Catalytic effects of Lewis acids on 1,3-DC reaction: A luminescent study

Competitive coordination by the nitrone and the dipolarophile to the Lewis acid catalysts like metal triflates controls the acceleration and deceleration of the catalyzed 1,3-dipolar cycloaddition reactions as compared to the uncatalyzed one. This fact has been established through variation in steady state fluorescence of the substrates in presence of catalyst. Li+ found to catalyze both the cycloaddition between α-p-chlorophenyl-N-phenyl nitrone (N1) and Benzylidene acetophenone (D1) as well as between N1 and 3-Phenyl-1-pyridin-2-yl-propenone (D2) efficiently. While Yb3+ can catalyze only the cycloaddition between N1 and D2. The experimental findings have been rationalized on the basis of DFT calculations and analysis based on the frontier molecular orbital energies and relative electrophilicity of the reactants. ► A fluorescence study of catalytic effect of an 1,3-DC reaction between an acyclic nitrone (N1) with two different dipolarophiles D1 and D2 in toluene. ► Yb3+ quenches the fluorescence intensity of N1 more efficiently than Li+. ► Li+ shows better interaction with both the two dipolarophiles D1 and D2 hence can accelerate the 1,3-DC reaction rate between N1 and D. ► Yb3+ can only be used as good catalyst for the 1,3-DC reaction between N1 and D2. ► Spectroscopic findings are rationalized with DFT calculated electrophilicity indices of the reactants.