Bicyclische Oxalamidine - Bausteine f�r hochsubstituierte 2,2?-Bipyridine und Benzolderivate

Autor: Rainer Beckert, Jörg Brandenburg, Peer Fehling, Helmar Görls, Manfred Döring
Rok vydání: 1996
Předmět:
Zdroj: Journal f�r Praktische Chemie/Chemiker-Zeitung. 338:430-435
ISSN: 1521-3897
0941-1216
DOI: 10.1002/prac.19963380184
Popis: Bicyclic Oxalic Amidines as Building Blocks for Highly Substituted 2,2′-Bipyridines and Benzene Derivatives The bis-imidoylchlorides 1 derived from oxalic acid exhibit a high regio- and chemoselectivity. As in the case of 2-picolylamine 2 the acylation with oxalyl chloride furnished the expected open chained oxalic diamides 3a while the imidoylchlorides 1 yield exclusively the new pyrido[1,2-a]-pyrazines 4. These heterocycles represent readily crystallisable and orange-red coloured compounds with a mesomeric dipolar aromatic substructure. The synthetic value of 4 is based on their easy transformation into highly substituted arenes and hetarenes. Thus, electron deficient dienophiles as dimethyl acetylenedicarboxylate lead to the bipyridines 6 via Hetero-Diels-Alder-Reaction and subsequent 1,5-hydrogen shift. In a complex reaction the derivatives of maleic acid 7a–c yield the bipyridines of type 9 while the new hexasubstituted arenes 10 can be isolated under anaerobic conditions and with an excess of dienophilic component. A x-ray structural determination of 10b shows an alternation of bond lenghts in the benzene ring. This can be considered as a distinct disturbance of aromaticity caused by the arrangement of substituents.
Databáze: OpenAIRE
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