Hydrogen Bond Promoted Methoxycarbonylation of Pentanediamine to Biobased Dicarbamate by Accelerating Proton Transfer

The methoxycarbonylation of amines into carbamates via the construction of a C–N bond is an important reaction in pharmaceutical and fine chemical syntheses. However, the methoxycarbonylation of amines with dimethyl carbonate (DMC) without metal-based catalysts or other base catalysts has rarely been studied, and the reaction mechanisms remain underexplored. Herein, efficient methoxycarbonylation of biobased pentanediamine (PDA) with DMC promoted by water is proposed. The addition of water as a catalyst resulted in a 4-fold increase in yield. The conducted kinetic studies showed that proton transfer from PDA to methoxy occurs through the hydrogen bond between the zwitterionic intermediate and water. In situ analyses have shown that OH– and water form hydrogen bonds with the ether O atom of DMC and hydroxyl H atoms of PDA, synergistically promoting the elimination of the methoxy group. The addition of water reduced the energy barrier of the methoxy group elimination from 16.3 to 0.6 kcal/mol, confirming the results of theoretical computations. Furthermore, the methyl (5-aminophenyl)carbamate intermediate was recycled into dimethyl pentane-1,5-diyldicarbamate without the use of an additional catalyst, which was mediated by the hydrogen bond between PDA and methyl (5-aminophenyl)carbamate. The reported mild methoxycarbonylation of biobased PDA under metal-free conditions is a green and sustainable method of synthesizing biobased dicarbamate.