Density functional study of the relative reactivity in the concerted 1,3-dipolar cycloaddition of nitrile ylide to disubstituted ethylenes

Density functional theory was used to perform a theoretical evaluation of ( E)-1,2-disubstituted ethylenes as dipolarophiles for the 1,3-dipolar cycloa ddition reaction. The reactivities of electron-withdrawing and -donating su bstituted ethylenes were examined by estimating their activation energies. The calculated activation energies predicted that the most reactive species is (E)-1,2-C2H2(NO)(2), whereas the least reactive is (E)-2-butene. Namely , it was demonstrated that 16-electron 1,3-dipole reactants with more elect ropositive substituents in terminal positions and ethylenes that possess mo re strongly electron-withdrawing substituents facilitate 1,3-dipolar cycloa ddition reactions. All of the theoretical results can be rationalized using the configuration mixing model. (C) 2001 John Wiley & Sons, Inc.