Department of Pharmaceutical Chemistry, University of Debrecen, Egyetem tér 1, 4032, Debrecen, Hungary.
Doctoral School of Pharmaceutical Sciences, University of Debrecen, Egyetem tér 1, 4032, Debrecen, Hungary.
Chemistry. 2019 Nov 18;25(64):14555-14571. doi: 10.1002/chem.201903095. Epub 2019 Oct 1.
A comprehensive optimization and mechanistic study on the photoinduced hydrothiolation of different d- and l- hexo- and pentoglycals with various thiols was performed, at the temperature range of RT to -120 °C. Addition of thiols onto 2-substituted hexoglycals proceeded with complete 1,2-cis-α-stereoselectivity in all cases. Hydrothiolation of 2-substituted pentoglycals resulted in mixtures of 1,2-cis-α- and -β-thioglycosides of varying ratio depending on the configuration of the reactants. Hydrothiolation of unsubstituted glycals at -80 °C proceeded with excellent yields and, except for galactal, provided the axially C2-S-linked isomers with high selectivity. Cooling was always beneficial to the efficacy, increased the yields and in most cases significantly raised the stereoselectivity. The suggested mechanism explains the different conformational preferences of the intermediate carbon-centered radicals, which is a crucial factor in the stereoselectivity of the reactions.
在室温至-120°C 的温度范围内，对不同的 d-和 l-己糖和戊糖与各种硫醇的光诱导氢硫加成反应进行了全面的优化和机理研究。在所有情况下，巯基都完全以 1,2-顺式-α-立体选择性加成到 2-取代的己糖上。2-取代的戊糖的氢硫加成反应导致 1,2-顺式-α-和-β-硫代糖苷的混合物，其比例取决于反应物的构型。在-80°C 下，未取代的戊糖的氢硫加成反应以优异的收率进行，除了半乳糖外，还以高选择性提供轴向 C2-S 连接的异构体。冷却总是有利于反应的效果，提高了收率，在大多数情况下显著提高了立体选择性。所提出的机理解释了中间体碳中心自由基的不同构象偏好，这是反应立体选择性的关键因素。
