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

Abstract

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-4-arylindanes. The same compounds were formed in the reaction of the cyclopentylidenemalononitrile dimer with aldehydes. It is suggested that the cyclopentylidenemalononitrile dimers undergo 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. © 1986, Walter de Gruyter. All rights reserved.