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).     

Naphthyridines. Part 3: First example of the polyfunctionally substituted 1,2,4-triazolo[1,5-g][1,6]naphthyridines ring system

Treatment of 1,2,4-triazoles (1) with diethylmalonate in bromobenzene gave 1,2,4-triazolo-[1,5-a]pyridines 2. Chlorination of 2 using POCl₃/DMF (Vilsmeier reagent) led to the isolation of 7-chloro-6-formyl-1,2,4-triazolo[1,5-a]pyridine derivative 4, which reacted with the stabilized ylid 5 to afford 6-ethoxycarbonylvinyl-1,2,4-triazolo[1,5-a]-pyridines 6. Azidation of 6 yielded the corresponding azido compound 7, (Scheme 2). Reduction of 7 with Na₂S₂O₄ gave the corresponding 7-amino compound 8, which cyclized in boiling DMF to give the novel 1,2,4-triazolo[1,5-g][1,6]naphthyridines 9. On the other hand, reacting 7 with one equivalent of PPh₃ (aza-Wittig reaction) in CH₂Cl₂ gave 7-imino-phosphorane derivative 10, and subsequent cyclization in boiling DMF afforded the new 1,2,4-triazolo[1,5-g][1,6]naphthyridine derivative 11 (Scheme 3). However, treatment of 10 with phenyl isothiocyanate in 1,2-dichlorobenzene at reflux temperature gave the new 1,2,4-triazolo[1,5-g][1,6]naphthyridine derivative 14 (Scheme 4). Refluxing 6 with excess of a primary amines 15a,b in absolute. EtOH yielded the corresponding 7-alkyl-amino-1,2,4-triazolo[1,5-a]pyridines 16a,b. These obtained amines 16a,b underwent intramolecular heterocyclization in boiling DMF to give the novel 9-alkyl-1,2,4-triazolo[1,5-g][1,6]-naphthyridines 17a,b, in excellent yields (Scheme 5).     

Three inorganic-organic hybrids of bismuth(III) iodide complexes containing substituted 1,2,4-triazole organic components with charaterizations of diffuse reflectance spectra

The reactions of two kinds of substituted 1,2,4-triazoles with BiI₃ yielded three inorganic-organic hybrids: [HL1]₄[Bi₆I₂₂]·[L1]₄·4H₂O (1) (L1=3-(1,2,4-triazole-4-yl)-1H-1,2,4-triazole); [HL2]₄[Bi₆I₂₂]·6H₂O (2); [HL2]₂[Bi₂I₈]·[L2]₂ (3) (L2=(m-phenol)-1,2,4-triazole). Both 1 and 2 have polynuclear anions of [Bi₆I₂₂]^4- to build up the inorganic layers and substituted 1,2,4-triazoles as the organic layers. Hybrid 3 consists of two BiI₅ square pyramids as inorganic layers. There exist hydrogen bondings and I?I interactions in the structures of 1, 2 and 3. Optical absorption spectra of 1, 2 and 3 reveal the presence of sharp optical gaps of 1.77, 1.77 and 2.07 eV, respectively, suggesting that these materials behave as semiconductors.     

Rapid, microwave-assisted synthesis of N1-substituted 3-amino-1,2,4-triazoles

A robust, regioselective synthesis of 3-amino-1,2,4-triazoles is described. This reaction employs a key intermediate 2, which is coupled to carboxylic acids in good yields to afford intermediates 3a-d. These entities, in turn, react with a variety of hydrazines or hydrazine hydrochlorides to provide proposed intermediates 4a-j, which under microwave conditions cyclize to the desired 3-amino-1,2,4-triazoles (compounds 5a-j). This approach permits the rapid synthesis of regioselective N1-substituted 3-amino-1,2,4-triazoles, and is shown to afford a variety of such compounds in 34-70% isolated yields.     

Novel efficient anticancer agents and DNA-intercalators of 1,2,3-triazol-1,8-naphthalimides: design, synthesis, and biological activity

Two novel series of 3-1,2,3-triazol-1,8-naphthalimides 5a-e, 7a-e were synthesized easily by employing ‘click reaction’. Their bioactivities were evaluated. Compounds 5a-e were found to be more toxic against MCF-7 cells while 7a-e were more potent against 7721 cells, in particular 7a, the IC₅₀ value of which against cell lines of MCF-7 and 7721 was 0.348 μM and 0.258 μM, respectively. Due to the phenyl group linked to 1,2,3-triazole, compound 5a not only showed higher DNA affinity but also more efficient DNA damaging ability than compound 7a.     

Synthesis, characterization, and alkyne cyclotrimerization chemistry of titanium complexes supported by calixarene-derived bis(aryloxide) ligation

Proximally bridged calix[4]arene compounds (DESC)H₂ (3), (DMSHC)H₂ (4), (DMSMC)H₂ (5), and (DPSC)H₂ (6), in which one R₂Si group (R=alkyl or aryl) bridges adjacent oxygens, were synthesized via reaction between dialkyl- or diaryldichlorosilane and the corresponding calix[4]arene. Treatment of p-tert-butylcalix[4]arene with Ph₂SiCl₂ at room temperature or (o-MeC₆H₄)₂SiCl₂ at 80 °C gave (ClPh₂SiCl)₂Calix-H₂ (7) and (o-Tol₂SiCl)₂Calix-H₂ (8), respectively. Titanium dichloride complexes 9-12 (L₂TiCl₂, where L₂=DESC, DMSHC, DMSMC, or DPSC) were prepared in high yield from reaction of 3-6 with TiCl₄. The molecular structures of 7 and 12 were established by single-crystal X-ray diffraction studies. Reduction of 9, 11, and 12 with activated magnesium (Mg*) in the presence of an excess of Me₃SiCCH produced titananorbornadiene complexes L₂Ti{η⁶-1,2,4-C₆H₃(SiMe₃)₃} (13-15, L₂=DESC, DMSMC, or DPSC), which were characterized in solution. Catalytic cyclotrimerization of both terminal and internal alkynes was achieved using catalyst systems derived from L₂TiCl₂ complexes 9-12 and Mg*. For unsymmetrically substituted internal alkynes, preference for 1,2,4-substitution decreased as the size difference of the substituent groups decreased. The cyclotrimerization of PhCCMe was more facile when the calixarene-derived bis(aryloxide) ligand was DPSC versus DMSMC, suggesting that the DPSC ligand may provide a less crowded titanium center and exert greater kinetic control over the course of the cyclotrimerization.     

Application of the aza-Wittig reaction to the synthesis of pyrazinothienotriazolopyrimidinones: a new tetracyclic ring system

A simple one-pot and efficient method is described for the synthesis of pyrazinothienopyrimidines 6 by domino processes involving aza-Wittig/intermolecular nucleophilic addition/intramolecular cyclization. A tandem aza-Wittig reaction of phosphazenes 7, derived from 6, with heterocumulenes (isocyanates, carbon disulfide or carbon dioxide) generates the pyrazinothienotriazolopyrimidinones 9, 11 and 12, respectively. Pyrazino[2′,3′:4,5]thieno[3,2-d]-1,2,4-triazolo[1,5-a]pyrimidin-4(3H)-ones 15 and bis(pyrazinothienotriazolopyrimidinones) 17 were synthesized by the intermolecular aza-Wittig reaction of phosphazenes 7 with acyl chlorides or α,ω-dichlorides followed by heterocyclization via imidoyl chloride intermediate 16. Further S-alkylation of 11 and reaction of 6 with phosgeniminium chloride produce 2-alkylthio- and 2-N,N-dimethylaminopyrazinothienotriazolopyrimidinones 13 and 19, respectively.     

Synthesis of novel 1,4-disubstituted-1,2,3-triazole semi synthetic analogues of forskolin by click reaction

New 1,4-disubstituted-1,2,3-triazole analogues of forskolin (5a-g, 6a-g) have been prepared by regioselective propargylation at 1-position followed by Cu(I) catalysed cycloaddition of different alkyl azides under the click reaction conditions. An interesting acyl shift in the base catalysed propargylation afforded a new series of 1,4-disubstituted-1,2,3-triazole analogues of forskolin (6a-g). These analogues have potential selective therapeutic applications as antihypertensive, antiglaucoma, antiasthma and antiobesity agents.     

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%.     

Salen-ligands based on a planar-chiral hydroxyferrocene moiety: Synthesis, coordination chemistry and use in asymmetric silylcyanation

Condensation of the O-protected hydroxyferrocene carbaldehyde (S_p)-1 with suitable diamines, followed by liberation of the hydroxyferrocene moiety leads to a new type of ferrocene-based salen ligands (3). While the use of ethylenediamine in the condensation reaction yields the planar-chiral ethylene-bridged ligand [(S_p,S_p)-3a], reaction with the enantiomers of trans-1,2-cyclohexylendiamine gives rise to the corresponding diastereomeric cyclohexylene-bridged systems [(S,S,S_p,S_p)-3b and (R,R,S_p,S_p)-3c], which feature a combination of a planar-chiral ferrocene unit with a centrochiral diamine backbone. Starting with the ferrocene-aldehyde derivative (R_p)-1, the enantiomeric ligand series (3d/e/f) is accessible via the same synthetic route.The (S_p)-series of these newly developed N₂O₂-type ligands was used for the construction of the corresponding mononuclear bis(isopropoxy)titanium (4a/b/c), methylaluminum (5a/b/c) and chloroaluminum-complexes (6a/b/c), which were isolated in good yields and identified by X-ray diffraction in several cases. The aluminum complexes (5/6) were successfully used in the Lewis-acid catalyzed addition of trimethylsilylcyanide to benzaldehyde, yielding the corresponding cyanohydrins in 45-62% enantiomeric excess.     

Singlet oxygen addition to chiral allylic alcohols and subsequent peroxyacetalization with β-naphthaldehyde: synthesis of diastereomerically pure 3-β-naphthyl-substituted 1,2,4-trioxanes

The synthesis of a series of eight β-naphthyl-substituted 1,2,4-trioxanes 3a-h by a sequence of singlet oxygen ene reaction of allylic alcohols 1a-h and Lewis acid catalyzed peroxyacetalization of the allylic hydroperoxides 2a-h with β-naphthaldehyde is reported. The ene reactions were performed by solid-state photooxygenation in dye-crosslinked polystyrene beads and resulted in mixtures of diastereoisomeric hydroperoxides 2. Boron trifluoride catalyzed peroxyacetalization resulted in the formation of 3, as well as the 1,2,4-trioxanes 4 and 5, which were formed via acid catalyzed β-hydroperoxy alcohol cleavage.     

Amphiphilic perfluoroalkylated sulfones and sulfonate betaines

Two types of perfluoro alkyl-containing amphiphilic sulfones 7-9 and 13-15, respectively, and sulfonate betaines 23-32 were prepared using 2-[(perfluoroalkyl)methyl]oxiranes (1-3, R_F = C₄F₉, C₆F₁₃, C₈F₁₇) or 3-(perfluoroalkyl)propyl iodides (16 and 17, R_F = C₆F₁₃, C₈F₁₇) as the starting compounds. The overall yields of two-step syntheses were above 90%. The compounds 7-9 were prepared by the reaction of oxiranes 1-3 with 2-sulfanylethan-l-ol and subsequent oxidation of intermediate sulfides. Similarly, the amphiphiles 13-15 were obtained by analogous reaction of oxiranes 1-3 with thiomorpholine and subsequent oxidation of the sulfur atom in the morpholine ring. In the syntheses of betaines 23-32, the starting compounds 1-3 or 16 and 17 were first reacted with dimethylamine followed by the ring-opening reaction of the intermediate fluoroalkyl(dimethyl)amines with propane-1,3- or butane-1,4-sultones.     

Synthesis of novel lariat azathia crown macrocycles containing two triazole rings and bis crown macrocycles containing four triazole rings

The 13-hydroxy macrocycles 7a-d were prepared in 40-50% yields by the condensation of 1,ω-bis(4-amino-1,2,4-triazol-3-ylsulfany)alkanes 2a-d with 1,3-bis(2-formyphenoxy)-2-propanol (9). Acylation of 7a-d with 2-chloroacetylchloride gave the corresponding esters 11a,b. Amination of 11a,b with different amines in acetone furnished exclusively the target lariat macrocycles 12a,b and 13 in 60-70% yields. Reaction of 2 equiv. of the macrocycles 11a,b with 1 equiv. of piperazine afforded the novel bis macrocyles 14a,b in 50-60% yields. Reduction of 7a-d with NaBH₄ afforded the corresponding 13-hydroxyazathia crown ethers 15a-d in 65-70% yields.     

Unexpected conversion of a polycyclic thiophene to a macrocyclic anhydride

Oxygenation of 2,5,9,12-tetra(tert-butyl)diacenaphtho[1,2-b:1′,2′-d]-thiophene (1, C₄₀H₄₄S) by peracids gave the cyclic sulfonic ester 4 (2,7,10,13-tetra(tert-butyl)diacenaphtho[1,2-c:1′,2′-e]oxathiin 5,5-dioxide, C₄₀H₄₄O₃S) which, when heated in nitrobenzene, is converted into a complex, macrocyclic anhydride 3 (C₈₀H₈₈O₃), which is derived from two molecules of 4. Further investigation found a likely intermediate in this reaction, 4,4′,7,7′-tetra(tert-butyl)-1,1′-biacenaphthylenylidene-2,2′-dione (5, C₄₀H₄₄O₂), apparently formed from 4 by additional oxidation. Anhydride 3 plausibly arises by Diels-Alder reaction of 4 and 5 followed by several ring fragmentations. The structures of 3, 4, and 5 were unambiguously established by X-ray crystallography.     

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.     

Syntheses of metabolites of ethyl 4-(3,4-dimethoxyphenyl)-6,7-dimethoxy-2-(1,2,4-triazol-1-ylmethyl)quinoline-3-carboxylate (TAK-603)

Convenient and efficient syntheses of ethyl 4-(3-hydroxy-4-methoxyphenyl)-6,7-dimethoxy-2-(1,2,4-triazol-1-ylmethyl)quinoline-3-carboxylate (1d) and 10-(3,4-dimethoxyphenyl)-7,8-dimethoxy-2H-pyridazino[4,5-b]quinolin-1-one (1e), metabolites of TAK-603 (1), have been achieved. Use of the methanesulfonyl as a protective group of the phenolic hydroxy for Friedel-Crafts reaction enabled a new simpler synthetic route of 1d in high yield. Chloromethyl derivative (23) was converted to formyl derivative (32) using the Kröhnke reaction, followed by cyclization with hydrazine, which formed a novel compound 1e.     

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.     

Synthesis of 5-endo-, 5-exo-, 6-endo- and 6-exo-hydroxylated analogues of epibatidine

A convenient, high-yield synthesis of N-Boc-7-azabicyclo[2.2.1]hept-5-en-2-one (7) was developed by SmI₂-mediated desulfonylation of 6. Thus, 5-endo-, 5-exo-, 6-endo-, and 6-exo-hydroxylated epibatidine analogues 2a,b and 3a,b were synthesized from 7 by using a Pd(PPh₃)₄-catalyzed reductive Heck coupling reaction and SmI₂-mediated reduction of the carbonyl group as the key steps. Other reaction conditions for the reductive Heck procedure and the reduction step were also investigated.     

Application of intramolecular cycloaddition/retro cycloaddition reactions for the synthesis of unsymmetrical 2,2′-bipyridine and 2-benzofuropyrazin-2-ylpyridine analogues

1,2,4-Triazines bearing cycloalkeno[c]pyridine substituents at the 5-position, 2a-d, prepared by an intermolecular Diels-Alder reaction of bi-5,5-triazines with cyclic enamines, were provided with an alkynyloxy or a 2-cyanophenoxy group at the 3-position of the triazinyl unit. A subsequent intramolecular Diels-Alder reaction of the former, followed by loss of N₂ leads to two new classes of 2,2′-bipyridine analogues containing different heterocyclic units, namely cycloalkeno[c]pyridine and 2,3-dihydrofuro- or 2,3-dihydropyrano[2,3-b]pyridine 8a-h; the intramolecular reaction of the 2-cyanophenoxy compound gives benzo[4,5]furo[2,3-b]pyrazine 10a-c.     

Synthesis and characterization of titanium alkyl, oxo, and diene complexes bearing a SiMe2-bridged phenoxy-cyclopentadienyl ligand and their catalytic performance for copolymerization of ethylene and 1-hexene

A series of titanium complexes bearing a SiMe₂-bridged phenoxy-cyclopentadienyl ligand were synthesized and characterized, and their catalytic behavior for copolymerization of ethylene and 1-hexene was investigated. Treatment of dimethylsilyl(2,3,4,5-tetramethylcyclopentadienyl)(3-tert-butyl-5-methyl-2-phenoxy)-titanium dichloride (1) with appropriate nucleophiles afforded dimethoxy complex 2, dimethyl complex 3, and dibenzyl complex 4. Standing a toluene solution of 2 in air afforded a dinuclear μ-oxo complex 5 as a single isomer. 1,3-Diene complexes 6-8 were prepared by reaction of 1 with the corresponding 1,3-dienes in the presence of 2 equiv. of n-BuLi. X-ray analysis of 1,4-diphenyl-1,3-butadiene complex 6 revealed that the diene ligand coordinates to titanium in s-cis fashion with a prone orientation. The newly prepared titanium complexes were applied to copolymerization of ethylene and 1-hexene upon activation with AlⁱBu₃ and [C₆H₅NMe₂H][B(C₆F₅)₄]. It was found that the alkyl complexes 3-4 and the diene complexes 6-8 showed higher activities than 1 at elevated temperature.