期刊
JOURNAL OF MASS SPECTROMETRY
卷 56, 期 3, 页码 -出版社
WILEY
DOI: 10.1002/jms.4707
关键词
density functional theory calculations; ESI(+)‐ MS; MS; indole; mechanism; N‐ methylation
资金
- Brazilian National Science Council (CNPq) [142476/2018-8] Funding Source: Medline
- São Paulo State Science Foundation (FAPESP) Funding Source: Medline
- School of Chemistry and EaStCHEM Funding Source: Medline
- SDumont Funding Source: Medline
- CESUP Funding Source: Medline
The N-methylation of indole with dimethylcarbonate produces different products depending on the catalyst used. Direct ESI(+)-MS monitoring allows for the interception and characterization of key intermediates in the reaction process. Contrasting mechanisms are observed in the reaction of DMC with indole under either DABCO or DBU catalysis.
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.
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