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

Abstract

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-1-arylidene-4-arylindanes. The same compounds were formed in the reaction of the cyclopentylidenemalono­nitrile dimer with aldehydes. It is suggested that the cyclopentylidenem alononitrile 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.