Thiadiazolium ylides: Substituted 2H-1,3,5-thiadiazines and 1,4,5-trisubstituted-imidazoles from 1,2,4- and 1,2,5-thiadiazolium-2-unsubstituted methanide (ylide) systems: ring expansions and ring interconversions via sulfur-nitrogen heterotriene intermediates. Mechanistic ab initio calculations. Azolium 1,3-dipoles
作者:Richard N. Butler、Martin O. Cloonan、John M. McMahon、Luke A. Burke
DOI:10.1039/a901148j
日期:——
Quaternisation of 3,5-diaryl-1,2,4-thiadiazoles with trimethylsilylmethyl triflate at 40 °C occurred at N-2. Separate desilylation of the salts resulted in a ring expansion to substituted 2H-1,3,5-thiadiazines 5. Heating of these with ethanolic sodium ethoxide caused sulfur extrusion and ring contraction to 2,4-disubstituted imidazoles 6. 3,4-Diaryl-1,2,5-thiadiazoles were less reactive to alkylation and trimethylsilylmethylation required heating at 80 °C. Treatment of the salts with CsF unexpectedly gave 1-trimethylsilylmethyl-4,5-diarylimidazoles 21. 1H, 13C, 15N NMR spectra are described and the mechanisms were studied by ab inito calculations with the GAUSSIAN94 series of programmes using the HF/6-31G* theoretical level.
3,5-二芳基-1,2,4-噻二唑在40°C下与三甲基硅基甲基三氟甲磺酸酯的季铵化反应发生在N-2位。分离的盐的脱硅基化导致环的扩展,生成了取代的2H-1,3,5-噻二唑啉5。将这些化合物与醇钠乙氧基加热,会导致硫原子的排出和环的收缩,生成2,4-二取代的咪唑6。3,4-二芳基-1,2,5-噻二唑对烷基化反应的活性较低,三甲基硅基甲基化反应需要在80°C下加热。用CsF处理盐意外地生成了1-三甲基硅基甲基-4,5-二芳基咪唑21。描述了其1H、13C、15N NMR谱,并通过使用HF/6-31G*理论水平的GAUSSIAN94系列程序进行了机制研究。