Differences between the Reaction of 2-Benzylidenecyclopentanone with Malononitrile and the Reaction of Cyclopentylidenemalononitrile with Aromatic Aldehydes; Synthesis of Strong Fluorescent o-Aminonitriles

Z. Naturforsch. 41b, 1471 — 1478 (1986); received June 5, 1986 2-Benzylidenecyclopentanone, Cyclopentylidenemalononitrile, o-Aminonitriles, Luminescent Spectra It was found that instead of the Knoevenagel condensation of cyclopentylidenemalononitrile with aromatic aldehydes, a complex reaction takes place leading to 5,7-dicyano-l-arylidene-4arylindanes. The same compounds were formed in the reaction of the cyclopentylidenemalono­ nitrile dimer with aldehydes. It is suggested that the cyclopentylidenemalononitrile dimers un­ dergo an electrocyclic ring opening leading to conjugated triene systems. These species are very reactive intermediates and may react with aldehydes in the next step. Bulky substituents in 2,5-dibenzylidenecyclopentanone hindered its Knoevenagel condensation with malononitrile but did not hinder its Michael addition leading to a 4H-pyrane derivative. Solutions of the obtained o-aminonitriles exhibit strong fluorescence in a variety of solvents.