Cu-Catalyzed [3+1+1] Cascade Cyclization of O-Acyl Oximes with Sulfur and Silyl Enol Ethers: Rapid Access to Naphthothiazoles.

A three-component cyclization reaction of O-acyl oximes, silyl enol ethers and elemental sulfur has been developed, in which silyl enol ether acts as a C1 synthon to participate in cyclization reaction and build a series of 2-aroylnaphthothiazoles and 2-aroylbenzothienothiazoles. The preliminary exploration of the reaction mechanism indicated that this transformation probably proceeded through a radical process, involving S⋅ as a key intermediate, enabling subsequent nucleophilic substitution with O-acyl oximes to afford iminosulfur radical, which undergoes 1,3-H shift to yield sulfur-centered radical intermediate. And then this intermediate undergoes radical addition with silyl enol ether, leading to the formation of the titled products through intramolecular cyclization and oxidation. Moreover, the products obtained exhibit favorable fluorescence properties, which indicates their potential application as functional materials.