Cycloadditionen von 3,4-Dimethoxyfuran an Benzochinone
1979; Wiley; Volume: 62; Issue: 7 Linguagem: Inglês
10.1002/hlca.19790620718
ISSN1522-2675
AutoresA. Hofmann, Ingeborg Wyrsch‐Walraf, Peter Xaver Iten, Conrad Hans Eugster,
Tópico(s)Oxidative Organic Chemistry Reactions
ResumoCycloadditions of 3,4‐dimethoxyfuran with benzoquinones Cycloaddition of 3,4‐dimethoxyfuran (3,4‐DF, 1 ) with 1,4‐benzoquinones furnishes isolable (2 + 4)‐adducts in high yield. The crystalline products with benzoquinone, 2‐methyl‐benzoquinone, 2,3‐dimethoxy‐benzoquinone have endo ‐configuration, whereas 2,3‐dimethyl‐benzoquinone gives the exo ‐adduct 4c exclusively. Halogens (Cl 2 , Br 2 ) add rapidly across the highly nucleophilic double bond of 3 or 4 in stereospecific cis ‐manner, and exclusively from the exo ‐side. The product 5c shows no sign of enolization to the hydroquinone; but with 3a and 3d the hydroquinones 6 were found. Methanolysis of 5 leads to the stable acetals 7 and 8 . On oxidation of the hydroquinones 7 the thermolabile quinones 10 were obtained. Preparative pyrolysis of 10a under relatively mild conditions (N 2 , 200°, 0.1 Torr) gives tetramethoxy ethene ( 11 ) and isobenzofuran‐4,7‐quinone 12 , a yellowish, crystalline and stable compound.
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