Hartung Jens, Daniel Kristina, Gottwald Thomas, Gross Andreas, Schneiders Nina
Fachbereich Chemie, Organische Chemie, Erwin-Schrödinger Strasse, Technische Universität Kaiserslautern, D-67663 Kaiserslautern, Germany.
Org Biomol Chem. 2006 Jun 7;4(11):2313-22. doi: 10.1039/b603480b. Epub 2006 May 9.
Microwave irradiation (2.45 GHz, 300-500 W) of N-(alkoxy)thiazole-2(3H)-thiones in low-absorbing solvents affords alkoxyl radicals, which were identified by (i) spin adduct formation (EPR-spectroscopy) and (ii) fingerprint-type selectivities in intramolecular additions (stereoselective synthesis of disubstituted tetrahydrofurans), beta-fragmentations (formation of carbonyl compounds), and C,H-activation of aliphatic subunits, by delta-selective hydrogen atom transfer. C-Radicals formed from oxygen-centered intermediates were trapped either by Bu(3)SnH, L-cysteine ethyl ester, the reduced form of glutathione (reductive trapping), or by bromine atom donor BrCCl(3) (heteroatom functionalization) The results suggest that microwave activation is superior to UV/Vis-photolysis and conductive heating for alkoxyl radical generation from N-(alkoxy)thiazolethiones. It offers by far the shortest reaction times along with the option to reduce the amount of trapping reagent significantly.
在低吸收溶剂中，对N -（烷氧基）噻唑 - 2（3H）-硫酮进行微波辐射（2.45 GHz，300 - 500 W）可产生烷氧基自由基，这些自由基可通过以下方式鉴定：（i）自旋加合物形成（电子顺磁共振光谱法），以及（ii）分子内加成（二取代四氢呋喃的立体选择性合成）、β-碎裂（羰基化合物的形成）和脂肪族亚基的C，H-活化中的指纹型选择性，通过δ-选择性氢原子转移实现。由以氧为中心的中间体形成的碳自由基可被Bu(3)SnH、L-半胱氨酸乙酯、还原型谷胱甘肽（还原捕获）捕获，或被溴原子供体BrCCl(3)（杂原子官能化）捕获。结果表明，对于从N -（烷氧基）噻唑硫酮生成烷氧基自由基，微波活化优于紫外/可见光光解和传导加热。它提供了迄今为止最短的反应时间，同时还可显著减少捕获试剂的用量。
