Jin Gong, Sun Jing, Yang Ren-Yin, Yan Chao-Guo
College of Chemistry &Chemical Engineering, Yangzhou University, Yangzhou 225002, China.
Sci Rep. 2017 Apr 13;7:46470. doi: 10.1038/srep46470.
The triethylamine promoted stepwise 1,3-dipolar cycloaddition reaction of N-phenacylbenzothiazolium bromides with nitroalkenes in ethanol resulted in a mixture of two isomeric tetrahydrobenzo[d]pyrrolo[2,1-b]thiazoles with cis/trans/cis- and all-trans-configurations. More importantly, the corresponding dihydrobenzo[d]pyrrolo[2,1-b]thiazoles can be selectively prepared in refluxing ethanol and the benzo[d]pyrrolo[2,1-b]thiazoles can be obtained in satisfactory yields by sequential dehydrogenation with DDQ as oxidizer. On the other hand, the similar cycloaddition reaction of N-phenacylbenzothiazolium bromides with 1-methy-1-nitroalkenes in refluxing ethanol afforded benzo[d]pyrrolo[2,1-b]thiazoles with splitting out of nitro group. The stereochemistry of the spiro compounds was clearly elucidated on the basis of NMR spectra and sixteen single crystal structures.
三乙胺促进的N-苯甲酰基苯并噻唑溴化物与硝基烯烃在乙醇中的逐步1,3-偶极环加成反应，生成了两种具有顺式/反式/顺式和全反式构型的异构四氢苯并[d]吡咯并[2,1-b]噻唑的混合物。更重要的是，相应的二氢苯并[d]吡咯并[2,1-b]噻唑可以在回流乙醇中选择性制备，并且以DDQ作为氧化剂通过连续脱氢可以以令人满意的产率获得苯并[d]吡咯并[2,1-b]噻唑。另一方面，N-苯甲酰基苯并噻唑溴化物与1-甲基-1-硝基烯烃在回流乙醇中的类似环加成反应，生成了脱去硝基的苯并[d]吡咯并[2,1-b]噻唑。基于核磁共振光谱和十六个单晶结构，明确阐明了螺环化合物的立体化学。
