Regio-and stereoselectivity of [2+3] cycloaddition of α-substituted nitroethenes with 1,3-dipoles propargyl-allene and allyl type

The paper is a critical review of available literature data about regio- and stereoselectivity of [2+3] cycloaddition reactions of α-substituted nitroethenes

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

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

(3+2)‐Cyclization Reactions of Unsaturated Phosphonites with Aldehydes and Thioketones

By exploiting the unique reactivity of ethynyl‐phosphonites we obtain novel P(V)‐containing five‐membered heterocycles via (3+2)‐cyclization reactions with aldehydes or cycloaliphatic thioketones in satisfactory to excellent yields. Whereas reactions with thioketones to yield 1,3‐thiaphospholes‐3‐oxides occur smoothly at room temperature with equimolar amounts of the starting materials in absence of any catalyst, the analogous conversions with aldehydes to generate 3‐oxides of 1,3‐oxaphospholes require addition of triethylamine as a base. We postulate a step‐wise (3+2)‐cyclization mechanism for the formation of the 1,3‐thiaphosphole ring based on DFT quantum chemical calculations. With this study, we introduce new cyclization reactions originating from unsaturated phosphonites as central synthetic building blocks to yield previously inaccessible stable phosphorus‐containing heterocycles with unexplored potential for the molecular sciences.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Alexander von Humboldt-Stiftung http://dx.doi.org/10.13039/100005156Peer Reviewe

Green in water sonochemical synthesis of tetrazolopyrimidine derivatives by a novel core-shell magnetic nanostructure catalyst

A green approach for the one-pot four-component sonochemical synthesis of 5-methyl-7-aryl-4,7-dihydrotetrazolo[1,5-a]pyrimidine-6-carboxylic esters from the reaction of 2-cyano-guanidine, sodium azide, various aromatic aldehydes and methyl or ethyl acetoacetate in the presence of a catalytic amount of Fe₂O₃@SiO₂-(CH₂)₃NHC(O)(CH₂)₂PPh₂ as a new hybrid organic–inorganic core–shell nanomagnetic catalyst is described. This is the first design, preparation, characterization and application of the present nanomaterial and also the first ultrasound irradiated synthesis of the biologically and pharmaceutically important heterocyclic compounds in water as a green solvent. This novel sonocatalysis/nanocatalysis protocol offers several advantages such as high yields, short reaction times, environmentally-friendly reaction media, easily isolation of the products, simple preparation, full characterization and recoverability of the nanocatalyst by an external magnet and reusing several times without significant loss of activity.The authors gratefully acknowledge the partial support from the Research Council of the Iran University of Science and Technology (IUST). The equipment in the Center of Synthesis and Analysis BioNanoTechno of University of Bialystok was funded by the EU as part of the Operational Program Development of Eastern Poland 2007–2013, project: POPW.01.03.00–20–034/09 and POPW.01.03.00-004/11. The support from the Polish National Science Centre (NCN grants number 2012/05/B/ST5/00362) is gratefully acknowledged.Ali Maleki: [email protected] Maleki - Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran University of Science and Technology, Tehran 16846-13114, IranJamal Rahimi - Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran University of Science and Technology, Tehran 16846-13114, IranOleg M. Demchuk - Department of Organic Chemistry, Maria Curie-Sklodowska University, Gliniana 33, Lublin 20-614, PolandAgnieszka Z. Wilczewska - Institute of Chemistry, University of Białystok, Ciołkowskiego 1K, 15-245 Białystok, PolandRadomir Jasiński - Institute of Organic Chemistry and Technology, Cracow University of Technology, Warszawska 24, Cracow, PolandJ. Zhu, H. Bienaymé, Multicomponent Reactions, John Wiley & Sons, 2006.A. Maleki, A. 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On the Question of Stepwise [4+2] Cycloaddition Reactions and Their Stereochemical Aspects

Even at the end of the twentieth century, the view of the one-step [4+2] cycloaddition (Diels-Alder) reaction mechanism was widely accepted as the only possible one, regardless of the nature of the reaction components. Much has changed in the way these reactions are perceived since then. In particular, multi-step mechanisms with zwitterionic or diradical intermediates have been proposed for a number of processes. This review provided a critical analysis of such cases

DFT study of the decomposition reactions of nitroethyl benzoates catalyzed by the 1,3-dimethylimidazolium cation

DFT calculations indicate that the decomposition reaction of nitroethyl benzoates in the presence of 1,3-dimethylimidazolium cation takes place much faster than in the case of the non-catalyzed process. Additionally, our calculations suggest one-step polar mechanism of title reactions

Sterical index: a novel, simple tool for the interpretation of organic reaction mechanisms

A new, simple index for the quantitative description of steric effects was proposed based on the results of DFT calculations. This effect was connected with the disturbance of synchronicity within transition states of the model Diels-Alder reaction. The obtained results offer the possibility of predicting steric effects determined by alkyl groups for a wide range of bimolecular processes