电化学吲哚二羟基化和羟基环化（Advanced Synthesis & Catalysis. 2020）

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DOI: 10.1002/adsc.202000158



摘要


我们描述了一种简单且可持续的MgBr2介导的吲哚与水的电化学脱芳二羟基化和羟基环化反应。MgBr2以亚化学计量量使用，作为电解质和潜在的氧化还原介质，间接地将吲哚核氧化成溴离子，参与上述反应（上述由百度翻译译文）。



主要内容


1、早期研究





2、反应条件优化




3、底物扩展





4、控制实验




5、CV分析


Figure 1. Cyclic voltammograms of reactants in a mixture of acetonitrile and water. A glassy carbon disc (diameter 3 mm) working electrode, a platinum wire counter electrode and a saturated calomel electrode (SCE) as reference electrode were used at a scan rate of 100 mV/s; 0.05 mmol 1 a and/or 0.025 mmol MgBr2, 1 mmol nBu4NBF4 in 10 mL of CH3CN/H2O (3:2) or CH3CN.



6、可能的机理





结论
In summary, a simple electrochemical protocol to perform the dearomative dihydroxylation and hydroxycyclisation of indoles in presence of MgBr2 without the need of an additional electrolyte has been described. We postulate that the major pathway involves the electrochemical generation of an electrophilic bromine reagent from MgBr2 which could lead to oxidation of the indole into a bromonium ion. Upon reaction with water, this intermediate is transformed into 2,3‐dihydroxyindolines. In presence of an intramolecular nucleophile and water, hydroxycyclization occurs leading to hydroxy‐tetrahydropyranoindolines or 2‐hydroxy‐3,3‐ spiroindolines.




实验细节

To a 10 mL vial with a stir bar were successively added the substituted indole 1, 10 or 12 (0.2 mmol), MgBr2 (0.05 mmol, 0.25 equiv), 2.0 mL of distilled H2O and 3.0 mL of CH3CN (0.04 M), The vial was covered with a screw-cap. The electrolysis was carried out at RT using a constant voltage of 5.00 V between a graphite anode and a platinum plate cathode (1.4 x 0.8 x 0.2 cm submerged in solution) with stirring (500 rpm). The complete consumption of the starting indole derivative was checked by TLC (35% to 50% AcOEt/petroleum ether). The reaction was then quenched with H2O and diluted with AcOEt. The organic and aqueous phases were separated. The aqueous phase was then extracted twice with AcOEt. The combined organic phases were then dried over MgSO4, filtered and concentrated under vacuum. The crude was then purified by flash column chromatography or preparative TLC (35% to 50% AcOEt/ petroleum ether).



原文链接

https://onlinelibrary.wiley.com/doi/full/10.1002/adsc.202000158





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