Dimethyl carbonate as an ambident electrophile.
[reaction: see text] 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 CH(2) 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).
Tundo
Pietro
P
Dipartimento di Scienze Ambientali, Università Ca' Foscari Venezia, Italy. tundop@unive.it
Rossi
Laura
L
Loris
Alessandro
A
D000588:Amines / Q000737:chemistry; D005561:Formates / Q000138:chemical synthesis / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry
D000588:Amines; D005561:Formates; D013455:Sulfur; C023025:methyl carbonate; D009584:Nitrogen; D010100:Oxygen