Unusual Anisotropic Effects from 1,3-Dipolar Cycloadducts of 4-Azidomethyl Coumarins

Abstract

4-Bromomethylcoumarins (1) reacted with sodium azide in aqueous acetone to give 4-azidomethyl-coumarins (2), which underwent 1,3-dipolar cycloaddition with acetylenic dipolarophiles to give triazoles (3). These triazoles (3) have been found to exhibit interesting variations in the chemical shifts of C(3)-H and C(4)-methylene protons. Protonation studies indicate that the shielding effect of the C(3)-H of coumarin is due to pi-electrons of the triazole ring, further supported by diffraction and computational studies.