Showing papers on "Nucleophile published in 1975"
TL;DR: In this article, N-tosylimino-aryl-iodinane was proposed to decompose the I-N ylide and the nitrene intermediate was formed and react with nucleophiles to afford the imine compounds.
Abstract: (Diacetoxyiodo)arene reacts with p-toluenesulfonamide in the presence of base to give the new type I–N ylide, N-tosyliminoaryliodinane. In the decomposition of this ylide, the nitrene intermediate is proposed to be formed and react with nucleophiles to afford the imine compounds.
218 citations
TL;DR: In this paper, a method of preparing masked α-secondary amino carbanions consists in nitrosation of the secondary amine, followed by metalation of resulting nitrosamine α-to the nitrogen, reaction with electrophiles, and subsequent denitrosation.
Abstract: There are basically two kinds of hetero atoms in organic molecules: one kind confers electrophilic character upon the carbon atom to which it is bound, and the other kind turns it into a nucleophilic site. The development of methods permitting transitions between the two resulting categories of reagents has become an important task of modern organic synthesis. The scope of such umpolung of the reactivity of functional groups is discussed for the case of amines as an example. A method of preparing masked α-secondary amino carbanions consists in nitrosation of the secondary amine, followed by metalation of the resulting nitrosamine α-to the nitrogen, reaction with electrophiles, and subsequent denitrosation. Many examples are given for each of these steps which illustrate the wide scope of the overall synthetic operation (electrophilic substitution at the α-C atom of the secondary amine). Preliminary applications and a method for avoiding the handling of nitrosamines are presented, and the report concludes with a brief account of the significance of nitrosamines in the study of carcinogenesis and mutagenesis.
160 citations
TL;DR: This chapter discusses and attempts to organize and correlate the different types of carbonyl–amine reactions found in proteins with their organic chemistry, and focuses on the carbonies–-amine reaction in biological processes, naturally occurring deteriorative reactions, and their commercial applications.
Abstract: Publisher Summary Reaction of a carbonyl group with an amino group is the key reaction in many enzymic and other biological processes, such as vision. This chapter discusses and attempts to organize and correlate the different types of carbonyl–amine reactions found in proteins with their organic chemistry. The chapter focuses on the carbonyl–-amine reaction in biological processes, naturally occurring deteriorative reactions, and their commercial applications. The most characteristic chemical property of amines is their ability to act as nucleophiles because they possess a lone pair of electrons on the nitrogen atom, while, the reactivity of the carbonyl bond is primarily because of the difference in electronegativity between carbon and oxygen, which leads to a significant contribution of the dipolar resonance form, oxygen being negative and carbon being positive. The rate of the carbonyl–amine reaction usually shows acharacteristic pH dependence that results in a bell-shaped curve. Formaldehyde reacts not only with primary amino groups in proteins, but also with sulfhydryl groups. Carbonyl–amine reactions play important roles in catalytic reactions in enzymes, cross-linking in structural proteins like collagen and elastin and the visual process.
146 citations
120 citations
TL;DR: Hb apparently owes its normal resistance to autoxidation to the isolation of the binding site from electron donors and nucleophiles and not to an unique kind of iron-O 2 bonding, which explains the effects of structural abnormality that render M-type Hbs susceptible to oxidation.
116 citations
98 citations
TL;DR: In this paper, the versatility of vinyl azides in organic reactions is demonstrated, showing that the reactive azide function is susceptible to thermolysis, photolysis, cycloadditions, and attack by nucleophiles and electrophiles.
Abstract: This review is designed to demonstrate the versatility of vinyl azides in organic reactions. The reactive azide function is susceptible to thermolysis, photolysis, cycloadditions, and attack by nucleophiles and electrophiles. The neighboring double bond accentuates the reactivity of the azide function and provides additional intramolecular pathways for reaction. Last but not least, the presence of an appreciable electron density at the β-vinyl carbon makes this class of compounds comparable with enamines in their reactions with electrophiles and 1,3-dipoles.
95 citations
TL;DR: In this article, the displacement reaction of various nonactivated aryl halides with cyanide ions was investigated in the presence of palladium salts, and the reduced palladium species was supposed to be the active catalyst.
Abstract: The displacement reaction of various non-activated aryl halides with cyanide ions was investigated in the presence of palladium salts. Various aryl iodides and bromides were converted into the corresponding aryl cyanides in good yields under mild conditions. The addition of certain substances, such as potassium hydroxide and potassium carbonate, enhanced the catalytic activity. Hexamethylphosphoric triamide, in which potassium cyanide was scarcely soluble, was an outstanding solvent for the reaction. The reduced palladium species was supposed to be the active catalyst.
93 citations
86 citations
85 citations
TL;DR: In this article, the infrared spectra of a functioning 7-μm-thick membrane catalyst were measured simultaneously with reaction rates in a steady-state flow reactor at 1 atm and 90-125 °C.
TL;DR: Tricarbonyl(η-methoxy- and tricarbonyls( η-halogeno-benzene)manganese salts have been obtained from the appropriate arenes with bromopentac-bonyl manganese and aluminium chloride.
Abstract: Tricarbonyl(η-methoxy- and tricarbonyl(η-halogeno-benzene)manganese salts have been obtained from the appropriate arenes with bromopentacarbonylmanganese and aluminium chloride. The ease of nucleophilic substitution increases sharply in the series of halogenoarene compounds linked to (OC)3Cr < (cp)Fe+ < (OC)3Mn+(cp =η-cyclopentadienyl). The high reactivity of the manganese complexes is utilised in the preparation of other functionally substituted arene complexes by reaction with amines or anionic nucleophiles. l.r. and n.m.r. study of the amino-substituted arene complexes establishes partial nitrogen to ring double bonding.
TL;DR: The presence of higher (greater than 0.2 M) concentrations of divalent anions A2- (hydrogenphosphate, sulfate) is found to accelerate as well as to change entirely the course of riboflavin photolysis: instead of 10-dealkylation to yield lumichrome, intramolecular addition of the 2'-hydroxyl group is finding to occur at the peri-position C(9).
Abstract: The presence of higher (greater than 0.2 M) concentrations of divalent anions A2- (hydrogenphosphate, sulfate) is found to accelerate as well as to change entirely the course of riboflavin photolysis: instead of 10-dealkylation to yield lumichrome, intramolecular addition of the 2'-hydroxyl group is found to occur at the peri-position C(9). The reaction is analogous to the "photohydration" of the flavin nucleus in the cationic state as described by Schollnhammer and Hemmerich [Eur. J. Biochem. (1974) 44, 561-577]. The final product of the new addition reaction arises from autoxidation of a dihydroflavin intermediate and exhibits the structure. It is thus representative for a new class of flavins ("cyclo-dehydroflavins"). Earlier reports on "anomalous" flavin photodegradation products absorbing around 410 nm [Holmstrom (1964) Ark. Kem. 22, 281; Massey and Atherton (1962) J. Biol. Chem 237, 2965] are readily explained. The reaction is found to depend strictly on the presence of a nucleophilic function in the N(10)-side chain, e.g. N(10)-CH2-C(OH)RR' or even N(10)-(CH2)2-SO3-. Quenching experiments suggest that the new reaction occurs via the singlet state 1FLox while the normal photolysis is mediated by the triplet 3Flox. The new photoaddition is though to occur via a Flavin-A2- complex which creates sterically favorable conditions for C(9)/O(2'alpha)-interaction.
TL;DR: In this paper, it was shown that thiobenzophenone reacts with butyllithium, phenyllithiam, and sodium ethoxide in ethanol giving benzhydryl butyl sulfide, benzhydriesulfide, and dibenzydryl disulfide.
Abstract: Thiobenzophenone reacts with butyllithium, phenyllithium, and sodium ethoxide in ethanol giving benzhydryl butyl sulfide, benzhydryl phenyl sulfide, and dibenzhydryl disulfide, respectively. On the other hand di-t-butyl thioketone affords 2,2,4,4-tetramethylpentane-3-thiol, 2,2,4,4-tetramethyl-3-phenylpentane-3-thiol, and 2,2,4,4-tetramethylpentane-3-thiol by the reaction with butyllithium, phenyllithium, and sodium ethoxide in ethanol, respectively. Product analyses and tracer experiments with deuteriums have revealed that these reactions proceed through a charge-transfer mechanism.
TL;DR: The results indicate that the ability of the 3' substituent of cephalosporins to stabilize electron density transferred to it can be an important factor in activating the beta-lactam toward nucleophilic attack.
Abstract: Molecular orbital calculations by the CNDO/2 method are used to study the molecular and electronic details involved in the initial phases of the opening of the beta-lactam ring of a model cephalosporin structure, 7-amino-3-acetoxymethyl-3-cephem. The effect of a simple nucleophile, OH-, approaching the carbonyl carbon center of the beta-lactam ring is monitored by following the charge redistributions that occur in the bicyclic system and in the 3 side chain. A migration of electron density to the ester oxygen of the CH2OAc group is observed with concomitant weakening of the CH2-OAc bond. The results are discussed in relation to the mechanism of acylation of bacterial cell wall enzymes by beta-lactam antibiotics and in relation to the hydrolysis of these molecules. The results indicate that the ability of the 3' substituent of cephalosporins to stabilize electron density transferred to it, i.e., the leavability of the 3' moiety, can be an important factor in activating the beta-lactam toward nucleophilic attack.
TL;DR: In this article, the reaction of a cationic iron-propargyl complexes with a wide range of nucleophiles (Nu) was studied. But the most common behavior was to add Nu to carbon-1 of the η2-allene fragment (with NaBH4, (C2H5)2NH, and P(C6H5), and nonselective reactions to yield a mixture of products (with CH3Li).
TL;DR: In this article, a group of nucleophiles (phosphines and phosphites) has been found which displace ethylene faster than reaction by the dissociative mechanism and at a rate which depends on the concentration of the nucleophile.
TL;DR: In the case of aroyl chlorides or acyl triflates, the intermediate vinyl cation can be attacked by the aromatic nucleus of the a royl group, leading to the formation of indenones.
TL;DR: Alkyl substituted aza-macrobicyclic polyethers are highly efficient catalysts in anion promoted two-phase reactions, such as nucleophilic substitutions, C-alkylations, cyclopropanations, and borohydride reductions.
Abstract: Alkyl substituted aza-macrobicyclic polyethers are highly efficient catalysts in anion promoted two-phase reactions, such as nucleophilic substitutions, C-alkylations, cyclopropanations, and borohydride reductions.
TL;DR: In this article, it was shown that the Me3Sn(CH2)n COR with n = 2,3 and R = Me, Ph has a structure involving intramolecular coordination between the carbonyl oxygen and the tin.
TL;DR: In this paper, a preference is indicated for endo ring protonation which is proposed to occur via an intermediate protonated metal species, which is perhaps realistic in view of the known attack of nucleophiles on the exo position of coordinated hydrocarbon rings.
TL;DR: Results indicate that collagen maturation involves nucleophilic addition of lysine and/or hydroxylysine residues to the electrophilic double bond of the reducible cross-links, yielding derivatives which are not only more stable but also capable of cross-linking more collagen molecules than their reducible precursors.
Abstract: During in vivo maturation, and also during in vitro incubation with physiological buffers, native collagen fibers display a progressive increase in tensile strength and insolubility. Paralleling these physiologically important changes is a progressive loss of the reducible cross-links which initially join the triple-chained subunits of collagen fibers. Although there is evidence suggesting that the reducible cross-links are gradually transformed into more stable, nonreducible cross-links during maturation, the nature of the transformation process and the structure of the stable "mature" cross-links has remained a mystery. In order to test the possibility that cross-link transformation involves addition of a nucleophilic amino acid residue to the reducible cross-links, histidine, arginine, glutamate, aspartate, lysine, and hydroxylysine residues were chemically modified, and the effect of each modification procedure on the in vitro transformation of reducible cross-links was ascertained. The results of these experiments indicated that destruction of histidine, arginine, glutamate, and aspartate residues has no measurable effect on the rate and extent of reducible cross-link transformation in hard tissue collagens. In contrast, modification of lysine and hydrocylysine residues with a wide variety of specific reagents completely blocks the transformation of reducible cross-links. Removal of the reversible blocking groups from lysine and hydroxlylysine residues then allows the transformation to proceed normally. These results indicate that collagen maturation involves nucleophilic addition of lysine and/or hydroxylysine residues to the electrophilic double bond of the reducible cross-links, yielding derivatives which are not only more stable but also capable of cross-linking more collagen molecules than their reducible precursors.
TL;DR: Using the trapped ion cyclotron resonance spectrometer in a configuration which allows for a static gas sample, it has been possible to initiate ion-molecule reactions, follow the reaction rate, and then detect the neutral products.
TL;DR: In this article, cyclohexadienyl and 6-exo-methyl- or -phenyl-cyclohexadianyl complexes bearing halogeno-, alkoxy-, or dialkyl-amino-substituents in the 1- or 2-positions are obtained by reaction of lithium tetrahydridoaluminate or methyl-or phenyl-lithium with the appropriately substituted (η-arene)tricarbonylmanganese salt.
Abstract: Cyclohexadienyl and 6-exo-methyl- or -phenyl-cyclohexadienyl complexes bearing halogeno-, alkoxy-, or dialkyl-amino-substituents in the 1- or 2-positions are obtained by reaction of lithium tetrahydridoaluminate or methyl-or phenyl-lithium with the appropriately substituted (η-arene)tricarbonylmanganese salt. Directive effects in these nucleophilic additions are compared with those observed for arene complexes of iron and chromium.
TL;DR: In this paper, a kinetic and thermodynamic investigation of the Meisenheimer complexes formed at C-5 of 4-nitro-7-X-benzofurazans has been carried out, which indicates some influence of resonance stabilization in the ground state due to cross-conjugation between X and the nitro- and (aza-) groups, the observed maximum rate lowering factor being ca. 5 for X = OMe.
Abstract: A kinetic and thermodynamic investigation of the Meisenheimer complexes formed at C-5 of 4-nitro-7-X-benzofurazans has been carried out. The results indicate some influence of resonance stabilization in the ground state due to cross-conjugation between X and the nitro- and (aza-) groups, the observed maximum rate lowering factor being ca. 5 for X = OMe. However the importance of repulsive interactions in the transition state between the linked group and the nucleophile is recognized. The conclusions are compared with some suggestions previously made for analogous complexes in trinitrobenzene.
TL;DR: In this paper, the authors outline the recent developments in the field of nucleophilic aromatic photosubstitution and discuss the suggested lines of investigation, illustrating the pathways and the intermediates of NAPs, the mechanism of the reaction steps, and the factors governing product composition and quantum yields.
Abstract: Publisher Summary This chapter outlines the recent developments in the field of nucleophilic aromatic photosubstitution The chapter addresses fundamental questions and discusses the suggested lines of investigation, illustrating the pathways and the intermediates of nucleophilic aromatic photosubstitution, the mechanism of the reaction steps, and the factors governing product composition and quantum yields The photohydrolyses are often very clean reactions with good quantum yields The reaction may follow a different course with different nucleophiles Experiments with 18 O-labelling have shown that m- nitrophenyl phosphate, upon illumination, undergoes hydrolytic attack by water at the phosphorus atom, whereas with hydroxide ion and methylamine genuine aromatic substitution through attack at the ring carbon atom takes place The reaction is first order in light intensity and zero order in the light absorbing aromatic reaction partner The results obtained by conventional flash photolysis and with laser photolysis are discussed in the chapter
TL;DR: The hypothesis is advanced that solvation is not a major factor in determining the α-effect of the t-butylhydroperoxide anion.
Abstract: The rates of reaction of t-BuOOK, t-BuOK, n-BuOOK, and p-MeC6H4OKwith p-nitrophenyl diphenylphosphinate 1 and with p-nitrophenyl benzoate 2 have been measured in toluene both in the absence and in the presence of crown polyether dicyclohexyl-18-crown-6 3a. The rates of nucleophilic displacementon 1 by HOO−, t-BuOO−, and some “nonalpha” oxyanions in water have also been determined. Solvent transfer from water to toluene results in increasing the nucleophilic reactivity of the t-butyl hydroperoxide anion. Rate ratios QQa are given which allow one to estimate the enhanced reactivity of t-BuOO− (an α-nucleophile) compared to oxygen nucleophiles of comparable base strength toward 1 and 2. These are for substrate 1, Qα (water) ≃ 6.5 and Qα (toluene) ≃ 2.7; for substrate 2, Qα (water) ≃ 5.5 and Qα (toluene) ≃ 5. The hypothesis is advanced that solvation is not a major factor in determining the α-effect of the t-butylhydroperoxide anion.