Abstract
Dimethylcarbonate (DMC) is an environmentally friendly substitute for dimethylsulfate (DMS) and methyl halides in methylation reactions. It is also a very selective reagent. The reactions of DMC with methylene-active compounds produce monomethylated derivatives with a selectivity not previously observed. The batchwise monomethylation of arylacetonitriles, arylacetoesters, aroxyacetonitriles, methyl aroxyacetates, benzylarylsulfones and alkylarylsulfones with DMC achieve >99% selectivity at 180-220°C in the presence of K2CO3. Mono-N-methylation of primary aromatic amines at 120-150 °C in the presence of Y- and X-type zeolites, achieved selectivities up to 97%. At high temperature (200°C) and in the presence of potassium carbonate as the catalyst, DMC splits benzylic and aliphatic ketones into two methyl esters; in contrast, DMC converts ketone oximes bearing a methylene group to 3-methyl-4,5-disubstituted-4-oxazolin-2-ones. Dibenzylcarbonate (DBzlC) exhibits similar reactivity, selectively monobenzylating methylene-active compounds.
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