β-硝基苯乙烯衍生物与二溴海因高度区域选择性氨溴加成反应

以β-硝基苯乙烯衍生物为底物, 二溴海因为氮源/卤素源, 乙腈作溶剂, 建立了碳碳双键上高度区域选择性氨溴加成反应新体系. β-硝基苯乙烯衍生物与二溴海因在室温无水碳酸钠催化下反应, 可高收率获得邻位氨溴加成产物, 最高收率达97%; β-甲基-β-硝基苯乙烯衍生物在氢氧化钾催化下回流反应, 也可高收率得到邻位氨溴加成产物, 最高收率达95%. 实验结果表明, 对于硝基苯乙烯衍生物, 当苯环4-位具有强供电子基团如CH₃O时, 可以得到单一的α-氨基-β-溴加成产物, 但其收率相对较低; 当硝基苯乙烯衍生物的苯环4-位有强吸电子基团如NO₂时, 反应收率则很高. 这一实验结果证明β-硝基苯乙烯衍生物(缺电子烯烃)与二溴海因的氨溴加成反应具有亲核加成的特征. 本文共考察了20种不同结构的β-硝基苯乙烯衍生物的氨溴加成反应情况, 其产物结构经核磁共振波谱及质谱分析确证, 并提出了可能的反应机理.

High Regioselective Aminobromination of β-Nitrostyrene Derivatives with 1,3-Dibromo-5,5-dimethyl Hydantoin†

A new protocol for the high regioselective aminobromination of β-nitrostyrene derivatives with 1,3-dibromo-5,5-dimethyl hydantoin(DBDMH) as nitrogen/bromine sources was developed. Two kinds of β-nitrostyrene derivatives got different reaction results under different reaction conditions. For the β-nitrostyrene derivatives, this protocol offered vicinal haloamine products in good to excellent yields(up to 97%) at room temperature in CH₃CN catalyzed by Na₂CO₃. For the β-methyl-β-nitrostyrene, the good to excellent yields(up to 95%)were also achieved refluxed in CH₃CN catalyzed by KOH. The strong electron-donating substituents(e.g., CH₃O) on the 4-position of benzene ring could deactivated the reaction activity of β-nitrostyrenederi-vetives with DBDMH. However, the vicinal haloamines were also afforded as the sole addition product. Whereas strong electron-withdrawing substituent(e.g., NO₂) could activated reaction activity remarkably and the vicinal haloamines were afforded as the sole addition product, too. The result revealed that the addition reaction has a nucleophilic addition feature. The aminobromination of 20 examples of β-nitrostyrenes were investigated in this work and the structure of all products were confirmed by the corresponding ¹H NMR, ¹³C NMR spectra and HRMS(ESI). A possible mechanism involving a nucleophilic conjugate addition was proposed.