Preparation and Reactions of Pyridinium Ylids via Decarboxylation of Pyridinium Betaines

Ylids are charged organic compounds with characters differ from regular organic compounds1. Nitrogen ylids, due to their instabilities, are not studied as vastly as phosphorus or sulfur ylids2. Nitrogen ylids are generally obtained by removing proton of the quaternary nitrogen salts with base3,4. In this work, we tried to study the generation of pyridinium ylids 4 via decarboxylation process in neutral condition and study the related reactions with electrophiles. The precursor of pyridiniu…     

Reactions of Tris(Perfluoroalkyl)Difluorophosphoranes and Their Derivatives with Nucleophilic Reagents

Abstract

This paper is concerned with the reactions of (R_f)₃PF₂ and (R_f)₃PO with N-, 0-, C-nucleophiles and fluoride ion. Either the replacement of one or two perfluoroalkyl radicals by different functional groups or the addition of reagent to electrophilic phosphorus occurs. These phosphinic oxides and phosphoranes readily add fluoride-ion with the expansion of phosphorus coordination: the former produces phosphoranes OP a new type (R_f)₃P(F)O_?Cs₊, while the latter stable substituted fluorophosphates of general formula M ₊[(R_f)₃ PF₃]_?. Based on these salts it was possible to synthesize aryldiazonium tris(perfluoroalkyl)trifluorophosphates, whose thermal decomposition leads to the formation of substituted fluorobenzenes with high yields. The reaction is a convenient modification of the Shieman methd. The approaches of the synthesis of phosphoranes containing simultaneously both perfluoroalkyl groups and nonfluorin-ated radicals are developed due to the reactions of tris-(perf luoroalkyl)dif luorophosphoranes with the lithium-organic compounds. The replacement of either fluorine atom or perfluoroalkyl radical by the nonfluorinated group depends on the lithium reagent nature:     

The Reactivity of 2,4,6-Tirphenylpyridinium Ylids

Nitrogen ylids1,2 are reactive species which are not studied as vastly as phosphorus or sulfur ylids3. We have been studying the chemistry of pyridinium ylids and in a previous paper4, we reported the generation of ylid 2 via decarboxylation of pyridinium betaine 1 and then studied the reaction with certain electrophile. In this work, we wish to report other type of reactions that observed and the reactivity of 2. a: R = H b: R = CH312- CO2refluxScheme 13a: A = EtOH b: A = PhCHOc…     

Studies on Ptc-Wittig Reaction of Diphenyl Ylids

Abstract

The phase transfer catalyzed (PTC) Wittig reaction has the advantage of not requiring additional catalyst due to the catalytic property of phosphonium salt itself. This report presents the studies on such a reaction of diphenyl-, di-alkyl- and methyl-2-butenyl phosphonium ylids which are produced in situ from the corresponding phosphonium salts.     

The Reaction of Phosphonium Ylids with o-Quinones and Triketones

Abstract

The reaction of 1,2-benzo [a] phenazine-8, 9-dione 1 and/or 1,2,3-indantrione 2, with phosphonium ylides has been studied. When 1 was reacted with two molar amounts of methoxy-(3a) and/or ethoxycarbonylmethylenetriphenylphosphorane (3b), in THF, at the reflux temp, for 3 hrs, dimethyl (4a) and/or diethyl 1,2-dihydrobenzo a furo [3,2-h] phenazine-1,2-dicarboxylate (4b), along with triphenylphosphine oxide and triphenylphosphine were obtained. On the other hand, reaction of equimolar amounts of ylides 3 with the red trione 2 in THF at room temp., afforded colourless crys tals of 2′,4′-dihydroxyspiro [indan-2,3′ (2′H)-indeno [1,2-b] pyran]-1,3,5′(4′H)-trione diacetate (5a) or dipropionate (5b), together with triphenylphosphine oxide. Formation of 6-membered dihydro aromatic ring like 5, is considered as a new reaction of phos phoranes. The structure of the new compounds 4 and 5 was confirmed and the reaction mechanisms are discussed.     

Ylids with a PH bond

Tertiary bis(methoxycarbonyl)methyl phosphines are reversibly isomerized to ylids with a PH bond. The phosphine- PH ylid equilibrium depends on the solvent nature, on the concentration, temperature and substituents at the phosphorus atom.     

Oxidation of heterocyclic nitrogen Ylids to nitro heterocycles. Comparison of a sulfilimine and a phosphine imine

Oxidation of 3-amino-4-(4-chlorophenyl)furazan ( 1 ) with peroxytrifluoroacetic acid (ptfa) gave azoxy(4-chlorophenylfurazan) ( 6 ) as the major product along with a small amount of 3-(4-chlorophenyl)-4-nitrofurazan ( 5 ). The dimethylsulfilimine 2 derived from 1 gave near quantitative yields of 5 when subjected to oxidation with either ptfa or m-chloroperoxybenzoic acid (mcpba). In contrast, both the trioctylphosphine imine 3 and the triphenylphosphine imine 4 derived from 1 were oxidized by mcpba to give 6 as the exclusive product.     

Recent Advances of Catalytic Enantioselective Heck Reactions and Reductive-Heck Reactions

Heck reaction is one of the most important carbon-carbon bond forming reactions with wide applications in organic synthesis.Considerable advances of enantiosele...     

Reactions of ketenes—IX Reactions between ketene acetals and diphenylketene

Monoalkylketene acetals and monoarylketene acetals react with diphenylketene to give acylketene acetals (VII). These compounds can further react with diphenylketene to give 2,4-pyronone 4-acetals (IX), which, by mild acid hydrolysis, yields 2,4-pyronones (X).

Reaction of methylketene diethylacetal with two equivalents of diphenylketene yields 3,3-di-phenyl-5-methyl-6-diphenylmethylentetrahydropyran-2,4-dione 4-diethylacetal (XIV) in addition to small quantities of the pyronone acetal IXb.     

Synthesis and Reactions of Ketenimines

Ketenimines R¹R²C?C?N? R³ were first reported in 1919, but the development of the chemistry of these compounds is of relatively recent origin. These heterocumulenes are becoming of increasing interest as a dehydrating agent for peptide syntheses, as a coreagent in dimethyl sulfoxide oxidations, and as a substrate in the synthesis of heterocycles by condensation with polar multiple bonds and dipolar systems. The cycloadditions are of special interest from the viewpoint of orbital symmetry considerations. Some unusual organometallic complexes of ketenimines have also been synthesized. Recently some triaryl ketenimines have been found to have insecticidal and miticidal activity. Polymeric ketenimines have been implicated as molecular precursors of life.     

氢膦烷的合成及其反应

氢膦烷能参与多种化学反应,可以衍生出许多类型的五配位磷化合物,而且在有机合成中也有重要的应用价值.本文结合作者的研究工作,对近年来氢膦烷研究的重要进展进行了评述.     

Preparation and Reactions of Octasilsesquioxanes

Because of the length scales involved, nanocomposite materials incorporate extensive interracial interactions that can result in non-linear changes in the composite property. Chemists often start from polymerizable inorganic and organic constituents in the molecule to build organic/inorganic hybrids that combine advantageous properties of disparate components.Silsesquioxanes (RSiO1.5)n, derived from e.g. RSiCl3 or RSi(OEt)3 by hydrolysis/condensation in a sol-gel process, are a class of silicate framework where each Si-atom is linked covalently to an organic radical R that chemically modifies the silicates. In addition to incompletely condensed silsesquioxanes is the completely condensed octasilsesquioxane. These octameric silsesquioxanes are in transition between small molecules and macroscopic materials with skeletal frameworks found in crystalline forms of silica and zeolites. SisO12(CH=CH2)8 1 has a cubic silica like core and 8 olefin functionalities as known for a long time yet with very few reactivity reports. The acidic hydrolytic polycondensation of (vinyl)Si(OEt)3 in the literature, leading to only less than 20% of 1,also suggests a large room for improvement. We have found that the H NMR spectra of mixtures containing 1 and either the Schrock's catalyst or the Grubbs' catalyst never exhibit vinylic 1H peaks attributable to the formation of products from self-metathesis. With a Pt/C catalyst, the H-Si bond of HSiMe2Cl adds to the vinylic double bond of 1, forming 2 that reacts with sufficient CH2=CHCH2OH to give 3. Upon treatment of the Grubbs' catalyst, a ring-closing metathesis occurs on the surface of the cubic Si8O12 framework. The results exhibit a strong proximity effect with which 3 transforms itself to 4. Alternatively 5 has been prepared.The Gmbbs' catalyst allows 5 to isomerize from Z- to E-configuration to produce 4 independentiy, thus demonstrating the ring-closing metathesis reactions of densely populated terminal olefins on Si8O12 surface.     

Carbocations and Electrophilic Reactions

The general concept of carbocations encompasses all cations of carbon containing compounds which can be differentiated into two distinct classes: trivalent (“classical”) carbenium ions and pentacoordinated (“nonclassical”) carbonium ions. In this paper the preparation and structural study (by NMR, IR, Raman and ESCA spectroscopy) of stable carbenium ions and carbonium ions are discussed. As is well known, trivalent carbenium ions play an important role in electrophilic reactions of π- and n-donor systems. Similarly, pentacoordinated carbonium ions are the key to electrophilic reactions of σ-donor systems (single bonds). The ability of single bonds to act as σ-donor lies in their ability to form carbonium ions via triangular two electron, three-center bond formation. Consequently there seems to be no principle difference between the electrophilic reactions of π- and σ-bonds except that the former react more easily, even with weak electrophiles, whereas the latter necessitate more severe conditions. The role of carbocations in electrophilic reactions of π- and σ-donor systems is discussed.     

Aromaticity and Pericyclic Reactions

Pericyclic reactions formally resemble the conversion of one Kekulé structure into another; the transition state may be “aromatic”, “nonaromatic”, or “antiaromatic”. Thermally induced pericyclic reactions proceed preferentially via aromatic transition states whereas their photochemical counterparts lead to products that are formed via antiaromatic transition states.