Kinetic and mechanistic study on the thermal reactivity of stabilized phosphorus ylides,part 3: [(Acetyl)(arylcarbamoyl)methylene]triphenylphosphoranes and [(alkoxycarbonyl)(arylcarbamoyl)methylene]triphenylphosphoranes and their thiocarbamoyl analogues

A series of five [(acetyl)(arylcarbabmoyl)methylene]triphenyl‐phosphoranes 1a–e and their thiocarbamoyl analogues 2a–e , [(alkoxycarbonyl)(arylcarbamoyl)methylene]triphenylphosphoranes 3a–e and their thiocarbamoyl analogues 4a–e were prepared and fully characterized. All ylides are found under conditions of flash vacuum pyrolysis to fragment giving arylisocyanate or isothiocyanate and acetyl ylides or alkoxy ylides which undergo thermal extrusion of Ph₃PO. A kinetic study shows that these reactions are unimolecular and are of first‐order nature with no significant substituent effect. The thiocarbamoyl ylides 2 react from 4.6 to 42 times faster than their carbamoyl ylides 1 , while the thiocarbamoyl ylides 4 react from 6.6 to 20.9 times faster than their carbamoyl ylides 3 . © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 6–16, 2007     

Reaction of chromone-3-carbaldehyde with α-amino acids—syntheses of 3- and 4-(2-hydroxybenzoyl)pyrroles

Azomethine ylides generated from the reaction of chromone-3-carbaldehyde with α-amino acids undergo 1,5-electrocyclization reactions to afford 3- and 4-(2-hydroxybenzoyl)pyrroles. These ylides can be trapped with dipolarophiles in 1,3-dipolar cycloaddition reactions to yield chromonyl pyrrolidines. The reaction of chromone-3-carbaldehyde with methyl glycinate gives a mixture of pyrrole, pyridine, and 3-aza-9-xanthenone derivatives.     

Synthesis of 2-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-carbonyl)-6,6-dimethyl-3-phenyl-3,5,6,7-tetrahydro-2H-benzofuran-4-one Derivatives via Multicomponent Reaction

A sequential one-pot, two-step reaction for an efficient preparation of 2-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-carbonyl)-6,6-dimethyl-3-phenyl-3,5,6,7-tetrahydro-2H-benzofuran-4-one derivatives has been described. One-pot reaction of in situ–formed benzopyran-substituted pyridinium ylides with aromatic aldehydes and dimedone gives corresponding 2,3-dihydrofurans in good yields. The structures of all the newly synthesized compounds were confirmed from their analytical and spectral data.     

The behavior of 2‐thioxo‐4‐thiazolidinones toward organophosphorus reagents

The reaction of 2‐thioxo‐4‐thiazolidinone ( 1a ) with phosphorus ylides 2a and 2b afforded compounds 5 and 6. On the other hand, formylmethylenetriphenylphosphorane (2c) reacts with 1a and its N‐methyl derivative 1b to give the new complicated phosphonium ylides 7a,b, respectively. Reactions of 1b with ylides 2a and 2d gave rise to the olefinic compound 8 and the new phosphorane product 9. Moreover, dialkyl phosphites 3a,b and trialkyl phosphites 4a–c react with 1a to give both the alkylated products 10a–c and the dimeric compounds 11,12. A mechanism is proposed to explain the formation of the new products.© 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 337–341, 1999     

4-Methylpyrimidinium ylides. Part 7: 3+2 Dipolar cycloadditions to non-symmetrical substituted alkenes and alkynes

The ability of 4-methylpyrimidinium ylides (as 1,3-dipoles) to react with activated non-symmetrical substituted dipolarophiles (alkenes and alkynes) is presented. 4-Methylpyrimidinium ylides did not react with alkenes. With alkynes the reactions are regiospecific, a single regioisomer being obtained. A possible mechanism for the reaction pathway is proposed. For the first time in the pyrimidinium ylides series both isomers resulting from bonding to the 2-and 6-positions of the heterocycle ring were obtained. The appropriate conditions in order to increase the selectivity of one of the isomers were determined.     

2-氟中氮茚衍生物的合成及表征

2-氟中氮茚衍生物的合成及表征;偶极反应;二氟乙烯基对甲苯磺酸酯;氟中氮茚;反应机理     

2-quinoxalinylnitrenes and 4-quinazolinylnitrenes: rearrangement to cyclic and acyclic carbodiimides and ring-opening to nitrile ylides

This work was undertaken with the aim to obtain direct evidence for the interrelationships between hetarylnitrenes, their ring-expanded cyclic carbodiimide isomers, and ring-opened nitrile ylides. Tetrazolo[1,5-a]quinoxaline 11T and tetrazolo[5.1-c]quinazoline 13T undergo valence tautomerization to the corresponding azides 11A and 13A on mild flash vacuum thermolysis (FVT). Photolysis in Ar matrixes at ca. 15 K affords the triplet nitrenes 12 and 14, identified by ESR, UV, and IR spectroscopy. The nitrenes are converted photochemically to the seven-membered ring carbodiimide 15 followed by the open-chain carbodiimide 22. The 3-methoxy- and 3-chloro-2-quinoxalinylnitrenes 24 yield the ring-expanded carbodiimides 26 very cleanly on matrix photolysis, whereas FVT affords N-cyanobenzimidazoles 28. The ring-opened nitrile ylides 36 and 49 are identified as intermediates in the photolyses of 2-phenyl-4-quinazolinylnitrene 32 and 7-nitro-2-phenyl-4- quinazolinylnitrene 47. In these systems, a photochemically reversible interconversion of the seven-membered ring carbodiimides 35 and 48 and the nitrile ylides 36 and 49 is established. Recyclization of open-chain nitrile ylides is identified as an important mechanism of formation of ring contraction products (N-cyanobenzimidazoles).     

The behavior of 2-chloroquinoline-3-carbaldehyde and 2-oxoquinoline-3-carbaldehyde toward stabilized methylenetriphenylphosphoranes and secondary amines

In this study use was made of the Wittig carbonyl olefination reaction and stereo-identification of the resulting alkenes. Condensation of 2-chloroquinoline-3-carbaldehyde with some selected stabilized phosphonium ylides yielded a mixture of the corresponding E and Z olefins in each case. On the other hand reaction of 2-oxoquinoline-3-carbaldehyde with the selected ylides afforded the respective olefins only in one of the possible stereoisomers. The reaction of 2-chloroquinoline-3-carbaldehyde with acetylmethylenetriphenylphosphorane produced the respective olefine together with acridin-3-ol. Heating of (E) and/or (Z)-methyl 3-(2-chloroquinolin-3-yl)acrylate with hydrazine hydrate yielded the corresponding propan-1-ol derivative. Dechlorination of (E)-ethyl 3-(2-chloroquinolin-3-yl)acrylate and/or (E)-4-(2-chloroquinolin-3-yl)but-3-en-2-one was effected upon treatment with morpholine or piperidine in absolute ethanol to give the respective enone derivatives.     

Observable azacyclobutenone ylides with antiaromatic character from 2-diazoacetyl-azaaromatics

Azacyclobutenone ylides 2 and 11 were generated in solution by laser flash photolysis of 2-diazoacetylpyridine (1) and 3-diazoacetylpyridazine (10), respectively, together with the corresponding ketenes. The ylides were identified by their characteristic IR and UV spectra: 2, nu (CH3CN) 1725 cm(-1), lambdamax 360 and 550 (br) nm; 11, nu (CH3CN) 1776 cm(-1), lambdamax 370 and 550 (br) nm. 2-Triisopropylsilyldiazoacetylpyridine 20 upon photolysis at 5 degrees C in CH3CN forms the ylide 21 as a rather persistent (T1/2 2 h at 25 degrees C) purple solution, nu (CH3CN) 1718 cm(-1), lambdamax 245, 378 and 546 (br) nm, but no ketene is observed. Quinolyl ylide 14 and pyridyl ylides 17 and 19 with Me and 2-pyridyl substituents, respectively, with characteristic IR and UV spectra were also generated. The 1H NMR spectrum of the pyridyl ring of 21 shows substantial upfield shifts relative to those of 20. Calculated nucleus-independent chemical shifts (NICS) for 2, 11, and 21 are comparable to those for benzocyclobutadiene (22) and benzocyclobutenone enolate (23), with substantial positive values for the 4-membered rings, while the NICS values for the 6-membered rings are significantly more positive than for benzene or pyridine. Significant bond alternation is also found in the calculated ylide structures, and these results suggest strong antiaromatic character for the 4-membered rings of 2, 11, 14, 17, 19, and 21, and greatly reduced aromatic character for the 6-membered rings.     

Synthesis and characterization of bromonium ylides and their unusual ligand transfer reactions with N-heterocycles

Stable aliphatic bromonium ylides (RfSO2)2C--Br+C6H4-p-CF3 (Rf = CF3, CF3(CF2)3) have been synthesized and structurally characterized for the first time. X-ray crystallographic analyses indicated a ylide structure with an sp2 hybridization of the ylide carbanions and with little double-bond character for the ylidic bond. The bromonium ylides selectively undergo transfer of the aryl group to nitrogen heterocycles, such as pyridines, yielding N-arylpyridinium salts. This is in a marked contrast to the reaction of the iodonium ylides, which produces pyridinium ylides through transylidations.     

Reaction of difluorocarbene with 2H-azirines: generation and transformations of strained azomethine ylides -- aziriniodifluoromethanides

The reaction of difluorocarbene with azirines affords a new type of azomethine ylides, viz., strained aziriniodifluoromethanides. 1,3-Dipolar cycloadditions of ylides derived from 2-unsubstituted 3-arylazirines to dimethyl acetylenedicarboxylate and aldehydes give derivatives of 2,2-difluoro-1-azabicyclo[3.1.0]hex-3-ene-3,4-dicarboxylic acids and 1,4-oxazin-3(4H)-ones, respectively. Ylides derived from 2-mono- and 2,2-disubstituted azirines undergo isomerization to 2-aza-1,3-diene derivatives. 2,2-Difluoro-1-azabicyclo[3.1.0]hex-3-enes are transformed into 2-fluoropyridine derivatives in high yields and react with amines to give 2,4-diamino-1-azabicyclo[3.1.0]hex-2-ene derivatives.     

Synthesis of carbocyclic hydantocidins via regioselective and diastereoselective phosphine-catalyzed [3 + 2]-cycloadditions to 5-methylenehydantoins

The phosphine-catalyzed [3 + 2]-cycloaddition of 5-methylenehydantoins 4 with the ylides 5, derived from addition of tributylphosphine to the 2-butynoic acid derivatives, 6a-d, gives spiro-heterocyclic products. The camphor sultam derivative 6b gives optically active products. Noteable was that the ylides derived from ethyl 2-butynoate and the 3-(2-butynoyl)-1,3-oxazolidin-2-one derivatives 6c and 6d gave spiro-heterocyclic products with reverse regioselectivities. The N,N-dibenzylprotected cycloadduct has been converted to carbocyclic hydantocidin and 6,7-diepi-carbocyclic hydantocidin.     

Pyranderivate durch [4+2]-cycloaddition zwischen α,β-ungesättigten carbonylverbindungen und phosphacumulenyliden

δ,β-unsaturated carbonyl compounds 1 and phosphacumulene ylides 2 undergo a [4+2]-cycloaddition with formation of pyran-substituted phosphoranes 3. Benzoic acid catalysed Hofmann degradation of 3 yields the deeply coloured pyran derivatives 5.     

ZnCl2-Catalyzed [4+1] Annulation of Alkylthio-Substituted Enaminones and Enaminothiones with Sulfur Ylides

Concise construction of furan and thiophene units has played an important role in the synthesis of potentially bioactive compounds and functional materials. Herein, an efficient Lewis acid ZnCl₂ catalyzed [4+1] annulation of alkylthio-substituted enaminones is reported, that is, α-oxo ketene N,S-acetals with sulfur ylides to afford 2-acyl-3-aminofuran derivatives. In a similar fashion, [4+1] annulation of the corresponding enaminothiones, that is, α-thioxo ketene N,S-acetals, with sulfur ylides efficiently proceeded to give multisubstituted 3-aminothiophenes. This method features wide substrate scopes as well as broad functional group tolerance, offering a concise route to highly functionalized furans and thiophenes.     

The behavior of 2‐substituted‐1,3‐diphenylpropane‐1,3‐tione toward organophosphorus reagents

The reaction of 2‐benzylidene‐1,3‐diphenylpropanetrione ( 1a ) with phosphorus ylides 2a–c afforded the new phosphonium ylides 4a–c . Trialkyl phosphites 3a–c react with 1a to give the respective dialkyl phosphonate products 5a–c . On the other hand, the olefinic compounds 6 and 7 were isolated from the reaction of 1b with Wittig reagents 2 . Moreover, trialkyl phosphites reacted with 1b to give products 8a–c . Possible reaction mechanisms are considered, and the structural assignments are based on analytical and spectroscopic evidence. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:57–64, 2000     

Copper‐Catalyzed Formal [4+2] Cycloaddition of Enoldiazoimides with Sulfur Ylides

Enoldiazoimides, a new subclass of enoldiazo compounds, generate enol‐substituted carbonyl ylides whose reactions with sulfur ylides enable an unprecedented formal [4+2] cycloaddition. The resulting multifunctionalized indolizidinones, which incorporate sulfur, are formed in good yields under mild reaction conditions. The uniqueness of this transformation stems from the role of the silyl‐protected enol, since the corresponding acetyldiazoimide failed to provide any cross‐products in metal‐catalyzed reactions with sulfur ylides. This copper‐catalyzed cycloaddition is initiated with the generation of enol‐substituted carbonyl ylides and sulfur ylides from enoldiazoimides and sulfonium salts, respectively, and proceeds through stepwise six‐membered ring formation, C?O and C?S bond cleavage, and silyl and acetyl group migration.     

Organosulfur phosphonium salt-mediated synthesis of functionalized thiopyran derivatives

Methyl 4-oxotetrahydro-2H-thiopyran-3-carboxylate as a CH-acid undergoes a mild reaction with acetylenic esters in the presence of triphenylphosphine to produce phosphorus ylides possessing thiopyran-4-one ring moiety. The resulted phosphorus ylides when heated in toluene afforded functionalized thiopyran derivatives through intramolecular Wittig reaction.     

Synthesis of Amino Acid Derived Cyclic Phosphorus Ylides

Abstract

We recently reported the thermal elimination of Ph₃PO from suitably protected aminoacyl ylides 1 as a route to acetylenic amino acid analogues 2. Pyrolysis of ylides such as 3 with a free amino group takes a different course. Ethanol is eliminated to give the c h i d cyclic ylides 4 which can be viewed as 3-triphenylphosphoranylidene tetramic acids. Specific examples prepared include 4 (R = Me, Pri), the parent compound 5 (from glycine) and the six-membered ring compound 6 (from p-alanine). Using a similar approach, bicyclic ylides such as 7 (from proline) can be prepared. In the case of the glutamate derived ylide 8, thermolysis initially gives a mixturc of 9 and 10 but these both cyclise to the bicyclic product 11 with time. The structure and reactivity of these interesting cyclic ylides are now being examined.     

Synthesis of spirooxindoles bearing 2,3-(or 2,5-)dihydrothiophene-2-thione moiety via [3+2] annulation of carbon disulfide with Morita-Baylis-Hillman carbonates of isatins

Various spirooxindoles bearing 2,3-(or 2,5-)dihydrothiophene-2-thione moiety have been synthesized via [3+2] annulation reaction of carbon disulfide and the nitrogen ylides derived from Morita-Baylis-Hillman carbonates of isatins. 2,3-Dihydro- and 2,5-dihydrothiophene-2-thione moieties were formed selectively depending on steric hindrance around the nitrogen ylides.     

[3+2]- Versus [4+2]-cycloaddition reactions of 3-methylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)acrylonitriles with N-substituted maleimides involving pyrrolidine-derived azomethine ylides

3-Methylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)acrylonitriles do not enter into [4+2]-cycloaddition reactions with maleimides to form the expected pyrrolo-pyridazines. Instead the formation of novel pyrrolo-pyridazines of type 4 takes place via a formal [3+2]-cycloaddition of initially formed pyrrolidine-derived azomethine ylides 7. The mechanism leading to the final product is discussed.