Stable Ylides Research Articles

P(MeNCH2CH2CH2)3N: An efficient promoter for the generation of nonstable and somewhat stable sulfur ylides from sulfonium salts

P(MeNCH2CH2CH2)3N: An efficient promoter for the generation of nonstable and somewhat stable sulfur ylides from sulfonium salts

Synthesis of α-Phenylthioacylmethylene Triphenylarsoranes and their Wittig-type Reactions

α-Phenylthio acylmethylene triphenylarsoranes, the first stable α-thiyl arsonium ylides, are prepared by phenylsulfenylation–transylidation reaction of the corresponding acylmethylene triphenylarsoranes with phenylsulfenyl chloride; Wittig reactions are carried out under mild reaction conditions on the arsonium ylides to provide α-phenylthio-α,β-unsaturated ketones.

Thermodynamics of Ylide Formation from Carbenes and Carbonyl Compounds

Thermodynamic parameters for the reaction of CH2 (singlet and triplet), CF2 and C(OH)2 carbenes with formaldehyde, acetaldehyde and acetone, forming carbonyl ylides, were determined using high level ab initio molecular orbital calculations. Singlet methylene forms a stable ylide with the three carbonyl compounds, with a deltaHº of -41.6 kcal/mol, -40.0 kcal/mol (E isomer), -44.5 kcal/mol (Z isomer) and -40.8 kcal/mol, respectively. Triplet methylene also forms a y lide with formaldehyde with a deltaE of -15.7 kcal/mol, resulting in the triplet ylide being formed reversibly. For the reaction with formaldehyde, the CF2 and C(OH)2 carbenes have a positive deltaHº of 13.0 kcal/mol and 22.0 kcal/mol, and a deltaGº of 25.3 kcal/mol and 34.0 kcal/mol, respectively. Due to its unfavorable free energy of formation, and the potential competition of direct 1,2 cycloaddition of carbene to the C=O group, CF2 and C(OH)2 should not react with carbonyl compounds forming ylides.

Ether Oxides: A New Class of Stable Ylides? A Theoretical Study of Methanol Oxide and Dimethyl Ether Oxide

The potential energy surfaces of neutral methanol oxide and dimethyl ether oxide and their anion and cation radicals have been calculated at the Becke3LYP/6-311++G(d,p) level of theory. Both neutral singlet methanol and dimethyl ether oxides are predicted to correspond to local minima on their potential energy surfaces. Natural bonding orbital (NBO) population analysis reveals a distinct ylidic character for these species. Upon increasing methyl substitution, the R2O+O- ylide structure is stabilized energetically because of the better charge distribution of the formally positive central oxygen atom; thus, the energy differences relative to the R2O + 3O exit channel decrease significantly. The barrier for the 1,2-hydrogen migration in methanol oxide to yield methyl hydroperoxide amounts to only 5 kcal/mol, whereas the methyl shift in dimethyl ether oxide to afford dimethyl peroxide demands >40 kcal/mol and can proceed by retention or inversion of the configuration at the migrating carbon. The kinetic stabilization of the latter is instead determined either by the loss of a methyl radical or by spin crossing to the triplet surface followed by O atom loss. For this process, the minimal-energy crossing point of the two neutral surfaces was located. The corresponding cation radicals of methanol and dimethyl ether oxide rest in rather deep wells, and their geometries are not too different from those of the neutrals. Therefore, neutralization-reionization mass spectrometry may allow generation and identification of the neutral species, provided that the cation-radical precursors can be made. Furthermore, the kinetic stability of neutral dimethyl ether oxide may be sufficient for its detection in matrix isolation experiments.

ChemInform Abstract: α,β‐Unsaturated Sulfones by the Wittig Reaction of Stable Ylide with Aldehydes under Microwave Irradiation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reactions of stabilized sulfur ylides with α,β-unsaturated alkoxychromiumcarbene complexes

Reaction of stabilized sulfur ylides with α,βunsaturated alkoxychromiumcarbene complexes in MeCN as solvent forms vinylenol ethers 3, cyclopropanes 4, and vinylcyclopropanes 5, depending on the reagent ratio, the temperature and the nature of the ylide. The results obtained in these reactions suggest that factors apart from steric hindrance may control the chemoselectivity of the addition. Less stable ylides would add preferentially to the carbene carbon, 1,4-addition increasing as the stability of the ylide does. For more stable ylides 1,4-addition is preferred and substitution at the β-carbon has little effect in the chemoselectivity. Methoxycarbonylmethylentriphenylphosphorane exclusively add to the carbene carbon while ethyl diazoacetate is unreactive towards α,β-unsaturated alkoxychromium-carbene complexes in the conditions studied.

Pyrolysis of Amino Acid Derived Stabilised Ylides as a Route to Chiral Acetylenic Amines and Amino Acids and Gaba Analogues

Abstract We recently reported the pyrolysis of stabilised ylides as a method for overall conversion of carboxylic acids to homologous acetylenic esters and terminal alkynes.1,2 This has now been applied successfully to amino acids. A wide range of alkoxycarbonyl protected amino acids have been converted to the stable crystalline ylides 1. These have been fully characterised, and upon FVP, eliminate Ph3PO to afford the protected acetylenic amino acids 2 in good yield and without significant racemisation. Subsequent reactions of these extremely versatile intermediates have been used to gain access to a wide variety of chiral amine and amino acids of great interest as potential selective enzyme inhibitors and components for modified peptide structures.

Searching for the ylide structure. An ab initio study of the H 2O…CCl 2 complex

The potential energy surface (PES) for the H 2O…CCl 2 complex has been investigated at the self-consistent field level with a DZP basis set in order to search for stationary points and to verify the possible formation of an ylide species. Six stationary points were located on the PES, being one minimum, three first-order transition states (TS) and two second-order TS structures. A stable ylide species was not found, and an explanation for this is given based on electrostatic grounds. The unique minimum corresponds to an H-bond structure, with a dissociation energy of 845.5 cm −1, calculated including zero point energy correction, a more extended basis set, electron correlation effects at the MP2 level and taking into account basis set superposition errors employing the counterpoise method.

ChemInform Abstract: Chalcones by the Wittig Reaction of a Stable Ylide with Aldehydes under Microwave Irradiation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: The Wittig Reaction of Stable Ylide with Aldehyde under Microwave Irradiation: Synthesis of Ethyl Cinnamates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Wittig Reaction of Stable Ylide with Aldehyde Under Microwave Irradiation: Synthesis of Ethyl Cinnamates

Abstract The Wittig reaction of stable ylide, triphenyl-carbethoxymethylene phosphorane, with aldehydes was performed within 5–6 minutes under microwave irradiation. Remarkable rate enhancements and dramatic reductions of reaction times have been observed. Thus, the Wittig reaction of stable ylide with aldehyde is optimized.

Chemistry of Silylketenes: Simple Preparation of Silylallenes by the Reaction of Silylketenes with Phosphorus Ylides.

Reaction of silylketenes 1a, b with stabilized ylides 2a-e readily gave silylallenes 3a-f in high yields. However, similar reaction of 1a with the less stable ylides 2f, g resulted in low yields of the allenes 3 g, h. Use of silylketenes 5a, c with an additional trimethylsilyl group overcame this problem to give silylallenes 3c, g-k directly in considerable to good yields. In this reaction, the additional trimethylsilyl group apparently worked as a masking group.

Reaction of Phosphorylated Quinone Methides with Trivalent Phosphoryl Compounds

Abstract By reaction of bisphosphoryl quinone methides 2 with diethyl phosphite or diphenylphosphine oxide, depending on sterical requirements, the trisphosphorylderivatives 4a and 4b or 5 and 6 respectively, are formed. The latter reaction represents a new phosphorylation of an aromatic nucleus. With triethylphosphite and 1a a stable ylide 8 was formed, while the betain 10, expected from 2a and triethylphosphite, immediately gave the trisphosphonate 4a by splitting off ethylene. Attempts to prepare the trisphosphonate 11 gave the phosphate-phosphonate 12, representing a new C-O-phosphoryl rearrangement.

Dicyanomethylenethiiranes from thioketenes and tetracyanoethylene oxide

Reaction of dialkylthioketenes with tetracyanoethylene oxide yields dicyanomethylenethiiranes in a sequence involving [3 + 2] cycloaddition, cycloreversion and rearrangement. In contrast, a thioketene with a sulfide moiety reacts preferentially on the latter to give the stable sulfur ylide 9.

ChemInform Abstract: Synthesis of Highly Stabilised Ylides from N‐(2‐(1,3‐Benzazolylmethyl))pyridinium Salts.

AbstractA series of new stable ylides such as (IV), (VII), (IX) and (XI) are prepared in a two‐phase system.

Synthesis of highly stabilised ylides from N- [2- (1,3-benzazolylmethyl)]pyridinium salts

A series of new stable ylides has been synthesized by the reaction of N-[2-(1,3-benzazolylmethyl)]-pyridinium salts with electrophiles such as carbon disulphide, isothiocyanate derivatives, phenylisocyanate and benzoyl chloride in a two-phase system. Preparation of pyridinium ketene dithioacetal derivatives and attempts to transform them into N-(diheteroarylmethyl)pyridinium ylides are also described.

The wittig reaction of benzofuran-2,3-diones.

The Wittig reaction of benzofuran-2, 3-diones (2), cyclic α-ketoesters, was examined. The reaction of 2 having an electron-donating substituent on the aromatic ring with a stable ylide afforded not 3-alkylidene-2(3H)-benzofuranones (4) but 2-alkylidene-3(2H)-benzofuranones (1) with high regioselectivity.

Triphenylbismuthonio-4,4-dimethyl-2,6-dioxocyclohexane-1-ide and Triphenylbismuthonio-4,4-dimethyl-2,6-dioxo-3,5-dioxan-1-ide. Preparation and Properties of the Stable Bismuthonium Ylides

Abstract The title two bismuthonium ylides were obtained in pure form and their reactions with some electrophiles were studied. In contrast with stable ylides of arsenic and antimony, these bismuthonium ylides readily react with aldehydes and isothiocyanates but they are inert towards ketones.

Generation of sulfur ylides by the desilylation of α-trimethylsilylbenzyl sulfonium salts

The [2,3]-sigmatropic rearrangement of sulfur ylides derived via the desilylation of several α-trimethylsilylbenzyl sulfonium salts has been studied. The initially formed ylide was found to rapidly equilibrate with the thermodynamically more stable ylide. In the absence of trapping reagents, a Sommelet-Hauser type rearrangement occurs.

ChemInform Abstract: Cyclo‐octa(def)carbazole, a New Heterocyclic Paratropic Ring System.

AbstractThe photolysis of the naphthylbenzotriazoles (I) gives the deep red cyclooctacarbazoles (II), a new heterocyclic ring system.