Unique feature of chain reactions of thiols with quinone imines: thiols as reactants and simultaneously catalysts at the rate-determining step of chain propagation

The isomerization of radical adducts, formed due to the addition of thiyl radicals to the cyclohexadiene ring of quinone imine, to phenoxyl and aromatic aminyl radicals is considered by quantum chemical methods (DFT/PBE and CCSD). Isomerization via the intramolecular transfer of the highly mobile H atom of the C—H bond to the O or N atoms from the position of PhS? radical addition to the cyclohexadiene ring of quinone imine cannot virtually occur because of the high activation energy comparable or even exceeding the C—H bond dissociation energy. An alternative bimolecular mechanism involving the thiol molecule, which is inserted into the transition state thus extending it to be favorable for the reaction to occur, was proposed. After the reaction, the thiol is regenerated, i.e., acts as both the reactant and catalyst of the chain reaction of quinone imine with thiol. The reasons for the high rate of the H atom transfer via this mechanism are considered.     

Catalytic effect of hydroxyl-containing compounds at the propagation step of the chain reaction of thiophenol with quinone imines

Russian Chemical Bulletin - Hydroxyl-containing compounds (water, methanol, and phenol) act as efficient catalysts of the chain reactions of thiophenol with quinone imines at their propagation...     

Chemistry of heterocyclic quinone imines. 7. formation of O- and C-derivatives in the reaction of phenothiazinone-3 with phenolates

With an activated reagent, the reaction of phenothiazinone-3 with phenol and m-cresol gives, besides 2-aroxy derivatives, also the products of C-substitution, viz., 2-hydroxyarylphenothiazinones-3.For communication 6, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 753–756, June, 1985.     

Kinetic parameters of radical reactions of 2-mercaptobenzothiazole with quinone imines

The chain reaction of N,N′-diphenyl-1,4-benzoquinone diimine with 2-mercaptobenzothiazole was studied by two methods developed earlier for the nonchain reaction of N-phenyl-1,4-benzoquinone monoimine with 2-mercaptobenzothiazole. In the methods used, the kinetic scheme of the reaction is simplified by creating conditions under which the rates of all stages except radical generation and decay can be neglected. One of the methods was updated. For the nonchain reaction of N-phenyl-1,4-benzoquinone monoimine with 2-mercaptobenzothiazole, both methods gave close results; for the chain reaction of N,N′-diphenyl-1,4-phenylenediamine with 2-mercaptobenzothiazole, the results differed by approximately one order of magnitude.     

The features of the kinetics of radical reactions of quinone imines with 2-mercaptobenzothiazole

Kinetics of the reactions of N-phenyl-1,4-benzoquinone monoimine and N,N′-diphenyl-1,4-benzoquinone diimine with 2-mercaptobenzothiazole in chlorobenzene at T = 343 K has been studied by using kinetical spectrophotometry method (periodic spectral measurements and/or monitoring the wavelengths of the absorption band of quinone imines in the visible region). Two general features of the reactions, namely, radical mechanism and the existence of two steps were found. Kinetic features depend on the structure of a quinone imine. A reaction between N,N′-diphenyl-1,4-benzoquinone diimine and 2-mercaptobenzothiazole at first (initial) steps proceeds in an autoinhibition mode and has two independent channels, one of which being radical-chain. The addition of an initiator strongly accelerates the reaction only at the initial step, on completion of which the reaction rate decreases significantly and do not depend on the presence of the initiator. This testifies to the proceeding of the reaction by a non-chain mechanism subsequently to the initial step. The interaction involving N-phenyl-1,4-benzoquinone monoimine proceeds by a radical non-chain mechanism from the very beginning up to the end, and at the initial steps it proceeds in the autoaccelerating mode. The initiator has no influence on the reaction rate. For the process of the interaction of N,N′-diphenyl-1,4-benzoquinone monoimine and 2-mercaptobenzothiazole in the presence of 4-hydroxydiphenylamine, a radical mechanism was proposed, that serves to describe the kinetic features of the reaction and to obtain a quantitative estimation of some of its kinetic parameters.     

Unusual cyclization of N-imidazolyl quinone imines with the formation of thiadiazole ring and its subsequent recyclization

2,6-Di-tert-butyl-4-{[2-(2-aryl-2-oxoethylthio)-1H-imidazol-1-yl]imino}cyclohexa-2,5-dien-1-ones under the action of bases give products of the 2,3-dihydroimidazo[2,1-b]thiazol- 3-ol series by subsequent recyclization reaction of the intermediate imidazo[2,1-b][1,3,4]thiadiazoles. The structure of imidazo[2,1-b]thiazol-3-ol is supported by the X-ray diffraction. The features of the cyclization processes of quinone imine derivatives were stimulated by DFT calculations using the wB97XD/6-311++G** method.     

The mercury-crown complexes and their interaction with quinone

The anodic dissolution of a mercury electrode in 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile proceeds in the presence of dibenzo-24-crown-8 (DB24C8) in two waves, which were ascribed to the formation of complexes of Hg(II) and Hg(I). Both the ligand and the complexes are adsorbed at the electrode. Much weaker complexation was observed in the case of dibenzo-18-crown-6. The complex of Hg(I)-DB24C8 formed in situ reduces benzoquinone catalytically at potentials about 300 mV more positive.     

Novel thermal reaction of Fischer carbene complexes with imines: synthesis of beta-methoxy allylic amine derivatives

[formula: see text] Alkyl-substituted chromium Fischer carbene complexes were found to react with various N-tosylimines to give beta-methoxy allylic amine derivatives under thermal conditions. This result is essentially distinct from the photochemical outcome in which beta-lactam derivatives are obtained.     

Reaction of thiols with N-bonded sulfenamide complexes of cobalt(III): steric effect and reaction pathway

The products and kinetics of the reaction of several thiols (RSH = 2-aminoethanethiol, cysteine, penicillamine, cysteine ethyl ester) with N-bonded sulfenamide complexes ([Co(en)(2)(NH(2)S(CH(2))(2)NH(2)](3+) (IA), [Co(en)(2)(NH(2)SCH(2)CH(CO(2)H)NH(2)](3+) (IC), [Co(en)(2)(NH(2)SC(CH(3))(2)CH(CO(2)H)NH(2)](3+) (IP)) have been studied. The reaction proceeds by nucleophilic attack at sulfur with cleavage of the N-S bond to form a disulfide and leave a coordinated NH(3) ligand. The kinetics (pH 4-10) reveal that the deprotonated thiol, RS(-), is the reactive nucleophile and that the N-deprotonated sulfenamide complex is unreactive. The reactions of IP are approximately 10(4) times slower than those of IA or IC, and the reasons and consequences of this large steric effect are discussed. It is concluded, on the basis of these and other observations from the literature, that there will be substantial steric retardation to nucleophilic attack at two-coordinate sulfur in a R-C(CH(3))(2)-S-X-R' unit because of the regiospecificity of the reaction. The acid dissociation constants of IP and the X-ray structure of its bromide salt also are reported.     

The reaction of N-Acyl imines with t-Butyl isocyanide

N-Acylimines and their derivatives react with t-butyl isocyanide only the in presence of acid catalysis. The major products of these; reactions are 5-aminooxazoles and 5-iminooxazolines. The structure of these compounds and some of their degradative chemistry is discussed.     

Trans-stereoselectivity in the reaction between homophthalic anhydride and imines

The reaction between homophthalic anhydride and imines in the presence of TiCl4 and diisopropyl ethyl amine is trans-selective. Under these conditions, the reaction using homochiral imines can be highly diastereoselective, thus allowing the synthesis of enantiopure 1,2,3,4-tetrahydro-1-oxoquinoline-4-carboxylic acids.     

Rhodium-catalyzed reaction of thiols with polychloroalkanes in the presence of triethylamine

[reaction: see text] RhCl(PPh(3))(3) catalyzes a reaction of thiols with polychloroalkanes in the presence of triethylamine. This reaction serves as a convenient new method to produce formaldehyde dithioacetals, ethylenedithioethers, thioformates, and dithiocarbonic esters under mild conditions.     

Photolytic reaction of chromium and molybdenum carbene complexes with imines : Synthesis of cepham, oxapenam, and oxacepham derivatives

A variety of substituted β-lactams, including a cepham analog, were synthesized by the photochemical reaction of [(methoxy)(methyl)carbene]chromium complexes with substituted imines. Oxazines and oxazolines were inert towards chromium carbene complexes. Oxazines were converted to bicyclic β-lactams by the photolytic reaction of molybdenum carbene complexes. Oxazolines were considerably less reactive and produced only low yields of β-lactam product and an equivalent amount of the corresponding oxazinone, incorporating two (MeO)(Me)C(CO) groups.     

A mechanistic evaluation of the amperometric response of reduced thiols in quinone mediated systems

The specificity of the reaction of benzoquinone with reduced thiol species has been investigated and the nature of the amperometric electrode response elucidated. The analytical applicability of the methodology has been assessed and it has been shown that through appropriate selection of the redox properties of the indicating quinone, interference from other electroactive species can be minimised. A discrepancy in the reaction stoichiometry has however been found between the glutathione and cysteine quinone adducts and the implications in interpreting the resulting sensor response are rationalised. The adaptation of the approach to disposable, screen printed electrode assemblies has been investigated.     

Hydrogenation of imines by rhodium-phosphine complexes

The hydrogenation of imines using RhCl(PPh₃)₃ and [Rh(PPh₃)₂(diene)]PF₆ as catalyst precursors is effective at room temperature under 1 atm of hydrogen, using alcohols as solvents. A water-diethylether phase-transfer system has been used for a solid imine. A catalytic cycle featuring hydrogen bonding between a coordinated alcohol and an imine, and involving a dialkylamido intermediate, is proposed.     

Acid-free aza Diels-Alder reaction of Danishefsky's diene with imines

[reaction: see text] A highly efficient aza Diels-Alder reaction of Danishefsky's diene with imines was found to occur in methanol in the absence of any acids at room temperature to give corresponding 2-substituted dihydro-4-pyridone derivatives in high yields. This reaction can be also carried out in a three-component one-pot reaction manner. The reaction was found to proceed through a Mannich-type condensation mechanism.     

Solvatochromism and solvation of ternary iron-diimine-cyanide complexes

Summary The solvatochromic behaviour of several complexes [Fe(LL)₂(CN)₂] with LL=Schiff base diimine has been established in a series of non-aqueous solvents, as has that of two analogues containing diazabutadiene ligands. Transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol, and for [Fe(bipy)₂(CN)₂] into several binary aqueous solvent series. The usefulness of solvatochromic shifts and transfer chemical potentials as indicators of selective solvation is discussed. Kinetics of oxidation of catechol and of 4-t-butyl catechol by [Fe(bipy)(CN)₄]^– in aqueous solution are described.     

Organocatalytic enantioselective Friedel-Crafts reaction of pyrrole derivatives with imines

A highly enantioselective Friedel-Crafts reaction of pyrrole derivatives with N-acyl imines catalyzed by chiral phosphoric acids was developed. The reactions produced the pyrrole derivatives in high yields and enantioselectivity.