http://www.mdpi.com/journal/molecules/special_issues/heterocyclic-chemistry/ Dear Colleagues, This special issue is dedicated to the publication of the latest research results in the field of Heterocyclic Chemistry, especially focusing on the synthesis, reactivity, structure, and biological activity of heterocyclic compounds. Prof. Dr. Norbert Haider Guest Editor Related Special Issues Advances in Heteroaromatic Chemistry in Molecules {snippet name="submission_info"} http://www.mdpi.com/1420-3049/16/3/2023/ Two salts of the mesoionic compounds 1,4-diphenyl-5-(5-nitro-2-furanyl)-1,3,4-thiadiazolium-2-thiol chloride (MC-1) and 4-phenyl-5-(5-nitro-2-furanyl)-1,3,4-thiadiazolium-2-phenylamine chloride (MC-2) were synthesized utilizing 1,4-diphenyl-thiosemicarbazide and 5-nitro-2-furoyl chloride as starting materials. Their structures were characterized by IR, 1H-NMR, 13C-NMR and elemental analysis. These compounds were analyzed for their influence on the effectiveness of norfloxacin, tetracycline, and erythromycin (standard antibiotics) against resistant strains of Staphylococcus aureus. MC-1 and MC-2, at sub-inhibitory concentrations of 16 μg/mL, favourably modulated the antibiotic activity of tetracycline by 16- and 32-fold, respectively (MIC), and that of erythromycin by 4-fold. http://www.mdpi.com/1420-3049/16/3/2023/ Mon, 28 Feb 2011 00:00:00 CET Molecules 2011-02-28 16 3 Article 2023 2031 1420-3049 Drug Resistance Modulation in Staphylococcus Aureus, a New Biological Activity for Mesoionic Hydrochloride Compounds 2011-02-28 doi: 10.3390/molecules16032023 Cledualdo Soares de Oliveira Vivyanne Dos Santos Falcão-Silva José Pinto Siqueira-Júnior David Peter Harding Bruno Freitas Lira Jorge Gonçalo Fernandes Lorenzo José Maria Barbosa-Filho Petrônio Filgueiras de Athayde-Filho http://www.mdpi.com/1420-3049/16/1/609/ Enaminone 1 was reacted with hydrazonoyl halides 2a-d to yield 3,4-disubstituted pyrazoles 6a-d. Coupling with arenediazonium chlorides afforded the 2-(arylhydrazono)-3-(1-naphthalenyl)-3-oxopropionaldehydes 13a-c. Compounds 13 could be utilized for the synthesis of a variety of arylpyrazoles, arylazolopyrimidines, and pyridazinones via reaction with hydrazines, aminoazoles, and active methylene derivatives, respectively. A comparative study of aforementioned reactions was carried out with chitosan as a basic ecofriendly catalyst under conventional heating as well as under pressurized microwave irradiation conditions. http://www.mdpi.com/1420-3049/16/1/609/ Mon, 17 Jan 2011 00:00:00 CET Molecules 2011-01-17 16 1 Article 609 623 1420-3049 Chemistry of the Enaminone of 1-Acetylnaphthalene under Microwave Irradiation Using Chitosan as a Green Catalyst 2011-01-17 doi: 10.3390/molecules16010609 Huwaida M. E. Hassaneen http://www.mdpi.com/1420-3049/15/11/8006/ A practical synthetic route for the preparation of 2-pyridyl and 3-pyridyl derivatives has been accomplished by utilizing a simple coupling reaction of stable 2-pyridylzinc bromides and 3-pyridylzinc bromides. The organozincs used in this study were easily prepared via the direct insertion of active zinc into the corresponding bromopyridines. The subsequent coupling reactions with a variety of different electrophiles have afforded the corresponding coupling products. Using highly active manganese, a variety of Grignard-type organomanganese reagents have been obtained. The subsequent coupling reactions of the resulting organomanganese reagents with several electrophiles have also been accomplished under mild conditions. http://www.mdpi.com/1420-3049/15/11/8006/ Mon, 08 Nov 2010 00:00:00 CET Molecules 2010-11-08 15 11 Review 8006 8038 1420-3049 Recent Advance in Heterocyclic Organozinc and Organomanganese Compounds; Direct Synthetic Routes and Application in Organic Synthesis 2010-11-08 doi: 10.3390/molecules15118006 Seung-Hoi Kim Reuben D. Rieke http://www.mdpi.com/1420-3049/15/9/6106/ The synthesis of the title compounds is described. Reaction of 1-substituted 2-pyrazolin-5-ones with 5-chloro-1-phenyl-1H-pyrazole-4-carbonyl chloride or 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbonyl chloride, respectively, using calcium hydroxide in refluxing 1,4-dioxane gave the corresponding 4-heteroaroylpyrazol-5-ols, which were cyclized into 1H-pyrano[2,3-c:6,5-c]dipyrazol-4(7H)-ones by treatment with K2CO3/DMF. The latter were converted into the corresponding thiones upon reaction with Lawesson’s reagent. Detailed NMR spectroscopic investigations (1H, 13C, 15N) of the ring systems and their precursors are presented. http://www.mdpi.com/1420-3049/15/9/6106/ Wed, 01 Sep 2010 00:00:00 CEST Molecules 2010-09-01 15 9 Article 6106 6126 1420-3049 Heterocyclic Analogues of Xanthone and Xanthione. 1H-Pyrano[2,3-c:6,5-c]dipyrazol-4(7H)-ones and Thiones: Synthesis and NMR Data 2010-09-01 doi: 10.3390/molecules15096106 Barbara Datterl Nicole Tröstner Dorota Kucharski Wolfgang Holzer http://www.mdpi.com/1420-3049/15/8/5174/ The 1-methyl-2-quinolone (MeQone) framework is often found in alkaloids and recently attention was drawn to unnatural MeQone derivatives with the aim of finding new biologically active compounds, however, low reactivity of the MeQone framework prevents the syntheses of versatile derivatives. A nitro group is one of the useful activating groups for this framework that enables a concise chemical transformation. Among nitroquinolones, 1-methyl-3,6,8-trinitro-2-quinolone (TNQ) exhibits unusual reactivity favoring region-selective cine-substitutions that afford 4-substituted 1-methyl-6,8-dinitro-2-quinolones upon treatment with nucleophilic reagents. Contrary to this, 1-methyl-3,6-dinitro-2-quinolone (3,6-DNQ) does not undergo any reaction under the same conditions. The unusual reactivity of TNQ is caused by steric repulsion between the methyl group at the 1-position and the nitro group at the 8-position, which distorts the MeQone framework. As a result, the pyridone ring of TNQ loses aromaticity and acts rather as an activated nitroalkene. Indeed, the pyridone moiety of TNQ undergoes cycloaddition with electron-rich alkenes or dienes under mild conditions, whereby a new fused ring is constructed on the [c]-face of the MeQone. Consequently, TNQ can be used as a new scaffold leading to versatile unnatural MeQone derivatives. http://www.mdpi.com/1420-3049/15/8/5174/ Fri, 30 Jul 2010 00:00:00 CEST Molecules 2010-07-30 15 8 Review 5174 5195 1420-3049 Chemistry of Nitroquinolones and Synthetic Application to Unnatural 1-Methyl-2-quinolone Derivatives 2010-07-30 doi: 10.3390/molecules15085174 Nagatoshi Nishiwaki http://www.mdpi.com/1420-3049/15/3/1918/ In this manuscript, we report clear evidence for the generation of aromatic cation radicals produced by using [hydroxy(tosyloxy)iodo]benzene (HTIB) in fluoroalcohol solvents such as 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The single-electron-transfer (SET) oxidation ability of HTIB to give cation radicals was first established by ESR and UV measurements. The reaction was broadly applied to various thiophenes, and unique thienyliodonium salts were directly synthesized by this method in excellent yields without the production of any harmful byproducts. http://www.mdpi.com/1420-3049/15/3/1918/ Wed, 17 Mar 2010 00:00:00 CET Molecules 2010-03-17 15 3 Article 1918 1931 1420-3049 Enhanced Reactivity of [Hydroxy(tosyloxy)iodo]benzene in Fluoroalcohol Media. Efficient Direct Synthesis of Thienyl(aryl)iodonium Salts 2010-03-17 doi: 10.3390/molecules15031918 Ito Ogawa Yamaoka Fujioka Dohi Kita http://www.mdpi.com/1420-3049/15/3/1722/ Despite the poor reputation of electron-deficient pyridazines in intermolecular Hetero Diels-Alder (HDA) reactions, 4,5-dicyanopyridazine (DCP) showed a surprising reactivity as a heterocyclic azadiene in inverse electron-demand HDA processes with different dienophiles. The use of alkenes, alkynes and enamines as 2p electron counterparts afforded dicyanocyclohexa-1,3-dienes and substituted phthalonitriles, respectively, while the use of suitable bis-dienophiles provides a general strategy for the one-pot synthesis of polycyclic carbo- and hetero-cage systemsthrough pericyclic three-step homodomino processes. HDA reactions with heterocyclic dienophiles allowed direct benzoannelation: in particular, pyrrole and indole derivatives were converted to dicyano-indoles and -carbazoles. In addition an unprecedented reactivity of DCP as a very reactive heterocyclic electrophile at the C-4 carbon was also evidenced: by changing the experimental conditions, cyanopyrrolyl- and cyanoindolyl-pyridazines were obtained through reactions of pyrrole and indole systems as carbon nucleophiles in formal SNAr2 processes where a CN group of DCP acts as leaving group. Thus, careful control of the reaction conditions allows exploitation of both pathways for the synthesis of different classes of heterocyclic derivatives. http://www.mdpi.com/1420-3049/15/3/1722/ Fri, 12 Mar 2010 00:00:00 CET Molecules 2010-03-12 15 3 Review 1722 1745 1420-3049 Reactivity and Synthetic Applications of 4,5-Dicyanopyridazine: An Overview 2010-03-12 doi: 10.3390/molecules15031722 Alfini Cecchi Giomi http://www.mdpi.com/1420-3049/14/9/3814/ The synthesis of several hitherto unknown heterocyclic ring systems derived from thioflavone is described. Coupling of various o-haloheteroarenecarbonyl chlorides with phenylacetylene gives 1-(o-haloheteroaryl)-3-phenylprop-2-yn-1-ones, which were treated with NaSH in refluxing ethanol to yield the corresponding bi- and tricyclic annelated 2-phenylthiopyran-4-ones. Detailed NMR spectroscopic investigations of the ring systems and their precursors are presented. http://www.mdpi.com/1420-3049/14/9/3814/ Fri, 25 Sep 2009 00:00:00 CEST Molecules 2009-09-25 14 9 Article 3814 3832 1420-3049 Heterocyclic Analogs of Thioflavones: Synthesis and NMR Spectroscopic Investigations 2009-09-25 doi: 10.3390/molecules14093814 Ferdinand C. Fuchs Gernot A. Eller Wolfgang Holzer http://www.mdpi.com/1420-3049/14/9/3187/ The compound 1-(2,6-dichlorophenyl)indolin-2-one (1), planned as a pro-drug of diclofenac (2), was easily synthesized in 94% yield by an intramolecular reaction in the presence of coupling agent (i.e., EDC). Compound 1 showed anti-inflammatory and analgesic activity without gastro-ulcerogenic effects. The chemical and enzymatic hydrolysis profile of the lactam derivative 1 does not indicate conversion to diclofenac (2). This compound is a new non-ulcerogenic prototype for treatment of chronic inflammatory diseases. http://www.mdpi.com/1420-3049/14/9/3187/ Wed, 26 Aug 2009 00:00:00 CEST Molecules 2009-08-26 14 9 Communication 3187 3197 1420-3049 Synthesis, ex Vivo and in Vitro Hydrolysis Study of an Indoline Derivative Designed as an Anti-Inflammatory with Reduced Gastric Ulceration Properties 2009-08-26 doi: 10.3390/molecules14093187 Man Chin Chung Jean Leandro Dos Santos Ednir Vizioli Oliveira Lorena Blau Renato Farina Menegon Rosângela Gonçalves Peccinini http://www.mdpi.com/1420-3049/14/7/2356/ N-Aryl-S,S-dimethylsulfimides 3(Ar = 4-NO2C6H4), 4 (Ar = Ph) and 5 (Ar = 4-Tol)react with Appel salt 1 to give the corresponding N-aryl-(4-chloro-5H-1,2,3-dithiazolylidene)benzenamines 8 (Ar = 4-NO2C6H4), 9 (Ar = Ph) and 10 (Ar = 4-Tol) in 84, 94 and 87% yields, respectively. The reaction proceeds in the absence of base and a proposed reaction mechanism is given. http://www.mdpi.com/1420-3049/14/7/2356/ Thu, 02 Jul 2009 00:00:00 CEST Molecules 2009-07-02 14 7 Article 2356 2362 1420-3049 The Reaction of 4,5-Dichloro-1,2,3-dithiazolium Chloride with Sulfimides: A New Synthesis of N-Aryl-1,2,3-dithiazolimines 2009-07-02 doi: 10.3390/molecules14072356 Andreas S. Kalogirou Panayiotis A. Koutentis