The use of dialkyl carbonates for safe and highly selective alkylations of methylene‐active compounds. A process without waste production

Abstract

AbstractThe non‐toxic compound dimethyl carbonate (DMC) can be used as a methylating and a methoxycarbonylating agent in place of methyl chloride and phosgene, respectively. We report here that DMC and other dialkyl carbonates (DAlkCs: dimethyl, diethyl and dibenzyl carbonates) allow very selective alkylations of a variety of CH2‐acidic compounds. Both arylacetonitriles and alkyl arylacetates react with DAlkCs to yield the mono‐C‐alkylated derivatives (α‐alkyl‐α‐arylacetonitriles and alkyl α‐alkyl‐α‐arylacetates) with a selectivity of up to 99%, at complete conversion. Likewise, the mono‐C‐methylation by DMC proceeds selectively also on (aryloxy)acetonitriles and methyl (aryloxy)acetates. The reactions are carried out at temperature of 180‐220°C in the presence of weak bases (usually K2CO3); under such conditions, DAlkCs efficiently replace the common and very toxic alkylating agents (dialkyl sulfates and alkyl halides). In addition to the high selectivity obtained and the intrinsic safety of the dialkyl carbonates, the reported reactions give rise to neither organic nor inorganic waste products.