Organic carbonates (pictured) are an important class of compounds that are easily available from CO or CO₂, and their selective reduction has attracted much interest. Dimethyl carbonate, in particular, has found application as a green methylating reagent.

Matthias Beller and colleagues, Leibniz-Institut für Katalyse, Rostock, Germany, have developed a reductive methylation of amines using organic carbonates to afford N-methyl amines, a key intermediate for organic synthesis. Established routes to N-methyl amines use CO₂ or formaldehyde as methylating agents, which require the use of high pressure. In contrast, the use of organic carbonates allows N-methylation of amines under ambient conditions.

Key to the reaction is a catalyst formed in situ from Karstedt’s complex ([Pt(CH₂=CHSiMe₂)₂O]) and 2,2′:6′,2”-terpyridine. With this catalyst system, the researchers were able to perform reductive methylations of a wide range of secondary amines, as well as formamide (an identified reaction intermediate), in up to 94 % yield. The catalyst was also applicable to the selective monomethylation of heterocyclic diamines. In the absence of amines, the system allowed the room-temperature reduction of carbonates to methanol.

• Convenient Reductive Methylation of Amines with Carbonates at Room Temperature,
  Yuehui Li, Iván Sorribes, Cristian Vicent, Kathrin Junge, Matthias Beller,
  Chem Eur. J. 2015.
  DOI: 10.1002/chem.201502917