A DFT computational study of the molecular mechanism of [3 + 2] cycloaddition reactions between nitroethene and benzonitrile N-oxides

Radomir Jasiński,Ewa Dresler,Ewa Jasińska

doi:10.1007/s00894-016-3185-8

Abstract

DFT calculations were performed to shed light on the molecular mechanism of [3 + 2] cycloadditions of simple conjugated nitroalkenes to benzonitrile N-oxides. In particular, it was found that these processes proceed by a one-step mechanism through asynchronous transition states. According to the latest terminology, they should be considered polar but not stepwise processes.

Highlights

IntroductionThe most versatile method of synthesizing Δ2-isoxazolines (3,4-dihydroisoxazoles) is through [3 + 2] cycloaddition reactions between nitrile N-oxides (which are allenyl-type threeatom components: TACs [1]) and alkenes [2,3,4,5,6]
The most versatile method of synthesizing Δ2-isoxazolines (3,4-dihydroisoxazoles) is through [3 + 2] cycloaddition reactions between nitrile N-oxides and alkenes [2,3,4,5,6]
We have found that the molecular mechanism of [3 + 2] cycloadditions of nitrile N-oxides to conjugated nitroalkenes requires comprehensive theoretical study using DFT methods

Summary

Introduction

The most versatile method of synthesizing Δ2-isoxazolines (3,4-dihydroisoxazoles) is through [3 + 2] cycloaddition reactions between nitrile N-oxides (which are allenyl-type threeatom components: TACs [1]) and alkenes [2,3,4,5,6]. It is worth mentioning that [3 + 2] These reactions are realized in a fully regioselective manner, giving high yields of 3-aryl-5-nitroisoxazolines (4) [6, 10]. It should be noted at this point that the molecular mechanism of these reactions is not well understood. Several examples of stepwise cycloadditions involving components other than conjugated nitroalkenes were described; for example, reactions between fluorinated alkenes [15] or phenylisocyanate [16] and N-alkylnitrones, dialkyl 2,3-dicyanobut-2-enedioates and azomethine ylides [17], dimethyl 2,3-dicyanofumarate and di(tert-butyl)diazomethane [18], as well as methyl nitrile N-oxide and tetraaminoethene [19]

Methods

Results

Conclusion