Mas-Roselló Josep, Cramer Nicolai
Laboratory of Asymmetric Catalysis and Synthesis, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
Chemistry. 2022 Feb 21;28(10):e202103683. doi: 10.1002/chem.202103683. Epub 2021 Dec 22.
Catalytic reduction of oximes represents a direct efficient approach to synthesize valuable hydroxylamine derivatives. However this transformation presents significant challenges: oximes are hard to reduce and, if reactive, reductive cleavage of the weak N-O bond often leads to primary amine side products. The first suitable systems involved the use of platinum-based heterogeneous catalysts with hydrogen as reductant and stoichiometric amounts of a strong Brønsted acid. More recently metal-free and transition-metal-based homogeneous catalysts have been developed, which display the highest turnovers (up to 4000). In the asymmetric variants, the E/Z-geometry of the oxime double bond affects significantly the stereoselectivity, sometimes requiring extra synthetic efforts in substrate preparation. This minireview provides an overview of the advances and limitations in catalytic oxime to hydroxylamine reduction. Emphasis is put on highlighting and comparing the practical aspects of the existing methods, such as their reaction conditions and substrate scope. Additionally, future directions for improving this young research area are suggested.
肟的催化还原是合成有价值的羟胺衍生物的一种直接有效方法。然而，这种转化面临重大挑战：肟难以还原，并且如果具有反应活性，弱N-O键的还原裂解通常会导致伯胺副产物。最早适用的体系涉及使用以氢气作为还原剂和化学计量的强布朗斯特酸的铂基多相催化剂。最近，已开发出无金属和基于过渡金属的均相催化剂，其显示出最高的转化率（高达4000）。在不对称变体中，肟双键的E/Z-几何构型对立体选择性有显著影响，有时在底物制备中需要额外的合成工作。本综述概述了催化肟还原为羟胺的进展和局限性。重点是突出和比较现有方法的实际方面，如它们的反应条件和底物范围。此外，还提出了改善这个新兴研究领域的未来方向。
