Browsing by Author "Daub, Wolfgang"

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    Darstellung von Didehydropyridinen aus (Trimethylsilyl)pyridinen
    (1991) Effenberger, Franz; Daub, Wolfgang
    Halogen-substituted (trimethylsilyl)pyridines 2, 3, 5 - 7 and trifluoromethylsulfonyloxy-substituted (trimethylsilyl)pyridines 9b, 11b are obtained from 2- and 3-halopyridines 1, 4 or hydroxypyridines 8, 10, and 12. Reactions of the 3- and 2-(trimethylsilyl)pyridines 2,9b and 11b with bases in the presence of furans 15 give only protodesilylation or hydrolysis products but no indication is found for the formation of a 2,3-didehydropyridine. 3-Bromo-4-(trimethylsilyl)pyridine (5a) reacts with KOCMe3 in the presence of furan (15a) to give a mixture of products from which the isoquinoline derivative 20 and the tert-butoxypyridines 23, 24 are formed by addition to 3,4-didehydropyridine. Under comparable conditions far higher yields of 3,4-didehydropyridines are obtained by treatment of the 3-halo-2,4-bis(trimethylsilyl)pyridines 7 with strong bases.
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    Zur Reaktion von Halogen(trimethylsilyl)benzolen mit Elektrophilen und Basen : Carbodesilylierung und Eliminierung als Konkurrenzreaktionen
    (1991) Effenberger, Franz; Daub, Wolfgang
    Elimination to dehydrobenzenes takes place as competitive reaction in the base-catalyzed carbodesilylation of 1-halo-2-(trimethylsilyl)benzenes 1 with carbonyl compounds 2 in the presence of furans 3, 6. Elimination is preferred with increasing leaving tendency of the halides (I > Br > > Cl > > F) and with decreasing reactivity of the carbonyl compounds. Exclusive elimination to 1,2-didehydrobenzenes - which are trapped with furans - occurs in the reaction when no electrophiles are present.