Comparative studies for selective deprotection of the N-arylideneamino moiety from heterocyclic amides: kinetic and theoretical studies. Part 2

4-Benzylideneamino-1,2,4-triazine-3,5(2H,4H)-diones (2-5), 6-styryl-1,2,4-triazine-3,5(2H,4H)-dione (6), and 6-styryl-2,3-dihydro-3-thioxo-1,2,4-triazin-5(4H)-one (7) were synthesized and pyrolyzed in the gas phase. The kinetic effect of changing the substituent on the triazine ring from hydrogen to methyl, phenyl, and styryl was measured. Analyses of the pyrolyzates of 2-5 showed the elimination products to be benzonitrile and the triazine fragment, while the pyrolyzates of 6 and 7 reveal the formation of cis- and trans-cinnamonitriles. Theoretical study of the pyrolysis reactions of 2-5 using an ab initio SCF method was investigated.     

Synthesis of 2-aryl-2H-[1,2,4]triazoloquinolin-3-one and 2-aryl-2H-[1,2,4]triazoloisoquinolin-3-one derivatives from α-chloroformylarylhydrazines hydrochloride

The reaction of α-chloroformylarylhydrazines hydrochloride with quinoline under air provided the corresponding 2-aryl-2H-[1,2,4]triazoloquinolin-3-ones 3a-3d in 33-42% yields and unexpected isomeric 2-aryl-2H-[1,2,4]triazoloisoquinolin-3-ones 4a-4d in 30-42% yields. These two isomers were isolated and fully characterized by spectroscopic methods including X-ray crystallography. By employing 3-methylquinoline as the starting material under the same condition, the reaction only gave compound 3e-3h as sole products in 70-82% yields without the formation of isomers. A plausible mechanism was proposed through electrophilic aromatic reaction, the tandem ring cyclization and ring-opening, and oxidation for the generation of 2-aryl-2H-[1,2,4]triazoloisoquinolin-3-ones (4).     

Synthesis of functional Δ-1,3,5-oxazaphospholene and 2H-1,4,2-diazaphosphole complexes via catalytic ring expansion reactions of a 2H-azaphosphirene complex

Catalytically-induced ring expansion of 2H-azaphosphirene complex 1 using ferrocenium hexafluorophosphate and acetone (2), diethylketone (3), cyclohexanone (4), benzaldehyde (5) or para-hydroxy-benzaldehyde (6) furnished selectively the Δ³-1,3,5-oxazaphospholene complexes 7-11, whereas with ortho- and para-hydroxy- or ortho- and para-amino-substituted benzonitriles the 2H-1,4,2-diazaphosphole complexes 16-19 were obtained. Two further findings are noteworthy: (1) The significant decreased reaction time in the case of the sterically more demanding carbonyl derivatives 2-4 and (2) the formation of diastereomers in the case of 10 and 11 with a ratio of 8:1 and 9:1, respectively. All products were characterized by NMR, MS and elemental analysis and the configuration of complexes 7 and 10a were determined by X-ray single-crystal diffraction analysis.     

Reaction of 1-substituted 3,5-diamino-1,2,4-triazoles with β-keto esters: synthesis and new rearrangement of mesoionic 3-amino-2H-[1,2,4]triazolo-[4,3-a]pyrimidin-5-ones

Reaction of 3,5-diamino-1-R-1,2,4-triazoles (R=Ph, Bn) with β-keto esters results in the reversible formation of N-(5-amino-1-R-1,2,4-triazol-3-yl)-substituted enaminoesters (8). Subsequent transformations depended on the reaction conditions. Compounds 8 undergo intermolecular reactions of condensation and amidation in the absence of solvent. However, in the presence of acetic acid they form 3-amino-5-oxo-2-R-2,5-dihydro-[1,2,4]triazolo[4,3-a]pyrimidin-4-ium-8-ides (10) followed by rearrangement to 3-amino-1-R-[1,2,4]triazolo[4,3-a]pyrimidin-5-ones (11). The transformation of 10 into 11 represents a new type of rearrangement in the azolopyrimidine series. Heating of enaminoesters 8 in ethanol with sodium ethoxide present, proved to be a suitable method for the preparation of the mesoionic compounds 10.     

Synthesis of a new class of azathia crown macrocycles containing two 1,2,4-triazole or two 1,3,4-thiadiazole rings as subunits

A series of new 1,2/1,3-bis[o-(N-methylidenamino-5-aryl-3-thiol-4H-1,2,4-triazole-4-yl)phenoxy]alkane derivatives 3a-d and bis[o-(N-methylidenamino-2-thiol-1,3,4-thiadiazole-5-yl)phenoxy]alkanes 6a-c were prepared by condensation of 4-amino-5-(aroyl)-4H-1,2,4-triazole-3-thiols 2a-b or 2-amino-5-mercapto-1,3,4-thiadiazole with bis-aldehydes 1a-c. Further reaction of compounds 3a-d and 6a-c with dibromoalkanes afforded the new macrocycles 5a-f and 8a-d. The cyclization does not require high dilution techniques and provides the expected azathia macrocycles in good yields, ranging from 55% to 68%.     

Synthesis of 4-aryl-5,5-dimethyl-5H-1,2,3-triazoles and 4-aryl-3-cyano-5,5-dimethyl Δ-pyrazolines by cycloaddition of 2-diazopropane with iminoethers and propenenitriles

A regiospecific 1,3-dipolar cycloaddition of 2-diazopropane 3 to iminoethers 1a-c, carried out at 0 °C, afforded in two steps the corresponding 4-aryl-5,5-dimethyl-5H-1,2,3-triazoles 5a-c. Under the same conditions, 3-arylpropenenitriles 2a-d led to 3-cyano-5,5-dimethyl Δ¹-pyrazolines 6a-d. Products 4-6 were obtained in good yields (69-85%).     

A novel transformation of 1-exo-substituted 2a-aroyl-1,2,2a,8b-tetrahydro-3H-benzo[b]cyclobuta[d]pyran-3-ones with sulfoxonium ylide to highly strained 2a-(1-arylethenyl)-1,2,2a,7b-tetrahydrocyclobuta[b]benzofurans

When 1-substituted 2a-aroyl-1,2,2a,8b-tetrahydro-3H-benzo[b]cyclobuta[d]pyran-3-ones (1) were treated with dimethylsulfoxonium methylide, 1-endo isomers (endo-1) gave 1-substituted 3-aroyl-1,2,4a,9b-tetrahydrodibenzofuran-4-ols (2) exclusively as expected. On the other hand, 1-exo isomers (exo-1) underwent a novel transformation to 1-substituted 2a-(1-arylethenyl)-1,2,2a,7b-tetrahydrocyclobuta[b]benzofurans (3), together with 2.     

Efficient dual catalytic enantioselective diethylzinc addition to the exocyclic CN double bond of some 1,2,4-N-triazinylarylimines using polymer-supported chiral β-amino alcohols derived from norephedrine

Chiral N,N-dialkylnorephedrines and their corresponding copolymers were evaluated as chiral ligands for the enantioselective diethylzinc addition to the exocyclic CN double bond of some 4-arylideneamino-3-mercapto-6-methyl-4H-1,2,4-triazin-5-ones 2a-f. The use of a dual catalytic system (amino alcohol/halosilane) in the titled asymmetric reaction was examined. The enantioselective ethylation reaction has been successfully carried out in the heterogeneous system even at low temperature. The corresponding 4-(1-arylpropyl)amino-3-mercapto-6-methyl-4H-1,2,4-triazin-5-ones 4a-f were obtained in high yields with high enantioselectivities using chiral polymers (up to 91% ee), which are almost the same as those obtained from homogeneous analogues (up to 92% ee). The diethylzinc reagent neither opened the 1,2,4-triazinyl heterocyclic ring nor attacked the carbonyl or the thione groups of the 1,2,4-triazinyl heterocyclic ring and the addition reaction took place exclusively at the exocyclic electrophilic carbon atom yielding the C-ethylated products 4a-f. Reductive cleavage of the 1,2,4-triazinyl heterocyclic ring led smoothly to the corresponding primary aromatic amines 11a-f without significant loss of enantiomeric purity. A suggestion about the possible transition state for the addition reaction is also presented.     

Nitrosation of hydrochlorothiazide and the modes of binding of the N-nitroso derivative with two macrocycles possessing an 18-membered crown ether cavity

The hydrochlorothiazide, 6-chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide-1,1-dioxide, (HCTZ), widely used as a diuretic and anti-hypertensive drug, was transformed into its N-nitroso-derivative, 6-chloro-4-nitroso-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide-1,1-dioxide (ON-HCTZ) by sodium nitrite in an acidic medium. The crystalline complexes of ON-HCTZ with 18-crown-6 (18C6) and cis-anti-cis-dicyclohexyl-18C6 (DCH6B) demonstrated different H-bonding modes from those present in the co-crystals of HCTZ with the same crown ethers. The influence of the nitroso-group on the binding mode and crystal packing is discussed.     

An efficient electrochemical method for a unique synthesis of new derivatives of 7H-thiazolo[3,2-b]-1,2,4-triazin-7-one

The electrochemical oxidation of catechols (1a-c) has been studied in the presence of 6-methyl-1,2,4-triazine-3-thion-5-one 3 in aqueous sodium acetate, using cyclic voltammetry and controlled-potential coulometry. A plausible mechanism for the oxidation of catechols and their reaction with 3 is presented. All the catechol derivatives (1a-c) were converted into 7H-thiazolo[3,2-b]-1,2,4-triazin-7-one derivatives (6a-c) through a Michael-type addition reaction of 3 to anodically generated o-quinones. The electrochemical syntheses of 6a-c were successfully performed in one pot in an undivided cell using an environmentally friendly method with high atomic economy.     

Facile synthesis of 4-phenylquinolin-2(1H)-one derivatives from N-acyl-o-aminobenzophenones

An efficient synthesis of 4-phenylquinolin-2(1H)-one derivatives has been achieved in a one-pot reaction from N-acyl-o-aminobenzophenones 1a-c (a: acyl=acetyl; b: acyl=propanoyl; c: acyl=heptanoyl) using NaH as a base. Treatment of 1 with NaH provided the quinolones 2a-c with 62-83% yields, whereas the reaction in the presence of alkyl iodide (alkyl=methyl, ethyl, n-octyl) gave the corresponding N-alkylated quinolones 3a-g in 75-95% yields. The alkylation reaction of 4-phenylquinolin-2(1H)-one 2a with alkyl halide gave a mixture of N-alkylated and O-alkylated products. Comparison of IR and NMR data of the N-alkylated and O-alkylated compounds with those of 2a-c indicated that 2a-c exist as the lactam form.     

First cross-coupling reactions on halogenated 1H-1,2,4-triazole nucleosides

The halogenated 1H-1,2,4-triazole glycosides 6-10 were synthesized by BF₃-activated glycosylation of 3(5)-chloro-1,2,4-triazole (2), 3,5-dichloro-1,2,4-triazole (3), 3,5-dibromo-1,2,4-triazole (4), and 3(5)-bromo-5(3)-chloro-1,2,4-triazole (5) with 1,2,3,4-tetra-O-pivaloyl-β-d-xylopyranose (1). The β-anomeric major products 3-chloro-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazole (6β), 3,5-dichloro-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazole (7β), and 3,5-dibromo-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazole (8β) were used as starting materials for transition metal catalyzed C-C-coupling reactions. Arylations of the triazole ring of 7β, and 8β were successful in 5-position with phenylboronic acid, 4-vinylphenylboronic acid, and 4-methoxyphenylboronic acid, respectively, under Suzuki cross-coupling conditions (products 11-17). Moreover, a Cu-catalyzed perfluoroalkylation of 8β is reported with 1-iodo-perfluorohexane yielding 3-perfluorohexyl-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazole (18). Compound 18 was depivaloylated to the trihydroxy derivative 19. The copper-mediated reaction of 8β with Rupert's reagent gave the bis(3-bromo-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazol-5-yl) (20).     

Substituent-induced regioselective synthesis of 1,2-teraryls and pyrano[3,4-c]pyran-4,5-diones from 2H-pyran-2-ones

Substituent-controlled regioselective synthesis of highly functionalized 1,2-teraryls 3a-k has been achieved through ring transformation of 6-aryl-4-(pyrrolidin-1-yl/piperidin-1-yl)-2H-pyran-2-one-3-carbonitriles 1a-g by aryl acetones 2a-c in the presence of powdered KOH in DMF in very good yield. Under similar reaction conditions, 6-aryl-4-methylsulfanyl-2H-pyran-2-ones 5a-f afforded 1,7-diaryl-2-methyl-4H,5H-pyrano[3,4-c]pyran-4,5-diones 6a-j as major products and 3,4-diaryl-2-methyl-6-methylsulfanylbenzonitriles as minor constituents 7a-j.     

Supramolecular nanostructured assemblies of different types of porphyrins with fullerene using TiO2 nanoparticles for light energy conversion

TiO₂ nanoparticles were modified with porphyrin derivatives, 5-[4-benzoic acid]-10,15,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (Ar-H₂P-COOH), 5-[4-benzoic acid]-10,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (H-H₂P-COOH), and 5,10,15,20-tetra[4-benzoic acid]-21H,23H-porphyrin (H₂P-4COOH). The porphyrin-modified TiO₂ nanoparticles were deposited on nanostructured OTE/SnO₂ electrode together with nanoclusters of fullerene (C₆₀) in acetonitrile-toluene (3/1, v/v) using an electrophoretic deposition technique to afford the porphyrin-modified TiO₂ composite electrode denoted as OTE/SnO₂/(porphyrin-modified TiO₂ nanoparticle+C₆₀)_n. The porphyrin-modified TiO₂ composite electrodes have efficient light absorbing properties in the visible region, exhibiting the photoactive response under visible light excitation using redox couple. The incident photon-to-photocurrent efficiency (IPCE) values of supramolecular nanostructured electrodes of porphyrin-modified TiO₂ nanoparticles with fullerene [OTE/SnO₂/(Ar-H₂P-COO-TiO₂+C₆₀)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂+C₆₀)_n] are much larger than those of the reference systems of porphyrin-modified TiO₂ nanoparticles without C₆₀ [OTE/SnO₂/(Ar-H₂P-COO-TiO₂)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂)_n]. In particular, the maximum IPCE value (41%) is obtained for OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n under the bias potential of 0.2 V versus SCE. This indicates that the formation of supramolecular complexes between porphyrins and fullerene on TiO₂ nanoparticles plays an important role in improvement of the light energy conversion properties.     

An efficient microwave assisted synthesis of novel class of Rhodanine derivatives as potential HIV-1 and JSP-1 inhibitors

(Z)-5-(2-(1H-Indol-3-yl)-2-oxoethylidene)-3-phenyl-2-thioxothiazolidin-4-one (7a-q) derivatives have been synthesized by the condensation reaction of 3-phenyl-2-thioxothiazolidin-4-ones (3a-h) with suitably substituted 2-(1H-indol-3-yl)-2-oxoacetaldehyde (6a-d) under microwave condition. The thioxothiazolidine-4-ones were prepared from the corresponding aromatic amines (1a-e) and di-(carboxymethyl)-trithiocarbonyl (2). The aldehydes (6a-h) were synthesized from the corresponding acid chlorides (5a-d) using HSnBu₃.     

Synthesis and chemistry of tricyclic cyclopropene-tricyclo[3.2.2.0]nona-2(4),6-diene

The 1,2-bridged tricyclic cyclopropene, tricyclo[3.2.2.0^2,4]nona-2(4),6-diene (1), has been synthesized by the elimination of 2-bromo-4-chlorotricyclo[3.2.2.0^2,4]-non-6-ene (5). Cyclopropene 1 will undergo different isomerizations in ether solution and in neat conditions. Compound 1 rearranged to an anti-Bredt compound 4 via diradical mechanism in ether and tricyclic compound 6 via vinyl carbene mechanism in neat conditions. Compound 1 can be trapped with DPIBF at different temperatures yielding different results: the exo-endo adduct 2 (exo-addition from the view of the cyclopropene and endo-addition from the view of bicyclo[2.2.2]octene) is a sole product at 0°C by slowly addition of methyllithium, and the exo-endo adduct 2, endo-endo adduct 9, anti-Bredt adduct 3, and styrene 8 are isolated at ether refluxing temperature. Styrene 8 is proposed to be formed from endo-endo adduct 9 by diradical mechanism. The chemistry of exo-endo adduct 2 and endo-endo adduct 9 is as well studied. The exo-endo adduct 2 undergoes hydration in trifluoroacetic acid to generate 1,3-cis-diol 11 followed by eliminations of water and formaldehyde to give naphthalene 12. The endo-endo adduct 9 reacts with water in tetrahydrofuran-containing silica gel to yield 1,4-cis-diol 10. Both 9 and 10 react with trifluoroacetic acid to form trans-3-hydroxy trifluoroacetate 13. Compound 13 will undergo hydrolysis and isomerization to generate 1,3-cis-diol 11 in trifluoroacetic acid.     

The reaction of 2-(1-hydropolyfluoro-1-alkenyl)-4H-3,1-benzoxin-4-ones with dinucleophilic reagents: a convenient route to fluoroalkylated nitrogen-containing tricyclic compounds

The reactions of 2-(1-hydropolyfluoro-1-alkenyl)-4H-3,1-benzoxin-4-ones (2) with hydrazine hydrate and phenyl hydrazine were investigated. The reaction of 2 with hydrazine hydrate in ethanol under reflux condition readily gave 2-fluoroalkyl-4H-pyrazolo[5,1-b]quinazolin-9-ones (3) in high yields. The reaction of 2 with phenyl hydrazine, however, resulted in the formation of 2-(2-phenyl-5-fluoroalkyl-2H-pyrazol-3-yl) benzoic acids (7). Further treatment of 7 with PPA gave 1-phenyl-4,9-dihydro-3-fluoroalkyl-1H-pyrozolo[3,4-b]quinolin-4-ones (4) in 65-80% overall yields.     

Effect of π-accepting substituent on the reactivity and spectroscopic characteristics of triarylbismuthanes and triarylbismuth dihalides

Competitive chlorination of p-substituted triarylbismuthanes 1 [(p-XC₆H₄)₃Bi; a: X = OMe, c: Cl, d: CO₂Et, e: CF₃, f: CN, g: NO₂] and trimesitylbismuthane (2,4,6-Me₃C₆H₂)₃Bi 1h by sulfuryl chloride was carried out against 1b (X = H) and the effect of these substituents on the formation of triarylbismuth dichlorides 2 was studied. The relative ratios 2/2b decreased with increasing electron-withdrawing ability of the substituents (2a/2b = 53/47, 2c/2b = 33/67, 2d/2b = 35/65, 2e/2b = 29/71, 2f/2b = 16/84, 2g/2b = 0/100, 2h/2b = 46/54), indicating a lowering of reactivity of the lone pair on the bismuth atom. Pd-Catalyzed degradation of 2a-g and their difluorides 3 giving biaryls 4 was promoted by the electron-withdrawing p-substituents in the equatorial aryl groups but suppressed by the more electronegative fluorine atoms in the apical positions. This is in fairly good accord with the stability of the trigonal bipyramidal geometry. The ¹³C NMR study of 1-3 showed that the signals due to the ipso carbons (C1) attached to the bismuth atom shift downfield with increasing electron-withdrawing nature of the p-substituents. No such tendency was observed in other aromatic ring carbons. The electronic effect on the C1 atoms, similar to that on the chlorination of 1 and degradation of 2 and 3, indicates the significant participation of the C1 atoms in these reactions through the Bi-C1 bonds.     

The role of botrydienediol in the biodegradation of the sesquiterpenoid phytotoxin botrydial by Botrytis cinerea

The biotransformation of botrydienediol (6) labelled with deuterium on carbons C-10 and C-15 has been studied. This has led to modification of some previous assumptions about the biodegradative route of botrydial. The [10-²H,15-²H]-botry-1(9)-4-diendiol (12) was transformed into dehydrobotrydienediol derivatives 13-15 but it was not incorporated into secobotryane skeleton (7). In addition, three new sesquiterpenoids have been isolated, which shed further light on the secondary metabolites of Botrytis cinerea. From the point of view of persistence of these toxins in the food chain, the easy biotransformation and different biodegradative routes of botrydial (1), seem to indicate that the toxin may not persist in the plant for a long time as it will be metabolized by the fungi and the plant.     

New reaction of ethenetetracarbonitrile with N-arylisoindolines

N-Arylisoindolines 1a-i react with ethenetetracarbonitrile 2 in aerated benzene by formation of [3-(2-aryl-3-dicyanomethylene-2,3-dihydro-1H-isoindol-1-ylidene)-2-aryl-2,3-dihydro-1H-isoindol-1-ylidene]propanedinitriles 8a-i (20-36%), N-aryl-3-dicyanomethylene-isoindol-2-ones 9a-i (15-21%) and N-arylphthalimides 10a-i (4-9%) as well as 1,1,2,2-tetracyanoethane 11 (35-55%). The structure of 8d has been unambiguously confirmed by a single crystal X-ray structure analysis. A rationale for the formation of products 8-11 is presented.