Autor: |
Fiorot RG; Department of Chemistry, Universidade Federal Fluminense (UFF), Outeiro de São João Batista, s/n, Niterói, Rio de Janeiro, 24020-141, Brazil. rodolfo.fiorot@ifrj.edu.br.; Instituto Federal de Educação, Ciências e Tecnologia do Rio de Janeiro, Rio de Janeiro, 21715-000, Brazil. rodolfo.fiorot@ifrj.edu.br., Vilhena FS; Department of Chemistry, Universidade Federal Fluminense (UFF), Outeiro de São João Batista, s/n, Niterói, Rio de Janeiro, 24020-141, Brazil., Carneiro JWM; Department of Chemistry, Universidade Federal Fluminense (UFF), Outeiro de São João Batista, s/n, Niterói, Rio de Janeiro, 24020-141, Brazil. jose_walkimar@id.uff.br. |
Abstrakt: |
1,3-Dipolar cycloaddition (1,3-DC) reactions are powerful synthetic tool to obtain highly functionalized 5-membered heterocycles, starting from a 1,3-dipole and a dipolarophile in a single step. The reactivity of these systems is usually rationalized in terms of Frontier Molecular Orbital Theory (FMOT), which neglects a possible contribution of an open-shell weakly coupled singlet-diradical specie. In this work, the broken-symmetry approach is used to estimate the singlet-diradical character of 18 dipoles of the second period of the periodic table, classified as allyl-type N-centered, allyl-type O-centered, and propargyl-type 1,3-dipoles, providing a rationalization for 1,3-DC reactivity. The intramolecular cyclization of bent allyl-type N- and O-centered dipoles into 3-membered rings was also analyzed, and revealed that the energetic change is associated with the spin densities of peripheral atoms. Finally, a close relationship between the energy for the ring-opening process of the cyclic configuration and the reactivity of 1,3-dipoles toward 1,3-dipolar cycloaddition reaction was also found. Graphical abstract. |