Showing papers on "Ylide published in 1993"
TL;DR: The ylidic properties of 1,3,4,5,tetramethyl-2-methyleneimidazoline 4, obtained by deprotonation of the pentamethylimidazolium ion 3, are revealed both by its physical and chemical properties; the X-ray structure of 4 is reported as discussed by the authors.
Abstract: The ylidic properties of 1,3,4,5-tetramethyl-2-methyleneimidazoline 4, obtained by deprotonation of the pentamethylimidazolium ion 3, are revealed both by its physical and chemical properties; the X-ray structure of 4 is reported.
142 citations
TL;DR: It was determined that two fluorine substituents, ortho and ortho' substituted relative to the azide group, are required to retard ring expansion and allow bimolecular capture of the singlet nitrene.
116 citations
TL;DR: In this paper, a cycloadduct was formed via a pyridinium ylide formed by attack of the nitrogen lone pair on the electrophilic keto carbenoid.
Abstract: The Rh(II)-catalyzed reaction of a-diazoacetophenone in the presence of 2-(methylthio)pyridine and dimethyl acetylenedicarboxylate gave 3-benzoyl-3,5-dicarbomethoxy-3,5-dihydro-5-(methylthio)indolizine. The formation of the cycloadduct proceeds via a pyridinium ylide formed by attack of the nitrogen lone pair on the electrophilic keto carbenoid. A related cyclization occurred using 1-diazo-3-[(2-pyridyl)thio]-2-propanone
86 citations
TL;DR: In the presence of suitable rhodium(II) catalysts, lactam derived β-ketosulfoxonium ylides can be transformed to β-oxonitrogen heterocycles, e.g. substituted 4-oxopyrrolidine, viaintermediates of carbenoid nature.
Abstract: In the presence of suitable rhodium(II) catalysts, lactam derived β-ketosulfoxonium ylides can be transformed to β-oxonitrogen heterocycles, e.g. substituted 4-oxopyrrolidine, viaintermediates of carbenoid nature.
81 citations
77 citations
TL;DR: In this paper, it was shown that diphenylacetylene is oxidized by oxo(salen)chromium(V) triflate and related complexes to form 1,2-diones.
Abstract: Alkyner are oxidized by oxo(salen)chromium(V) triflate and related complexes 2 to form 1,2-diones. The oxidation of diphenylacetylene proceeds by formation of an intermediate which reacts more rapidly with a second equivalent of oxometal complex to form benzil. The intermediate is most likely a metallaoxetene or a related species, such as a metallocarbene. Reactions of phorphorus or nitrile ylides with 2 proceed to form carbonyl compounds (and phosphine oxide or nitrile) in a manner consistent with participation of Similar intermediates. The reactions appear to be related mechanistically to alkene epoxidation by the same oxometal complexes
57 citations
TL;DR: In this article, a range of diazocarbonyl compounds containing two different functional groups has been prepared, and their rhodium(II) catalysed decomposition studied as a means of probing the chemoselectivity of carbenoid intermediates.
47 citations
TL;DR: In this article, a rearrangement is induced which includes a proton migration from an endo-to the exocyclic CH2 group to give 5-methyl-1,1,3,3-tetraphenyl-1λ5,2λ3, 3,3λ51-triphosphinine (5), a novel 1,2,3 triphosphabenzene species.
Abstract: 1,1-Bis[(diphenylphosphanyl)methyl]ethene (3) reacts with PCl3 or AsCl3 in the presence of SnCl2 as a reducing agent to form cationic heterocycles in which the two newly generated phosphonium centers are bridged by two-coordinate, negatively charged phosphorus (4a) or arsenic (4b) centers. Hexachlorostannate(IV) dianions function as counterions to these heterocycles, in which the exocyclic methylene group is retained. By treatment of 4a with a base a rearrangement is induced which includes a proton migration from an endo-to the exocyclic CH2 group to give 5-methyl-1,1,3,3-tetraphenyl-1λ5,2λ3,3λ51-triphosphinine (5), a novel 1,2,3-triphosphabenzene species. The reaction of the arsenic compound 4b with base did not yield the corresponding arsa-diphosphabenzene, but gave only decomposition products. Compound 4b · 0.5 CH3CN has been studied by X-ray crystallography. The six-membered heterocycle shows a chair conformation with an arsenic atom solely coordinated by two phosphorus atoms at roughly equal distances with a sharp angle P – As – P of only 93.0(1)°.
45 citations
TL;DR: In this paper, a Wittig reaction with a-chloro, a-bromo and a-iodo ylides derived from (2-MeOCH2C6H4)3P was used to obtain enol ethers with remarkably high cis/trans ratios.
43 citations
TL;DR: In this article, the Wittig reaction of nonstabilized ylides with benzaldehyde and benzophenone was investigated by means of carbonyl 14 C kinetic isotope effects, substituent effects, and isotope-scrambling and probe experiments.
Abstract: The Wittig reaction of nonstabilized ylides with benzaldehyde and benzophenone was investigated in detail by means of carbonyl- 14 C kinetic isotope effects, substituent effects, and isotope-scrambling and probe experiments. The reaction with benzophenone gave the carbon isotope effects and the Hammett p values of considerable magnitude both in Li salt-free and salt-present conditions. In contrast, they are quite small for the reaction with benzaldehyde. Enone-isomerization and dehalogenation probe experiments indicated that the nonstabilized ylide has enough ability to transfer an electron to benzaldehyde and benzophenone
40 citations
TL;DR: In this paper, a concise approach to the synthesis of anti-tumor compound, goniofufurone, starting from dialdo-xylose is described starting from the Wittig reaction of the title ylide.
TL;DR: The rhodium(II) carboxylate catalyzed decomposition of several α-diazo esters and amides has been studied in this article, where a series of 5-keto-1diazos acetates were prepared by acylation of α-hydroxy ketones using the (p-toluenesulfonyl)hydrazone of glyoxylic acid chloride.
Abstract: The rhodium(II) carboxylate catalyzed decomposition of several α-diazo esters and amides has been studied. A series of 5-keto-1-diazo acetates were prepared by acylation of α-hydroxy ketones using the (p-toluenesulfonyl)hydrazone of glyoxylic acid chloride. Treatment of these compounds with Rh(II) acetate afforded products derived from carbenoid insertion into solvent. When the hydrogen atom of the diazo carbon was replaced with an electron-withdrawing substituent, smooth cyclization occurred to produce a carbonyl ylide dipole which was subsequently trapped with different dipolarophiles. A series of N-alkyl-2-diazo-π-oxobutylamides, when treated with a catalytic quantity of rhodium(II) acetate, gave furo[3,4-c] furans in good yield. The reaction proceeds via addition of a rhodium stabilized carbenoid onto the acetylenic π-bond to give a vinyl carbenoid which subsequently cyclizes onto the neighboring carbonyl group to produce the furan ring. N-Alkynyl-substituted 2-diazoacetamides were also found to cyclize onto the tethered alkyne unit. The resulting rhodium carbenoid can undergo intramolecular and bimolecular cyclopropanation depending on both electronic and conformational factors. Rotamer population of the starting diazoamide was also found to influence product distribution
TL;DR: In this article, the energy barrier of P-chlorinated phosphorus ylides was estimated by NMR techniques and shown to be at least 83 kJ mol−1 for the rotation around the PC.
Abstract: Halide abstractions from P-chlorinated phosphorus ylides 9a–c either by AlCl3 or SnCl2 yield unsymmetrical methylene phosphonium ions 10a–c in which energy barriers > 83 kJ mol–1 for the rotation around the PC have been estimated by NMR techniques. The salts with AlCl4– counteranions are stable, but compounds with SnCl3– anions decompose stereoselectively to unsymmetrical methylene phosphanes, SnCl2, and ButCl.
TL;DR: The key intermediate 2b for 3,5-cyclovitamin D ring A synthon 13 was prepared in 80% yield as a diastereomeric mixture (70:30) via intramolecular cyclopropanation from iodonium ylide 10b.
TL;DR: In this article, the reactions of WCl 2 (NPh)(PMePh 2 ) 3 with a number of triphenylphosphoranes were surveyed, and alkylidene transfer was observed for variously substituted aryl ylides.
Abstract: The reactions of WCl 2 (NPh)(PMePh 2 ) 3 with a number of triphenylphosphoranes were surveyed, and alkylidene transfer to give W(=CHR)Cl 2 (NPh)(PMePh 2 ) 2 was observed for variously substituted aryl ylides Ph 3 =CHAr', where Ar'=C 6 H 5 , C 6 H 4 -p-Me, C 6 H 4 -m-Me, C 6 H 4 -o-Me, C 6 H 4 -p-OEt, C 6 H 4 -o-OMe, C 6 H 4 -p-CF 3 , C 6 F 5 , o-Np, and m-Np, for the vinyl ylide Ph 3 P=CH-CH=CMe 2 , and also for the bis(ylide) Ph 3 P=CH-C 6 H 4 -C 6 H 4 -CH=PPh 3 . A mechanism is proposed for the transfer reaction
TL;DR: In this article, a scheme reminiscent of Wallach's imidazole synthesis starting from N.N′-dialkyloxamides was described, which support a mechanism involving nitrite ylide species and allow a better understanding of the Wallach reaction.
Abstract: The reaction of the N-benzylamides of N-heterocyclic carboxylic acids 3 and 6–9 with phosphorus pentachloride affords heterocondensed imidazoles 4 and 10–14 by a scheme reminiscent of Wallach's imidazole synthesis starting from N.N′-dialkyloxamides. Kinetic and labelling experiments are described which support a mechanism involving nitrite ylide species and allow a better understanding of the Wallach reaction. The limiting parameter for the formation of heteroanellated imidazoles is the electron availability of the heterocyclic ring.
TL;DR: In this paper, an intermediate thiocaronyl ylide of type E (Scheme 4), generated by the 1.3-dipolar cycloaddition of diazomethane with the exocyclic CS bond of 1 and elimination of N2, has been established by X-ray crystallography.
Abstract: Reaction of 1,3-Thaiazole-5(4H)-thiones and Diazometane
Reaction of 4,4-dimethyl-1,3-thiazol-5(4H)-thiones 1 with diazomethane in Et2O at −78° or 0° leads to a mixture of the corresponding 1,4-dithiane 10,1,3-dithiole 11, thiirane 12, 4,5-dihydro-5methylidene-1,3-thiazole 13, and 1,3-thiazol-5(4H)-one 14 (Scheme 3). The structures of 10a, 11a, and 11bhave been established by X-ray crystallography. The formation of the products can be explained via an intermediate thiocaronyl ylide of type E (Scheme 4), generated by the 1.3-dipolar cycloaddition of diazomethane with the exocyclic CS bond of 1 and elimination of N2. Head-to-head dimerization of E yields 10, 1, 3-dipolar cycloaddition of E and 1 gives the ‘Schonberg product’ 11, and cyclization of E leads to 12, which undergoes a desulfurization to give 13. The thiazolone 141 is formed by hydolysis of E. The similarity of the ratio of the products at −78° and at 0° shows that, in contrast to the reaction of 1 and 2-diazopropane, the elimination of N2 in the primary cycloadduct already occurs at −78°.
TL;DR: In this article, a possible reaction pathway is proposed in order to explain the reactivity of cyclic 7-membered β-diketones with two different carbonyl groups with alkynes and nitriles under mild conditions.
Abstract: The reactions of phenyliodonium ylides of cyclic 7-membered β-diketones bearing two different carbonyl groups with alkynes and nitriles under mild conditions lead to cyclization products and exhibit remarkable regioselectivity. A possible reaction pathway is proposed in order to explain this reactivity
TL;DR: The authors derived from α-amino esters, undergo cycloaddition reactions as stabilized ylides, with imines in good yields, with a good yield of 1.
TL;DR: The mesoionic thioisomuchnone system was prepared from the rhodium(II) acetate catalyzed cyclization of a diazothioamide and was found to undergo smooth 1,3-dipolar cycloaddition with N-phenylmaleimide as discussed by the authors.
Abstract: The mesoionic thioisomuchnone system was prepared from the rhodium(II) acetate catalyzed cyclization of a diazothioamide and was found to undergo smooth 1,3-dipolar cycloaddition with N-phenylmaleimide. In contrast to this system, the rhodium(II) reaction of an α-diazo-β-oxo ester containing a thiocarbonyl group produced a cyclic thiocarbonyl ylide which extruded sulfur from a transient episulfide intermediate
TL;DR: In this article, the title compounds were synthesized from the mono-diEt-acetal of acetyleneddicarbaldehyde and 2-thioxo-1,3- dithioles through three key steps: cycloaddition, dimerization-desulphurization of the resulting thials, and after deketalization, fourfold Wittig olefination of the tetraformyl TTF-vinylogs 4 with the P-ylids Wα-γ bearing the 1,3dithiol-2
TL;DR: A series of 1,3-bis(1H-azol-1-yl)-2-aryl-2-propanols 17 were synthesized in an one-pot procedure by reacting l-aryl 2-(1,2,4-triazol)-l-yl) with dimethylsulfoxonium methide as mentioned in this paper.
TL;DR: In this paper, a series of fluorinated aryl azides and fluorinated azidobenzoates were studied by laser flash photolysis techniques, and it was determined that two fluorine substituents, ortho and ortho' substituted relative to the azide group, are required to retard ring expansion and allow bimolecular capture of the singlet nitrene.
Abstract: A series of fluorinated aryl azides and fluorinated azidobenzoates were studied by laser flash photolysis techniques. Using the pyridine ylide probe method it was possible to determine whether a singlet nitrene or ring-expanded ketenimine ylide is the trappable intermediate that is generated at ambient temperature. It was determined that two fluorine substituents, ortho and ortho' substituted relative to the azide group, are required to retard ring expansion and allow bimolecular capture of the singlet nitrene. LFP of ortho, ortho' difluorinated aryl azides in methanol produces the ground triplet state of the nitrene. The results are consistent with chemical analysis of reaction mixtures. The implications of this data for the design of photoaffinity labeling reagents are discussed.
TL;DR: In this article, Wittig olefination with various alkylidene triphenylphosphoranes in high E:Z selectivities (90:10 − 97:3) and without racemization of the α-silylaldehydes.