Pyridinium Methylides Research Articles

The synthesis of indolizin-1-ylphosphonates via the reaction of ethynylphosphonates with pyridinium methylides

The synthesis of indolizin-1-ylphosphonates via the reaction of ethynylphosphonates with pyridinium methylides

Divergent syntheses of spirooxindoles from oxindole-embedded four-membered synthon via cycloaddition reactions

The construction of five and six membered heterocycle fused spirooxindoles was achieved via the [4 + 1] and formal [4 + 2] cycloadditions between our rationally designed four-membered synthons and pyridinium methylides and α-bromoacetophenones, respectively.

ChemInform Abstract: Reactions of o‐Quinone Methides with Pyridinium Methylides: A Diastereoselective Synthesis of 1,2‐Dihydronaphtho[2,1‐b]furans and 2,3‐Dihydrobenzofurans.

AbstractThis new method proceeds with complete diastereoselectivity giving the title compounds as trans‐isomers exclusively.

Catalytic Asymmetric Syntheses of Quinolizidines by Dirhodium-Catalyzed Dearomatization of Isoquinolinium/Pyridinium Methylides–The Role of Catalyst and Carbene Source

Convenient access to highly enantioenriched substituted quinolizidines has been achieved by chiral dirhodium(II) carboxylate-catalyzed dearomatizing formal [3 + 3]-cycloaddition of isoquinolinium/pyridinium methylides and enol diazoacetates. Coordination of Lewis basic methylides to dirhodium(II) prompts the rearrangement of the enol-carbene that is bound to dirhodium to produce a donor-acceptor cyclopropene. The donor-acceptor cyclopropene is in equilibrium with the dirhodium-bound enol-carbene and undergoes both enantioselective [3 + 3]-cycloaddition from the dirhodium-bound enol-carbene and diastereoselective [3 + 2]-cycloaddition by uncatalyzed reaction of the cyclopropene with isoquinolinium or pyridinium methylides. Increasing the mol % of catalyst loading suppresses the [3 + 2]-cycloaddition pathway.

Synthesis and physico-chemical properties of a novel series of aromatic electron acceptors based on N-heterocycles

The synthesis of a novel series of N-based heterocyclic salts using a simple and efficient N-alkylation of 1,2-bis(4-pyridyl)ethane with reactive halides is reported. These compounds can be transformed into the corresponding pyridinium methylides by addition of a base. The former exhibit an unstable absorption bands at 395–410 nm. The structures of the salts were fully characterized by UV–vis, IR, NMR and MS spectroscopy and elemental analysis. The pK values of selected compounds were also determined and the acid–basic equilibrium was investigated by UV–vis spectrophotometry. The thermal stability of all species was determined by thermogravimetric analysis.

Synthesis of the First Example of a Tetrahydroindeno[2,1‐c]azonine System by the Reaction of 2,3‐Dihydro‐1H‐indeno[2,1‐c]pyridinium Methylide with Methyl Acetylenedicarboxylate.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Substituent-Dependent Anomeric Effects as a Source of Conformational Preference in Pyridinium Methylides

A systematic density functional theory level investigation of differently substituted pyridinium methylides was carried out to determine the role of C(ylidic) lone-pair-associated hyperconjugative and negative hyperconjugative interactions in deciding conformational preferences. Deviation from the coplanar orientation of the carbanionic center with the pyridine ring and its substituent dependence has been found to correlate well with the relative opportunities for conjugative and negative hyperconjugative interactions of a ylidic moiety with different substituent groups present at the ylidic carbon. The contribution of individual n-->pi* conjugative, n-->sigma* negative hyperconjugative, and sigma-->pi* hyperconjugative interactions in a particular conformation of pyridinium dichlorophosphinomethylides was assessed from donor-acceptor stabilization energies, as obtained from natural bond orbital (NBO) analysis. The relative extent of conjugative and negative hyperconjugative interactions with the substituents present at the ylidic carbon plays an important role in permitting the delocalization of ylidic charge into the pyridine ring, thereby controlling the relative orientation of the latter with the carbanionic plane.

Reactions of alkyl diazoacetates with pyridinium ylides

Pyridinium (methoxycarbonyl)methylide generated from (methoxycarbonyl)methyl-pyridinium halides under the action of K2CO3 reacts with alkyl diazoacetates in CH2Cl2 at 20 °C, resulting in the successive addition of three CHCOOMe fragments from the ylide to form 3,6-bis(alkoxycarbonyl)-4,5-diazaoctadienoic acid diesters. Heating of the latter in the presence of pyridine leads to their isomerization to give tetraalkyl tetrahydropyridazine-tetracarboxylates in high yields. Under more drastic conditions (refluxing xylene in the presence of pyridine), the acyclic tetraesters undergo another transformation to form pyrrole-tetracarboxylic acid esters in yields of up to 60%.

Halochromism of pyridinium azomethine ylides stabilized by dicyanopyrazine group

Reactions of 2-bromomethyl-3-phenyl-5,6-dicyanopyrazine with methyl substituted pyridine gave dicyanopyrazylmethylene pyridinium bromides. These salts were changed to their corresponding methylides by the addition of a base, which were restored by the addition of an acid. The pyridinium methylides exhibited intense visible absorption. This study was attempted to apply the pyridinium halides with a dicyanopyrazine group to a reversibly colored material to gain an external response. The 1,3-dipolar cycloaddition reaction of such pyridinium azomethine ylides containing a stabilized dicyanopyrazine group with dimethyl acetylenedicarboxylate (DMAD) afforded the indolizine derivatives.

Carbanion substituent effects on 1-disubstituted 4-(4′-pyridyl)pyridinium methylide structures using 13C NMR spectroscopy and DFT method

The structure of 1-disubstituted 4-(4′-pyridyl)pyridinium methylides or 4,4′-bipyridinium monoylides ( 2– 5) with a wide range of carbanion substituents, were determined using 13C NMR signals in dimethylsufoxide (DMSO- d 6) solution. For the first time, we developed a systematic determination of 13C NMR chemical shifts of the ylidic carbon using a long-range correlated ( 1H– 13C) HMBC experiments. The chemical shift values are discussed in terms of magnetic and/or electronic effects of the ylidic carbon substituents. From the extracted NMR parameters and the results of accompanying quantum chemical DFT calculations for a three-dimensional (3D)-structure representation, we found a long distance electronic effect where the aromatic heterocycle C2C6 and C4 centers are perturbed according to the electron acceptor strengths of ylidic carbon substituents in all monoylides ( 2– 5c) capable to stabilize in a planar conformation. No significant perturbation on C2C6 and C4 centers are found in all other monoylides ( 2– 5a, b) that adopted a non-planar conformation. Good similar linear dependences of the chemical shift variation Δ (calculated by the differences of analogous C2C6 and C4 chemical shifts in non-planar and planar monoylides) with the ylidic carbon chemical shifts modulated by the strength of electron acceptor substituents pointed out the resonance interaction or the delocalization phenomena of the ylidic carbon charge on the heterocycle.

Novel Generation of PyridiniumYlides fromN-(Silylmethyl)pyridone Analogs via1,4-Silatropy and their 1,3-Dipolar Cycloadditions Leading toN-Heteropolycycles

Non-stabilized pyridinium methylides were successfully generated from N-(siliymethyl)pyridone analogs via 1,4-silatropy and the resulting 1,3-dipoles were trapped by reaction with acetylenic and olefinic dipolarophiles to afford N-heteropolycycles. The method does not require the use of any additives or strong bases.

Pyridinium dichlorophosphinomethylides

AbstractSeven new pyridinium dichlorophosphinomethylides 2 have been obtained from dichlorophosphinylation of the pyridinium methylides generated in situ. 2 give 1,3‐bis(alkoxycarbonyl)‐2‐phosphaindolizines 4 through 1,5‐electrocyclization of the intermediate, bis(pyridinium ylidyl)phosphenium chloride 3 which is generated either from disproportionation of 2 or from the reaction of 2 with pyridinium methylide. Formation of 3 has been confirmed by carrying out a crossed reaction. 3‐Substituted 2 forms 4 regiospecifically. Intramolecular 1,5‐cyclocondensation of 2‐methylpyridinium dichlorophosphinomethylide is preferred over its disproportionation. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:602–609, 2001

Reaction of diphenylborinic acid with pyridinium and phosphonium bisacyl methylides. Crystal and molecular structures of resulting B,N- and B,P-betaines

Reaction of pyridinium and phosphonium 2-carboxy-1-formyl-2-oxoethylides with oxybis(diphenylborane) yields 5-(2-oxo-1-(pyridinio or phosphonio)ethylidene)-2,2-diphenyl-1,3-dioxa-2-borata-4-cyclopentanones, which represent novel types of boron nitrogen and boron phosphorus betaines, respectively. Crystals of 5-(2-oxo-1-pyridinioethylidene)-2,2-diphenyl-1,3-dioxa-2-borata-4-cyclopentanone,1a, are monoclinic, a = 15.589(3), b = 12.366(2), c = 20.1869(11) Å, β = 111.227(2)°, Z = 8 (two independent molecules), space group P21/a; and those of 5-[2-oxo-1-(triphenylphosphonio)ethylidene]-2,2-diphenyl-1,3-dioxa-2-borata-4-cyclo-pentanone,11, are monoclinic, a = 9.6922(7), b = 25.027(2), c = 11.3041(4) Å, β= 92.1418(13)°, Z = 4 (two independent molecules), space group P21. The structures were solved by direct methods and refined by full-matrix least-squares procedures to R (F, I [Formula: see text] 3σ(I)) = 0.047 and 0.042 (Rw (F2, all data) = 0.096 and 0.088), respectively, for 1a and 11.Key words: pyridinium ylides, phosphonium ylides, bisacyl methylide diphenylboron chelates, boron nitrogen betaines, boron phosphorus betaines, organoboron compounds, crystal structures.

Efficient robotic synthesis. Multi-component preparation of a tricyclic template by solid phase Tsuge reaction

Sequential cycloaddition of maleimides and nitrile oxides to resin-bound pyridinium methylides gives, after cleavage, maleimide-fused indolizinium carboxylates. The reaction occurs under mild conditions and has been automated on the ACT 496 synthesiser, providing an efficient multi-component robotic synthesis of a diversely substituted tricyclic template from a monocyclic precursor.

ChemInform Abstract: Synthesis of Sulfur Containing Annulated Indolizines by Intramolecular (3 + 2)Cycloaddition with Pyridinium Methylides.

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Characterization of [C6H7N]+˙ radical cations by tandem mass spectrometry

AbstractCollisional Activation, charge‐stripping and neutralization/reionozation mass spectra allow the identification of six [C6H7N]+˙ isomers, namely the molecular ions of the three isomeric picolines, 1+˙–;3+˙, ionized 2‐ and 4‐methylene dihydropyridines, b—c, and ionized pyridinium methylide, a. The implication of the distonic forms a and b in some fragmentation reactions of funct of onalized (position 2) pyyridines is briefly discussed. Molecular orbital calculations indicate the b>a>1+˙ stability sequence.

Fluorocarbon derivatives of nitrogen. Part 19. Synthesis and mass spectrometric analysis of some pyridinium (tetrafluoro-4-pyridyl)-methylides

Nine new pyridinium methylides have been synthesised via S NAr displacement of the 4-fluorine from pentafluoropyridine with pyridinium phenacylide [ → py +C̄(COPh)C 5F 4N-4] and a range of pyridinium alkoxycarbonylmethylides [ → py +C̄(CO 2R)C 5F 4N-4, R = Me, Et, Pr n, Pr i, CH 2CCl 3, CH 2CF 3, CH 2Ph, CH 2CH 2Ph]. A detailed analysis of the mass spectrometric fragmentation patterns for the alkoxycarbonyl compounds has been carried out. Spectroscopic data has also been obtained for pyridinium methylides synthesised from pyridinium ethoxycarbonylmethylide and 3-chlorotetrafluoropyridine or octafluorotoluene.

ChemInform Abstract: New Synthesis of the 1‐Pyrazoline Ring.

AbstractThe diazoazafluorene (I) reacts with the pyridinium methylides, generated in situ from the phenacylpyridinium bromides (II), to give the spiro compounds (III) and (IV).

ChemInform Abstract: Tandem 1,3‐Dipolar Cycloadditions of Pyridinium or Isoquinolinium Methylides with Olefinic Dipolarophiles Leading to Cycl(3.2.2)azines. “Enamine Route” as a New Generation Method of Azomethine Ylides.

AbstractCycloaddition reaction of the pyridinium methylides, generated in situ from (I), with the maleimides (II) yields the monocycloadducts (III) which undergo a second cyclization reaction with the olefines (II) or (V) to form the biscycloadducts (IV) or (VI).

ChemInform Abstract: Synthesis of Indolizines from N‐(2,2,2‐Trifluoroethyl)pyridinium Triflate. Evidence for the Generation of Pyridinium (Trifluoromethyl)methylide.

AbstractThe methylide (II), formed by treatment of pyridinium triflate (I) with bases, is trapped with the acetylenes (III) to produce the dihydroindolizines (IV) which are partly dehydrogenated to form the indolizines (V).