Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Bl. 9, Acad. G. Bonchev Str., 1113 Sofia, Bulgaria.
Molecules. 2021 Nov 14;26(22):6865. doi: 10.3390/molecules26226865.
A series of squaric acid amides (synthesized in 66-99% isolated yields) and a set of chiral aminoalcohols were comparatively studied as ligands in a model reaction of reduction of α-chloroacetophenone with BH•SMe. In all cases, the aminoalcohols demonstrated better efficiency (up to 94% ), while only poor asymmetric induction was achieved with the corresponding squaramides. A mechanistic insight on the in situ formation and stability at room temperature of intermediates generated from ligands and borane as possible precursors of the oxazaborolidine-based catalytic system has been obtained by H DOSY and multinuclear 1D and 2D (H, B, C, N) NMR spectroscopy of equimolar mixtures of borane and selected ligands. These results contribute to better understanding the complexity of the processes occurring in the reaction mixture prior to the possible oxazaborolidine formation, which play a crucial role on the degree of enantioselectivity achieved in the borane reduction of α-chloroacetophenone.
研究了一系列丁二酸酰胺（以 66-99%的分离产率合成）和一组手性氨基醇，作为模型反应α-氯苯乙酮与 BH·SMe 还原的配体进行了比较。在所有情况下，氨基醇都表现出更好的效率（高达 94%），而相应的丁二酰胺则仅实现了较差的不对称诱导。通过 H DOSY 和等摩尔混合的硼烷和选定配体的多核 1D 和 2D（H、B、C、N）NMR 光谱，获得了关于配体和硼烷原位形成和在室温下稳定的中间体的机理见解，这些中间体可能是基于噁唑硼烷的催化体系的前体。这些结果有助于更好地理解在可能形成噁唑硼烷之前反应混合物中发生的过程的复杂性，这对硼烷还原α-氯苯乙酮所达到的对映选择性程度起着至关重要的作用。
