Oxygen Atom Transfer as Key To Reverse Regioselectivity in the Gold(I)-Catalyzed Generation of Aminooxazoles from Ynamides

We report on gold­(I)-catalyzed oxidative
annulation involving ynamides,
nitriles, and 2,3-dichloropyridine N-oxide. The application
of 2,3-dichloropyridine N-oxide as an oxygen atom
transfer reagent reverses the regioselectivity to give 5-amino-1,3-oxazoles, in comparison with the previously reported syntheses
of aminooxazoles based on gold-catalyzed nitrene transfers to ynamides
to furnish 4-amino-1,3-oxazoles. The developed oxygen
atom transfer approach allows the generation of 1,3-oxazoles containing
a variety of sulfonyl-protected alkylamino groups in the fifth position
of the oxazole ring (29 examples; up to 88% yields). In addition,
the use of N-substituted nitriles, namely cyanamides,
leads to the facile generation of difficult-to-obtain 2,5-diaminooxazoles.
The process is feasible for wide ranges of ynamides or nitriles, and
it can be conducted in gram scale.