Preparation of axially chiral N,N′-diarylimidazolium and N-arylthiazolium salts and evaluation of their catalytic potential in the benzoin and in the intramolecular stetter reactions
Preparation of axially chiral N,N′-diarylimidazolium and N-arylthiazolium salts and evaluation of their catalytic potential in the benzoin and in the intramolecular stetter reactions
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DOI：
10.1002/ejoc.200300762
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发表时间：
2004-04-26
影响因子：
2.8
通讯作者：
Bach, T
中科院分区：
文献类型：
--
作者：
Pesch, J;Harms, K;Bach, T
制备N-芳基取代的咪唑14 b、15 b和噻唑17-22、25，它们含有立体轴并且可以阻转异构体形式存在。咪唑鎓盐15 b可由2-异丙基苯胺（12 b）和双乙酰（11）经三步反应制得（产率19%），而它们的叔丁基类似物的合成失败。内消旋异构体meso-15 b占优势（dr = 90/10）。手性噻唑鎓盐rac-17（53%产率）和rac-22（49%产率）由2-叔丁基苯胺（12 a）分两步制备。由α-溴代薄荷酮（23）和苯胺12 a获得对映体纯的噻唑鎓盐19（27%总产率）。与咪唑鎓盐15 b相比，噻唑鎓盐被证明是苯甲醛（12）的安息香缩合和α，不饱和酯19 a的分子内Stetter反应中的合适催化剂。用催化剂19（20摩尔%）获得的最佳结果是产物2的产率为85%（40%ee）和产物10a的产率为75%（50%ee）。催化剂19的立体轴在催化活性卡宾中间体28中不是构型稳定的。催化剂作为非对映阻转异构体19和26的混合物以70：30至75：25的比例回收。((C)Wiley-VCH Verlag GmbH & Co. KGaA，69451魏因海姆，德国，2004）。
N-Aryl-substituted imidazoles 14b, 15b and thiazoles 17-22, 25 were prepared which contain a stereogenic axis and which can occur as atropisomers. The imidazolium salts 15b could be obtained from 2-isopropylaniline (12b) and diacetyl (11) in three steps (19% yield) whereas the synthesis of their tert-butyl analogues failed. The meso-isomer meso-15b prevailed (dr = 90/10). The chiral thiazolium salts rac-17 (53% yield) and rac-22 (49% yield) were prepared in two steps from 2-tert-butylaniline (12a). The enantiomerically pure thiazolium salt 19 was obtained from alpha-bromomenthone (23) and the aniline 12a (27% overall yield). In contrast to the imidazolium salts 15b, the thiazolium salts proved to be suit-able catalysts in the benzoin condensation of benzaldehyde (12) and in the intramolecular Stetter reaction of the a, unsaturated ester 19a. The best results obtained with catalyst 19 (20 mol%) were 85% yield of product 2 (40% ee) and 75% yield of product 10a (50% ee). The stereogenic axis of catalyst 19 is not configurationally stable in the catalytically active carbene intermediate 28. The catalyst is recovered as a mixture of diastereomeric atropisomers 19 and 26 in a ratio of 70:30 to 75:25. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).