Reactions of benzimidazole-2-thiol with N-alkyl-1-aza-1,3-enynes

Reactions of N-alkyl-1-aza-1,3-enynes with benzimidazole-2-thiol in anhydrous dimethylformamide have been studied. The structure of the obtained compounds has been elucidated from the NMR data.     

Reactivity of N-Phenyl-1-Aza-2-Cyano-1,3-Butadienes in the Diels-Alder Reaction

It is found that N-phenyl-2-cyano-1-azadiene 4, prepared via a two-step, one-pot, sequence from acrylanilide, undergoes efficient [4 + 2] cycloaddition with a complete range of electron rich, electron poor, and neutral dienophiles under remarkably mild thermal conditions (90-120 degrees C for 20-48 h). Regiospecific formation of the alpha-cycloadduct wherein the dienophile substituent is alpha to nitrogen is observed for vinyl ethers and styrene, whereas the Diels-Alder reactions with methyl acrylate and methyl vinyl ketone (MVK) produce alpha/beta mixtures in which the alpha-cycloadduct is the major regioisomer (approximately 4-5:1). An essentially identical reaction pattern was observed in the Diels-Alder reaction of N-(p-methoxyphenyl)-2-cyano-1-azadiene 18 and the 4-methyl-substituted azadiene 27. For compound 19 derived from cycloaddition of 18 with ethyl vinyl ether, facile conversion to the dihydropyridine 21 through loss of EtOH on brief acid treatment was also noted. The 2,4-cis-disubstitution pattern confirmed by X-ray diffraction for the major cycloadduct 29 isolated from the reaction of 27 with styrene provides evidence for the endo mode of cycloaddition in the Diels-Alder reaction of N-phenyl(aryl)-2-cyano-1-azadienes. Calculation of the frontier orbital energies and coefficients, as well as the transition state geometries for the [4 + 2] cycloaddition of N-phenyl-2-cyano-1-azadiene 4 with methyl vinyl ether, styrene, and MVK were carried out at the RHF AM1 level (MOPAC, Version 5.0). The FMO treatment indicates that the reaction of 4 with methyl vinyl ether occurs under LUMO(diene) control, whereas in contrast, the corresponding cycloaddition with MVK occurs preferably under HOMO(diene) control. A high degree of asynchronicity is observed in the calculated transition states for reaction of 4 with the three representative dienophiles. In all cases the transition states leading to the alpha-cycloadducts are lower in energy than those giving the beta-products. However, at the AM1 level the exo cycloaddition mode is found to be the preferred, this result contrasting with experimental results for azadiene 27.     

On the Reaction between 1-Aza-1,3-dienes and Push-Pull Olefins of the Acyloxymethylidene-malononitrile Type

 The reaction between push-pull olefins of the acyloxymethylidene-malononitrile type and α, β-unsaturated hydrazones affords selectively 5-alkyl-2-cyano-6-(N′,N′-dimethylhydrazono)-hexa-2,4-dienenitriles. No [4+2]-cycloaddition products were detected. The structure elucidation of the obtained compounds and possible reaction mechanisms are discussed.     

On the Reaction between 1-Aza-1,3-dienes and Push-Pull Olefins of the Acyloxymethylidene-malononitrile Type

Summary.  The reaction between push-pull olefins of the acyloxymethylidene-malononitrile type and α, β-unsaturated hydrazones affords selectively 5-alkyl-2-cyano-6-(N′,N′-dimethylhydrazono)-hexa-2,4-dienenitriles. No [4+2]-cycloaddition products were detected. The structure elucidation of the obtained compounds and possible reaction mechanisms are discussed. Received March 9, 2000. Accepted March 20, 2000     

Unusual Reaction of 1,3-Benzothiazole-2-thiol with Iodomethyl(dimethyl)phenylsilane in the Presence of Iodine

Russian Journal of Organic Chemistry - The three-component reaction of 1,3-benzothiazole-2-thiol with iodomethyl(dimethyl)phenylsilane and molecular iodine in the absence of a base and...     

Copper-catalyzed synthesis of 1,3-enynes

[reaction: see text] We report a copper(I)-catalyzed procedure for the synthesis of 1,3-enynes. This method affords a variety of enynes in good to excellent yields. This method can tolerate a variety of functional groups, does not require the use of expensive additives, and is palladium-free.     

A protodesilylation route for 2-Aza-1,3-diene synthesis

A new methodology for 2-aza-1,3-diene synthesis involving protodesilylation reactions of N-1-triethylsilylallyl-imines and their propargyl analogs is described. Synthetic sequences for the preparation of these allyl and propargyl imines starting with propargyl amine are presented. The silylallyl and silylpropargyl imines are transformed to 2-azadiene products by use of CsF induced desilylation via a pathway involving generation and regioselective γ-protonation of intermediate 1-imino-allyl and propargyl anions. Alkylative-desilylation of the silylallyl and propargyl imines leads to generation of N-1-alkylallyl-imines and propargyl analogs via α-alkylation of intermediate anions. Finally, the stereochemistry of azadiene formation has been probed by use of the conversion of N-(1-triethylsilylpropen-1-yl) benzaldimine to 1-phenyl-2-aza-1,3-pentadiene. Solvent, water concentration and a metal cation complexing agent all appear to influence the stereoselectivity of this process.     

Phosphirenes and Azaphosphetines: IX. 1-Aza-2-phospha-1,3-dienes, 1,2-Azaphosphetines,and 1-Aza-2-phosphacyclohexa-2,4-dienes in Reactions with P-Bromoimino-N-(tri-tert-butylphenyl)phosphine with 1-Dialkylamino-1-alkynes

The reaction of P-bromoimino-N-(tri-tert-butylphenyl)phosphine with 1-dialkylamino-1-alkynes primarily forms 1-aza-2-phosphabitadienes. The latter are unstable and can further rearrange into 1,2-azaphos-phetines or take up one more aminoacetylene molecule to give 1-aza-2-phospha-2,4-cyclohexadienes.     

Reaction of 1,3-Dibromo- and 1,3-Dichloroacetone with 2-Aminoazaheterocycles

The reactions of 1,3-dibromoacetone with 2-aminoazines and 2-aminoazoles has been carried out for the first time and the pure intermediate quaternary salts have been isolated. They undergo cyclization to the corresponding imidazoazines and imidazoazoles containing a bromomethyl group. Similar condensations were carried out with 1,3-dichloroacetone.     

Synthesis of S- and S-S-Organosilicon Derivatives of 1,3-Benzothiazole-2-thiol

Russian Journal of Organic Chemistry - The reactions of 1,3-benzothiazole-2-thiol and di(1,3-benzothiazol-2-yl) disulfide with (iodomethyl)silanes containing exocyclic and endocyclic silicon atoms...     

Oxidation of 1-methyl-1H-imidazole-2-thiol with chlorine dioxide

Oxidation of 1-methyl-1H-imidazole-2-thiol with chlorine dioxide was performed for the first time, and the results were shown to depend on the oxidation conditions. Optimal conditions were found for the preparation of 1-methylimidazole-2-sulfonic acid, 2,2′-disulfanediylbis(1-methylimidazole) hydrochlorite, and 1-methyl-3-sulfo-3H-imidazolium chloride. A new salt, 4-methylanilinium 1-methyl-1H-imidazole-2-sulfonate, was isolated.     

Unexpected Regioselective Reactions of 2-(Bromomethyl)-1,3-thiaselenole with 1-Methyl-1H-imidazol-2-thiol,Accompanied by Rearrangements

Russian Journal of Organic Chemistry - The previously unknown regioselective reactions of 2-(bromomethyl)-1,3-thiaselenole with 1-methyl-1H-imidazol-2-thiol were used to develop efficient synthetic...     

Reaction of 1-Aryl-1,3,4,4-tetrachloro-2-azabuta-1,3-dienes with aminoazoles

Reactions of polychlorinated 2-aza-1,3-dienes of the general formuls ArCCl=NCCl=CCl₂ with 3(5)-aminopyrazoles, 3(5)-amino-1,2,4-triazoles, and 5-aminotetrazole led to the formation of substituted pyrazolo[1,5-a][1,3,5]triazines, [1,2,4]triazolo[1,5-a][1,3,5]triazines, and 2-azido-1,3,5-triazine derivatives whose structure was reliably established by spectral methods and X-ray analysis.     

Stepwise Construction of Polynuclear Complexes of Rhodium and Iridium Assisted by Benzimidazole-2-thiol. NMR and X-ray Diffraction Studies

Reactions of [M(2)(&mgr;-Cl)(2)(cod)(2)] (cod = 1,5-cyclooctadiene, M = Rh, Ir) with benzimidazole-2-thiol (H(2)Bzimt) afford the mononuclear complexes [MCl(H(2)Bzimt)(cod)] (M = Rh (1), Ir (2)) for which a S-coordination of the ligand is proposed based on their spectroscopic data. The dinuclear complexes [M(2)(&mgr;-HBzimt)(2)(cod)(2)] (M = Rh (3), Ir (4)) are isolated from the reaction of [M(acac)(cod)] and benzimidazole-2-thiol. They contain the monodeprotonated ligand (HBzimt(-)) bridging the two metals in a &mgr;(2)-(1kappaN,2kappaS) coordination mode and in a relative cis,cis-HT arrangement. Complexes 3 and 4 react with the appropriate species [M(cod)(Me(2)CO)(2)](+) to afford the trinuclear cationic aggregates [M(3)(&mgr;-HBzimt)(2)(cod)(3)](+) (M = Rh (5), Ir (6)) and with the [M'(2)(&mgr;-OMe)(2)(cod)(2)] compounds to give the homo- and heterotetranuclear complexes [MM'(&mgr;-Bzimt)(cod)(2)](2) (M = M' = Rh (7), Ir (8); M = Ir, M' = Rh (9)) containing the dideprotonated ligand (Bzimt(2)(-)). The trinuclear neutral complexes [M(3)(&mgr;-Bzimt)(&mgr;-HBzimt)(cod)(3)] are intermediates detected in the synthesis of the tetranuclear complexes. Protonation of 9 with HBF(4) gives the unsymmetrical complex [Ir(2)Rh(&mgr;-HBzimt)(2)(cod)(3)]BF(4) (10). This reaction involves the protonation of the bridging ligands followed by the removal of one "Rh(cod)" moiety to give a single isomer. The molecular structure of [Rh(2)(&mgr;-Bzimt)(cod)(2)](2) (7) has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P2(1)/n, a = 20.173(5) ?, b = 42.076(8) ?, c = 10.983(3) ?, beta = 93.32(2) degrees, Z = 8, 7145 reflections, R = 0.0622, and R(w) = 0.0779. The complete assignment of the resonances of the (1)H NMR spectra of the complexes 3, 4, and 7-9 was carried out by selective decoupling, NOE, and H,H-COSY experiments. The differences in the chemical shifts of the olefinic protons are discussed on the basis of steric and magnetic anisotropy effects.     

Silaborations of 1,3-enynes - substrate controlled allene/1,3-diene selectivity

Silaboration of 1,3-enynes catalyzed by group 10 metal complexes affords 1,3-dienes with vinylborane and vinylsilane functions or 1,2-dienes with allylborane and vinylsilane functions. The type of product formed is determined by the size of the alkyne substituent.     

Reaction of hexamethyldisiloxane with 2-ethoxy-1,3-dioxolane

The reaction of hexamethyldisiloxane with 2-ethoxy-1,3-dioxolane is described. It is shown that cleavage of the endo- and exocyclic carbon-oxygen bonds of the ortho ester occurs under mild conditions (16–20C) in the presence of acidic catalysts with the formation of 2-(trimethylsiloxy)ethyl formate, the subsequent transformation of which leads to ethyl formate, trimethylethoxysilane, and 1,2-bis(trimethylsiloxy)ethane.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1607–1611, December, 1989.