In-plane aromaticity in 1,3-dipolar cycloadditions. solvent effects, selectivity, and nucleus-independent chemical shifts

The aromaticity and the regiochemistry of several 1,3-dipolar cycloadditions have been studied computationally. It is found that all the transition structures associated with concerted supra-supra processes are in-plane aromatic, and this aromaticity is compatible with a ring current circulating along the molecular plane. Solvent effects enhance the activation barrier of the reaction and diminish its synchronicity, with little impact on aromaticity. According to our calculations,aromaticity is important but does not determine the regiochemistry of the reaction. Other phenomena such as electrostatic interactions and solvent effects can modify the regiochemical and the stereochemical outcome.