Fp. Cossio et al., In-plane aromaticity in 1,3-dipolar cycloadditions. solvent effects, selectivity, and nucleus-independent chemical shifts, J AM CHEM S, 121(28), 1999, pp. 6737-6746
The aromaticity and the regiochemistry of several 1,3-dipolar cycloaddition
s have been studied computationally. It is found that all the transition st
ructures associated with concerted supra-supra processes are in-plane aroma
tic, and this aromaticity is compatible with a ring current circulating alo
ng the molecular plane. Solvent effects enhance the activation barrier of t
he reaction and diminish its synchronicity, with little impact on aromatici
ty. According to our calculations,aromaticity is important but does not det
ermine the regiochemistry of the reaction. Other phenomena such as electros
tatic interactions and solvent effects can modify the regiochemical and the
stereochemical outcome.