We report improved protocols for the synthesis of thiazolium precatalysts from primary amines, carbon disulfide, and α-halo ketones. For N-alkyl-substituted derivatives, yields of the corresponding thiazolethiones can be dramatically improved by isolating the intermediate dithiocarbamates. In most cases, meta-chloroperbenzoic acid can advantageously replace H2O2 in acetic acid for the oxidation of
我们报告了从伯胺、二硫化碳和 α-卤代酮合成噻唑鎓预催化剂的改进方案。对于N-烷基取代的衍生物,通过分离中间体二硫代氨基甲酸酯可以显着提高相应噻唑硫酮的产率。在大多数情况下,间氯过苯甲酸可以有利地代替乙酸中的H 2 O 2以将噻唑硫酮氧化成噻唑鎓。该方法应用于合成具有 2-金刚烷基N取代基的噻唑鎓、相应的持久卡宾及其二聚体。
A Family of Thiazolium Salt Derived N-Heterocyclic Carbenes (NHCs) for Organocatalysis: Synthesis, Investigation and Application in Cross-Benzoin Condensation
作者:Isabel Piel、Marius D. Pawelczyk、Keiichi Hirano、Roland Fröhlich、Frank Glorius
DOI:10.1002/ejoc.201100870
日期:2011.10
A family of thiazolium salt derived N-heterocycliccarbenes (NHCs) bearing sterically demanding aryl substituents on the nitrogen and with varying backbone substitution patterns have been synthesized. Investigation of the catalytic activity of these NHCs in a number of benzoin-type coupling reactions revealed markedly different levels of reactivity and selectivity. To elucidate the underlying factors