Dipolmoment und Konformation von Imino-äther-Derivaten

By means of the dipole moments of several imidic acid esters the conformation at the C? O bond and the configuration at the C?N bond have been determined. Use was made of the graphical comparison of a phenyl-derivative with the para-substituted analogue [7] in combination with cyclic model compounds having forced stereochemistry. The results obtained are conclusive for the N-alkyl-derivatives which are in the Eap form A. The imidic acid esters which are unsubstituted at the nitrogen are prevailingly in the same Eap conformation A; another conformation, probably the Zap form B, may also be present in smaller amounts.     

Unzipping and scrambling reaction-induced sequence control of copolymer chains via temperature changes during cationic ring-opening copolymerization of cyclic acetals and cyclic esters

A temperature change-dependent sequence transformation of copolymer chains was demonstrated by a method based on tandem depolymerization and transacetalization reactions during the cationic ring-opening copolymerization of cyclic acetals and cyclic esters. In this study, the position of polymerization-depolymerization equilibrium was controlled by the reaction temperature rather than by the decrease in monomer concentration under vacuum conditions, as in our previous study. First, the conditions for efficient copolymerization were optimized, with a particular focus on the structures of cyclic acetals and cyclic esters. Subsequently, sequence transformation induced by temperature change was examined during the copolymerization of 2-methyl-1,3-dioxepane (generated in situ from 4-hydroxybutyl vinyl ether) and δ-valerolactone using EtSO₃H. The homosequence length of cyclic acetals decreased during depolymerization (unzipping) at the oxonium chain ends upon increasing the temperature from 30 to 90 °C, while transacetalization (scrambling) of the main chain transferred midchain cyclic acetal homosequences to the oxonium chain ends. As a result of the cycle of unzipping and scrambling reactions, an alternating-like copolymer was obtained. Interestingly, the possibility of reversible sequence transformation upon heating and cooling was also demonstrated.     

A study of the tautomerism of the N-butyl-4(2)-methoxycarbonyl-pyrrolid-3-ones and their hydrochlorides

The tautomerism of N-butyl-2-methoxycarbonyl-4-methylpyrrolid-3-one (I), N-butyl-4-methoxycarbonylpyrrolid-3-one (II), N-butyl-4-methoxycarbonyl-2-methylpyrrolid-3-one (III), N-butyl-4-methoxycarbonylpyrrolid-3-one hydrochloride (IV), and N-butyl-4-methoxy-carbonyl-2-methylpyrrolid-3-one hydrochloride (V) has been studied by UV and IR spectroscopy. It has been found that the esters I–V are highly ionized in aqueous and ethanolic solutions at concentrations of 10^?2–10^?3 M. On passing from methyl cyclopentran-1-one-2-carboxylate to the esters II and III the position of the equilibrium in heptane and CCl₄ shifts in the direction of the keto form. On passing from the esters II and III to the esters IV and V, the position of the equilibrium shifts in the direction of the enol. Meyer's relationship is not satisfied for the esters II and III, while it is satisfied for the esters IV and V. Hypotheses have been put forward on the causes of the phenomena mentioned.     

Carbonylation of diols and their ethers and esters with ruthenium catalysts: synthesis of lactones and hydroxyacids ethers and esters

Diols and their formic or acetic esters can be carbonylated to give lactones or the corresponding hydroxyacid esters of ethers in the presence of carbonylruthenium iodide systems, [Ru(CO)₃I₃]⁻/alkyl or metal iodide, at a temperature of 200°C and CO pressure of 10-20 MPa. The reaction in the case of 1,3-propanediol gives γ-butyrolactone, with a selectivity of 60-% . Side reactions of homologation to 1,4-butanediol derivatives and hydrogenolysis to n-propyl derivatives by H₂ produced by the water gas shift reaction (WGSR) also occur, together with acid-catalyzed dehydration to give linear polypropylene glycols, α,ω-diols with more than 3 carbon atoms in the chain preferentially give hydroxyacid esters and ethers.The cyclic ether by-products and linear polyether by-products can be further activated and carbonylated under the reaction conditions to give lactones or hydroxy-acid derivatives thus increasing the total yield of carbonylation products. The formation of H₂ by WGSR involving water produced by the acid-catalyzed dehydration reactions, and the subsequent hydrogenolysis and homologation reactions cannot be avoided.     

A study of the tautomerism of the N-butyl-4(2)-methoxycarbonyl-pyrrolid-3-ones and their hydrochlorides

The tautomerism of N-butyl-2-methoxycarbonyl-4-methylpyrrolid-3-one (I), N-butyl-4-methoxycarbonylpyrrolid-3-one (II), N-butyl-4-methoxycarbonyl-2-methylpyrrolid-3-one (III), N-butyl-4-methoxycarbonylpyrrolid-3-one hydrochloride (IV), and N-butyl-4-methoxy-carbonyl-2-methylpyrrolid-3-one hydrochloride (V) has been studied by UV and IR spectroscopy. It has been found that the esters I–V are highly ionized in aqueous and ethanolic solutions at concentrations of 10^–2–10^–3 M. On passing from methyl cyclopentran-1-one-2-carboxylate to the esters II and III the position of the equilibrium in heptane and CCl₄ shifts in the direction of the keto form. On passing from the esters II and III to the esters IV and V, the position of the equilibrium shifts in the direction of the enol. Meyer's relationship is not satisfied for the esters II and III, while it is satisfied for the esters IV and V. Hypotheses have been put forward on the causes of the phenomena mentioned.     

SIFT studies of the reactions of H3O+, NO+ and O+2 with a series of volatile carboxylic acids and esters

We report the results of a selected ion flow tube (SIFT) study of the reactions of H₃O⁺, NO⁺ and O⁺₂ with some nine carboxylic acids and eight esters. We assume that all the exothermic proton transfer reactions of H₃O⁺ with all the acid and esters molecules occur at the collisional rate, i.e. the rate coefficients, k, are equal to k_c; then it is seen that k values for most of the NO⁺ and O⁺₂ reactions also are equal to or close to k_c. The major ionic products of the H₃O⁺ reactions with both the acids and esters are the protonated parent molecules, MH⁺, but minor channels are also evident, these being the result of H₂O elimination from the excited (MH⁺)1 in some of the acid reactions and an alcohol molecule elimination (CH₃OH or C₂H₅OH) in some of the ester reactions. The NO⁺ reactions with the acids and esters result in both ion-molecule association producing NO⁺M in parallel with hydroxide ion (OH⁻) transfer with some of the acids, and parallel methoxide ion (CH₃O⁻) and ethoxide ion (C₂H₅O⁻) transfer as appropriate with some of the esters. The O⁺₂ reactions proceed by dissociative charge transfer with the production of two or more ionic fragments of the parent molecules, the different isomeric forms of both the acid and the ester molecules resulting in different product ions.     

Intramolecular Allylations of Carbonions

In the general centaxt of examining a variety of organic, reactions which probably proceed via cyclic transition stares, we predicted scme years ago² that the aniens (II) produced by the action of appropriate bases on allylic esters(I) would undergo intramolecular rearrangement to form the iscmeric carboxylate anions (III).     

Gold(I)‐Catalyzed Divergence in the Preparation of Bicyclic Enol Esters: From Exclusively [3C+2C]‐Cycloaddition Reactions to Exclusive Formation of Vinylcyclopropanes

With the use of benzonitrile‐stabilized Au^I catalyst [Au(IPr)(NCPh)]SbF₆ ( Ic ; IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene), a spectrum of reactivity is observed for propargyl ester 4 a with cyclic vinyl ethers, ranging from exclusively [3C+2C] cycloaddition reactions to exclusively cyclopropanation depending only on the structure of the substrate. Some initially formed cyclopropanation products rearrange into the corresponding formally [3C+2C] cycloaddition products after treatment with fresh Au^I complex at 80 °C. Vinylcyclopropanes formed from dihydrofuran and dihydropyran resisted such rearrangement, even in the presence of fresh Au^I catalyst at elevated temperature. This study addresses an important mechanistic question concerning whether the five‐membered‐ring products were produced by a direct [3C+2C] cycloaddition reaction or by a sequential cyclopropanation/ring‐expansion reaction. A dual pathway is proposed for the Au^I‐catalyzed reactions between propargyl esters and cyclic vinyl ethers. The different behavior among vinyl cyclic ethers is attributed to the difference in the polarization of the π bond. Highly polarized bonds appear to undergo the cycloaddition reaction whereas less polar π‐bonds produce cyclopropanes.     

Heterogeneous versus Homogeneous Copper(II) Catalysis in Enantioselective Conjugate‐Addition Reactions of Boron in Water

We have developed Cu^II‐catalyzed enantioselective conjugate‐addition reactions of boron to α,β‐unsaturated carbonyl compounds and α,β,γ,δ‐unsaturated carbonyl compounds in water. In contrast to the previously reported Cu^I catalysis that required organic solvents, chiral Cu^II catalysis was found to proceed efficiently in water. Three catalyst systems have been exploited: cat. 1: Cu(OH)₂ with chiral ligand L1 ; cat. 2: Cu(OH)₂ and acetic acid with ligand L1 ; and cat. 3: Cu(OAc)₂ with ligand L1 . Whereas cat. 1 is a heterogeneous system, cat. 2 and cat. 3 are homogeneous systems. We tested 27 α,β‐unsaturated carbonyl compounds and an α,β‐unsaturated nitrile compound, including acyclic and cyclic α,β‐unsaturated ketones, acyclic and cyclic β,β‐disubstituted enones, acyclic and cyclic α,β‐unsaturated esters (including their β,β‐disubstituted forms), and acyclic α,β‐unsaturated amides (including their β,β‐disubstituted forms). We found that cat. 2 and cat. 3 showed high yields and enantioselectivities for almost all substrates. Notably, no catalysts that can tolerate all of these substrates with high yields and high enantioselectivities have been reported for the conjugate addition of boron. Heterogeneous cat. 1 also gave high yields and enantioselectivities with some substrates and also gave the highest TOF (43 200 h^?1) for an asymmetric conjugate‐addition reaction of boron. In addition, the catalyst systems were also applicable to the conjugate addition of boron to α,β,γ,δ‐unsaturated carbonyl compounds, although such reactions have previously been very limited in the literature, even in organic solvents. 1,4‐Addition products were obtained in high yields and enantioselectivities in the reactions of acyclic α,β,γ,δ‐unsaturated carbonyl compounds with diboron 2 by using cat. 1, cat. 2, or cat. 3. On the other hand, in the reactions of cyclic α,β,γ,δ‐unsaturated carbonyl compounds with compound 2 , whereas 1,4‐addition products were exclusively obtained by using cat. 2 or cat. 3, 1,6‐addition products were exclusively produced by using cat. 1. Similar unique reactivities and selectivities were also shown in the reactions of cyclic trienones. Finally, the reaction mechanisms of these unique conjugate‐addition reactions in water were investigated and we propose stereochemical models that are supported by X‐ray crystallography and MS (ESI) analysis. Although the role of water has not been completely revealed, water is expected to be effective in the activation of a borylcopper(II) intermediate and a protonation event subsequent to the nucleophilic addition step, thereby leading to overwhelmingly high catalytic turnover.     

Gas-Phase reactions of O 2 −. with alkyl and aryl esters of benzenedicarboxylic acids

The reactions of O ₂ ^?. with alkyl and aryl esters of benzenedicarboxylic acids have been studied under negative-ion chemical ionization (NICI) conditions via a conventional chemical ionization source. Reaction mechanisms have been elucidated by using ion isolation techniques on a Fourier transform ion cyclotron resonance mass spectrometer. In addition, ¹⁸O ₂ ^?. has been used as the reagent and the products of competitive reactions that involve the mixed esters of benzenedicarboxylic acids have been studied. O ₂ ^?. reactions with the alkyl esters of 1,2- and l,3-benzenedicarboxylic acids are attributed to S_N2 displacement at the O-alkyl carbon. The spectra of mixed alkyl esters show that O ₂ ^?. attack is reduced at sterically hindered alkyl groups. In contrast with the spectra of 1,2- and l,3-benzenedicarboxylic acids, the spectra of 1,4-benzenedicarboxylic acids are dominated by M^?. production. Reactions of O ₂ ^?. with phenyl benzoates and the aryl esters of benzenedicarboxylic acids proceed via addition-elimination pathways. Experiments with mixed alkyl-aryl benzenedicarboxylic acid esters show that the addition-elimination reaction pathway is preferred over O-alkyl S_N2 displacement. The O₂/ Ar-NICI mass spectra show features that can be used to distinguish 1,2-, 1,3-, and 1/4-benzenedicarboxylic acid esters. Molecular and fragment ions provide structural information complementary to that generated under electron ionization and chemical ionization conditions.     

Pyridazines. LXX. Reactions of azidoazolopyridazines with unsaturated compounds

Cycloaddition reactions of azidoazolopyridazines with unsaturated esters, cyclic enol ethers, styrene, 2-vinyl-pyridine, bicyclo[2.2.1]heptene, dicyclopentadiene and dehydrobenzene were investigated. The reaction proceed via the intermediate Δ² -1,2,3-triazolines which were in most cases termolabile and decomposed further to give the final products which were enamines, imines of fused aziridines.     

Synthesis of stereoisomeric 1,3-dimethyl- and 1,2,5-trimethyl-4-acyl(benzoyl)-4-piperidinols

In order to synthesize stereoisometric 4-acyl(benzoyl)-1, 3-dimethyl and-1, 2, 5-trimethyl-4-piperidinols, the reaction of the geometrical isomers of 4-cyano-1, 3-dimethyl- and -1, 2, 5-trimethyl-4-piperidinols and the amines and imidic esters corresponding to them with some alkyl- and arylmagnesium halides, leading to the corresponding isomeric piperidinic α-ketols, has been studied. The dependence of the reactivity of the geometrical isomers of the compounds studied on the spatial orientation of their functional groups has been shown.     

Optically active cyclic and linear poly(aryl esters) based on chiral 1,1′-bi-2-naphthol

Three optically active poly(aryl esters)—poly(terephthalyl esters) (PTEs), poly(isophthalyl esters) (PIEs) and o-phthaloyl ester (OPE)—were prepared from chiral 1,1-bi-2-naphthol reacted with terephthaloyl chloride (TPC), isophthaloyl chloride (IPC) and o-phthaloyl chloride (OPC), respectively, by condensation reactions. The ring-forming properties of 1,1′-bi-2-naphthol with the three biacid chlorides have been studied. It is found that the products formed by the optically active binaphthol and TPC are mainly linear poly(terephthalyl esters) (PTEs), while the polycondensates of the chiral binaphthol and IPC consist of both cyclic and linear PIEs, and the product formed by optically active binaphthol and OPC is a wholly monocyclic o-phthaloyl ester (OPE), i.e. 1,1-bi-2-naphthyl o-phthalate. The pure optically active cyclic dimer, trimer and tetramer of PIEs were successfully separated from their product mixture by preparative TLC. The specific rotations [α]_D²⁵ were +210 and −214.8 for the cyclic (R)- and (S)-dimer of PIEs, +177.2 and −179.1 for the cyclic (R)- and (S)-trimer of PIEs and +80.3 and −80.8 for the (R)- and (S)-tetramer of PIEs, respectively. Their characterizations were carried out by MALDI-TOF MS, GPC, CD, etc.     

An Influence of Structure of Ester on Results of Its Macrocyclization Reaction with α,ω-Diamine

Abstract

Sodium methoxide was found to be an excellent catalyst in the reaction of diesters with diamines leading to macrocyclic diamides. Time of reaction was shortened to several hours (in the case of reactive esters) or to several days (in the case of less reactive esters). The template effect of Na⁺ ion was excluded. It was also proposed that the electron density on the carbonyl group in various esters was responsible for different results of amidation reactions. Decrease in electron density increases the reactivity of the carbonyl group. For esters 1–5, the inductive effect of the heteroatom at the α position to the carbonyl group influences reactivity mostly.     

The reactions of H3O+, NO+ and O with several flavourant esters studied using selected ion flow tube mass spectrometry

The reactions of H₃O⁺, NO⁺, and O with nineteen ester compounds occurring naturally in plants, and having important flavourant properties, were examined using selected ion flow tube mass spectrometry (SIFT‐MS). The H₃O⁺ reactions primarily generate [R₁COOR₂·H]⁺, and may also produce [R₂]⁺ fragment ions and/or fragmentation within the ester linkage. Collisional association/adduct ions, [R₁COOR₂·NO]⁺, are the main products formed in the NO⁺ reactions, although the carboxyl fragment ion is also detected frequently. The identification of the parent compound may be made more easily in the H₃O⁺ and NO⁺ reactions. The inclusion of O reactions in the analysis provides additional information, which may be applied when the identity of a parent compound cannot be determined solely from the H₃O⁺ and NO⁺ analysis. Consideration of the product ions generated with the three precursors suggests that SIFT‐MS can differentiate between many of the esters investigated, including isomers, although the product ions generated in the reactions with some esters are too similar to allow independent quantification. Our data therefore suggest that SIFT‐MS may be a useful tool to rapidly analyse and quantify flavourant esters in complex gas mixtures. Copyright © 2010 John Wiley & Sons, Ltd.     

Preparation of 3-hydroxyisoindolin-1-ones and o-acylbenzamides. A study of ring-chain tautomerism

3-Hydroxyisoindolinones (ring form) as well as their chain tautomers, o-acylbenzamides, were prepared from the reactions of 3-benzalphthalide 1 , 3-halophthalides 3 , and o-acylbenzoic acids 6 or their esters 7 with amines 2 , and those of phthalimides 4 with Grignard reagents 5 . The characteristic spectroscopic properties of ring and chain forms are observed in the ir and ¹³C-nmr spectra. The significance of the spectroscopic results is discussed, as is the relationship between the structure of the products and the position of the ring-chain equilibrium.     

Electron impact and chemical ionization mass spectrometry of cyclic boronate derivatives of sphingosines and related compounds

Electron impact and isobutane chemical ionization mass spectrometric data are reported for cyclic boronate esters of sphinganine and 4-sphingenine and of the related N-ethyl, N-dimethylaminomethylene and acetone Schiff base compounds. Fragmentation of the 6-membered boronate ring is promoted by the presence of the 2-amino or 2-imino substituent and by Δ⁴ unsaturation. Evidence is presented for a transannular interaction stabilizing the ion formed by loss of the alkyl or aryl group, attached to the boron atom, in the case of the N-dimethylaminomethylene derivatives. An NH₂ migration is postulated to occur in 4-sphingenine boronates under electron impact. Mass spectrometric data are also reported for 4D-hydroxysphinganine bis-boronates.     

Stereochemistry of organophosphorus cyclic compounds—II : Stereospecific synthesis of cis- and trans 2-halogeno-2-oxo-4-methyl-1,3,2-dioxaphosphorinans and their chemical transformations

cis- and trans-2-Chloro-2-oxo-4-methyl-1,3,2-dioxaphosphorinans have been obtained by stereospecific reactions of diastereomerically pure 2-methoxy-4-methyl-1,3,2-dioxaphosphorinans or 2-hydrogen-2-oxo-4-methyl-1,3,2-dioxaphosphorinans with chlorine and sulphuryl chloride, respectively. Similarly, the action of the corresponding brominating agents on isomeric phosphites and phosphonates afforded pure cis- and trans-2-bromo-2-oxo-4-methyl-1,3,2-dioxaphosphorinans. It has been shown that halogenolysis proceeds with retention of configuration at the P atom. On the basis of the ¹H- and ³¹P-NMR spectra conformation of the halogenoanhydrides obtained has been discussed briefly.It has been also found that model nucleophilic substitution reactions occur with inversion of configuration at the P atom in the cyclic halogenoanhydrides.     

Diastereoselective synthesis of substituted 2,3,4,5‐tetrahydro‐1H‐1‐benzazepine‐5‐carboxylic esters by a tandem reduction‐reductive animation reaction

An efficient, diastereoselective synthesis of substituted and unsubstituted 2,3,4,5‐tetrahydro‐1H‐1‐benzazepine‐5‐carboxylic esters has been developed based on the tandem reduction‐reductive amination reac tion. Catalytic hydrogenation of a series of 2‐(2‐nitrophenyl)‐5‐oxoalkanoic esters initiates a reaction sequence involving (1) reduction of the aromatic nitro group, (2) condensation of the N‐hydroxylamino (or amino) nitrogen with the side chain carbonyl, and (3) reduction of the seven‐membered cyclic imine. Cyclizations that produce 2‐alkyl‐2,3,4,5‐tetrahydro‐1H‐1‐benzazepine‐5‐carboxylic esters are diastereose lective for the product having the C2 alkyl and the C5 ester groups cis. In these reactions, the transannular ester group exerts a strong stereodirecting effect on the reduction of the cyclic imine intermediate, though not as strong as that observed in previous closures of 2‐alkyl‐1,2,3,4‐tetrahydroquinoline‐4‐carboxylic esters. This decrease in diastereoselectivity is attributed to (1) the greater distance between the ester and the imine double bond and (2) the increased conformational mobility of the larger ring, both of which diminish the stereodirecting effect of the ester. Finally, formation of the seven‐membered ring is sufficiently slow that reaction with the side chain ester group competes with heterocycle formation in several of the reactions.     

Cyclic ions in the mass spectra of trimethylsilyl derivatives of substituted o-dihydroxybenzenes

The mass spectra of trimethylsilyl (TMS) ethers/methyl esters of phenolic acids containing o-dihydroxybenzene groups have base peaks at [M?119]⁺ instead of the usual [M?15]⁺ and [M?31]⁺ that are characteristic of TMS/methyl esters of monohydroxyphenolic acids. These ions, formed by the loss of 31+88 u from the parent ion, possess a cyclic moiety as proven by substitution of deuterium atoms for hydrogen atoms in the TMS groups of the methyl esters of 3,4,5-trihydroxybenzoic (gallic), 3,4-dihydroxybenzoic (protocatechuic) and β-(3,4-dihydroxyphenyl)propenoic (caffeic) acids. Although these cyclic ions are the base peaks in TMS-derivatized o-dihydroxyphenolic acid esters, similar ions represent intense peaks but not necessarily the base peak in other derivatized compounds such as 1,2-dihydroxybenzene, 1,2-dihydroxy-3-methyl- and 1,2-dihydroxy-4-methyl-benzenes and flavan-3-ols that possess o-dihydroxybenzene groups. Compounds possession m- or p-dihydroxybenzene groups do not form these cyclic ions; therefore, this procedure for derivatization and interpretation of mass spectra is valuable for the identification of compounds containing o-dihydroxybenzene groups in complex mixtures of isomeric compounds.