Volume 91, Issue 5

Syntheses, properties, structure aspects and reactivity of non- and aromatically carbo- and heterocyclic annulated 1H - and 3H -1,3-azaphospholes are compared to illuminate the impact of annulation, substituent effects, aromatic stabilization and π-excess at phosphorus of the 1H -isomers, to demonstrate the current knowledge and open questions in this field of research.

In this paper, we highlight some addition/cycloaddition reactions of allenylphosphonates and allenylphosphine oxides, mostly based on the work done in our laboratory. Thus the electrophilic addition of iodine monochloride (ICl) with allenylphosphine oxides affords cyclic phosphonium salts rather than γ-chloro-β-iodovinylphosphine oxides (NMR, HRMS, X-ray) that exhibit rather unusual downfield shifts in the 31 P NMR spectra. These compounds undergo hydrolysis to afford γ-hydroxy-β-iodovinylphosphine oxides; the hydroxymethyl group in these compounds can be oxidized by Dess-Martin periodinane to afford the corresponding aldehyde-substituted vinylphosphine oxides. A [2+2] cycloaddition product of an allenylphosphonate has also been structurally characterized. Other reactions that are highlighted include those leading to ( Z )/( E )-β-aminovinylphosphonates, β-ketophosphonates (and their utility in Horner-Wadsworth-Emmons reaction), indolyl/furanyl/isocoumaranyl/naphthyl phosphine oxides, thiophosphorylated phosphonates and azo-substituted coumarin phosphonates.

Group 6 metal (Cr, Mo, W) carbonyl complexes react with cyclo -(P 5 Ph 5 ) to afford the phosphorus-rich complexes [Cr(CO) 5 { cyclo -(P 5 Ph 5 )-κ P 1 }] ( 1 ), [{Cr(CO) 5 } 2 {μ- cyclo -(P 5 Ph 5 )-κ P 1 , P 3 }] ( 2 ), [M(CO) 4 { cyclo -(P 5 Ph 5 )-κ P 1 , P 3 }] (with M=Cr ( 3 ), Mo ( 4 ), W ( exo - 5 , endo -5 )) depending on the reaction conditions. Complexes 1–5 were characterised by 31 P{ 1 H} NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. The cyclopentaphosphane remains intact and acts as monodentate ( 1 ), bridging ( 2 ) or bidentate ( 3–5 ) ligand. Compounds exo - 5 and endo -5 are configurational isomers and essentially differ in the orientations adopted by the phenyl rings attached to the uncoordinated phosphorus atoms. The 31 P{ 1 H} NMR spectra show five multiplets for an ABCDE spin system. Theoretical calculations showed that exo - 5 and endo - 5 are practically isoenergetic, which is in good agreement with the observed equilibrium in solution between exo - 5 and endo - 5 . The thermal properties of the complexes have also been evaluated.

Approaches for preparation of P–H bond containing derivatives directly from white phosphorus are summarized in this microreview. Transfer hydrogenation of P 4 involving the activation and reaction of white phosphorus in the coordination sphere of transition metal complexes is a convenient and powerful route to the hydrogenated compounds. Electrochemical methods have also become popular in modern synthetic chemistry; these provide easy access to highly reactive intermediates, which can be selectively generated in situ and used for subsequent synthetic processes. These electrochemical routes provide efficient and environmentally safe methods for preparation of phosphorus derivatives bearing P–H bond. The mechanisms of the proposed processes and the nature of the intermediates formed in the overall electrochemical process are disclosed. The methods elaborated operate under the principals of “green chemistry” and can be considered as efficient alternatives to some classical pathways.

This account outlines the results obtained in the author’s laboratory on the application of phosphonates in the synthesis of various classes of biologically active cyclopentenones and cyclopentanones. In the first place two general methods for the synthesis of mono-, 1,2- and 1,4-dicarbonyl compounds are presented. The first is based on the use of α-phosphoryl sulfides in conjunction with the Horner reaction while in the second method the oxygenation reaction of α-phosphonate carbanion is a key step. The utility of these two approaches to 1,4-diketones as precursors of cyclopentenones was exemplified by the synthesis of dihydrojasmone and ( Z )-jasmone. The use of simple phosphonates, α-phosphoryl sulfides and β- and γ-ketophosphonates as starting reagents in the synthesis of cyclopentanoid antibiotics (methylenomycin B, racemic desepoxy-4,5-didehydromethylenomycin, enantiomeric sarkomycins) is presented. The synthesis and reactivity of achiral 3-(phosphorylmethyl)cyclopent-2-enone and chiral diastereoisomeric camphor protected 3-(phosphorylmethyl)-4,5-dihydroxycyclopent-2-enones as building blocks is discussed as a platform for developing a new access to a variety of bioactive cyclopentenones. The utility and value of achiral phosphonate building block is demonstrated by the synthesis of racemic and enantiopure prostaglandin B 1 methyl esters and enantiomeric phytoprostanes B 1 type I and II. The range of biologically active compounds prepared from chiral diastereoisomeric cyclopentenone phosphonates is wider. Herein the total syntheses of the following target compounds are presented: enantiomeric isoterreins, natural (−)-neplanocin A and its unnatural (+)-enantiomer, anticancer prostaglandin analogues (enantiomers of TEI-9826, NEPP-11, iso -NEPP-11). The design and synthesis of racemic and four enantiopure stereoisomers of an antiulcer drug rosaprostol is also described.

A variety of gold(I) and copper(I) complexes based on heterocyclic phosphine platform has been obtained. Due to the presence of exocyclic chromophoric pyridyl groups in the ligands complexes demonstrate noticeable phosphorescence. Cyclic nature of the phosphine ligands is responsible for supramolecular host-behavior of the complexes. Unique structure of complexes on a scaffold of the cyclic PNNP ligands favors the stimuli-induced structural reorganizations followed by stimuli-responsive luminescence. This, in turn, makes the complexes versatile building blocks for bottom-up design of smart nanomaterials for analytical and biomedical applications.

Nature-like technologies can be considered as a logical development of green chemistry principles implemented to design novel materials and processes aimed at mimicking and reproducing natural life-sustaining mechanisms on molecular level. Humic substances which penetrate throughout the entire environment and represent from 50 to 90% of organic matter in soil and water ecosystems, play multiple life-sustaining functions on Earth. To name a few, HS regulate transport and availability of biogenic elements to plants, immobilize and mitigate toxicity of hazardous elements in the contaminated ecosystems, protect plants from non-specific abiotic stresses, play key role for fertility of soils determining water-retention and structure. Here we represent a novel platform for nature-inspired synthesis of soft and hybrid (nano)materials aimed at their use for soil and water clean up, carbon sequestration, soil fertility restoration. It is based on a smart use of natural hyperbranched polyelectrolytes – humic substances, which possess multiple functional groups including carboxyl, hydroxyl, amide, and others. Multiple functional groups of HS make them amenable both for classical chemical modification as well as for producing interpolyelectrolyte complexes. In this work, we present both approaches for manufacturing silicon-containing humic derivatives and supramolecular complexes with acquired new property – self-adhesion to both inorganic and bio-surfaces. The synthesis is conducted using humic materials from different sources and functional organosilanes. Self-assembly of the supramolecular silicon-humic systems occurs with formation of humic-silsesquioxane networks capable to adhere to mineral surfaces. This process is similar to immobilization of organic coatings to mineral surfaces. We have shown how this process can be realized in the ground waters for the purposes of the environmental clean up. We have also proposed to use the silicon-humic complexes for improving humus content of soils and for reconstructing soil restoration processes both in the lab and in the field. Another field of our research is synthesis of iron-containing humics-stabilized nanoparticles (NPs), which can be used as a source for plants nutrition instead of synthetic iron chelates. The idea is based on the natural phenomenon that in soils, water-stable sols of iron-containing NPs are formed due to complexing with HS, which can bind large amounts of poorly ordered iron (hydr)oxides providing for stabilization of colloidal iron in the form of NPs. It has been numerously shown that the presence of HS improves iron acquisition by plants in soils, but there was no systematic study so far with respect to a relationship between size and crystallinity of humics-stabilized iron-containing NPs and their availability to plants. We have conducted such a study and could establish conditions when humics-stabilized NPs could be taken up by plants with similar efficiency as FeEDTA. The presented data demonstrate good prospects for a use of green humics-based materials in nature-like technologies. We also hope that these studies will give rise to new branch of chemistry and technology which can be called ecoadaptive chemistry and technology.

A sustainable strategy for the neat production and surface functionalization of nanocellulose from wood pulp is disclosed. It is based on the combination of organocatalysis and click chemistry (“organoclick” chemistry) and starts with nanocellulose production by organic acid catalyzed hydrolysis and esterification of the pulp under neat conditions followed by homogenization. This nanocellulose fabrication route is scalable, reduces energy consumption and the organic acid can be efficiently recycled. Next, the surface is catalytically engineered by “organoclick” chemistry, which allows for selective and versatile attachment of different organic molecules (e.g. fluorescent probes, catalyst and pharmaceuticals). It also enables binding of metal ions and nanoparticles. This was exemplified by the fabrication of a heterogeneous nanocellulose-palladium nanoparticle catalyst, which is used for Suzuki cross-coupling transformations in water. The disclosed surface functionalization methodology is broad in scope and applicable to different nanocelluloses and cellulose based materials as well.