Synthesis of α-(Nitroaryl)benzylphosphonates via Oxidative Nucleophilic Substitution of Hydrogen in Nitroarenes

Electron-Deficient Acetylenes as Three-Modal Adjuvants in SNH Reaction of Pyridinoids with Phosphorus Nucleophiles

Publications covering a new easy metal-free functionalization of pyridinoids (pyridines, quinolines, isoquinolines, acridine) under the action of the system of electron-deficient acetylenes (acetylenecarboxylic acid esters, acylacetylenes)/P-nucleophiles (phosphine chalcogenides, H-phosphonates) are reviewed. Special attention is focused on a S_N^H reaction of the regioselective cross-coupling of pyridines with secondary phosphine chalcogenides triggered by acylacetylenes to give 4-chalcogenophosphorylpyridines. In these processes, acetylenes act as three-modal adjuvants (i) activating the pyridine ring towards P-nucleophiles, (ii) deprotonating the P-H bond and (iii) facilitating the nucleophilic addition of the P-centered anion to a heterocyclic moiety followed by the release of the selectively reduced acetylenes (E-alkenes).

Metal-free SHN cross-coupling of pyridines with phosphine chalcogenides: polarization/deprotonation/oxidation effects of electron-deficient acetylenes

Terminal acylacetylenes act as trimodal auxiliaries in SHN cross-coupling of pyridines with phosphine chalcogenides. The reaction proceeds via phosphorylation of the pyridine 2 position followed by 2 → 4-migration of phosphoryl moieties.

Electrophilic and Nucleophilic Aromatic Substitutions are Mechanistically Similar with Opposite Polarity

Confrontation of the recently formulated general mechanism of nucleophilic substitution in electron-deficient arenes with the well-known mechanism of electrophilic substitution revealed that these fundamental processes are mechanistically identical but proceed according to opposite polarity-an Umpolung relation. In this viewpoint this apparently controversial concept is supported by discussion of a variety of experimental results.

Synthetic Methodologies for Perfluoroaryl-Substituted (Diaryl)methylphosphonates, -Phosphinates via SNAr Reaction

The new synthetic methodologies for perfluoroaryl-substituted (diaryl)methylphosphonates, -phosphinates via nucleophilic aromatic substitution (S_NAr) were developed. Benzylphosphonate and α-fluorobenzylphosphonate reacted with a wide variety of perfluoroarenes via S_NAr reaction. The reaction took place quickly and gave perfluoroarylated phosphonates in high yields. Highly diastereoselective S_NAr reaction with binaphthyl-based chiral phosphinates was further carried out.

New 2,6-diaminopyridines containing a sterically hindered benzylphosphonate moiety in the aromatic core as potential antioxidant and anti-cancer drugs

A series of 2,6-diaminopyridines was synthesized for the first time, containing phosphoryl sterically hindered phenolic fragments in the aromatic core. The antioxidant activity of these compounds was investigated, 2,6-diaminopyridine derivatives were shown to exhibit higher activity in comparison with their structural analogues. For dialkyl/diphenyl [(3,5-di-tert-butyl-4-hydroxyphenyl) (2,6-diaminopyridin-3-yl) methyl] phosphonates, their structural analogues based on meta-phenylenediamine, phosphorus-containing sterically hindered phenols and the corresponding cyclohexadienones cytotoxicity against tumor lines of epithelioid carcinoma of the cervix uteri (M-Hela) and breast adenocarcinoma (MCF-7) has been studied in vitro, as well as on normal human Chang liver cell lines. Diphenyl [(3,5-di-tert-butyl-4-hydroxyphenyl) (2,6-diaminopyridin-3-yl) methyl] phosphonate was shown to be the most active against the epithelioid line M-Hela - IC₅₀ comprises 7.4 μM. It was shown that apoptosis induced by the lead compound proceeds along the internal pathway of caspase-9 activation. It was established that all studied compounds do not possess hemolytic activity.

How Does Nucleophilic Aromatic Substitution Really Proceed in Nitroarenes? Computational Prediction and Experimental Verification

The aim of this paper is to present a correct and complete mechanistic picture of nucleophilic substitution in nitroarenes based on the results obtained by theoretical calculations and experimental observations coming from numerous publications, reviews, and monographs. This work gives the theoretical background to the very well documented experimentally yet still ignored observations that the addition of nucleophiles to halo nitroarenes resulting in the formation of σ(H) adducts, which under proper reaction conditions can be transformed into the product of the SNArH reaction, is faster than the competing process of addition to the carbon atom bearing a nucleofugal group (usually a halogen atom) resulting in the "classic" SNAr reaction. Only when the σ(H) adduct cannot be transformed into the SNArH reaction product, SNAr reaction is observed.

Reactions of nucleophiles with nitroarenes: multifacial and versatile electrophiles

In this overview, it is shown that there are many initial reactions between nitroarenes and nucleophiles: addition to the electron-deficient ring at positions occupied by halogen and hydrogen atoms, addition to the nitro group, single-electron transfer (SET), and other types of initial reactions. The resulting intermediates react further in a variety of ways to form products of nucleophilic substitution of a halogen atom (SN Ar), a hydrogen atom (SN ArH), and others. Many variants of these processes are briefly discussed, particularly in relation of rates of the initial reactions and further transformations.

Nucleophilic substitution of hydrogen in electron-deficient arenes, a general process of great practical value

The aim of this tutorial review is to present two main messages. First, addition of nucleophilic agents to electron-deficient arenes proceeds faster in positions occupied by hydrogen than in those, equally activated, occupied by halogens or other nucleofugal groups. Thanks to numerous ways of further, fast conversion of the produced sigma(H) adducts into products of nucleophilic substitution of hydrogen, this is the main primary reaction between nucleophiles and electron-deficient arenes. Conventional nucleophilic substitution of halogen, S(N)Ar reaction, is a secondary process that takes place when ways for fast further conversion of sigma(H) adducts are not available. The second message is that nucleophilic substitution of hydrogen is an efficient tool in organic synthesis. In order to stress the preference for nucleophilic substitution of hydrogen, halonitroarenes are chosen as examples of reacting electron-deficient arenes, but it is obvious that the presence of halogen is not necessary for substitution of hydrogen.