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  • 1
    Electronic Resource
    Electronic Resource
    Transition metal- and acid-induced transformations of 6-siloxy-substituted 5,6-dihydro-4H-1,2-oxazines: Preparation of pyrroles, nitrones, 1,4-dicarbonyl compounds and derivatives thereof (1990)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1990 (1990), S. 469-474 
    Details
    ISSN: 0170-2041
    Keywords: 1,2-Oxazines, transformations of ; Pyrroles ; Molybdenum, hexacarbonyl- ; 1,4-Dicarbonyl compounds ; Oximes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A variety of 6-siloxy-substituted 5,6-dihydro-4H-1,2-oxazines (abbreviation: 1,2-oxazines) 1, 3 could be transformed into di- and trisubstituted pyrroles 2, 4 by means of molybdenum hexacarbonyl. The mechanism of this deoxygenating ring contraction is discussed. With two bicyclic 1,2-oxazines an acid-catalyzed fragmentation affording α-methylenecycloalkanones 7 has been observed, while other 1,2-oxazines rearrange in methanolic acid to give nitrones 9, 10. The desilylation of 6-siloxy-substituted 1,2-oxazines 1, 3 employing NEt3 · 3 HF is a very general and smooth process providing 6-hydroxy-1,2-oxazines 11, 12 or their corresponding acyclic tautomers 13, 14 in high yields. For two examples of 11 deoximations by use of formalin could be achieved with moderate efficiency giving 1,4-dicarbonyl compounds 15.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199019900189
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  • 2
    Electronic Resource
    Electronic Resource
    Correction (1990)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1990 (1990), S. 833-833 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1990199001156
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of 6H-1,2-oxazines by hetero Diels-Alder reactions of nitroso alkenes towards methoxyallenes (1991)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 553-562 
    Details
    ISSN: 0170-2041
    Keywords: 6H-1,2-Oxazines ; Methoxyallene ; Nitroso alkene ; Hetero Diels-Alder reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Regioselective hetero Diels-Alder reactions of in-situ generated nitroso alkenes 2-4 with methoxyallene derivatives 1 provide 4H-1,2-oxazines 5-7 with an exo-methylene group at C-5. These primary cycloadducts are smoothly transformed into conjugated 6H-1,2-oxazines 11-13 by base or acid catalysis. The bicylic nitroso alkene 17 and methoxyallene (1a) combine to give the tricyclic 1,2-oxazine 18, thus demonstrating that an exo-transition state is favoured in this [4+2] cycloaddition. The reaction of the sterically hindered methoxyallene 1h with nitrosostyrene affords the cycloadduct 22 in low yield. 22 is very likely formed by a two-step Diels-Alder reaction via a zwitterion. Allene derivatives lacking a methoxy group are not sufficiently reactive towards nitroso alkenes and do not provide 1,2-oxazines.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1991199101101
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  • 4
    Electronic Resource
    Electronic Resource
    Unerwartete Bildung von γ-Lactamen aus 6H-1,2,-Oxazinen unter Lewis-Säure-Einwirkung (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 621-624 
    Details
    ISSN: 0170-2041
    Keywords: 6H-1,2-Oxazines ; γ-Lactams ; Lewis acids ; Ring contraction ; Phosphite, trimethyl ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unexpected Formation of γ-Lactams from 6H-1,2-Oxazines Promoted by Lewis AcidsThe reaction of 6H-1,2-oxazine 1 with trimethylsilyl cyanide in the presence of titanium tetrachloride provides α,β-unsaturated γ-lactam 3. Similarly, Lewis acid-promoted addition of trimethyl phosphite towards 1 affords a mixture of γ-lactams 8 and 9. The structure of 9 was established by X-ray analysis. A plausible mechanism for the formation of these γ-lactams by Lewis acid-induced ring contraction is proposed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1992199201106
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  • 5
    Electronic Resource
    Electronic Resource
    Reductive Transformations of 6H-1,2-Oxazines with Hydride Reagents: Formation of Aziridines and 3-Hydroxyalkylated 1,2-oxazines (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 1155-1157 
    Details
    ISSN: 0170-2041
    Keywords: 1,2-Oxazines ; Aziridines ; Hydride reagents ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6H-1,2-Oxazines 1 and 3 are converted into aziridines 2 and 4, respectively, by reduction with LiAlH4. Reduction of 1,2-oxazine 5 lacking the 6-alkoxy substituent leads to phenyl ketone 6, 6-Alkoxy-substituted 1,2-oxazine-3-carboxylates 7, 9, and 11 are reduced with NaBH4 to give the corresponding 3-hydroxymethylated compounds 8, 10, and 12 in good yields.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301186
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  • 6
    Electronic Resource
    Electronic Resource
    6-Siloxy-Substituted 5,6-Dihydro-4H-1,2-oxazines as Key Building Blocks for Natural Products (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 709-714 
    Details
    ISSN: 0170-2041
    Keywords: Pyrenophorin ; (Z)-Jasmone ; 1,2-Oxazine ; Pheromones ; Pyrroles ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methyl (E)-5-bromo-4-oxo-2-pentenoate (6) and the corresponding oxime 5 were prepared in high yields by starting from methyl levulinate (3). The novel nitrosoalkene 8, generated in situ from oxime 5, smoothly added to silyl enol ether 7 to give 1,2-oxazine 9 and nitrone 10 as byproduct. Methods are described transforming intermediate 9 into unsaturated diketo ester 11, or oximes 13, 15, and 18, which may serve as precursors of pyrenophorin. Reductive ring cleavage of 1,2-oxazine 9 with Raney nickel efficiently afforded the saturated diketo ester 19. Its intramolecular aldol reaction gave cyclopentenone derivative 20, which is a known precursor of (Z)-jasmone. Cycloaddition of methyl α-nitrosoacrylate to silyl enol ether 22 provided 1,2-oxazine 23. This compound was directly converted into the ant-trail pheromone 24 by hexacarbonylmolybdenum-promoted ring contraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1992199201119
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