On the Question of Zwitterionic Intermediates in the [3+2] Cycloaddition Reactions between Aryl Azides and Ethyl Propiolate.

The molecular mechanism of the [3+2] cycloaddition reactions between aryl azides and ethyl propiolate was evaluated in the framework of the Molecular Electron Density Theory. It was found that independently of the nature of the substituent within the azide molecule, the cycloaddition process is realized via a polar but single-step mechanism. All attempts of localization as postulated earlier by Abu-Orabi and coworkers' zwitterionic intermediates were not successful.

Fully Selective Synthesis of Spirocyclic-1,2-oxazine N-Oxides via Non-Catalysed Hetero Diels-Alder Reactions with the Participation of Cyanofunctionalysed Conjugated Nitroalkenes.

Hetero Diels-Alder (HDA) reactions with the participation of E-2-aryl-1-cyano-1-nitroethenes and methylenecyclopentane were evaluated on the basis of experimental as well as quantumchemical data. It was found that contrary to most known HDA reactions, title processes are realised under non-catalytic conditions and with full regiocontrol. The DFT study shows, without any doubt, the polar but single-step reaction mechanism.

Full Regio- and Stereoselective Protocol for the Synthesis of New Nicotinoids via Cycloaddition Processes with the Participation of Trans-Substituted Nitroethenes: Comprehensive Experimental and MEDT Study.

[3 + 2] Cycloaddition reactions with the participation of -C-(3-pyridyl)--methylnitrone and series of -2-R-nitroethenes were both experimentally and theoretically explored in the framework of Molecular Electron Density Theory. It was found that all considered processes are realized under mild conditions and in full regio- and stereocontrol. The ELF analysis additionally showed that the studied reaction proceeds by a two-stage, one-step mechanism.

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

The regioselective [3 + 2] cycloaddition (32CA) reactions of a series of aryl-substituted nitrile -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.