The Participation of 3,3,3-Trichloro-1-nitroprop-1-ene in the [3 + 2] Cycloaddition Reaction with Selected Nitrile N-Oxides in the Light of the Experimental and MEDT Quantum Chemical Study.

Karolina Zawadzińska,Przemysław Woliński,Tomasz Krawczyk,Karolina Kula,Radomir Jasiński,Barbara Mirosław,Mar Ríos-Gutiérrez

doi:10.3390/molecules26226774

Abstract

The regioselective zw-type [3 + 2] cycloaddition (32CA) reactions of a series of aryl-substituted nitrile N-oxides (NOs) with trichloronitropropene (TNP) have been both experimentally and theoretically studied within the Molecular Electron Density Theory (MEDT). Zwitterionic NOs behave as moderate nucleophiles while TNP acts as a very strong electrophile in these polar 32CA reactions of forward electron density flux, which present moderate activation Gibbs free energies of 22.8–25.6 kcal·mol−1 and an exergonic character of 28.4 kcal·mol−1 that makes them irreversible and kinetically controlled. The most favorable reaction is that involving the most nucleophilic MeO-substituted NO. Despite Parr functions correctly predicting the experimental regioselectivity with the most favorable O-CCCl3 interaction, these reactions follow a two-stage one-step mechanism in which formation of the O-C(CCl3) bond takes place once the C-C(NO2) bond is already formed. The present MEDT concludes that the reactivity differences in the series of NOs come from their different nucleophilic activation and polar character of the reactions, rather than any mechanistic feature.

Highlights

IntroductionNOs, which usually present a zwitterionic electronic structure, participate in zwitterionic-type (zw-type) 32CA reactions, which demand favorable nucleophilic/electrophilic interactions between the reagents to take place experimentally
Given that TNP 2 is classified as a very strong electrophile with ω = 3.27 eV and as a very poor nucleophile with N = 0.67 eV, and considering the zwitterionic nature of the NOs, it is expected that the zw-type 32CA reaction involving 1b should be the most favorable one, and that the reactivity should decrease in the order 1b > 1a > 1c > 1d > 1e
The topological analysis of the Electron Localization Function (ELF) of NOs 1a–e allows characterizing their zwitterionic structure, just as that of the simplest acetonitrile oxide, being able to participate in zw-type 32CA reactions

Summary

Introduction

NOs, which usually present a zwitterionic electronic structure, participate in zwitterionic-type (zw-type) 32CA reactions, which demand favorable nucleophilic/electrophilic interactions between the reagents to take place experimentally. Substitution may change the parent electronic structure of the simplest TACs and, the reactivity of actual experimental TACs. Aryl NOs are one of the most common types of experimentally used NOs. The theoretical study of the 32CA reactions of benzonitrile oxide with several alkenes such as N-vinyl pyrrol [8], carvone [9], tomentosin [10], 3-nitroprop-1-ene [11] and methyl acrylate [12] allowed confirming the zwitterionic reactivity of aryl NOs in zw-type 32CA reactions, in which, interestingly, the C-C single bond was always formed prior to the

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