Alkyl Methyl Carbonates as Methylating Agents. The O-Methylation of Phenols
- 1 February 2000
- journal article
- letter
- Published by Georg Thieme Verlag KG in Synlett
- Vol. 2000 (2) , 272-274
- https://doi.org/10.1055/s-2000-6488
Abstract
The O-methylation reaction of a variety of phenols (ArOH: Ar = Ph, p-CH3C6H4, p-ClC6H4, o- and p-CH3COC6H4, and 2-naphthyl) can be conducted in a highly selective manner by using asymmetric alkyl methyl carbonates CH3OCOOR (R = n-Pr, 3b; n-Bu, 3d; CH3O(CH2)2O(CH2)2, 3e) as alkylating agents. For example, at 150 °C, phenol can be quantitatively converted into anisole in 4.5 h, using 2-(2-methoxyethoxy)ethyl methyl carbonate 3e in the presence of K2CO3 as a catalyst. Compared to the methylation reactions using dimethyl carbonate which require sealed pressurized reaction vessels, asymmetric alkyl methyl carbonates allow much simpler and safer alkylations at ambient pressure. The selectivity towards O-methylation is scarcely affected by the temperature (in the range of 120-150 °C), while it depends on the nature and on the amount of the solvent. DMF and triglyme (triethylene glycol dimethyl ether) have proven to be the better reaction media.Keywords
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