1,3-Dipolar cycloadditions of thionitroso compounds (R–NS): a density functional theory study

Abstract

The cycloaddition reactions of 1,3-dipoles, including fulminic acid (HCNO) and the simple azides (XNNN, X = H,CH₃,NH₂), with thionitroso compounds (R–NS, R = H, NH₂) as dipolarophiles have been studied by density function procedures using the hybrid B3LYP exchange correlation function and 6–311G(d,p) basis functions. For each system, two (HCNO) or four (azide) distinct transition structures have been located and the intrinsic reaction coordinate path was constructed. It appears in all cases that activation energies for the cycloadditions are rather low, ranging from 0 to 30 kJ mol^–1. The additions are not stereospecific, the energy difference between transition structures having cis and trans dispositions of the N–R groups being rather small (less than a few kJ mol^–1). The addition shows a certain regioselectivity in which the attack of the O-atom of HCNO and N(R) of the azides to the S-atom of the dipolarophile is preferred. This regiochemistry is explained using recently developed DFT-based reactivity descriptors, such as local softness and Fukui functions. The hardness and polarizability profiles of the supersystem along the IRC paths were also discussed.