转自:无金属催化的硼酸和对甲苯磺酰腙的C-C键形成的偶联反应
酯基,氨(胺)基,醛酮在此反应条件下都不受影响。
General procedure for the reductive coupling of tosylhydrazones 1 with boronic acids 2.
A reaction tube was charged with potassium carbonate (207.3 mg, 1.5 mmol), the boronic acid 2 (1.5 mmol), the tosylhydrazone 1 (1.0 mmol) and dioxane (4.3 mL). The system was heated at 110 ºC with stirring and reflux. The reaction was monitored by GCMS. When the reaction was completed, the crude reaction mixture was allowed to reach room temperature, the solvent was eliminated and a saturated solution of NaHCO3 and dichloromethane were added and the layers were separated. The aqueous phase was extracted three times with dichloromethane. The combined organic layers were washed with two portions of a saturated solution of NaHCO3, brine and then dried over MgSO4 and filtered. Solvent was removed under reduced pressure. If necessary, products were purified by chromatography on silica gel or alumina.
由于制备腙的反应极易进行,醛酮也可以直接制备腙不用分离,直接加入硼酸进行此反应,反应效果也很好。
General procedure for the one pot reductive coupling of carbonyl compounds 4 with boronic acids 2.
A solution of the carbonyl compound 4 and tosylhydrazine in 4 mL of dioxane was stirred at 80 ºC for 90 min in a reaction tube provided with a reflux condenser. Then, potassium carbonate (207.3 mg, 1.5 mmol) and the boronic acid 2 (1.5 mmol) were added to the reaction mixture. The system was heated at 110ºC with stirring and reflux. The reaction was monitored by GCMS. When the reaction was completed, the crude reaction mixture was allowed to reach room temperature, the solvent was eliminated and a saturated solution of NaHCO3 and dichloromethane were added and the layers were separated. The aqueous phase was extracted three times with dichloromethane. The combined organic layers were washed with two portions of a saturated solution of NaHCO3, brine and then dried over MgSO4 and filtered. Solvent was removed under reduced pressure. If necessary, products were purified by chromatography on silica gel or alumina.
反应机理
腙盐II加热分解得到重氮化合物III,反应可能通过两种不同的反应历程进行:一种是重氮化合物III先和芳基硼酸反应通过中间体IV重排消除氮气得到烷基硼酸VII;另一种是先消除氮气得到卡宾,再和芳基硼酸反应,重排后得到烷基硼酸VII。最后碱性条件下脱硼得到最终产物。
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