A Continuous Methylation of Phenols and N,H-Heteroaromatic Compounds with Dimethyl Carbonate

The methylation of phenolic substrates has been reevaluated using sulfolane as solvent instead of DMF. The change of solvent gave in all cases cleaner production of the anisole products in very good yields. The reaction requires 0.1 equiv of DBU, 2–3 equiv of DMC, and 2–5 vols of sulfolane depending on the substrate. At 220 °C the reaction time is 10 min. Sulfolane is completely stable under the reaction conditions, excluding unwanted impurities from the solvent. The reaction could also be extended to NH-indole and NH-imidazole derivatives utilizing 0.1 equiv of DBU and 2–3 equiv of DMC in 2 vols of sulfolane. All NH-heteroaromatic compounds gave clean N-methylation.

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