Triflic acid promoted synthesis of polycyclic aromatic compounds

The triflic acid (CF₃SO₃H) promoted cyclizations of 2-styrylbiaryls are found to be useful for the synthesis of polycyclic aromatic compounds, including functionalized derivatives of polycyclic aromatic compounds and heterocyclic systems. The reaction involves cationic cyclization followed by an elimination of benzene from the intermediate product.     

Reactions of some quinazoline compounds with ethoxymethylenemalonic acid derivatives

The reactions of ethyl (1,4-dihydro-4-oxoquinazolin-2-yl)acetate 4 and 2-aminoquinazolin-4(1H)-one 5 with diethyl ethoxymethylenemalonate (EMME), (ethoxymethylene)malononitrile (EMMN) and ethyl (ethoxymethylene)cyanoacetate (EMCA) are reported, and rather different results are obtained to those previously found with quinoline analogs. Reaction of 4 with EMME gives a pyrido[1,2-a]quinazoline, while with EMMN and EMCA ethyl 2-(pyridin-2-yl)aminobenzoates are formed, presumably by ring-opening of intermediate pyrido[2,1-b]quinazolines. Reaction of 5 with EMME likewise results in ultimate cyclization onto N-1 of the quinazoline, while the EMMN and EMCA reactions give isolable pyrimido[2,1-b]quinazolines. These are readily cleaved under mild conditions.     

A cascade process toward the synthesis of fused polycyclic dihydropyridines

The synthesis of fused polycyclic dihydropyridines was achieved using a cascade process comprising a Suzuki coupling, a nucleophilic cyclization and a hydrogen migration. Several functional groups are tolerated in this reaction and the methodology could be applied with success to quinoline and isoquinoline derivatives.     

Ruthenium- and platinum-catalyzed sequential reactions: selective synthesis of fused polycyclic compounds from propargylic alcohols and alkenes

A simple method for the preparation of fused polycyclic compounds by an intramolecular cyclization of propargylic alcohols bearing an alkene moiety at a suitable position has been developed, where the presence of both Ru and Pt catalysts promotes a sequence of catalytic cycles in the same medium. This sequential system can be applied to an intermolecular reaction between a propargylic alcohol and an alkene to obtain the corresponding bicyclo[3,1,0]hex-2-ene derivative. These sequential reactions provide a conceptually new type of cycloaddition system between propargylic alcohols and alkenes.     

Endo-oxacyclizations of polyepoxides: biomimetic synthesis of fused polycyclic ethers

Boron trifluoride-etherate promotes the endo-selective oxacyclization of polyepoxides derived from various acyclic terpenoid polyalkenes, including geraniol, farnesol, and geranylgeraniol, providing an efficient and stereoselective synthesis of substituted oxepanes and fused polyoxepanes. The mechanism of the oxacyclization reaction probably involves intramolecular nucleophilic addition of epoxide oxygen to open another epoxide that is activated as an electrophile by the Lewis acid. These oxacyclizations proceed stereospecifically with inversion of configuration upon opening of each epoxide to provide trans-fused polycyclic products. The oxacyclization cascade is terminated by a tethered nucleophile, which may be the carbonyl oxygen of a ketone, ester, or carbonate, or a trisubstituted alkene. The best oxacyclization yields are generally observed with tert-butyl carbonate as the terminating nucleophile, although in some cases the oxacyclization products include formation of tert-butyl ethers as a minor product. The oxacyclization transformations described herein may mimic ring-forming steps in the biosynthesis of trans-syn-trans-fused polycyclic ether marine natural products.     

Polymer sorbents with hydrazide moieties for water treatment applications

The possibility was explored for synthesizing sorbents containing hydrazide moieties, suitable wastewater and water treatment applications. Waste polymers containing ester groups served as the starting material. Polymer derivatives containing hydrazide moieties in the side chain (poly(meth)acrylic acid hydrazides [1–3] and their copolymers with vinyl alcohol [4]) were tested as precursors for synthesis of polymers with oxydiazole rings [5, 6], modifiers of cement compositions [7, 8], textile finishing agents [9–11], and supports for RNA immobilization [12].     

Photochemical synthesis of heteroatom-containing polycyclic aromatic compounds

Anthra[2,1-b]furan, anthra[2,1-b]benzo[d]furan, anthra[2,1-b]thiophene, anthra[1,2-b]thiophene, anthra[2,1-b]benzo[d]thiophene, anthra[2,1-b]pyrrole and naphtho[2,3-c]carbazole derivatives were synthesized in fairly good yields by a one-pot photocycloaddition reaction of 2,3-disubstituted 1,4-naphthoquinone with 1,1-diarylethylene. This is the first reported synthesis of these aromatic compounds.     

Lewis acid mediated diastereoselective synthesis of fused fluorinated spiroketal as potential biologically active compounds

A series of substituted dibenzalacetones prepared using standard procedures were condensed with 5-methyl, 5-phenyl, and 5-trifluoromethyl-1,3-cyclohexanediones respectively, in toluene containing BF₃·OEt as the Lewis acid catalyst. The reaction was found to be highly diastereoselective (dr, 9:1). The resulting spiroketals 1a-r were formed in moderate to good yields. In addition, a synthetically and biologically useful by-product identified as chromenone 7 was observed.     

Microwave assisted synthesis of some new fused 1,2,4-triazines bearing thiophene moieties with expected pharmacological activity

Rapid and efficient solvent-free synthesis of 4-amino-3-mercapto-6-[2-(2-thienyl)vinyl]-1,2,4-triazin-5(4H)-one 1 under microwave irradiation is described. Some new fused heterobicyclic nitrogen systems such as 1,2,4-triazino[3,4-b][1,3,4]thiadiazinones, 1,3,4-thiadiazolo[2,3-c][1,2,4]triazinone and pyrazolo[5,1-c]-[1,2,4]triazine-7-carbonitrile, have been synthesized by treatment of 1 with bifunctional oxygen and halogen compounds, CS?/KOH and malononitrile via heterocyclization reactions, in addition to some uncondensed triazines. Structures of the products have been deduced from their elemental analysis and spectral data (IR, 1H-NMR, 13C-NMR). Select new synthesized compounds were screened as anticancer agents, with some showing activity as cytotoxic agents against different cancer cell lines.     

Chromium-mediated synthesis of polycyclic aromatic compounds from halobiaryls

[reaction: see text] Reaction of 2,2'-dihalobiphenyl with butyllithium followed by the addition of chromium(III) chloride and alkynes afforded the corresponding phenanthrene derivatives via formal [4 + 2] cycloaddition. A variety of alkynes could be used for this reaction, such as alkyl, aryl, silyl, and alkoxycarbonyl alkynes. Repetitive process of the reaction gave more extended polycyclic compounds such as benzo[g]chrysene and azacyclopentaphenalene derivatives.     

A new stereocontrolled approach to fused polycyclic compounds containing a diketopiperazine ring

Representative (1S)- and (4S)-alkyl-1,4-dihydropyrazino[2,1-b]quinazoline-3,6-dione lactim ethers were regio- and diastereoselectively alkylated after metallation to give the corresponding 1,4-trans-isomers with retention of the stereocentres. The results were compared with the previously studied lactams. The (1R,4S)-dialkyl derivatives obtained by C(1)-alkyation with bifunctional reagents were lately cyclized to complex polycyclic compounds through a second N(2)-alkylation promoted by sodium iodide.     

Porphyrins fused with unactivated polycyclic aromatic hydrocarbons

A systematic study of the preparation of porphyrins with extended conjugation by meso,β-fusion with polycyclic aromatic hydrocarbons (PAHs) is reported. The meso-positions of 5,15-unsubstituted porphyrins were readily functionalized with PAHs. Ring fusion using standard Scholl reaction conditions (FeCl(3), dichloromethane) occurs for perylene-substituted porphyrins to give a porphyrin β,meso annulated with perylene rings (0.7:1 ratio of syn and anti isomers). The naphthalene, pyrene, and coronene derivatives do not react under Scholl conditions but are fused using thermal cyclodehydrogenation at high temperatures, giving mixtures of syn and anti isomers of the meso,β-fused porphyrins. For pyrenyl-substituted porphyrins, a thermal method gives synthetically acceptable yields (>30%). Absorption spectra of the fused porphyrins undergo a progressive bathochromic shift in a series of naphthyl (λ(max) = 730 nm), coronenyl (λ(max) = 780 nm), pyrenyl (λ(max) = 815 nm), and perylenyl (λ(max) = 900 nm) annulated porphyrins. Despite being conjugated with unsubstituted fused PAHs, the β,meso-fused porphyrins are more soluble and processable than the parent nonfused precursors. Pyrenyl-fused porphyrins exhibit strong fluorescence in the near-infrared (NIR) spectral region, with a progressive improvement in luminescent efficiency (up to 13% with λ(max) = 829 nm) with increasing degree of fusion. Fused pyrenyl-porphyrins have been used as broadband absorption donor materials in photovoltaic cells, leading to devices that show comparatively high photovoltaic efficiencies.     

Barbituric acid in the synthesis of fused 1,7-phenanthroline derivatives

New 7-aryl(hetaryl)-7,8,9,10,11,12-hexahydropyrimido[5,4-b][1,7]phenanthroline-9,11-diones have been synthesized by three-component condensation of barbituric acid with quinolin-5-amine and aromatic or heteroaromatic aldehydes.     

An efficient non-catalytic, regioselective approach to the synthesis of angularly fused polycyclic systems

A novel approach to the synthesis of partially reduced different ring sizes of PAH analogs with sec.amino and nitrile functionalities is delineated through base-induced ring transformation of 4-sec.amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles by a carbanion, generated in situ from cyclopentanone, cyclohexanone, cycloheptanone, and cyclooctanone separately in good yields. An increase in the size of cycloalkanone ring beyond cyclooctanone restricts the ring transformation under analogous reaction conditions possibly due to bulky conformation of higher homologs. The synthetic method provides an efficient general route for the construction of angularly fused partially reduced polycyclic aromatic hydrocarbons: 5-sec.amino-2,3,6,7-tetrahydro-1H-cyclopenta[c]phenanthrene-4-carbonitriles, 6-sec.amino-2,3,4,7,8-pentahydro-1H-benzo[c]phenanthrene-5-carbonitriles, 7-sec.amino-2,3,4,5,8,9-hexahydro-1H-cyclohepta[c]phenanthrene-6-carbonitriles, and 8-sec.amino-2,3,4,5,6,9,10-heptahydro-1H-cycloocta[c]phenanthrene-7-carbonitriles.     

Green route synthesis of Schiff's bases of isonicotinic acid hydrazide

Abstract

Imines constitute a class of therapeutic agents that possess a broad spectrum of pharmacological activity. The conventional method for synthesis of imines by nucleophilic addition of amines to ketones or aldehydes requires long reaction times along with the use of organic solvents and a glacial acetic acid catalyst. We report the synthesis of Schiff's bases of isonicotinic acid hydrazide by novel, green routes using sonication, stirring, and microwave irradiation, respectively. Initial results are reported and indicate that by employing greener methods under aqueous conditions, high yields and shorter reaction times can be achieved.     

The synthesis of poly(acrylic acid hydrazide) and poly(methylacrylic acid hydrazide) and their reaction products with ribonucleoside dialdehydes

Atactic and syndiotactic poly(acrylic acid hydrazide) and atactic, syndiotactic and isotactic poly(methylacrylic acid hydrazide) have been reacted with the di-aldehydes derived from adenosine, guanosine, inosine, cytidine and uridine to give polymers each containing a single type of base residue. Not all of the hydrazide residues of the polymeric hydrazides reacted; guanosine dialdehyde gave the most reaction and inosine dialdehyde the least. Isotactic poly(methylacrylic acid hydrazide) was much less reactive than the other polymeric hydrazides. The adenine-containing and the cytosine-containing polymers with atactic backbones had a low solubility in water whereas those with syndiotactic backbones had a relatively high solubility. For a given polymeric hydrazide backbone the adenine-containing polymers were always the least soluble in water. Most of the ribonucleoside dialdehyde-containing polymers, with the exception of those containing uridine dialdehyde, had only a low solubility in salt solution (0.3M sodium chloride, 0.03M trisodium citrate). No evidence could be obtained for any interaction of these polymers with polynucleotides.     

Eco-friendly synthesis of 2-azetidinone analogs of isonicotinic acid hydrazide

Abstract

2-Azetidinones possess broad and potent activity due to presence of β-lactam ring and has been established as one of the biologically important scaffolds. The synthesis of N-(4-aryl-2-oxoazetidinone)-isonicotinamide by novel methods of stirring and sonication are described. The conventional method for synthesis of 2-azetidinones involves use of Dean–Stark water separator for the removal of water from the reaction with long reaction time (12–16 h reflux) at a very low temperature (?70 to ?90°C). The microwave method reported requires inert atmosphere of nitrogen gas for the synthesis of 2-azetidinones. We report herein the synthesis of 2-azetidinone analogs of isonicotinic acid hydrazide by novel green route methods of sonication and stirring using molecular sieves. Results indicate that higher yields and shorter reaction times can be achieved by employing novel green route methods of synthesis.