Cobalt-Catalyzed Regioselective Photochemical Synthesis of 1H-Tetrazoles
Visible-Light Driven Regioselective Synthesis of 1H-Tetrazoles from Aldehydes through Isocyanide-Based [3+2] Cycloaddition.
Green Chem. 2018;
18 October 2018 (online)
Key wordscobalt catalysis - photocatalysis - tetrazoles - graphitic carbon nitride - aldehydes - cycloaddition
A cobalt-doped polymeric graphitic carbon nitride catalyst (Co@g-C3N4) was prepared by calcination of urea followed by treatment with Co(OAc)2·4H2O in aqueous methanol (eq. 1). Co@g-C3N4 catalyzed the reaction of aldehydes with sodium azide under visible-light irradiation and air to give the corresponding 5-substituted 1H-tetrazoles in up to 95% yield (eq. 2). The authors propose an isocyanide intermediate, formed through a Co@g-C3N4-induced photocatalytic 1,2-phenyl migration from C to N.
Co@g-C3N4 was characterized by means of SEM, XPS, XRD, FTIR, UV-Vis, EDX, TEM, and photoluminescence analyses. In the reaction of 4-chlorobenzaldehyde with sodium azide, the catalyst was recovered by filtration and reused four times without significant loss of its catalytic activity.