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Chemical Reviews 09/2011; 111(12):7749-73. · 40.20 Impact Factor
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ABSTRACT: Nitrogen heterocycles are widespread in nature and their applications in bioactive pharmaceuticals, agrochemicals and functional materials are well known. A number of protocols have been developed for their syntheses. This review article covers an updated (published during 2005-2008) summary of transition metal-catalyzed approaches for the syntheses of five- and six-membered ring heterocycles with one nitrogen atom via carbon-nitrogen bond forming reactions. The syntheses of five-membered ring heterocycles include pyrroles, pyrrolidines, indoles, oxindoles, isoindoles, indolizines and carbazoles. The syntheses of six-membered nitrogen heterocycles covered are pyridines, piperidines, quinolines and isoquinolines. In some cases, mechanistic rationalizations for the formation of the heterocycles have also been discussed.
Current Organic Chemistry 05/2011; 15(11):1760-1801. · 3.06 Impact Factor
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ABSTRACT: A series of symmetrical bent-shaped materials with six alkoxy chains at the terminal position has been designed and synthesized. All except one exhibit columnar mesophase behavior. The mesomorphic properties of the compounds have been studied with the help of polaralizing optical microscopy (POM) and differential scanning colorimetry (DSC) experiments.
Molecular Crystals and Liquid Crystals 12/2010; 518(1):160-167. · 0.58 Impact Factor
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ABSTRACT: A new class of thiophene-based cholesteryl and ferrocenyl derivatives was synthesized and characterized by common analytical techniques. Liquid-crystalline properties were investigated by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). Thiophene-based cholesteryl derivatives show homeotropic liquid-crystalline phase sequence crystal → smectic A → cholesteric → isotropic, whereas the ferrocenyl derivative is nonmesomorphic. The effects of thiophene ring, terminal group, and length of the polymethylene spacers on the mesomorphic behavior are discussed.
Molecular Crystals and Liquid Crystals 12/2010; 524(1):17-25. · 0.58 Impact Factor
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ABSTRACT: A series of symmetrical disc-shaped materials with a heteroaromatic 1,3,5-s-triazine core and nine alkoxy chains at the peripheral position has been designed and synthesised in a simplified way. All the compounds show hexagonal columnar mesophase. The mesomorphic properties of the compounds have been characterised with the help of polarising optical microscopy (POM), differential scanning calorimetry (DSC) and temperature controlled low angle XRD-experiments.
Liquid Crystals. 11/2010; 37(11):1459-1464.
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ABSTRACT: A one-step efficacious method for the construction of a variety of substituted furano-, pyrano-, and pyrrolocoumarins and pyrroloquinolones in good to excellent yields has been developed.
Synthetic Communications 07/2010; 40(14):2147-2157. · 1.06 Impact Factor
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ABSTRACT: Heterocyclic compounds are versatile building blocks in organic synthesis. These are important part in various natural products and bioactive compounds. Several methodologies have been developed to synthesize these heterocyclic compounds. This review article covers an updated (published during 2005 to 2008) summary of transition-metal catalyzed approaches for the syntheses of commonring heterocycles containing more than one heteroatom via the selective formation of carbon-heteroatom bonds. The five-membered ring heterocycles with two nitrogen atoms include imidazoles, pyrazoles, indazoles, imidazoindolones etc. and heterocycles with one nitrogen and one oxygen atoms include oxazoles, isoxazolines, isoxazolidines etc. Other five-membered heterocycles with one nitrogen and one sulfur atoms as well as one oxygen and one phosphorus/sulfur/silicon atoms have also been included here. Six-membered heterocycles containing two nitrogen atoms such as pyrimidines, pyrazines, phenazines, quinoxazolines etc. have been incorporated. Other six-membered heterocycles containing one nitrogen and one oxygen/sulfur atoms as well as one oxygen and one phosphorus atoms have also been included. Some heterocycles containing three or more heteroatoms have been discussed.
Current Organic Chemistry 04/2010; 14(8):846-887. · 3.06 Impact Factor
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ABSTRACT: be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
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ABSTRACT: A homologous series of Schiff's bases consisting of a benzophenone moiety as the central core has been synthesized. Schiff's bases were prepared starting from benzophenone by a sequence of reactions, viz., nitration followed by reduction and heating the resulting diamino derivative with 4-formyl-3-hydroxyphenyl 4-(alkyloxy)benzoate. Higher homologues of this series exhibit mesomorphism, but the lower homologues do not seem to possess any liquid crystalline property. The B2 mesophase was characterized by DFT study for orientation of dipole moment. Dipolar interaction and intramolecular H-bonding (N–H) have been considered to discuss the origin of the B2 phase in this homologous series of benzophenone moiety derived systems.
Molecular Crystals and Liquid Crystals 12/2009; 515(1):125-134. · 0.58 Impact Factor
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ABSTRACT: This brief review article describes the progress made in the synthesis of medium- and large-sized carbocyclic and heterocyclic rings by the application of the palladium-catalyzed reactions.
Current Organic Chemistry 04/2009; 13(7):731-757. · 3.06 Impact Factor
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Synthetic Communications 01/2008; 38(5):754-766. · 1.06 Impact Factor
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ABSTRACT: Synthesis of macrocyclic compounds including natural products with varying complexities by ring closing metathesis is described. Twelve to very large rings that have been synthesized in moderate to good yields and the synthesis of larger rings as a part of bi- or poly-cyclic systems are also described in this review. The effectiveness of the Grubbs' catalyst towards the RCM in presence of free alcohols, epoxides as well as with various silyl ethers is also presented. In addition to these, the application of RCM towards the syntheses of various naturally occurring macrolides, lactams and unnatural cyclic poly ethers, catenanes etc. are described.
Current Organic Chemistry 09/2007; 11(15):1339-1365. · 3.06 Impact Factor
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Synthetic Communications 01/2007; 37(9):1477-1484. · 1.06 Impact Factor
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Chemistry Letters 11/2006; 35(12):1430-1431. · 1.59 Impact Factor
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ABSTRACT: 4-(2'-Bromoaryloxymethylene)-9-methyl-2,3,9-trihydrothiopyrano[2,3-b]indoles under tri-n-butyltin hydride mediated aryl radical cyclization furnished exclusively the 4-{2'-benzo(2',3'-dihydro)furo}-9-methyl-2,3,9-trihydrothiopyrano[2,3-b]indoles in excellent yield (75-80%) via 4-exo-trig cyclization, opening of the oxetene ring, and 5-endo-trig cyclization.
Organic Letters 09/2006; 8(18):4059-62. · 5.86 Impact Factor
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Synthetic Communications 08/2006; · 1.06 Impact Factor
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Synthetic Communications 08/2006; 32(8)(1271–1274 (2002)):1271-1274. · 1.06 Impact Factor
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ABSTRACT: A practical synthesis of spiro-naphthyridinone derivatives is described by the combination of the Claisen rearrangement and ring-closing metathesis/ring-closing enyne metathesis process. The RCM or RCEM proceeded smoothly in the presence of Grubbs' first generation catalyst at room temperature under a nitrogen atmosphere.
Organic & Biomolecular Chemistry 07/2006; 4(12):2393-8. · 3.70 Impact Factor
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ABSTRACT: Hitherto unreported indole-annulated pentacyclic heterocycles containing oxygen, nitrogen and sulfur have been synthesised by thermal Claisen rearrangement followed by Lewis acid catalysed Claisen rearrangement. 9-Acetyl-4-aryloxymethyl-2,9-dihydro-thiopyrano[2,3-b]indoles are regioselectively synthesised in 80-85 % yield by thermal rearrange-ment of 2-(4`-aryloxybut-2`-ynylthio)-1-acetylindoles. A second, Lewis acid catalysed, rearrangement gave 7-acetyl-11c-methyl-4b,5,7,11c-tetrahydro-[1]benzo-furo-[2`,3`: 4,5]-thiopyrano[2,3-b]-indoles in yields of 85-90 %. The thermal Claisen rearrangement in refluxing N,N-diethylaniline for 3 h gave the same products in lower yield (50-54 %).
Journal of Chemical Research 04/2006; 2006(5):281-285. · 0.04 Impact Factor
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ABSTRACT: [reaction: see text] 4-(4'-Aryloxybut-2'-ynylthio)[1]benzopyran-2-ones are refluxed in chlorobenzene to afford 4-aryloxymethylthiopyrano[3,2-c][1]benzopyran-5(2H)-ones which are subsequently subjected to heating in o-dichlorobenzene in the presence of N,N-diethylaniline and then treated with pyridine hydrotribromide to give [6,6]pyranothiopyrans in almost quantitative yield.
Organic Letters 09/2002; 4(16):2629-31. · 5.86 Impact Factor
