Depending on the catalyst used, N‐methylation of indole with dimethylcarbonate (DMC)—an environmentally friendly alkylation agent—yields different products. With 1,4‐diazabicyclo[2.2.2]octane (DABCO), the reaction forms only N‐methylated indole, but with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), both N‐methylated and N‐methoxycarbonylated indole are formed. Using direct ESI(+)‐MS monitoring to collect actual snapshots of the changing ionic composition of the reaction solution, we report on the interception and characterization of key intermediates for such reactions. Although a mechanism has been proposed with methoxycarbonylated base as the key intermediate for both DBU and DABCO, the ESI(+)‐MS data and B3LYP‐D3/6‐311+G** calculations suggest that the reaction of DMC with indole under either DABCO or DBU catalysis follows contrasting mechanisms.

中文翻译：

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使用DABCO或DBU作为催化剂揭示吲哚与碳酸二甲酯进行N-甲基化的机理

根据所使用的催化剂，吲哚与碳酸二甲酯（DMC）（一种环境友好的烷基化剂）的N-甲基化会产生不同的产物。用1,4-二氮杂双环[2.2.2]辛烷（DABCO），该反应仅形成N-甲基化的吲哚，但与1,8-二氮杂双环[5.4.0]十一碳-7-烯（DBU），均被N-甲基化和N生成甲氧基羰基吲哚。使用直接ESI（+）-MS监测收集反应溶液中离子组成变化的实际快照，我们报告了此类反应的关键中间体的截留和表征。尽管已经提出了以甲氧羰基化碱为DBU和DABCO的关键中间体的机理，但ESI（+）-MS数据和B3LYP-D3 / 6-311 + G **计算表明，在任一条件下DMC与吲哚的反应DABCO或DBU催化遵循不同的机理。