N-Heterocyclic Carbene Based Ruthenium-Catalyzed Direct Amide Synthesis from Alcohols and Secondary Amines: Involvement of Esters

A well-defined N-heterocyclic carbene
based ruthenium
complex was developed as a highly active precatalyst for the direct
amide synthesis from alcohols and secondary amines. Notably, reaction
of 1-hexanol and dibenzylamine afforded 60% of the corresponding amide
using our catalytic system, while no amide formation was observed
for this reaction with the previously reported catalytic systems.
Unlike the previously reported amidation with less sterically hindered
alcohols and amines, involvement of ester intermediates was observed.