Special Issue

Ekkehard Winterfeldt's Special Issues, Vol. 74, No. 1, 2007

97 data found. 31 - 60 listedFirst Previous Next Last
Paper | Special issue | Vol 74, No. 1, 2007, pp. 265 - 271
Published online: 1st May, 2007
DOI: 10.3987/COM-07-S(W)3
Synthesis of Alternariol through an Intramolecular Biaryl Coupling Reaction Using Palladium Reagent

Hitoshi Abe,* Tomoko Fukumoto, Yasuo Takeuchi, and Takashi Harayama*

*Faculty of Pharmaceutical Science, Okayama University, 1-1-1 Tsushima-naka, Okayama 700-8530, Japan

Abstract

The facile synthesis of alternariol was accomplished through an intramolecular biaryl coupling reaction of the phenyl benzoate derivative, which was prepared by the simple esterification of the corresponding phenol and benzoic acid using a palladium reagent. The regioselectivity during the biaryl coupling reaction was also investigeted.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 273 - 281
Published online: 8th June, 2007
DOI: 10.3987/COM-07-S(W)4
Intramolecular Benzylic Cyclization with Nitrenium Ions Generated from N-Acylaminophthalimides Using Phenyliodine(III) Bis(trifluoroacetate): Formation of Phenyl Substituted Lactams

Akira Nagashima, Takeshi Sakamoto, and Yasuo Kikugawa*

*Faculty of Pharmaceutical Sciences, Josai University, 1-1 Keyakidai, Sakado, Saitama 350-0295, Japan

Abstract

N-Phthalimido-N-acylnitrenium ions generated from N-acylaminophthalimides using phenyliodine(III) bis(trifluoroacetate) in polyfluoro alcohols do not undergo intramolecular aromatic substitution reactions. Instead, intramolecular cyclization to the benzylic position occurs to afford lactams having a phenyl group substituted at the α-position to the ring nitrogen. These reactions proceed in moderate to good yields.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 283 - 292
Published online: 3rd July, 2007
DOI: 10.3987/COM-07-S(W)5
Palladium(II)-Catalyzed Cyclization of Urethanes and Its Application to a Total Synthesis of 1-Deoxynojirimycin

Hajime Yokoyama, Hisatake Kobayashi, Masahiro Miyazawa, Seiji Yamaguchi, and Yoshiro Hirai*

*Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama, 930-0887, Japan

Abstract

We have employed a palladium(II)-catalyzed cyclization of allylic alcohol as a key reaction to achieve a total synthesis of the azasugar 1-deoxynojirimycin from D-mannitol. This reaction should be useful for the stereoselective construction of natural poly-substituted piperidine derivatives.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 293 - 307
Published online: 27th July, 2007
DOI: 10.3987/COM-07-S(W)6
Synthesis and Transformation of N,N-Dimethylaminomethylidene Derivatives of Indolylglycines and Some Other Dipeptides

Renata Jakse, Ljubo Golic, Anton Meden, Uros Groselj, Jurij Svete,* and Branko Stanovnik*

*Department of Organic Chemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, P.O. Box 537, SI-1000 Ljubljana, Slovenia

Abstract

Indolyl glycinates (3, 7, and 11) were transformed with t-butoxybis(dimethylamino)methane (Bredereck’s reagent) into 3-[(dimethylamino)methylidene]-2,3-dihydropyrazino[1,2-a]indole-1,4-dione (4), 3-(dimethylamino)-2-[(1H-indol-3-ylcarbonyl)amino]propenoate (8), and 2-(1-methyl-1H-indol-2-yl)-1,3-oxazol-5(4H)-one derivative (12). Dipeptides (16a-c) were transformed with Bredereck’s reagent into the hydantoin (imidazolidine-2,4-dione) derivatives (17a-c).

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 309 - 320
Published online: 3rd July, 2007
DOI: 10.3987/COM-07-S(W)7
Synthesis and Reactions of 3-Ethynyl-2-(triphenylphosphoimino)-1-azaazulenes

Noritaka Abe,* Kentaro Nagamatsu, Tomoyuki Ariyoshi, Hiroyuki Fujii, Yoshiko Murakami, Shoji Tagashira,* and Akikazu Kakehi

*Applied Molecular Bioscience, Graduate School of Medicine, Yamaguchi University, Yamaguchi 753-8512, Japan

Abstract

3-(Trimethylsilylethynyl)- and 3-(phenylethynyl)-2-(triphenylphosphoimino)-1-azaazulenes were synthesized by the Appel reaction of the corresponding 2-amino-3-ethynyl-1-azaazulenes. Reaction of 3-(phenylethynyl)-2-(triphenylphosphoimino)-1-azaazulene (8b) with Cu(OTf)2 gave 3-(2-oxophenethyl)-2-(triphenylphosphoimino)-1-azaazulene (11), 3-(1,2-dioxophenethyl)-2-(triphenylphosphoimino)-1-azaazulene (12), and 2-amino-3-(1,2-dioxophenethyl)-1-azaazulene (13). The structure of 13 was decided by X-ray structure analysis, and the structure of 12 was discussed by molecular orbital calculation. Reaction of 8b with aryl isocyanate in the presence of benzoyl peroxide gave 1,10-diazabenz[a]azulene derivative.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 321 - 329
Published online: 27th July, 2007
DOI: 10.3987/COM-07-S(W)8
Electronic Structures and Molecular Orbial Calculations of Oppositely Dinaphthalo- and Dianthraco-Substituted D2h Type Metal-Free Phthalocyanine Congeners

Osamu Matsushita, Atsuya Muranaka, Yayoi Kobayashi, and Nagao Kobayashi*

*Department of Chemistry, Analytical Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan

Abstract

Phthalocyanine congeners substituted with two naphthalene or anthracene units on opposite sides (1 and 2) have been synthesized and their spectroscopic properties investigated by electronic absorption and magnetic circular dichroism (MCD) spectroscopy in conjunction with quantum chemical calculations. These compounds exhibited several intense absorption peaks in the 600-900 nm region. The geometry of possible tautomers for these macrocycles were optimized at the density functional level (B3LYP/6-31G*), and the absorption spectra were reproduced using Hartree-Fock theory based on ZINDO/S Hamiltonian.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 331 - 337
Published online: 27th July, 2007
DOI: 10.3987/COM-07-S(W)10
Exochromone: Structurally Unique Chromone Dimer with Antifungal and Algicidal Activity from Exophiala Sp.

Hidayat Hussain, Karsten Krohn,* Siegfried Draeger, and Barbara Schulz

*Department of Chemisry, University of Paderborn, Warburger Str. 100, 33098 Paderborn, Warburger Str. 100, 33098 Paderborn, Germany

Abstract

A unique highly substituted chromone dimer, named exochromone (1a), in addition to the known steroids ergosterol (2) and 5α,8α-epidioxyergosterol (3) were isolated from endophytic fungus Exophiala sp.. The structure of the new compound was elucidated on the basis of spectroscopic data. Preliminary studies showed that exochromone is antifungal and antialgal against Microbotryum violaceum and Chlorella fusca, respectively.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 339 - 350
Published online: 27th July, 2007
DOI: 10.3987/COM-07-S(W)11
Synthesis of spiro-Annelated Isochromanones by Ring Expansion of Benzocyclobutenones in the Presence of Lithium Diisopropylphosphide

Stefanie C. Kohser, Krishna Gopal Dongol, and Holger Butenschön*

*Institut für Organische Chemie, Universität Hannover, Schneiderberg 1B, D-30167 Hannover, Germany

Abstract

spiro-Annelated isochromanones are prepared by treatment of benzocyclobutenone with lithium diisopropylphosphide - borane adduct (LDP-BH3), which is easily accessible by metalation of the air stable diisopropylphosphane-borane adduct. The reaction takes place at very mild reaction conditions and involves an oxyanion driven ring opening. As a substituted example the synthesis of the first trifluoromethyl-substituted isochromanone derivative is reported.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 351 - 356
Published online: 4th September, 2007
DOI: 10.3987/COM-07-S(W)12
Thermal Reaction of 5-Aryl-6-trifluoromethyl-3,6-dihydro-2H-[1,3,4]oxadiazines Accessing 5-Trifluoromethylimidazoles

Yasuhiro Kamitori,* Tomoko Sekiyama, and Etsuji Okada

*Department of Chemical Science and Engineering, Faculty of Engineering, Kobe University, Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan

Abstract

Thermal reaction of 5-aryl-6-trifluoromethyl-3,6-dihydro-2H- [1,3,4]oxadiazines (2) readily obtainable from 3-aryl-3-dimethylhydrazono- 1,1,1-trifluoro-2-propanones (1) afforded 4-aryl-1-methyl-5-trifluoromethyl- imidazoles (3) in moderate to good yields. Mechanism for this thermal transformation reaction is also discussed.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 357 - 367
Published online: 20th September, 2007
DOI: 10.3987/COM-07-S(W)13
Chalcogen Atom Competition in the Coordination of Bicyclic β-Lactam Derivatives to a Dirhodium Tetracarboxylate Complex

Edison Díaz Gómez, Jadwiga Frelek, Magdalena Woznica, Patrycja Kowalska, Jaroslaw Jazwinski, and Helmut Duddeck*

*Institute of Organic Chemistry, Leibniz University Hannover, Schneiderberg 1B, D-30167 Hannover, Germany

Abstract

NMR spectra of five enantiopure β-lactam derivatives with varying oxygen and sulfur atoms (1 to 5) have been recorded in the presence of an equimolar amount of a 2:1-mixture of (R)-Rh* and (S)-Rh* [(R/S)-Rh*]. No carboxylate ligand exchange between the two enantiomeric dirhodium complexes was observed. In general, sulfur is a much better donor than oxygen in axial coordination to rhodium. If both chalcogen atoms are equal (S in 1 and O in 4) the doubly bonded atom is the prefered binding site (C9=X). In the compounds with mixed chalcogen atoms, sulfur prevails as donor regardless of its bond order. This behaviour can be rationalized by comparing calculated molecular orbital energies and electronic charges. Olefinic groups do not contribute to binding significantly. All β-lactam derivatives were enantiopure so that it was possible to monitor significant chemical shift differences of the 1H, 13C and 19F NMR resonances for the two Rh* enantiomers. An experiment with racemic 4-vinyloxyazetidin-2-one (6) and (R)-Rh* suggests that the dirhodium method is effective for enantiodifferentiation of β-lactams.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 369 - 382
Published online: 4th October, 2007
DOI: 10.3987/COM-07-S(W)15
Synthesis of New 1,3,8-Trisubstituted Purine-2,6-diones and 1,3,6-Trisubstituted Thiazolo[2,3-f]purine -2,4-diones

Alaa M. Hayallah and Michael Famulok*

*Institute of Chemical Biology and Medicinal Chemistry Unit, University of Bonn, Gerhard-Domagk-Str.1, D-53121 Bonn, Germany

Abstract

New 1,3,8-trisubstituted purine-2,6-diones and 1,3,6-trisubstituted thiazolo[2,3-f]purine-2,4-diones were designed and synthesized as agents with potential biological activities. The final products were obtained by cyclization of carboxamide intermediates using 1,1,1,3,3,3,-hexamethyldisilazane. This procedure gave higher yields, and was more convenient and easier in purification compared to other methods. We also found polyphosphoric acid to be the most efficient agent in the cyclization of 8-[2-(p-(un)substituted-phenyl)-2-oxo-ethylsulfanyl]-1,3-dipropyl-3,7-dihydro-purine-2,6-diones to 1,3-dipropyl-6-substituted)-1H-thiazolo[2,3-f]purine-2,4-diones.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 383 - 396
Published online: 20th September, 2007
DOI: 10.3987/COM-07-S(W)16
A Novel Sodium Iodide-Promoted Ring Transformation of 2-Amino-4,5-dihydro-3-furancarbonitriles to 2-Pyrrolidinones and Dihydropyrans

Hiroshi Maruoka, Fumi Okabe, and Kenji Yamagata*

*Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan

Abstract

A novel and efficient approach to 2-pyrrolidinones and dihydropyrans via the ring transformation of 3-phenacylated tetrahydro-2-imino-3-furancarbonitriles in the presence of sodium iodide is described. The key feature in the ring transformation is that C-phenacylation of 2-amino-4,5-dihydro-3-furancarbonitriles using phenacyl bromides, e.g. phenacyl bromide, 4-chlorophenacyl bromide and 4-methoxyphenacyl bromide, proceeds smoothly and the ring-opening intermediate having leaving group such as iodide ion is produced.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 397 - 409
Published online: 21st September, 2007
DOI: 10.3987/COM-07-S(W)18
A Novel Heterospirocyclic 2H-Azirin-3-amine as Synthon for 3-Aminothiolane-3-carboxlic Acid

Joëlle L. Räber, Kathrin A. Brun, and Heinz Heimgartner*

*Institute of Organic Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland

Abstract

The heterospirocyclic 2H-azirin-3-amine (9), i.e., N-methyl-N-phenyl-5-thia-1-azaspiro[2.4]hept-1-en-2-amine, was prepared from the commercially available thiolane-3-one (10) via the corresponding 3-carbonitrile (11) and 3-thiocarboxamide (14). This azirine reacted with thiobenzoic acid to give 3-benzoylamino-N-methyl-N-phenylthiolane-3-thiocarboxamide (15). With N-protected valine, the protected dipeptides (16) and (17), which contain a heterocyclic amino acid, were obtained as mixtures of diastereoisomers.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 411 - 420
Published online: 4th September, 2007
DOI: 10.3987/COM-07-S(W)20
Chemistry of Tetrahydroisoquinoline Antitumor Natural Products: Preparation and Antitumor Activity of Analogues of Cribrostatin 4

Emi Saito, Naomi Daikuhara, and Naoki Saito*

*Graduate School of Pharmaceutical Sciences, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan

Abstract

The two-step transformation of saframycin G (9) into saframycin F (1b) and renieramycin O (11) into renieramycin Q (2) is described, along with the results of cytotoxicity studies.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 421 - 436
Published online: 2nd October, 2007
DOI: 10.3987/COM-07-S(W)21
Glycosylation-Induced Asymmetric Synthesis of 1-Substituted Tetrahydroisoquinolines

Petra Allef and Horst Kunz*

*Department of Organic Chemistry, University of Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany

Abstract

Activation of imines by N-glycosylation and simultaneous diastereodifferentiation in reactions of the formed N-glycosyl iminium ions provide new stereoselective routes to 1-substituted tetrahydroisoquinolines. Pictet-Spengler reactions induced by N-galactosylation of β-arylethyl imines of aromatic aldehydes give 1-aryl tetrahydroisoquinolines with high stereoselectivity. Glycosylation-induced addition of dialkylzinc reagents to 3,4-dihydroisoquinoline furnish 1-alkyl-tetrahydroisoquinolines with excellent diastereoselectivity.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 437 - 445
Published online: 5th October, 2007
DOI: 10.3987/COM-07-S(W)22
Practical and Efficient Processes for the Preparation of 4-(4-Aminophenyl)morpholin-3-ones on a Larger Scale: Precursor of Factor Xa Inhibitors

Werner W. K. R. Mederski,* Peter Ludwig Wendel, and Markus Woissyk

*Preclinical Pharmaceutical Research, Merck KGA, Frankfurter Str. 250, 64271 Darmstadt, Germany

Abstract

Factor Xa inhibitors are interesting targets for the development of antithrombotic agents. Our personal efforts in the discovery of small molecule inhibitors led to the compounds EMD 495235 and EMD 503982, which entered preclinical and clinical studies, respectively. Therefore, kilograms of both drugs in particular 4-(4-aminophenyl)morpholin-3-one moieties have to be provided. The scale-up results of these special P-4 ligands will be described herein.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 447 - 459
Published online: 21st September, 2007
DOI: 10.3987/COM-07-S(W)23
Electrophile-Induced Ether Transfer: An Expedient Route to 2-Cyanotetrahydropyrans

Rendy Kartika and Richard E. Taylor*

*Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, IN 46556, U.S.A.

Abstract

Electrophile-induced ether transfer reactions of alkoxymethyl ether protected homoallylic alcohols with cyanide quench provide cyanoether adducts in high yield and excellent 1,3-syn-stereoselectivity. Subsequent base-mediated cyclization then provides the corresponding 2,4,6-trisubstituted cyano-tetrahydropyran.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 461 - 472
Published online: 21st September, 2007
DOI: 10.3987/COM-07-S(W)25
Preparation of Ethylene Glycol Adducts at 2,3-Positions of Indoles with Hypervalent Iodine

Naoki Okada, Kaori Misawa, Mariko Kitajima, and Hiromitsu Takayama*

*Laboratory of Molecular Structure and Biological Function, Graduate School of Pharmaceutical Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Abstract

An efficient method for protection-deprotection of the 2,3-bond of indoles was developed. Treatment of various indole derivatives with hypervalent iodine-ethylene glycol in the presence of ammonium chloride provided 2,3-ethylene glycol bridged adducts in excellent yields. The adducts, which possessed a masked form of pyrrole moiety in the indole nucleus, could be converted back to the mother indoles under mild reductive conditions.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 473 - 489
Published online: 30th October, 2007
DOI: 10.3987/COM-07-S(W)67
Palladium-Catalyzed Domino-Wacker-Carbonylation Reaction for the Enantioselective Synthesis of Chromans and Benzodioxins

Lutz F. Tietze,* Julia Zinngrebe, Dirk A. Spiegl, and Florian Stecker

*Institute of Organic and Biomolecular Chemistry, Georg-August-University, Tammannstr. 2, D-37077 Göttingen, Germany

Abstract

A palladium-catalyzed domino reaction for the formation of chromans 9 as well as 10 and benzodioxines 13 is described starting from the alkenes 6 as well as 8 and the allyl phenyl ethers 12. The domino reaction comprises an enantioselective intramolecular Wacker oxidation, a subsequent CO-insertion and a nucleophilic substitution of the intermediately formed palladium-species.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 491 - 506
Published online: 13th November, 2007
DOI: 10.3987/COM-07-S(W)27
Utilization of the Antiaromatic 2H-Indol-2-one Ring System for the Synthesis of Substituted Spiro-Oxindoles

Dylan B. England, Gokce Merey, and Albert Padwa*

*Department of Chemistry, Emory University, 1515 Pierce Dr., Atlanta, Georgia 30322, U.S.A.

Abstract

The utility of the quasi-antiaromatic 2H-indol-2-one system for the synthesis of substituted oxindoles and spiro-oxindoles was investigated. The highly reactive 2H-indol-2-one could be readily generated by treating a 3-hydroxy substituted 1,3-dihydroindol-2-one with a Lewis acid. Stepwise addition of various π-substrates such as styrene, furan and thiophene to the 2H-indol-2-one system occurs smoothly to produce a carbocation intermediate which subsequently undergoes proton loss to afford substituted oxindoles. The cyclization was also carried out in an intramolecular fashion to give spiro-substituted oxindoles in good yield.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 507 - 519
Published online: 5th October, 2007
DOI: 10.3987/COM-07-S(W)29
Cyclic Acetals as Precursors of Substituted Isochromans and Naphthoxepines

Daniel García, Francisco Foubelo,* and Miguel Yus*

*Department of Organic Chemistry, Faculty of Sciences and Institute of Organic Synthesis (ISO), University of Alicante, P.O. Box 99, 03080 Alicante, Spain

Abstract

The reaction of 6,8-dioxabenzocycloheptenes 3 or 8,10-dioxacycloocta[de]naphthalenes 5 [easily prepared from the dibenzylic diols 1 and 4, respectively, and a carbonyl compound] with an excess of lithium and a catalytic amount of DTBB (2.5 mol %) in THF at temperatures ranging between -78 and -60 °C leads, after hydrolysis with water, to the corresponding homobenzylic alcohols 6 and 7, respectively. Cyclization of compounds 6 and 7 under acidic conditions (85% H3PO4 for diols 6 and p-TsOH for diols 7) affords the expected isochromans 8 and naphthoxepines 9, respectively.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 521 - 532
Published online: 2nd October, 2007
DOI: 10.3987/COM-07-S(W)30
First Ring Contraction-Desulfurization of 1-(Arylcarbonyl)pyrido[2,1-c]-1,4-thiazines to 1-(Arylcarbonyl)indolizines and Its Application to 3-Arylthieno[3,2-a]indolizine Synthesis

Akikazu Kakehi,* Hiroyuki Suga, Yuichi Goto, and Nobuhiro Yamaguchi

*Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan

Abstract

The ring contraction-desulfurization route from transient 1-(arylcarbonyl)pyrido[2,1-c]-1,4-thiazine intermediates, generated in situ from the treatment of the corresponding pyridinium salts with a base and then a dehydrogenation agent, to 1-(arylcarbonyl)indolizines was first observed. By using this route three 1-arylcarbonyl-6,8-dimethylindolizines having the protected 2-thiol group were prepared and their transformation to 2-acyl-3-arylthieno[3,2-a]indolizine derivatives were performed in good yields.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 533 - 543
Published online: 4th December, 2007
DOI: 10.3987/COM-07-S(W)31
Reactions of Glycosan-Annelated Oxolactams

Swantje Thiering, Joachim Thiem,* and Jürgen Kopf

*Institute of Organic Chemistry, Faculty of Science, University of Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany

Abstract

Starting with 4-imido-mannosan and 2-imido-galactosan derivatives Norrish-Yang cyclization led to saccharide-annelated azepanediones and azocanediones. Following N-protection these lactams could be opened to give higher branched-chain carbohydrate components of the 4-amino-3-dehydro type. In some cases concomitant rearrangement reactions were observed to give α,β-unsaturated hydroxy lactams as well as saccharides linked to substituted furans.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 545 - 552
Published online: 21st September, 2007
DOI: 10.3987/COM-07-S(W)32
Facile One-Pot Synthesis of Functionalized Acetylenes from Aryl and Heteroaryl Aldehydes Using Lithium Trimethylsilyldiazomethane

Yoshiyuki Hari, Koji Date, Toyohiko Aoyama*

*Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan

Abstract

The reaction of aryl and heteroaryl aldehydes with lithium trimethylsilyldiazomethane followed by treatment with n-BuLi and then electrophiles in one-pot efficiently afforded functionalized acetylenes.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 553 - 568
Published online: 12th October, 2007
DOI: 10.3987/COM-07-S(W)34
Synthesis of Amide-Substituted Isoxazoles and Pyrazoles via Regioselective [3+2] Cycloadditions of Terminally Unsubstituted Ynamides

Hongyan Li, Lingfeng You, Xuejun Zhang, Whitney L. Johnson, Ruth Figueroa, and Richard P. Hsung*

*Department of Chemistry, Division of Pharmaceutical Sciences, University of Wisconsin, 777 Highland Aenue, Madison, WI 53705-2222, U.S.A.

Abstract

A series of regioselective [3 + 2] cycloadditions of terminally unsubstituted ynamides with nitrile oxides and ethyl α-diazoacetate is described here. These reactions provide an excellent synthetic entry to de novo 5-amide-substituted isoxazoles via a Cu(I)-catalyzed pathway and 3-amide-substituted pyrazoles via a thermally driven cycloaddition.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 569 - 594
Published online: 4th October, 2007
DOI: 10.3987/COM-07-S(W)36
Di- and Triarylsubstituted Pyrroles by Sequential Regioselective Cross-Coupling Reactions

Sven Schröter and Thorsten Bach*

*Chair of Organic Chemistry I, Technical University of Munich, Lichtenbergstrasse 4, D-85747 Garching, Germany

Abstract

The di- and tribrominated pyrroles, such as methyl 3,4,5-tribromopyrrole-2-carboxylate (1), ethyl 3,4,5-tribromopyrrole-2-carboxylate (2), methyl 4,5-dibromopyrrole-2-carboxylate (3), and 4,5-dibromo-2-nitropyrrole (4), were prepared and evaluated for their use in successive Suzuki cross-coupling reactions. It was shown that monosubstitution at the 5-position is feasible with a variety of boronic acids 5 using Pd2(dba)3 (dba = dibenzylideneacetone) and tri(2-furyl)phosphane as the catalyst in a solvent system of an arene (mesitylene or toluene), ethanol and water (5/1/1). Starting from 2 and 4 the corresponding 5-substituted products 8 (8 examples, 33-65% yield) and 17 (9 examples, 34-86% yield) were obtained. Further Suzuki cross-coupling reactions at the remaining di- or monobromo-substituted positions were feasible as exemplified by the synthesis of the corresponding triarylpyrroles 9, 16 and diarylpyrroles 18-20.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 595 - 605
Published online: 16th October, 2007
DOI: 10.3987/COM-07-S(W)37
New Dimeric Flavans from Gambir, an Extract of Uncaria gambir

Shoko Taniguchi, Kayo Kuroda, Naomi Yoshikado, Kou-ichi Doi, Masahiro Tanabe, Takashi Shibata, Takashi Yoshida, and Tsutomu Hatano*

*Faculty of Pharmaceutical Science, Okayama University, 1-1-1 Tsushima-naka, Okayama 700-8530, Japan

Abstract

Three new dimeric flavans, catechin-(4α→8)-ent-epicatechin (7), gambirflavan D1 (8), and gambirflavan D2 (9), were isolated from gambir (an extract from the leaves and young twigs of Uncaria gambir), and their structures were determined based on spectroscopic and chemical data.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 607 - 616
Published online: 26th October, 2007
DOI: 10.3987/COM-07-S(W)38
Synthesis, Crystal Structure, and Magnetic Properties of 4-(2-Methyl-1-azaspiro[4.5]deca-1-oxyl-2-yl)phenol

Yoshiaki Uchida, Nagahisa Matsuoka, Hiroki Takahashi, Satoshi Shimono, Naohiko Ikuma, and Rui Tamura*

*Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan

Abstract

The two polymorphic forms (α and β) of the racemate of the title chiral nitroxide radical were separately obtained by changing the composition ratio of the recrystallization solvent (hexane/Et2O). Both polymorphs existed as a racemic compound; the thermally less stable α-form was monoclinic (space group, C2/c), and the stable β-form was orthorhombic (Pbca). The origin of the formation of the racemic compound crystals for the α- and β-forms was interpreted in terms of the formation of a strong intermolecular head-to-tail type of hydrogen bond between a nitroxyl group and the nearest hydroxy group in a pair of R and S enantiomers giving a heterochiral cyclic dimer and a heterochiral 1D chain, respectively, by X-ray crystallographic analysis. Furthermore, magnetic susceptibility measurements of the two polymorphs indicated the presence of weak antiferromagnetic interactions, which were rationalized in terms of the formation of homochiral and heterociral 1D chains in the crystal structures of the α- and β-forms, respectively, by DFT calculations.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 617 - 627
Published online: 16th October, 2007
DOI: 10.3987/COM-07-S(W)39
Formal Total Synthesis of Hemibrevetoxin B via the Intramolecular Allylation Followed by Ring-Closing Metathesis

Isao Kadota,* Takashi Abe, Yukako Ishitsuka, Abeda S. Touchy, Ryoko Nagata, and Yoshinori Yamamoto

*Faculty of Science, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan

Abstract

A formal total synthesis of hemibrevetoxin B (1) is described. Intramolecular allylation of α-chloroacetoxy ether 10, prepared from carboxylic acid 11 and alcohol 12, was carried out with MgBr2·OEt2 to give 27. Ring-closing metathesis of 27 furnished tetracycle 29, which was converted to a known synthetic intermediate 9, to complete a formal total synthesis of 1.

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Paper | Special issue | Vol 74, No. 1, 2007, pp. 629 - 635
Published online: 5th October, 2007
DOI: 10.3987/COM-07-S(W)40
Efficient Synthesis of Substituted Indoles and Benzazoles by Oxidative Aromatization Using Activated Carbon-Molecular Oxygen System

Yukiko Nomura, Yuka Kawashita, and Masahiko Hayashi*

*Department of Chemistry, Faculty of Science, Kobe University, Nada-Ku, Kobe 6557-8501, Japan

Abstract

Efficient synthesis of substituted indoles was achieved by oxidative aromatization of indolines using activated carbon-molecular oxygen (O2) system. Benzazoles (benzimidazole and benzothiazoles) were also prepared by the reaction of 1,2-phenylenediamine and 2-aminobenzenethiol with formaldehyde in the presence of activated carbon under oxygen atmosphere.

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