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 reg io- and chemoselectivity. As in the case of 2-picolylamine 2 the acyla tion with oxalyl chloride furnished the expected open chained oxalic d iamides 3a while the imidoylchlorides 1 yield exclusively the new pyri do[1,2-a]-pyrazines 4. These heterocycles represent readily crystallis able and orange-red coloured compounds with a mesomeric dipolar aromat ic substructure. The synthetic value of 4 is based on their easy trans formation 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-hydro gen shift. In a complex reaction the derivatives of maleic acid 7a-c y ield the bipyridines of type 9 while the new hexasubstituted arenes 10 can be isolated under anaerobic conditions and with an excess of dien ophilic component. A x-ray structural determination of 10b shows an al ternation of bond lenghts in the benzene ring. This can be considered as a distinct disturbance of aromaticity caused by the arrangement of substituents.