π-Extended conjugate phenylacetylenes. Synthesis of 4-[(E) and (Z)-2-(4-ethenylphenyl)ethenyl]pyridine. Dimerization, quaternation and formation of charge–transfer complexes

The conjugate (E)- and (Z)-(4′-pyridylethenyl)-4-phenylethyne and ) has been satisfactorily prepared by two different routes: (a) by dehydrohalogenation of 4′-pyridylethenyl-4-phenyl-β-chloroethene; (b) by the Wittig reaction between p-(iodobenzyl)(triphenyl)phosphine ylide and 4-pyridinecarboxaldehyde, E/Z isomer separation, and cross-coupling with 2-methyl-but-3-yn-2-ol followed the propanone elimination. The Glaser oxidative dimerization of yields (Z,Z)-1,4-di[(4′-pyridylethenyl)-4-phenyl]-buta-1,3-diyne in good yield, . was obtained by phase transfer oxidative dimerisation of in presence of their N-methyl salt . Mono- and di-N-methylated salts of conjugate and , were obtained by quaternation with iodomethane. The di-N-methylated salt forms charge–transfer complexes with TCNE, TCNQ and TMPD.