The 9-(β-pyridylmethylene)-4-azafluorene was obtained as the mixture of the Z- and E-isomers. Condensation of 4-azafluorene with methiodides of 3-formylpyridine afforded the methiodides of these isomers which were isolated in discrete form. Their configuration was established. It was established using the example of the reduction of the methiodide of the Z-isomer by sodium borohydride that the β-pyridinium portion of this quaternary salt is completely reduced to the piperidyl. ©1999 Kluwer Academic/Plenum Publishers.