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  • Cross coupling  (2)
  • Heterocycles  (2)
  • 1
    Electronic Resource
    Electronic Resource
    The Twofold Heck Reaction on 1,2-Dihalocycloalkenes and Subsequent 6π-Electrocyclization of the Resulting (E, Z, E)-1,3,5-Hexatrienes: A New Formal {2+2+2}-Assembly of Six-Membered Rings (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1521-1534 
    Details
    ISSN: 1434-193X
    Keywords: Heck reaction ; Cross coupling ; Palladium ; Catalysis ; 6π-Electrocyclization ; Cyclohexa-1,3-dienes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,6-Disubstituted (E, Z, E)-1,3,5-hexatrienes (4 and 5) were prepared by vicinal twofold Heck coupling reactions from 1,2-dibromocyclopentene (1), 1,2-dibromocyclohexene (2), 1,2-diiodocyclopentene (8), 1,2-diiodocyclohexene (9), 1-bromo-2-trifluoromethanesulfonyloxycyclohex-1-ene (11), or 1-chloro-2-nonafluorobutanesulfonyloxycyclohex-1-ene (19) with alkenes 3, e. g. methyl, tert-butyl, menthyl, 8-phenylmenthyl acrylate, styrene, and alkenylsilanes, respectively, in moderate to mostly good and very good yields (20-92 %). The coupling of alkenylsilanes 3f-k could only be achieved with the 1,2-diiodocycloalkenes 8 and 9, respectively. The corresponding hexatrienes 5 with two different substituents in the 1- and 6-positions were prepared by a sequence of two coupling reactions with different alkenes from 1-chloro-2-nonafluorobutanesulfonyloxycyclo-hex-1-ene (19) or by Wittig-Horner-Emmons olefination of 2-bromocyclohexene-1-carbaldehyde (24) and subsequent Heck reaction of the resulting (E,Z)-bromodienes 25. Several of the hexatrienes (4aa, ee, 5aa, ee, al, am, el) readily underwent a 6π-electrocyclization upon heating in an inert atmosphere to give the 5- or 6-ring-annelated cis-5,6-disubstituted cyclohexadienes 26, 27 (50-95 %). Starting from 5am 2,3-disubstituted tetrahydronaphthalene 28am was formed under oxidative conditions (air) in the reaction and in the work-up procedure. The bissilyl-substituted derivatives 4ff, jj, 5ff did not cyclize under thermal conditions, apparently due to the steric demand of the two silyl substituents which would have to end up cis with respect to each other in the cyclohexadiene products.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Palladium-Catalyzed Self-Cross Coupling of o-Bromo-trans-stilbenes To Yield 9,10-Bis(arylmethylene)-9,10-dihydroanthracenes© (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2289-2299 
    Details
    ISSN: 1434-193X
    Keywords: Palladium ; Cross coupling ; Arenes ; Cyclizations ; Polycycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Under Palladium catalysis [Pd(OAc)2, K2CO3, LiCl, Bu4NBr, DMF] o-bromo-trans-stilbene (trans-7a) reacts to give 9,10-dibenzylidene-9,10-dihydroanthracene (4a) with formation of a new six-membered ring. The (Z) diastereomer crystallizes preferentially to give pure (Z)-4a, as proved by X-ray crystal structure analysis. A variety of substituted o-bromostilbenes and heterocyclic analogs 7 were prepared by Wittig olefination of o-bromobenzaldehyde with substituted benzyltriphenylphosphonium ylides, Wittig-Horner-Emmons olefination of arenecarbaldehydes with diethyl o-bromobenzylphosphonate or Wittig olefination of substituted benzaldehydes with substituted (o-bromobenzyl)-diphenylphosphonium ylides, respectively. The cis-o-bromostilbenes were photoisomerized to the trans diastereoisomers trans-7 by irradiation in the presence of diphenyl disulfide. All of these o-bromo-trans-stilbenes trans-7a-g and trans-7j, k under palladium catalysis reacted to the corresponding 9,10-bis(arylmethylene)-9,10-dihydroanthracenes 4, mostly as mixtures of (E) and (Z) diastereomers (50-97 % yield). The (Z) diastereomer of the parent 4a and the alkyl-substituted compounds 4c and 4e could be purified by simple crystallization, and in some runs, only (Z)-4a, c, e were obtained. Among the heterocyclic analogs trans-7h, i only the furyl derivative trans-7h reacted (76 % yield) cleanly, whereas the pyridine analog trans-7i gave a mixture of products from which the rather sensitive product 4i could not be isolated in pure form. The cis-o-bromostilbenes cis-7a, c cyclized to phenanthrenes under the same conditions (70-71 % yield). The UV spectra of compounds 4a, c-k are similar to that of anthracene, and so are the oxidation and reduction potentials of (Z)-4a.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    An Easy Access to 1-Azaspiropentane-2-carboxamides - The First Derivatives of a New Type of Amino Acids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2017-2024 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Azaspiropentanes ; Heterocycles ; Peptides ; Strained molecules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azaspiropentanecarboxamides 10 and 12 are formed with remarkable ease in two steps in a one-pot operation from methyl 2-chloro-2-cyclopropylideneacetate (4) by addition of a primary amine in tetrahydrofuran and subsequent treatment with sodium hydride/triethylamine in the presence of another equivalent of a primary amine or ammonia. Achievable yields of the amides 10, 12 were moderate to good (27-59%, 12-48%), while the corresponding esters 9 could only be obtained in poor yields (4-14%). The new α-amino acid amides are surprisingly stable, and they can be incorporated into small peptides as demonstrated with the preparation of the glycine 13e and the spirocyclopro-paneoxazoline derivative 14e.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Total Synthesis of TAN-1057 A/B, a New Dipeptide Antibiotic from Flexibacter sp. PK-74 (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 777-783 
    Details
    ISSN: 1434-193X
    Keywords: Antibiotics ; Dipeptides ; Heterocycles ; β-Amino acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: TAN-1057 (1a, b) - a new natural dipeptide antibiotic active against methicillin resistant strains of Staphylococcus aureus - was synthesized starting from Nα, Nδ, Nω-tri-Z-L-arginine 20b via the corresponding diazoketone 21b. This upon photolysis rearranged to the ketene which was trapped by (±)-2,4,5,6-tetrahydro-5-methylamino-2-ureidopyrimidin-4-one (3) to yield the fully protected dipeptide 23 (30%). The latter was deprotected by hydrogenolysis to give the final compound as a mixture of two epimers - TAN-1057A, B - isolated previously from a strain of Flexibacter sp. PK-74. The intermediate 3 was prepared from 3-amino-2-(N-Z-N-methylamino)propionic acid methyl ester hydrochloride (16) and 2-methyl-2-thiopseudobiuret hydroiodide (18) in one step in 35% yield.
    Type of Medium: Electronic Resource
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