571. Epub 2025 May 13.
Organoboronic acids impact numerous fields of application from organic synthesis to drug discovery and materials science. However, their highly polar nature makes them challenging to handle, purify, and characterize. Boronic esters help overcome these issues, and pinacol esters (Bpin) have become the dominant boronic acid surrogate in organic synthesis. Despite its popularity, Bpin is not without drawbacks. Its formation from pinacol is intrinsically reversible in the presence of water or alcohols, which may cause premature release leading to losses during reactions and purification. This reversibility complicates the hydrolytic regeneration of free boronic acids, which often requires additional steps to destroy the pinacol by-product. Although other boronyl protecting groups exist, their removal requires harsh pH conditions. To address these issues, we developed xanthopinacol boronates (Bxpin), a robust protecting group for boronic acids with excellent orthogonality in various chemical reactions and mild irreversible removal under catalyzed photoredox conditions. Xpin boronates can be obtained directly by irradiation of a mixture of free boronic acid and xanthone with UV light, causing an in situ dimerization of xanthone to the required xanthopinacol. The unique attributes of xpin boronates were further studied by UV-vis spectrophotometry, X-ray crystallography, cyclic voltammetry, and various stability tests.
有机硼酸在从有机合成到药物发现和材料科学等众多应用领域都有重要影响。然而，它们的高极性使其在处理、纯化和表征方面具有挑战性。硼酸酯有助于克服这些问题，频哪醇酯（Bpin）已成为有机合成中主要的硼酸替代物。尽管其很受欢迎，但Bpin并非没有缺点。在水或醇存在下，由频哪醇形成Bpin本质上是可逆的，这可能导致过早释放，从而在反应和纯化过程中造成损失。这种可逆性使游离硼酸的水解再生变得复杂，通常需要额外步骤来破坏频哪醇副产物。虽然存在其他硼酰基保护基团，但它们的去除需要苛刻的pH条件。为了解决这些问题，我们开发了呫吨频哪醇硼酸酯（Bxpin），这是一种用于硼酸的强大保护基团，在各种化学反应中具有出色的正交性，并且在光催化氧化还原条件下可温和且不可逆地去除。呫吨硼酸酯可通过用紫外光照射游离硼酸和呫吨的混合物直接获得，使呫吨原位二聚为所需的呫吨频哪醇。通过紫外可见分光光度法、X射线晶体学、循环伏安法和各种稳定性测试进一步研究了呫吨硼酸酯的独特性质。
