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  • 1
    Electronic Resource
    Electronic Resource
    Die Dipol-Route zu Furo-/Thieno-Pyrrolen und α-Pyridonen, sowie deren Benzo-Derivaten (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 247-259 
    Details
    ISSN: 0009-2940
    Keywords: Pyrroles, heteroannulated ; α-Pyridones, heteroannulated ; Pentalenes, dihetero- ; Nitrones ; Heterocyclizations, 1,7-dipolar ; Diels-Alder reactions ; Singlet oxygen ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Novel Route to Isoannulated Heteroaroamtic Compounds, 2[1].  -  The Dipole Route to Furo/Thieno Pyrroles and α-Pyridones, and Their Benzo DerivativesA new methodology involving 1,7-dipolar cyclizations of conjugated dipoles followed by a multistep rearrangement affording ring-contracted products has been employed for the synthesis of various examples of the title compounds. Under different thermolysis conditions the annulated alkynyl nitrones 15-19, 45, and 46 are converted into isoannulated pyrroles and α-pyridones, respectively, with yields up to 90% (general reaction A → B + C). The product distribution is strongly influenced by the nature of the terminal substituent R, hence supporting a mechanism with oxo carbenes as central intermediates which undergo either 6-π cyclization to the pyrrole systems or Wolff rearrangement leading to conjugated ketenes, the precursors of the observed α-pyridones (see Scheme 1). Diels-Alder reactions were performed with benzofuropyridone 40a, napthopyridone 62 as well as with the corresponding dihydronaphtho compounds 64a, b. Whereas the tert-butyl derivatives 22b, 23b and 41b are rather unreactive against dienophiles, they are easily transformed into the cyclic imides 31, 32 and 52, respectively, under the influence of oxygen and light suggesting the formation and subsequent [4 + 2] cycloaddition of 1O2 as important steps.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270135
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  • 2
    Electronic Resource
    Electronic Resource
    Ein neuer Weg zu isoanellierten Heteroaromaten, 1. Synthese und Reaktionen von Furofuranen, Thienofuranen, Furobenzofuranen und Benzothienofuranen (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 975-995 
    Details
    ISSN: 0009-2940
    Keywords: Pentalenes, dihetero- ; Cyclizations, 1,7-dipolar ; Carbonyl ylides ; Cycloallenes ; Diels-Alder reactions ; o1-Quinodimethanes, hetero analogues ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Novel Route to Isoannulated Heteroaromatic Compounds, 1. - Synthesis and Reactions of Furofurans, Thienofurans, Furobenzofurans, and BenzothienofuransA general method for the synthesis of furo-and thienofurans 4-7 has been developed. The reaction principle is based on the thermal transformation of suitably structured epoxyhexenynes (15-19) following the general reaction sequence 1→2→3 (annulation type A). Derivatives of the so far unknown diheteropentalenes furo[3,4-b]furan (4b, c, d, g, h), furo-[3,4-b]benzofuran (6b, d, e, 45) as well as benzo[4,5]thieno-[2,3-c]furan (7b, d) are obtained by short-time thermolysis. Likewise two representatives of the previously reported thieno[2,3-c]furan system are prepared (5b, c). By flash vacuum thermolysis the benzo-annulated epoxyhexenyne 19b rearranges in poor yield to the isobenzofuran 52 (identified as dimethyl acetylenedicarboxylate adduct 47) and 2-cyano-α1-naphthol (46). The structure of the furo[3,4-b]furan 4b has been established by X-ray structural analysis. A mechanistic explanation of the transformation of the epoxyhexenynes to diheteropentalenes is proposed. Indications for the occurrence of carbenes as product-determining species are obtained with the phenylcyano-substituted oxiranes 15c, h and 17e which - in additon to the furofurans 4c, h and 6e - lead to the furylindenes 31c, h/32c, h and 41, resp. The Diels-Alder reactivity of the furo-and thienofurans 4g, 5b, c, and 6b has been examined.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260419
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    Paper (German National Licenses)
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