Unveiling the mechanism of N-methylation of indole with dimethylcarbonate using either DABCO or DBU as catalyst

Tipo
Artigo
Data de publicação
2021
Periódico
Journal of Mass Spectrometry
Citações (Scopus)
4
Autores
Vendramini P.H.
Zeoly L.A.
Cormanich R.A.
Buehl M.
Eberlin M.N.
Ferreira B.R.V.
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Resumo
© 2021 John Wiley & Sons, Ltd.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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1 ,4-diazabicyclo[2.2.2]octane , 1 ,8-diazabicyclo[5.4.0]undec-7-ene , Dimethyl carbonate , Ionic composition , N-methylation , Reaction solutions
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