Efficient oxidative ipso-fluorination of para-substituted phenols using pyridinium polyhydrogen fluoride in combination with hypervalent iodine(III) reagents

Diacetoxyiodobenzene (PIDA) and bis(trifluoroacetoxy)iodobenzene (PIFA) in the presence of pyridinium polyhydrogen fluoride (PPHF) are effective for the fluorination of para-substituted phenols to give a variety of 4-fluorocyclohexa-2,5-dienones in a good yield. (R,S)-1,1′-Bi-5,6,7,8-tetrahydro-2-naphthol (and its monoacetate) yields atropoisomeric fluorocyclohexadienones. The 4-substituted carbamate open-chain phenols were readily converted to fluorohydroindolenone and fluorohydroquinolenone derivatives by intramolecular conjugate addition.     

The Behavior of Phosphorus Reagents Towards Substituted Diazine and Hydrazine Derivatives

Summary. The reaction of dibenzoyldiazine with phosphorus ylides afforded the new 2-[(benzoylhydrazono)phenylalkyl]but-2-enedioic acid dialkylesters. Moreover, ethyl-2(triphenylphosphoranylidene)propionate reacts with dibenzoyldiazine to give the olefinic compound and triphenylphosphine oxide. On the other hand, oxovinylidene-triphenylphosphorane reacts with dibenzoyldiazine to give a new phosphorane adduct. Trialkyl phosphites react with dibenzoyldiazine to yield the dialkyl phosphonate products. The reaction of dibenzoylhydrazide with Wittig reagents gave rise to the new 3,7-diphenylpyrazolo[1,2-α]pyrazole-1,5-diones. Possible reaction mechanisms are considered, and the structural assignments are based on analytical and spectroscopic results.     

Pyridinium chlorochromate catalyzed oxidation of alcohols to aldehydes and ketones with periodic acid

A facile pyridinium chlorochromate (PCC) catalyzed (2 mol %) oxidation of alcohols to ketones and aldehydes using 1.05 equiv of H₅IO₆ in acetonitrile is described here.     

An Unusual Synthesis of Arylazo Substituted Azaphospha [5, 1-A] Quinolines by Reaction of N-Alkylarylazo Quinolinium Salts with Phosphorus Trichloride

1,2-Dialkyl-3-arylazo quinolinium chloride 1 having N-methylene group activated by the insertion of arylazo site react with phosphorus trichloride to give N-(dichloro phosphinomethylene) quinolinium ylide 2 . The site of the reaction is determined by the relative activation of 1- and 2-methylene groups, in the absence of sufficient activation of N-methylene group, reactions occur at the 2-methylene group to give dichloro phosphinylated anhydrobases 5 and 11.     

Pressure Effect on Molecular and Lattice Dynamics in Pyridinium Nitrate

Measurements of spin-lattice relaxation time T 1 , second moment M 2 and neutron scattering have been performed for a polycrystalline sample of pyridinium nitrate as a function of hydrostatic pressure and temperature. The structure of this compound has also been analysed by the HF/6-31 G method. The results of the measurements and calculations have confirmed that reorientation of the pyridinium cation takes place between the potential minima of different values, and the asymmetry parameter decreases with increasing temperature. The temperature dependence of the asymmetry parameter is modified by the pressure applied. The presence of the hydrogen bond in this compound implies a very small activation volume and is responsible that the crystal does not undergo a phase transition to the disordered phase.     

Enantioselective cyclopropanation reaction using a conformationally fixed pyridinium ylide through a cation-π interaction

Using a chiral pyridinium ylide with a fixed conformation through a cation-π interaction performs enantioselective cyclopropanation of electron-deficient olefins. ¹H NMR, X-ray structural analysis and DFT calculations elucidated the self-complexation and the face-to-face arrangement between the pyridinium and the phenyl rings. The absolute configuration of the product was determined after conversion into a bicyclic cyclopropane derivative.     

Extraction of Pb (II) and Co (II) using N,N-dioctylsuccinamate based room temperature ionic liquids containing aliphatic and aromatic cations

Synthesis and Characterization of six novel N,N-dioctylsuccinamate based room temperature ionic liquids (RTILs) bearing imidazolium, pyridinium, ester imidazolium, and quaternary ammonium cations is reported. Extraction of Pb(II) and Co(II) by these RTILs has been investigated. Ionic liquids (ILs) synthesized were [C₄mim][N₈₈SA], [C₈mim][N₈₈SA], [C₄Py][N₈₈SA], [C₈Py][N₈₈SA], [α-mim-ester][N₈₈SA] and [N₂₂₄₄][N₈₈SA] termed as L1, L2, L3, L4, L5 and L6 respectively. Liquid-liquid extraction was performed and all the six systems showed excellent extractability results for both Pb(II) and Co(II). During the process of extraction several factors i.e., nature of cation, pH of the aqueous phase, equilibration time, and initial metal ion concentration were investigated. The extraction efficiency of above 98 % for all types of extractants was observed. The nature of cation its concentration, equilibration time, and pH of the aqueous phase significantly influenced the extraction efficiency. Maximum extraction was observed at pH values between 4 and 8 and optimum contact time was observed to be 40–45 min. Increasing the metal ion concentration decreased the extraction efficiency. The extraction efficiency of both metal ions decreased in the order [N₈₈SA][C₈mim] (L2) > [α-mim-Ester][N₈₈SA] (L5) > [N₈₈SA][C₄mim] (L1). This is evident from the order of extraction behaviour that increasing the bulkiness of cation, results in stronger complexation, hence increasing extraction.     

Synthesis of New Phosphonium Ylides Containing Thiophene and Furan Rings and Study of Their Reaction with Mercury(II) Halides: Spectral and Structural Characterization

Reactions of phosphonium ylides (4‐MeC₆H₄)₃PCHC(?O)(2‐C₄H₃S) (tptpy), Ph₃PCHC(?O)(2‐C₄H₃O) (fppy), and (4‐MeC₆H₄)₃PCHC(?O)(4‐BrC₆H₄) (bbtppy) with HgX₂ (X=Cl, Br, and I) in equimolar ratios in MeOH as solvent leads to the binuclear products 1 – 3 (Scheme 1). The bridge‐splitting reaction of the binuclear complex [{HgI₂(bbtppy)}₂] ( 3c ) by DMSO yields the mononuclear complex [HgI₂?(bbtppy) (DMSO)] ( 3d ) (Scheme 2). This bridge‐splitting reaction can also be a method for the synthesis of mononuclear products. C‐Coordination of the ylide and O‐coordination of DMSO are demonstrated by a single‐crystal X‐ray‐analysis of the mononuclear complex 3d . Characterization of the obtained compounds was also performed by means of elemental analysis and IR and ¹H‐, ³¹P‐, and ¹³C‐NMR spectroscopy. A theoretical study of some Hg^II complexes with phosphonium ylides is also reported.     

One-pot approach to the synthesis of novel 12H-chromeno[2′,3′:4,5]imidazo[1,2-a]pyridines in aqueous media

The chromeno-imidazo[1,2-a]pyridine scaffold was generated in an one pot condensation/cyclization reaction involving a salicylaldehyde and 1-(cyanomethyl)pyridinium chloride, in aqueous sodium carbonate solution. These novel compounds were isolated in 47-71% yield. The reaction pathway was followed by ¹H NMR spectroscopy allowing a clear understanding of the side reactions involved in the process.Different mono-substituted pyridinium chlorides were synthesized and reacted with mono-substituted salicylaldehydes and a detailed discussion of the scope of the synthetic method is also presented.     

Short synthesis of functionalized pentalongin derivatives using pyridinium ylid chemistry

3-Substituted pentalongin derivatives possessing an acetal function at C-1 were synthesized by cyclization of acylmethylnaphthoquinones. The latter naphthoquinones were prepared starting from 2-dioxolanylnaphthoquinone by means of both a stoichiometric and a catalytic method deploying various pyridinium ylids.