Ylide Intermediates Research Articles

Current Status of Acrylamide Research in Food: Measurement, Safety Assessment, and Formation

Relatively high amounts of acrylamide have recently been reported in carbohydrate-rich foods under low moisture conditions. This sparked intensive investigations into acrylamide, encompassing its occurrence, chemistry, and toxicology/potential health risk in the human diet. Robust and efficient analytical methods have been developed to obtain reliable quantitative data. Recent epidemiological studies failed to evidence an association of cancer incidence and dietary acrylamide exposure. The link of acrylamide in foods to Maillard-type reactions and, in particular, to asparagine has been a major step in elucidating feasible chemical formation routes. Decarboxylation of the Schiff base derived from asparagine and a carbonyl reactant plays a key role in acrylamide formation leading to azomethine ylide intermediates, which offer an attractive mechanistic explanation of the acrylamide amounts found experimentally, including the fact that acrylamide is preferentially formed in the presence of fructose, as compared to glucose or alpha-dicarbonyls. However, the physical state of the reaction system may also affect acrylamide formation by influencing molecular mobility, particularly under low moisture conditions. Current research deals mainly with mitigation studies to reduce acrylamide during food processing and the role of water.

Three‐Component Reaction of Aryl Diazoacetates, Alcohols, and Aldehydes (or Imines): Evidence of Alcoholic Oxonium Ylide Intermediates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Transformations of tetrahydrobenzo[ b][1,6]naphthyridines and tetrahydropyrido[4,3- b]pyrimidines under the action of dimethyl acetylene dicarboxylate

10-Cyanotetrahydrobenzo[ b][1,6]naphthyridines 3 , 4 undergo addition of DMAD, followed by a Stevens rearrangement of the intermediate ylide to yield methyl dioates 8 and 9 . An alternative transformation sequence starts with migration of the dimethyl butenedioate anion to the carbon of the CN group, followed by the addition of 1 mol of water, to provide succinates 10 and 11 . In contrast, tetrahydropyrido[4,3- b]pyrimidines 5– 7 undergo a tandem cleavage process, involving one molecule of solvent. The resulting enamines are easily cleaved by strong acids, to give dihydropyrymidinylethylamines, which are scarcely available by other synthetic means.

Diastereoselective synthesis of dialkyl 4,5,5-triacetyl-3-methylcyclopent-3-ene-1,2-dicarboxylates

Tetraacetylethane (3,4-diacetylhexane-2,5-dione) undergoes a smooth reaction with dialkyl acetylenedicarboxylates in the presence of triphenylphosphine to produce phosphorus ylide intermediates, which undergo a diastereoselective intramolecular Wittig reaction to produce dialkyl 4,5,5-triacetyl-3-methylcyclopent-3-ene-1,2-dicarboxylates in good yields.

The Diastereoselective Synthesis of Quaternary Substituted Thioindolines from Sulfur Ylide Intermediates

The Rh(II)-catalyzed coupling of chiral 2-thiopyranylindoles with vinyl diazoacetates results in the generation of indolines having quaternary substitution at C3 in high diastereoselectivity.

Three-Component Reaction of Aryl Diazoacetates, Alcohols, and Aldehydes (or Imines): Evidence of Alcoholic Oxonium Ylide Intermediates

The Rh(II)-catalyzed three-component reaction of aryl diazoacetates, alcohols and aldehydes was explored, which provided evidence of alcoholic oxonium ylide formation for O-H insertion. A new C-C bond formation reaction where alcoholic oxonium ylides were trapped by electron-deficient aryl aldehydes (or imines) was realized.

Divergence of Carbonyl Ylide Reactions as a Function of Diazocarbonyl Compound and Aldehyde Substituent: Dioxolanes, Dioxolenes, and Epoxides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Pyrroles from 1‐Dialkylamino‐3‐phosphoryl(or phosphanyl)allenes Through 1,5‐Cyclization of Conjugated Azomethine Ylide Intermediates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reactions of dimethoxycarbene with carbon–sulfur double bonds

AbstractUnlike electrophilic carbenes, which react at sulfur to produce thiocarbonyl ylide intermediates, dimethoxycarbene (DMC), generated by thermolysis of an oxadiazoline at 110°C in benzene in a sealed tube, reacts at carbon, possibly to generate a zwitterionic intermediate, or at both carbon and sulfur in a concerted process that generates a thiirane. In case of the strained 2,2,4,4‐tetramethylcyclobutane‐1,3‐dithione (2), an assumed zwitterion undergoes ring expansion. In analogous reactions, unstrained thiones afford thiiranes, possibly by ring closure of the postulated intermediates or by concerted addition. Desulfurization of thiiranes, which occurs spontaneously in some instances, results in the formation of ketene acetals, many of which hydrolyze during workup. O‐Alkyl thioesters and xanthates react to afford products via insertion of the DMC into C—O or C—S bonds, respectively. Copyright © 2004 John Wiley & Sons, Ltd.

Sila-Pummerer rearrangement of cyclic sulfoxides: computational study of the mechanism.

The sila-Pummerer rearrangement of organosilicon cyclic sulfoxides proceeds via the two transition states, the first one with pentacoordinated Si that connects the reagent and the intermediate ylide and the second one that connects the ylide and the product of rearrangement.

Stereoselective Synthesis of Highly Functionalized Trifluoromethylated Cyclobutenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Divergence of carbonyl ylide reactions as a function of diazocarbonyl compound and aldehyde substituent: dioxolanes, dioxolenes, and epoxides.

The products from dirhodium(II) acetate-catalyzed reactions between diazocarbonyl compounds and a series of benzaldehydes demonstrate the extent of competition between intramolecular and intermolecular trapping of carbonyl ylide intermediates and the electronic effects that govern these transformations. With dimethyl diazomalonate, competition exists between dioxolane and epoxide formation so that with p-anisaldehyde only epoxide formation is observed and with p-nitrobenzaldehyde only 1,3-dioxolane products are formed. With methyl diazoacetoacetate, intramolecular trapping of the intermediate carbonyl ylide results in the sole production of dioxolenes. However, the vinyldiazoacetate analogue of methyl diazoacetoacetate, as its tert-butyldimethlsilyloxy derivative, only produces epoxides in its reactions with substituted benzaldehydes.

Synthesis of pyrroles from 1-dialkylamino-3-phosphoryl(or phosphanyl)allenes through 1,5-cyclization of conjugated azomethine ylide intermediates.

1-Dialkylamino-1,3-diaryl-3-diphenylphosphanylallenes 3a-e are thermally converted into a-annulated 3,5-diarylpyrroles 6a-f and [a]-annulated benzo[c]azepines 7a,b,d. These transformations are likely to include conjugated azomethine ylide intermediates that can undergo either a 1,5- or a 1,7-electrocyclization. The periselectivity is markedly shifted toward 1,5-cyclization when the diphenylphosphanyl substituent is replaced by the diphenylphosphoryl group. Thus, 1-dialkylamino-3-(diphenylphosphoryl)allenes 4a-f yield pyrroles 6 exclusively and with improved yields, unless the 3-aryl substituent in the allene is too electron-rich (e.g., benzodioxol-5-yl, 4f --> 7f). The preparation and thermal transformation of aminoallenes 4 over three or four steps can be conducted as a one-pot procedure, thus providing a convenient synthesis of [a]-annulated 3,5-diarylpyrroles from enaminoketones.

1,3‐Dipolar Cycloaddition Reactions of Pyridinium Azomethine Ylides Containing 5,6‐Dicyanopyrazines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of deuterated fatty acids to investigate the biosynthetic pathway of disparlure, the sex pheromone of the gypsy moth, Lymantria dispar.

The preparation and characterization of a series of deuterium-labeled intermediates used in the study of the biosynthetic pathway for disparlure, the sex pheromone of Lymantria dispar, is reported. The synthetic route starts with propargyl alcohol, and the deuterium atoms are introduced by deuteration of an alkyne precursor in the presence of Wilkinson's catalyst. The olefinic bond was created by the Wittig reaction of a suitable aldehyde with a common tetradeuterated phosphonium ylide intermediate. The presence of the expected label and its correct location were confirmed by both MS and 13C NMR. These compounds were successfully used to elucidate the disparlure biosynthetic pathway.

A Novel Three‐Component Reaction Catalyzed by Dirhodium(II) Acetate: Decomposition of Phenyldiazoacetate with Arylamine and Imine for Highly Diastereoselective Synthesis of 1,2‐Diamines.

[reaction: see text] A practical highly diastereoselective synthesis of 1,2-diamines through carbon-carbon bond formation involving an ammonium ylide intermediate is reported for the first time. By treating methyl phenyldiazoacetate with arylamine and imine in the presence of dirhodium acetate, the erythro diastereomer of methyl 1,2-diaryl-1,2-diaminopropanoate is formed with stereochemical preferences greater than 10:1.

Stereoselective Synthesis of Highly Functionalized Trifluoromethylated Cyclobutenes

1,1,1-Trifluoro-4-arylbutan-2,4-diones undergo a smooth reaction with dialkyl acetylenedicarboxylates and triphenylphosphine to produce phosphorus ylide intermediates, which undergo stereoselective intramolecular Wittig reaction to produce dialkyl 4-arylcarbonyl-3-trifluoromethyl-cyclobut-2-ene-1,2-dicarboxylates in good yields.

Cascade Transformations of (2,2‐Diaryl‐3,3‐dichloroaziridin‐1‐yl)acetates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

1,3-Dipolar Cycloaddition Reactions of Pyridinium Azomethine Ylides Containing 5,6-Dicyanopyrazines

The intermolecular 1,3-dipolar cycloaddition reaction of azomethine ylides with carbon-carbon double or triple bonds represents an efficient and convergent method for the construction of heterocyclic structures containing a single nitrogen atom. 1 One of the most frequently employed methods for the generation of azomethine ylide involves the thermolysis of an aziridine. 2 However, the ring opening of aziridines to azomethine ylides is limited to those having substituent groups capable of stabilizing the dipole centers. Desilylation of α-trimethylsilylonium salts represents another convenient method of generating azomethine ylide. 3 More recently it has been found that nonstabilized azomethine ylides can be generated by the deprotonation of amine Noxides. 4 Azomethine ylides are too unstable to be isolated, and are typically used in situ. Of the various types of azomethine ylides, the pyridinium azomethine ylides are among the most attractive synthetically because they are easily prepared from the appropriate N-alkylpyridinium salt with base and their cycloadducts, the indolizines, have been used as synthetic building blocks. 5 In our continuing efforts to develop functional dyes based on dicyanopyrazine chromophores, we have become interested in pyridinium azomethine ylides containing dicyanopyrazines and their 1,3-dipolar cycloaddition reaction with dipolarophiles, because the indolizine cycloadducts, containing dicyanopyrazines, might meet our purpose. Dyes and pigments generally possess satisfactory color, and good color fastness properties against light and heat, and additional properties such as near infrared absorption, pleochroism, and photoconductivity. 6 The majority of these properties are caused by intramolecular charge-transfer interactions involving π-electrons and intermolecular π-π interactions of the dye chromophores. 7 In this paper, we report the generation of pyridinium azomethine ylide intermediates and the results of 1,3-dipolar cycloaddition reactions of the ylides with dipolarophiles to provide indolizines containing 5,6-dicyanopyrazine. The preparation of methyl or phenyl substituted 2-bromomethyl5,6-dicyanopyrazine 1 is described in a previous report. 6b

A theoretical rationalization of the asymmetric induction in sulfinyl-directed [5C + 2C] intramolecular cycloadditions.

A computational DFT examination (B3LYP/6-31G and B3LYP/6-311+G//B3LYP/6-31G) of the thermal [5C + 2C] cycloaddditions of 6-acetoxy-3-pyranones and 3-silyloxy-4-pyrones with tethered alkenyl sulfoxides confirms that the high level of diastereofacial selectivity obtained is ultimately due to the preference of the alkenesulfinyl group to adopt a well-defined conformation in the transition state of the reaction. This conformation, which is different from that found in the ground state, is most probably dictated by dipolar interaction effects between the sulfoxide and the oxidopyrylium ylide intermediate.