FMO treatment of the reactivity and stereochemistry of the cycloaddition processes using ASED-MO method

Frontier molecular orbitals treatment of the reactivity of the 1-substituted pyridinium-3-oxide betaines as 4 pi-1,3-dipole as well as the stereochemical criteria accompanied the cycloaddition reactions is studied using ASED-MO theory. The calculations show that the effect of the pyridazinyl substituent on increasing the reactivity of the betaines is due to small HOMO-LUMO energy separation. The betaines with small energy gap are able to dimerize. Also, it is shown from the calculations that the reaction of betaines with pi-electron deficient dipolarophiles is dipole HOMO-controlled. The interaction between the frontier molecular orbitals is important to rationalize the stereoselectivity of the cycloaddition processes. (C) 2000 Elsevier Science B.V. All rights reserved.