Ruthenium(II)-Catalyzed Regioselective Ortho Amidation of Imidazo Heterocycles with Isocyanates

Direct ortho amidation
at the phenyl ring of 2-phenylimidazo heterocycles
with aryl isocyanates has been achieved via a chelation-assisted cationic
ruthenium­(II) complex catalyzed mechanism. The methodology provides
a straightforward, high-yielding regioselective approach toward the
synthesis of an array of ortho-amidated phenylimidazo heterocycles
without prior activation of C­(sp2)–H. This also
reports the first method for coupling of aryl isocyanates with the
imidazo­[1,2-a]­pyridine system via a pentacyclometalated
intermediate. The methodology is found to be easily scalable and could
be applied toward the selective ortho amidation of 2-heteroarylimidazo­[1,2-a]­pyridine frameworks.