Chemoselective Synthesis of Stable Phosphorus Ylides from 6-Azauracil and Mechanistic Investigation of the Reaction by UV Spectrophotometry

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of NH-acids such as 6-azauracil. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon–carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. To determine the kinetic parameters of the reactions, they were monitored by UV spectrophotometry. The second order fits were automatically drawn, and the values of the second order rate constants (k₂) were automatically calculated using standard equations. At the temperature range studied, the dependence of the second order rate constant (Ln k₂) on reciprocal temperature was in agreement with the Arrhenius equation. This provided the relevant plots to calculate the activation energy of all the reactions. Furthermore, useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also concentration of reactants on the rate of reactions. The proposed mechanism was confirmed according to the obtained results, and a steady-state approximation and first step (k₂) of the reaction was recognized as a rate-determining step on the basis of experimental data.     

NMR study,theoretical calculations for assignment of the Z‐ and E‐isomers,and kinetics investigation of stable phosphorus ylides involving a 2‐mercapto‐4,6‐dimethyl pyrimidine

In the present work, NMR, theoretical, kinetics, and mechanism investigations were undertaken for a one‐pot condensation reaction between 2‐mercapto‐4,6‐dimethyl pyrimidine and dialkyl acetylenedicarboxylates in the presence of triphenyphosphine containing novel stable phosphorus ylides 4a–c . Herein, theoretical calculations have been employed for assignment of the most stable isomers (Z or E) of phosphorus ylides 4a,c by natural population analysis, atoms in molecules methods, and CHelpG keyword, in which E‐ 4(a, c) are more stable forms as the majors. The ¹H, ¹³C, and ³¹P NMR data of these ylides are consistent with results obtained from theoretical calculations. In addition, kinetic investigation of new ylides was undertaken by ultraviolet spectrophotometry. Useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also the concentration of reactants on the rate of reactions. The proposed mechanism was confirmed according to the obtained results and a steady‐state approximation, and the first step (k₂) of the reaction was recognized as a rate‐determining step on the basis of the experimental data. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:462–474, 2010; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20632     

Kinetics and Mechanism of the Reactions Between Triphenylphosphine,Dialkyl Acetylenedicarboxilates and a NH-Acid,Pyrazole, by UV Spectrophotometry

Kinetic studies were made of the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of a NH-acid such as pyrazole. To determine the kinetic parameters of the reactions, the reaction progress was monitored by UV spectrophotometry. The second-order fits were automatically drawn and the values of the second-order rate constant (k ₂) were automatically calculated using standard equations. In the temperature range studied, the dependence of ln k ₂ on the reciprocal temperature was consistent with the Arrhenius equation. Furthermore, useful information was obtained from studies of the effect of solvent, structure of the reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also the concentration of reactants on the rate of reaction. The mechanism was confirmed to involve a steady-state condition with the first step of the reaction being the rate-determining step.     

UV spectrophotometric study of the kinetics and mechanism of the reactions between triphenylphosphine, dialkyl acetylenedicarboxylates and NH-acid

To determine the kinetic parameters of the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of an NH-acid, such as 2,3-di-hydroxybenzaldehyde, the reactions were monitored by UV spectrophotometry. The second order fits were automatically drawn and the values of the second order rate constants (k₂) were calculated using standard equations as part of the program. The dependence of the second order rate constant (lnk₂) on the reciprocal temperature was in agreement with the Arrhenius equation, in the temperature range studied, providing the relevant plots to calculate the activation energy of all reactions. Furthermore, we evaluated the effects of solvent, structure of different alkyl groups within the dialkyl acetylenedicarboxylates, and their concentration on the rates of reactions. The proposed mechanism was confirmed by experimental results and steady-state approximation. The first step (k₂) of the reaction was recognized as the rate determining step on the basis of experimental data.     

Kinetic Investigation of the Reaction between Triphenylphosphine,Dialkyl Acetylenedicarboxylate,and Carbazole by the UV Spectrophotometry Technique

The major objectives of the work undertaken were to carry out kinetic studies of the reaction between triphenylphosphine and dialkyl acetylenedicarboxylate in the presence of strong NH-acids, such as carbazole. To determine the kinetic parameters of the reaction, it was monitored by the UV spectrophotometer technique. The values of the second order rate constant (k ₂ ) were automatically calculated using standard equations within the program when the second order fits of the mentioned reactions were automatically drawn by the software associated with a Cary UV spectrophotometer model Bio-300 at an appropriate wavelength. At the temperature range studied, the dependence of the second order rate constant (Ln k) on reciprocal temperature was in agreement with the Arrhenius equation. This provided the relevant plots to calculate the activation energy of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent and different alkyl groups within the dialkyl acetylenedicarboxylates on the rate of reactions.     

Kinetics and Mechanism Investigation of the Reaction between Triphenylphosphine, Di-tert-butyl Acetylenedicarboxilate and OH-Acid

Kinetic studies were made for the reaction between triphenylphosphine, di‐tert‐butyl acetylenedicarboxilate in the presence of OH‐acid, such as 2‐hydroxy‐4‐methoxybenzaldehyde. To determine the kinetic parameters of the reaction, it was monitored by UV spectrophotometery. The second order fits were automatically drawn by the software associated with a Cary UV spectrophotometer model Bio‐300 at appropriate wavelength. The values of the second order rate constant (k₂) were calculated using standard equations within the program. At the temperature range studied the dependence of the second order rate constant (ln k₂) on reciprocal temperature was in a good agreement with Arrhenius equation. This provided the relevant plots to calculate the activation energy of the reaction. Furthermore useful information was obtained from studies of the effect of solvent and concentration of reactants on the rate of reaction. Proposed mechanism was confirmed according to the obtained results and steady state approximation and first step (k₂) of reaction was recognized as a rate‐determining step on the basis of experimental data. In addition, assignment of more stable isomers (Z or E) was investigated using the theoretical study.     

A Simple Synthesis of Stable Phosphorus Ylides from Indole and Some of Its Derivatives

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of strong NH acids, such as indole and 2-methyl indole, 3-methyl indole, and 5-boromo indole. These stable ylides exist in a solution as a mixture of two geometrical isomers as a result of the restricted rotation around the carbon–carbon partial double bond resulting from the conjugation of the ylide moiety with the adjacent carbonyl group.     

A Simple Synthesis of Stable Phosphoranes Derived from Imidazole Derivatives

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of strong NH-acids, such as imidazole, 2-methylimidazole, 4-methylimidazole, 2-ethylimidazole, benzimidazole, and 5,6-dimethylbezimidazole. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon–carbon partial double bond resulting from the conjugation of the ylide moiety with the adjacent carbonyl group.     

Triphenylphosphine Mediated Efficient Synthesis of 4-Substituted-1-methyl-2,5-dioxo-3-imidazolines

Summary.  Stable crystalline phosphorus ylides are obtained in excellent yields from the 1:1:1 addition reaction between 1-methylparabanic acid (1-methylimidazoline-2,4,5-trione) and dialkyl acetylenedicarboxylates in the presence of triphenylphosphine. These ylides exist in solution as a mixture of two geometric isomers. This is due to the restricted rotation around the carbon–carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. These ylides undergo smooth intramolecular Wittig reaction followed by an electrocyclic ring opening to produce dialkyl (E)-2-(1-methyl-2,5-dioxo-3-imidazolin-4-yl)-but-2-enedioates in good yields. Corresponding author. E-mail: isayavar@yahoo.com Received March 26, 2002; accepted (revised) April 24, 2002     

Further Insight into the Mechanism of the Novel Multicomponent Reactions Involving Isoquinoline and Dimethyl Acetylenedicarboxylate in the Presence of 3‐Methylindole: Theoretical and Experimental Approach

The kinetics of the reactions among isoquinoline, dimethyl acetylenedicarboxylate, and 3‐methyl indole (as NH‐acid) was studied using UV spectrophotometry. The overall rate constant (k_ov) was evaluated from the slope of the plot of k_obs versus reactant concentration. A large deal of useful information was obtained from the study of the effects of solvent, temperature, and reactants and concentration on the reaction rates. Based on experimental data and theoretical concepts, the reaction's first step (k₁) was recognized as the rate‐determining step. Theoretical studies were performed to evaluate potential energy surfaces of all components participated in the reaction mechanism. Furthermore, the proposed mechanism was confirmed by the obtained results. The probable reaction path and product configuration were suggested based upon the theoretical results.     

An Efficient Synthesis of Stable Phosphorus Ylides Derived from Triphenylphosphine,Dialkyl Acetylenedicarboxylates,and an NH-Acid

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of strong NH-acids, such as benzotriazole, 5-methylbenzotriazole, 5-chlorobenzotriazole, pyrrole, 2-acetylpyrrole, pyrrole-2-carboxaldehyde, 4-nitro-acetanilide, 4-methoxyacetanilide, 4-bromoacetanilide, 4-methylacetanilide, 2-methyl-acetanilide, and 2,6-dimethylacetanilide. These stable ylides exist in a solution as a mixture of two geometrical isomers as a result of the restricted rotation around the carbon–carbon partial double bond resulting from the conjugation of the ylide moiety with the adjacent carbonyl group.     

NMR study and AIM analysis for assignment of the two Z- and E-isomers in phosphorane containing a 2-thiazoline-2-thiol

Triphenylphosphine reacts with dialkyl acetylenedicarboxylates in the presence of a SH-heterocyclic compound such as 2-thiazoline-2-thiol to generate stable phosphorus ylides. These stable ylides exist in solution as a mixture of the two geometrical isomers as a result of restricted rotation around the carbon–carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. In the recent work, NMR study and the assignment of more stable Z- or E-isomers as the major form were investigated by using natural population analysis (NPA).     

Triphenylphosphine Mediated Simple Synthesis of Vinyl-Substituted Benzimidazoles

N -isopropenylbenzimidazolone undergoes a smooth reaction with triphenylphosphine and dialkyl acetylenedicarboxylates to produce highly functionalized salt-free phosphorus ylides in good yields. These stabilized phosphorus ylides exist as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. These ylides are converted to dialkyl 2-(1-isopropenyl-1H-benzimidazol-2-yl)-but-2-enedioates in boiling toluene.     

Efficient,Simple Synthesis of Stable Phosphorus Ylides Derived from 4-Aryl Urazoles

Crystalline phosphorus ylides are obtained in nearly quantitative yields from the 1:1:1 addition reaction between triphenylphosphine, dialkyl acetylenedicarboxylates, and 4-aryl urazoles.     

An Efficient Synthesis of Stable Phosphorus Ylides Derived from Hydantoin and 5,5-dialkylhydantoins

Stable crystalline phosphorus ylides are obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of strong NH-acids, such as hydantoin and 5,5-dialkylhydantoins. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group.     

A Three‐Component One‐Pot Synthesis of Functionalized 5,5‐Dicyanocyclopenta‐1,3‐dienes from Arylidene­malononitriles,Activated Acetylenes,and KCN or KSCN

The reaction of dialkyl acetylenedicarboxylates with arylidenemalononitriles in the presence of KSCN in MeCN led to a mixture of dialkyl (3E)‐4‐aryl‐3‐(arylideneamino)‐5,5‐dicyanocyclopenta‐1,3‐diene‐1,2‐dicarboxylates and dialkyl 4‐aryl‐5‐cyanothiophene‐2,3‐dicarboxylates. When these reactions were performed in the presence of KCN, only the functionalized 5,5‐dicyanocyclopenta‐1,3‐dienes were obtained.     

A Facile,One-Pot Synthesis of Azoic Compounds and Anthraquinone Derivatives Containing Dialkyl Phosphoryl Moieties in Multicomponent Reactions

Protonation of the reactive 1:1 intermediates produced in the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates by 1-amino-anthraquinone or 1,5-diphenylcarbazone as a core dye leads to vinyl phosphonium salts, which undergo Michael addition with conjugate base of NH compounds to produce stable phosphorus ylides as novel dyes in fairly good yields. These ylides can exist in two geometrical isomers (Z) and (E) for 3, because the negative charge of the ylide moiety of these compounds are strongly conjugated with the adjacent carbonyl group. Rotation around the carbon–carbon double bond is slow in the (Z) and (E) geometrical isomers on the NMR time scale at ambient temperature. These compounds are assigned by their IR, ¹H, ¹³C NMR spectral data as well as their mass spectroscopic data.     

Chemoselective Synthesis of Functionalized 2,5-Dihydro-2-thioxo-1H-imidazoles from 5,5-Diarylthiohydantoins and Activated Acetylenes

Stable crystalline phosphorus ylides are obtained in excellent yields from the 1:1:1 addition reaction between 5,5-diarylthiohydantoins and dialkyl acetylenedicarboxylates in the presence of triphenylphosphine. These phosphoranes undergo a smooth intramolecular Wittig reaction followed by an electrocyclic ring opening to produce dialkyl 2-(2,5-dihydro-5,5-diaryl-2-thioxo-1H-imidazol-4-yl)but-2-enedioates in good yields.     

Triphenylphosphine-Catalyzed Simple Synthesis of Vinyl-Substituted Saccharins

Saccharin (1,1-dioxo-1,2-dihydro-1 u 6 -benzo[ d ]-isothiazol-3-one) undergoes a smooth reaction with dialkyl acetylenedicarboxylates in the presence of triphenylphosphine to produce highly-functionalized salt-free sulfur-containing ylides in nearly quantitative yields. These stabilized phosphorus ylides exist as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. These ylides are converted to dialkyl 2-(1,1-dioxo-1 H -1 u 6 -benzo[ d ]-isothiazol-3-yl)-but-2-enedioates in boiling toluene.     

An Efficient One-Pot Synthesis and Temperature Dependence of NMR Spectra of Nitrogen-Containing Phosphorus Ylides

The addition of triphenylphosphine to dialkyl acetylenedicarboxylates in the presence of trifluoroacetamide, a NH acid, leads to stable crystalline phosphorus ylides in exellent yields. These stable ylides exist as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond, resulting from conjugation of the ylide moiety with the adjacent group.