Azines pyrrole ring

A pyrrole ring may be formed from azines and either anhydrous nickel chloride or paUadium(II) chloride. Palladium-assisted C—C bond formation connecting one benzene ring to another is also a useful method. A review of transition metal-mediated heterocyclizations was published in 1980 [B-S6]. Bis(methyl-thio)methylenemalonic acid derivatives annulate two methylene groups [2881]. 

Cobaltous bromide Pyrazoline and pyrrole ring from azines... 

The synthesis of tetra[6,7]quinoxalinoporphyrazines 130, 131 in which pyrrole rings had been annulated to benzene instead of pyr-azine rings is shown above on examples 66. This involves the initiated... 

Entry to the ugibohlin, phakellin, and isophakellin ABC ring systems was achieved via intramolecular N(l)-C(3) cyclizations of the Weinreb amide 169 of pyrrole-proline 168 or its brominated derivatives to give the bispyrrolopyr-azine 170 (Scheme 12) <2005TL249>. 

Reedijk and co-workers have prepared and studied a variety of Ru(ll) complexes of pyridyl- and pyrazinyl-substituted 1,2,4-triazoles of which 26 is an example. In ail cases the heterocyclic ligands were chelated to the metal center via one azole and one azine nitrogen atom and, in addition to various electrochemical and spectroscopic studies, pKa values for the pyrrole proton of the triazole ring were obtained. The Ru(bpy)2 + com-... 

Perimidine is one of the few azines in which the lone pair of a pyrrole-like nitrogen participates in the 7t-system of the molecule. Perimidine is therefore a 14-7t electron system, isoelectronic with the phenalenyl anion. An important consequence of this interaction is a transfer of electron density from the heterocyclic ring into the naphthalene moiety. Therefore perimidine exhibits simultaneously the characteristics of both 7r-deficient and 7t-excessive systems <87H(26)I029>. 

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