Dimethyl carbonate as an ambident electrophile

The features of various anions having different soft/hard character (aliphatic and aromatic amines, alcohoxydes, phenoxides, thiolates) are compared with regard to nucleophilic substitutions on dimethyl carbonate (DMC), using different reaction conditions. Results are well in agreement with the Hard-Soft Acid-Base (HSAB) theory. Accordingly, the high selectivity of monomethylation of CH2 acidic compounds and primary aromatic amines with DMC can be explained by two different subsequent reactions, which are due to the double electrophilic character of DMC. The first step consists of a hard-hard reaction and selectively produces a soft anion, which, in the second phase, selectively transforms into the final monomethylated product, via a soft-soft nucleophilic displacement (yield > 99% at complete conversion, using DMC as solvent).