Showing papers on "Pyran published in 2004"

A Clean One-pot Synthesis of Tetrahydrobenzo(b)pyran Derivatives Catalyzed by Hexadecyltrimethyl Ammonium Bromide in Aqueous Media

Abstract: An efficient and convenient approach to the synthesisof 2-amino-3-cyano-4-aryl-7,7-dimethyl-5-oxo-4 H -5,6,7,8-tetra-hydrobenzo[ b ]pyran derivatives using hexadecyltrimethyl ammoni-um bromide (HTMAB) as the catalyst (10 mol%) is described. Thismethod provides several advantages such as neutral conditions,high yields and simple work-up procedure, in addition water waschosen as a green solvent. Key words: tetrahydrobenzo[ b ]pyran, hexadecyltrimethyl ammo-nium bromide, aqueous media With increasing environmental concerns, more and morechemists are devoted to the area of ‘green synthesis’which means the reagents, solvent and catalyst are en-vironmentally friendly. In modern organic chemical re-search, Wender defined the ‘ideal synthesis’ as one inwhich the target components are produced in one step, inquantitative yield from readily available and inexpensivestarting materials in resource-effective and environmen-tally acceptable process. 1 The one-pot multicomponentcondensations represent a possible instrument to performa near ideal synthesis because they possess one of theaforementioned qualities, namely the possibilities ofbuilding-up complex molecules with maximum simplicityand brevity.

Synthesis and Characterization of New Red-Emitting Polyfluorene Derivatives Containing Electron-Deficient 2-Pyran-4-ylidene-Malononitrile Moieties

Abstract: A novel series of red-light-emitting copolymers derived from fluorene and 2-pyran-4-ylidene−malononitrile (PM) have been synthesized through a palladium-catalyzed Suzuki coupling reaction. The polymers were characterized by FT-IR, NMR, and elemental analysis. All these polymers are completely soluble in common organic solvents, such as THF, CH2Cl2, CHCl3, and toluene, and they have good thermal stability with onset decomposition temperature (Td) of 406−407 °C and glass-transition temperature (Tg) of 73−186 °C. Cyclic voltanmetry studies reveal that these copolymers have low-lying LUMO energy levels ranging from −3.53 to −3.57 eV and HOMO energy levels ranging from −5.77 to −5.79 eV, which indicated that they may be promising candidates for electron-transporting or hole-blocking materials in light-emitting diodes. These polymers in thin films can emit strong red photoluminescence (PL) around 641−662 nm with the corresponding additional peaks in the range 704−712 nm upon photoexcitation. Double-layer LEDs f...

Total syntheses of (+)-chloropuupehenone and (+)-chloropuupehenol and their analogues and evaluation of their bioactivities.

Abstract: Tetracyclic pyrans (+)-chloropuupehenone (1) and (+)-chloropuupehenol (5) and its C8-R-isomer (+)-3 were synthesized via a one-pot condensation of 1-chloro-2-lithio-3,5,6-tris(tert-butyldimethylsilyloxy)benzene (8) with (4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-2,5,5,8a-tetramethylnaphthalene-1-carboxaldehyde (7). The major condensation product, (4aS,6aR,12bS)-2H-9,10-bis(tert-butyldimethylsilyloxy)-11-chloro-1,3,4,4a,5,6,6a,12b-octahydro-4,4,6a,12b-tetramethyl-benzo[a]xanthene (4), after desilylation provided tetracyclic pyran (+)-(4aS,6aR,12bS)-2H-11-chloro-1,3,4,4a,5,6,6a,12b-octahydro-4,4,6a,12b-tetramethyl-benzo[a]xanthene-9,10-diol (3). At a dosage of 42 mg/rat over 8 h, pyran diol 3 inhibited the intestinal absorption of cholesterol by 71% in rats. Tetracyclic pyran 4 was also converted to o-quinone 28, which inhibited cholesteryl ester transfer protein (CETP) activity and L1210 leukemic cell viability with IC(50) values of 31 and 2.4 microM, respectively. Diol (+)-5 inhibited CETP activity with an IC(50) value of 16 microM. The minor condensation product, (4aS,6aS,12bS)-2H-9,10-bis(tert-butyldimethylsilyloxy)-11-chloro-1,3,4,4a,5,6,6a,12b-octahydro-4,4,6a,12b-tetramethyl-benzo[a]xanthene (6), was transformed into (+)-5 and (+)-1. A stepwise stereoselective synthesis of (+)-1 was also developed utilizing an oxyselenylation ring-closure reaction. The synthetic sequence also produced four biologically active naturally occurring drimanic sesquiterpenes, (+)-drimane-8alpha,11-diol (34), (-)-drimenol (38), (+)-albicanol (39), and (-)-albicanal (31) as intermediates.

Synthesis of pyran and pyranone natural products.

Abstract: : An overview of the synthesis of the fungal metabolites (+)-dermolactone, (–)-semixanthomegnin, (+)- and (–)-mellein, (–)-ochratoxin α, (–)-(1 R ,3 S )-thysanone, the enantiopure ventiloquinones L, E and G, and 8-desmethyleleutherin from a common chiral intermediate, is presented. Further methodology leading potentially toward extended quinones such as (3 S ,3' S )-xylindein is also outlined. Keywords: Stereospecific synthesis; fungal metabolites; quinones; isochromanones. Introduction Biologically active aromatic systems with appended pyran or pyranone (δ-lactone) rings are widespread in nature, being found in a wide variety of organisms, including fungi. Our interest in these molecules was ignited by our need to synthesise just one member of the group in order to establish the absolute stereochemical configuration of that natural product, but has subsequently broadened in scope to become the first versatile total synthesis of a number of natural products in enantiomerically pure form.

Indeno-fused photochromic naphthopyrans, naphthols and photochromic articles

Abstract: Described are photochromic materials of indeno [2',3':3,4]naphtho[1,2-b]pyran structure, characterized in that they have a nitrogen or sulfur containing substituent at the 11-position ring atom, are substantially free of spiro-substituents at the 13-position and have been adapted to provide an increase in the sensitivity, visible lambda max or a combination thereof as measured in the Indenonaphthopyran Photochromic Performance Test. Optional substituents can be present at the other positions of the indeno [2',3':3,4]naphtho [1,2-b]pyran structure. Also described are naphthols used to produce the photochromic materials and photochromic articles that contain or that have coatings containing at least one of the novel photochromic materials or combinations thereof with other photochromic materials.

Process for producing a pyran compound

Abstract: The invention relates to a process for producing a mixture of a pyran represented by the formula (II) and a hydroxypyran represented by the formula (III) by reacting aldehyde (I) with isoprenol. wherein R 1 represents an alkyl or alkenyl group having 1 to 12 carbon atoms, an optionally alkyl- or alkoxy-substituted aryl group having 6 to 12 carbon atoms in total, or the like. Further, the hydroxypyran compound in the resulting mixture is subjected to dehydration reaction in the presence of an acid to produce a pyran compound represented by the formula (II).

Pyran compound or at least one derivative thereof

Abstract: The invention relates to pyran derivatives of the formula I and to a process and intermediates for their preparation and derivatisation, and to the use thereof in liquid-crystalline media.

Studies on the Trypanocidal Activity of Semi-Synthetic Pyran[b-4,3]naphtho[1,2-d]imidazoles from β-Lapachone.

Abstract: We synthesized new naphthoimidazoles from beta-lapachone with an aromatic moiety linked to the imidazole ring, using phenylic and heterocyclic aldehydes. The most active compound against Trypanosoma cruzi had a p-methyl group linked to the phenyl ring, presenting an EC(50) value of 15.5 +/- 2.9 microM. No reliable correlation could be established with the biological activity and the structure of in the phenylic series. For the heterocyclic series, activity was associated with a three bond-distance from nitrogen to the imidazole ring, in accordance with our previous work.

Pyran derivatives containing an exocyclic double bond

Abstract: The invention relates to pyran derivatives of formula I and processes and intermediates for their preparation and derivatisation, and the use thereof in liquid-crystalline media.

A Clean One-Pot Synthesis of Tetrahydrobenzo[b]pyran Derivatives Catalyzed by Hexadecyltrimethyl Ammonium Bromide in Aqueous Media.

Abstract: An efficient and convenient approach to the synthesisof 2-amino-3-cyano-4-aryl-7,7-dimethyl-5-oxo-4 H -5,6,7,8-tetra-hydrobenzo[ b ]pyran derivatives using hexadecyltrimethyl ammoni-um bromide (HTMAB) as the catalyst (10 mol%) is described. Thismethod provides several advantages such as neutral conditions,high yields and simple work-up procedure, in addition water waschosen as a green solvent. Key words: tetrahydrobenzo[ b ]pyran, hexadecyltrimethyl ammo-nium bromide, aqueous media With increasing environmental concerns, more and morechemists are devoted to the area of ‘green synthesis’which means the reagents, solvent and catalyst are en-vironmentally friendly. In modern organic chemical re-search, Wender defined the ‘ideal synthesis’ as one inwhich the target components are produced in one step, inquantitative yield from readily available and inexpensivestarting materials in resource-effective and environmen-tally acceptable process. 1 The one-pot multicomponentcondensations represent a possible instrument to performa near ideal synthesis because they possess one of theaforementioned qualities, namely the possibilities ofbuilding-up complex molecules with maximum simplicityand brevity.

Convenient and versatile synthesis of spiro(furan-2,3-indol[2]ones) and spiro(pyran-2,3-indol[2]ones)

Abstract: Novel functionalized spiro-3-oxindoles of potential use for the synthesis of natural product analogues and pharmaceutically active compounds were prepared from substituted isatins by a convenient and versatile base-catalyzed condensation and ring-closure reaction. Moreover, a side product consisting of an at present unknown bicyclic skeleton has been isolated.