Mechanistic Pathways in Amide Activation: Flexible Synthesis of Oxazoles and Imidazoles

The preparation of
substituted aminooxazoles and aminoimidazoles
from α-arylamides and α-aminoamides through triflic anhydride-mediated
amide activation is reported. These reactions proceed via the intermediacy
of nitrilium adducts and feature N-oxide-promoted
umpolung of the α-position of amides as well as a mechanistically
intriguing sequence that results in sulfonyl migration from nitrogen
to carbon. Quantum-chemical mechanistic analysis sheds light on the
intricacies of the process.