Convenient method for the synthesis of C-phosphorylated N-arylformamidines

C-Phosphorylated (P^V) arylformamidines have been prepared by the reaction of N-arylamidotrichloromethyl derivatives of phosphorus, thiophosphorus, and selenophosphorus acids with secondary amines. Dependence of the reaction on the nature of chalcogene, electronic and steric factors has been studied. By reduction of N-arylformamidinophosphonoselenides the corresponding C-phosphorylated (P^III) arylformamidines have been synthesized.     

Kinetic study of oxidation of galactose by N-bromo phthalimide in the presence of cationic micelle in acidic medium

The kinetics of micellar catalyzed oxidation of galactose by N-bromophthalimide was studied in the presence of acidic medium at 308?K. The oxidation reaction exhibits first-order kinetics with respect to oxidant (N-bromophthalimide), fractional order with respect to substrate (galactose) and positive fractional order with respect to HClO₄ on the rate of reaction. The rate of the reaction increased with decreasing the dielectric constant of the medium. With a progressive increase in the concentration of CTAB, the rate of reaction increased and after reaching peak k _obs, decreased at higher concentrations of CTAB. There catalytic roles are best explained by Berezin??s model. The influence of salts on the reaction rate was also studied. The various activation parameters have been calculated. The rate constant and binding constant with the surfactant have also been evaluated. A suitable mechanism consistent with the experimental findings has been proposed.     

Temperature vs. time sequences to palliate deactivation in parallel and in series-parallel with the main reaction: parametric study

The calculation of temperature vs. time sequences to palliate catalyst deactivation in an integral reactor has been studied either by maintaining constant the conversion at the reactor outlet in a simple reaction or by maintaining constant the concentration of a given component at the outlet in a complex reaction system. The experimental systems studied, which are a simple one (dehydration of 2-ethylhexanol) and a complex one (isomerization of cis-butene), have kinetic models of the Langmuir-Hinshelwood-Hougen-Watson type for the main reaction and deactivation, with deactivation by coke dependent on the concentration of the reaction components. In the reaction of dehydration of 2-ethylhexanol deactivation occurs in parallel with the main reaction and in the isomerization of cis-butene deactivation occurs in series-parallel with the main reaction. A parametric study has been carried out for both reaction systems. The sequences calculated have been experimentally proven in an automated reaction apparatus.     

A novel and practical synthesis of S-(1- and 2-halogenoalkyl)sugars by reaction of carbohydrate S-(O,O-dialkyl)phosphorodithioates and monothioates with fluoride anion

A useful synthesis has been developed of S-(1- and 2-halogenoalkyl)sugars in high yield and purity. Readily available sugar S-(O,O-dialkyl)phosphorodithioates undergo S-P bond rupture on reaction with fluoride ions to yield the corresponding sugar thiolates, which further react in situ with dichloromethane or 1,2-dihalogenoalkanes in the reaction medium. In this reaction, the halogenoalkanes play the role of both reactants and solvents.     

Nonisocyanate polyurethanes from amines and cyclic carbonates: Kinetics and mechanism of a model reaction

The kinetic features of a model reaction of the formation of nonisocyanate urethanes from cyclic carbonates and amines have been determined through the use of the example of the interaction of ethylene with n-butylamine in n-butanol and dioxane at different temperatures. The reaction proceeds via two parallel routes involving one or two amine molecules with an activation energy of 7.0 or 2.5 kcal/mol, respectively, in n-butanol and 14.0 or 3.7 kcal/mol in dioxane. The relative contributions of these routes to the observed reaction rate depend on the amine concentration and the temperature. In accordance with the density functional theory, the activation barriers have been calculated and data on the structures of the transition states and the role of the proton-donor solvent in the reaction mechanism have been obtained.     

Kinetics of solvolysis reactions of pentaarylantimony compounds in 2-octanol

Tetraphenyl-p-tolylantimony, m-chlorophenyltetraphenylantimony and p-methoxyphenyltetraphenylantimony have been prepared and subjected to solvolysis in 2-octanol at temperatures ranging from 50–65°. First order rate constants have been determined, and a plot of log k X 10⁵ vs. σ has been found to be linear, with p = 1.12. The value for the specific rate constant of the pentaphenylantimony reaction cannot be measured directly owing to solubility problems, but it can be calculated by use of the Hammett equation. Analysis of the rate data by the method of parallel first-order reactions gives results which are in agreement with experimental data for the reaction period extending from the time at which a homogeneous solution is formed to the end of the reaction. Partial rate factors for formation of benzene and the substituted benzene have been calculated for each reaction, and these data plus the activation parameters have been used as the basis for suggested mechanisms of the solvolysis reactions. Preliminary studies have also been carried out on the effects of 2-octanoxide anion on the solvolysis reactions. In the case of the p-methoxyphenyltetraphenylantimony reaction, second order kinetics were observed (first order with respect to the pentaarylantimony compound and first order with respect to the 2-octanoxide anion). Although precise rates could not be obtained for the reactions of the other pentaarylantimony compounds with sodium 2-octanoxide, qualitative evidence indicated that the anion exerts a major influence in each case.     

MM3 force field prediction of the enantioselective preference in the asymmetric synthesis of a chiral 2-cyclohexen-1-ol using a chiral lithium amide reagent

Enantioselective preference in the asymmetric synthesis where cyclohexene oxide is transformed enantioselectively to chiral (S)- or (R)-2-cyclohexen-1-ol by the reaction with the appropriate chiral lithium amide reagent has been evaluated theoretically using the MM3 force field. The plausible possible structures for each precursor (reaction intermediate complex) leading to a (S)- or (R)-2-cyclohexen-1-ol have been optimized with the extended MM3 force field applicable to the lithium amide functional group, and the populations of their (S)- or (R)-reaction intermediate complexes at an ambient temperature (298 K) were calculated. The initial structure for evaluating the reaction intermediates of this asymmetric synthesis was constructed on the basis of the optimized ab initio transition state structure (MP2/6-31+G^∗) comprising lithium amide LiNH₂ and propene oxide. To the thus obtained transition state structure composed of LiNH₂ and propene oxide, the other remaining Cartesian coordinates for the actual reaction intermediates composed of the chiral lithium amides and cyclohexene oxide were added to make the reaction intermediate structure. The conformational search for the reaction intermediate has been carried out by using the Stochastic search Algorithm, and the optimized geometries and their conformational energies (steric energies) have been calculated by the MM3 force field. The populations calculated from the conformational energies of the reaction intermediate leading to the (S)- or (R)-2-cyclohexen-1-ol were shown to be linearly well correlated with the experimentally reported enantiomer excess (% ee) values. The critical factors to control the enantioselectivity were investigated on the basis of the optimized structures of the reaction intermediate complexes. The MM3 force field approach was shown to be applicable to the theoretical evaluation of the enantioselectivity and be useful for designing a new functional chiral lithium amide reagent for the asymmetric synthesis.     

Synthesis of new steroidal derivatives by the reaction of steroid-amino acid conjugates with N,N′-dicyclohexyl-carbodiimide. Unusual formation of steroidal imide derivatives

Several new steroid derivatives have been synthesised by the reaction of steroid-amino acid conjugates with N,N′-dicyclohexyl-carbodiimide. Selectivity of the reaction was found to depend greatly on the properties of the amino acid moiety. While the reaction of the glycine derivative led to the corresponding 5(4H)-oxazolone, an unusual imide formation together with an N-acylurea side product was observed in the case of conjugates of l-alanine, l-phenylalanine and l-methionine. The structures of the new products, steroidal imide and N-acylurea derivatives, were determined by various spectroscopic methods.     

A palladium complex with a new hemilabile amino- and sulfur-containing phosphinite ligand as an efficient catalyst for the Heck reaction of aryl bromides with styrene. The effect of the amino group

A palladium complex with a new hemilabile amino- and sulfur-containing phosphinite ligand has been synthesised and its crystal structure determined. This system efficiently catalyses the Heck reaction of aryl bromides with styrene at 130°C after 24 h, with turnover numbers of up to 100000 and with a selectivity towards trans-stilbenes ranging from 91.5 to 96.3%. The analogous sulfur-containing phosphinite without the amino group has also been synthesised and subjected to the Heck reaction. The constructive role of the amino group on the formation of the P,S-chelate palladium complex as well as in the Heck reaction is discussed.     

Diastereospecific addition of Grignard reagents to 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxaldehyde

The reaction of both enantiomers of 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxaldehyde 1 with EtMgBr and PhMgBr has been studied. It has been found that addition of a Grignard reagent to the carbonyl group of 1 proceeds diastereospecifically. The configuration of the sp³ stereogenic centre formed in this reaction has been determined by single crystal X-ray diffraction and can be explained assuming exo-attack of the nucleophile on the s-cis-conformation of 1. The circular dichroism spectra of the product 1,1′-diphosphaferrocenyl alcohols are also reported and discussed.     

Stereochemistry of the aldol condensation of benzaldehydes with alpha-chloro esters : An example of the gauche effect of adjacent polar bonds

Under irreversible conditions, the stereochemical course of the aldol condensation of benzaldehydes with esters R¹CHClCO₂R (R¹ = H or Me) in the presence of NaH, NaOR or KOR depends only on the nature of R. Solvent and temperature have negligible effects. The reaction has been performed with eight ortho- or para-substituted benzaldehydes; only in the case of o-methoxybenzaldehyde has a different stereochemical result been obtained. Possible transition states for the Darzens reaction are discussed and it is shown that all of the data are consistent with a mechanism involving addition of a pyramidal carbanion to the aldehyde CO group via the rotameric forms predicted on the basis of the gauche effect     

Degradation thermique des trois isomeres Ortho,meta, para du polymethoxymethylstyrene

A kinetic study of the overall thermal decomposition of the three isomers (ortho, meta and para) of polymethoxymethylstyrene has been carried out. The reaction order is one over a wide interval of mass loss, for the meta and para polymers; there is no order for the first one. The corresponding activation energy has been calculated as 32.5 kcal mol⁻¹ for the meta polymer and 31 kcal mol⁻¹ for the para polymer.The volatile compounds, identified by gas chromatography coupled with mass spectrometry, are chiefly monomers. The thermal decomposition reaction is probably a depolymerization reaction coupled with crosslinking for the meta and para isomers.     

Kinetic and mechanistic investigations on the oxidation of N’-heteroaryl unsymmetrical formamidines by permanganate in aqueous alkaline medium

Kinetic studies on the oxidation of two substituted azinyl formamidines (Azn-Fs), namely N,N-dimethyl-N’-(pyrimidin-2-yl) formamidine (Pym-F) and N,N-dimethyl-N’-(pyridin-2-yl) formamidine (Py-F), by alkaline permanganate have been performed by spectrophotometry. The spectroscopic and kinetic evidence reveals the formation of 1:1 intermediate complexes between the oxidant and substrates. The influence of pH on the oxidation rates indicated that the reactions are base-catalyzed. The reactions show identical kinetics, being first order each in [MnO₄ ^?]₀ and [Azn-F]₀, but with a fractional first-order dependence on [OH^?]. The effect of temperature on the reaction rate has been studied. Increasing ionic strength has no significant effect on the rate. The final oxidation products of Pym-F and Py-F were identified as 2-aminopyrimidine and 2-aminopyridine, respectively, in addition to dimethyl amine and carbon dioxide. Under comparable experimental conditions, the oxidation rate of Py-F is higher than that of Pym-F. A reaction mechanism adequately describing the observed kinetic behavior is proposed, and the reaction constants involved in the different steps of the mechanism have been evaluated. The activation parameters with respect to the rate-limiting step of the reactions, along with thermodynamic quantities, are presented and discussed.     

(NH 4 )Zn 2 (PO 4 )(HPO 4 ): Hydrothermal Synthesis and Reaction with n-Alkylamine Vapours

(NH₄)Zn₂(PO₄)(HPO₄) was synthesized under mild hydrothermal conditions in the presence of urea. The reaction with n-alkylamines has been investigated by exposing the solid to amines vapor. The new materials were characterized by chemical and thermal analysis, powder X-ray diffraction, and IR spectroscopy. In addition, the simultaneous reaction of this compound with two or more n-alkylamine different molecules was investigated. The reaction of large n-alkylamine molecules was observed to be faster if there is a shorter alkyl chain amine acting as a catalyst, yielding on completion single amine materials. In the case of a vapor mixture of several amines, the compound obtained depends on the reaction time.     

Application of NO2/supercritical CO2 system for safe and selective nitration of adamantanes and tertiary alkyl bromides

A concise safe approach for selective nitration and nitroxylation of tert-alkanes, in particular adamantane, and tert-alkyl bromides utilizing NO₂ in supercritical CO₂ medium has been established. Major reaction products were tert-alkyl nitro compounds and tert-alkyl nitrates depending on the reaction conditions.     

An efficient synthesis of 6H,7H-chromeno[4,3-b]chromenes and 6,7-dihydrothio chromeno[3,2-c]chromenes as 9-substituted xanthene like analogs

An efficient synthetic route with good overall yields to access 7-aryl/heteroaryl/alkyl substituted 6H,7H-chromeno[4,3-b]chromene, and 6,7-dihydrothiochromeno[3,2-c]chromene scaffolds has been developed. The route to these xanthene-like analogs involves a three-step reaction sequence: (1) Michael addition of readily available phenol and thiophenol to 4-chloro-2,2-dimethyl-2H-chromene-3-carbaldehyde, (2) Grignard reaction of different aryl, heteroaryl and alkyl magnesium bromides on the resulting carbaldehydes followed by (3) FeCl₃ catalyzed spontaneous intramolecular Friedel-Craft’s reaction on the diarylmethyl carbinols.     

On the reaction of 3-bromo-2-nitrobenzo[b]thiophene with some ortho-substituted anilines: an analysis of the products of reaction and of their NMR and MS properties

The title reaction, carried out in DMF in the presence of triethylamine or potassium carbonate, has furnished the ‘expected’ 3-amino-2-nitrobenzo[b]thiophenes 2o together with the ‘unexpected’ 2-amino-3-nitrobenzo[b]thiophenes 3o, thus recalling the situation observed with other weak nucleophiles in the presence of non-nucleophilic bases. The effects (electronic as well as steric) of the ortho-substituent (OH, NH₂, OMe, Me, Et, F, Cl and Br) on the course of the reaction have been investigated, determining their influence on yields and product ratios (2o/3o). An analysis of ¹³C NMR and MS spectra of 2o and 3o has been carried out. Ab initio computations on 2of, 2oi, 3of and 3oi at DFT level have furnished informations on their geometry and stability in the gas phase, thus allowing to assign a role to their stability on the course of the reaction as well as on some EI-MS results.     

Stereoselective synthesis of (1R,2S)- and (1S,2R)-1-amino-cis-3-azabicyclo[4.4.0]decan-2,4-dione hydrochlorides: bicyclic glutamic acid derivatives

Asymmetric synthesis of (1R,2S)- and (1S,2R)-1-amino-cis-3-azabicyclo[4.4.0]decan-2,4-diones has been achieved. The underlying second generation asymmetric synthesis proceeds via a Strecker reaction with commercially available (R)-1-phenylethylamine (1-PEA) as chiral auxiliary, TMSCN as cyanide source and racemic ethyl 2-(2-oxocyclohex-1-yl)ethanoate. A ring closure addition-elimination reaction between an amide nitrogen and the ester functionality leads to the 1-amino-3-azabicyclo[4.4.0]decan-2,4-diones. The absolute configurations of the title compounds have been assigned based on detailed NMR-spectroscopic analysis and X-ray data.     

Experimental and DFT study of the aza-Diels-Alder reaction between cyclopentadiene and protonated benzylimine derivated from glyoxylates

The Diels-Alder reaction of protonated N-benzyl imine of methyl glyoxylate with cyclopentadiene in different solvents gave mixtures of exo/endo adducts. The exo/endo selectivity of the reaction was elucidated by NMR experiments. Theoretical calculations by means of density functional theory (DFT) at the B3LYP/6-31G(d) level have also been performed to elucidate the molecular mechanism of this reaction. The DFT results suggest a highly asynchronous concerted mechanism, which in turn can explain the preferred exo stereoselectivity of the reaction. Inclusion of solvent effects enhances the exo selectivity, and this effect increases with the polarity of the solvent, in good agreement with the experimental findings.     

Reactions of chloroalkyl-gem-dichlorocyclopropanes with amines

N-Alkylation of primary and secondary amines with monochloroalkyl-gem-dichlorocyclopropanes under conditions of thermal and microwave heating results in the corresponding amino-gem-dichlorocyclopropanes. With microwave irradiation heating, the reaction time has been decreased to 1 h, the yields of the amines containing gem-dichlorocyclopropane moiety being the same. Formation of the bicyclic amine in reaction of cis-2,3-dichloromethyl-gem-dichlorocyclopropane with primary amines under conditions of phasetransfer catalysis has been studied.