Masked N-Heterocyclic Carbene-Catalyzed Alkylation of Phenols with Organic Carbonates

Matthew Y. Lui, Alexander K.L. Yuen, Anthony F. Masters, Thomas Maschmeyer*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

Abstract

An easily prepared masked N-heterocyclic carbene, 1,3-dimethylimidazolium-2-carboxylate (DMI-CO2), was investigated as a “green” and inexpensive organocatalyst for the alkylation of phenols. The process made use of various low-toxicity and renewable alkylating agents, such as dimethyl- and diethyl carbonate, in a focused microwave reactor. DMI-CO2 was found to be a very active catalyst and excellent yields of a range of aryl alkyl ethers were obtained under relatively benign conditions. The observed difference in the conversion behavior of phenol methylation, in the presence of either the carbene or 1,8-diazabicycloundec-7-ene (DBU) catalyst, was rationalized on the basis of mechanistic investigations. The primary mode of action for the N-heterocyclic carbene is nucleophilic catalysis. Activation of the dialkyl carbonate electrophile results in concomitant evolution of an organo-soluble alkoxide, which deprotonates the phenolic starting material. In contrast, DBU is initially protonated by the phenol and thus consumed. Subsequent regeneration and participation in nucleophilic catalysis only becomes significant after some phenolate alkylation occurs.

Original languageEnglish
Pages (from-to)2312-2316
Number of pages5
JournalChemSusChem
Volume9
Issue number17
DOIs
Publication statusPublished - 8 Sep 2016
Externally publishedYes

Scopus Subject Areas

  • Environmental Chemistry
  • Chemical Engineering(all)
  • Materials Science(all)
  • Energy(all)

User-Defined Keywords

  • alkylation
  • carbenes
  • lignin
  • organic carbonates
  • organocatalysis

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