Photo-oxidative Ruthenium(II)-Catalyzed Formal [3 + 2] Heterocyclization of Thioamides to Thiadiazoles

An operationally simple and sustainable
one-pot photo-oxidative
formal [3 + 2] heterocyclization of β-ketothioamides with aryldiazonium
salts catalyzed by Ru­(bpy)3Cl2 has been realized
to provide 2,4-disubstituted 5-imino-1,2,3-thiadiazoles in good to
high yields under mild reaction conditions for the first time. The
reaction proceeded via an α-phenylhydrazone adduct of thioamides
leading to 1,2,3-thiadiazoles via N–S bond formation at room
temperature. Notably, the products possess Z-stereochemistry
with regard to the exocyclic CN double bond at the 5-position
of the ring.