Photoinduced 1,3-Dipolar Cycloadditions of Cyclic Enones and 2,5-Disubstituted Tetrazoles: An Unprecedented Pathway to Polysubstituted Pyrazolines and Pyrazoles

Abstract

We report herein the syntheses of original pyrazolines and pyrazoles through 1,3-dipolar cycloaddition of cyclic enones with 2,5-disubstituted nitrile imines achieved via photochemical activation of 2,5-diaryl substituted tetrazoles. Monitoring of the reactions, similar to nitrile imine-mediated tetrazole-ene cycloadditions (NITEC), could be performed by means of UV-vis absorption and emission measurements. The presence or absence of substituents in the alpha position of the ketone function makes it possible to direct these reactions towards the selective formation of pyrazoles or pyrazolines. The choice of the cyclic enones and 2,5-disubstituted tetrazoles proved crucial for the fluorescence properties of the polycyclic derivatives obtained.