Understanding the Regioselectivity and the Molecular Mechanism of [3 + 2] Cycloaddition Reactions between Nitrous Oxide and Conjugated Nitroalkenes: A DFT Computational Study

Abstract

Regiochemical aspects and the molecular mechanism of the [3 + 2] cycloaddition between nitrous oxide and conjugated nitroalkenes were evaluated on the basis of the wb97xd/6-311 + G(d) (PCM) computational study. It was found that, independently of the nature of the nitroalkene, all considered processes are realized via polar, single-step mechanisms. All attempts at the localization of hypothetical zwitterionic intermediates were unsuccessful. Additionally, the DFT computational study suggested that, in the course of the reaction, the formation of respective Δ2-4-nitro-4-R1-5-R2-1-oxa-2,3-diazolines was preferred from the kinetic point of view.

Thermal [3+2] cycloaddition reactions as most universal way for the effective preparation of five-membered nitrogen containing heterocycles

“…The construction of oxa-2,3-diazole molecular system is theoretically possible via 32CA with the participation of nitrous oxide as the TAC and alkenes [46]. However, thesetype transformations require dramatic conditions and lead to unstable cycloadducts.…”

Energetic Aspects and Molecular Mechanism of 3-Nitro-substituted 2-Isoxazolines Formation via Nitrile N-Oxide [3+2] Cycloaddition: An MEDT Computational Study

“…Independently of the energetic aspects and their influence on the regioselectivity, the main processes also require a detailed mechanistic evaluation. According to the actual state of knowledge, different types of molecular mechanisms can occur during the [3+2] cycloaddition reactions: (a) polar mechanisms (one-step synchronous mechanism, one-steptwo-stage asynchronous mechanism, and stepwise zwitterionic mechanism) [61][62][63][64], or (b) non-polar mechanisms (one-step synchronous mechanism, one-step-two-stage asynchronous mechanism, and stepwise biradical mechanism) [65,66].…”