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.

本研究首次实现了以三(2,2'-联吡啶)二氯化钌(Ru(bpy)3Cl2)为催化剂，β-酮硫代酰胺与芳基重氮盐之间的操作简便且绿色可持续的一锅法光氧化型形式上的[3+2]杂环化反应，可在温和反应条件下以中等到较高产率得到2,4-二取代-5-亚氨基-1,2,3-噻二唑类产物。该反应以硫代酰胺的α-苯腙加合物为中间体，在室温下通过N-S键环合生成1,2,3-噻二唑类产物。值得注意的是，该类产物在环5位的环外C=N双键处具有Z型立体化学构型。