Reactions introducing 4-cyano-5-dicyanomethylene-2-oxo-3-pyrrolin-3-yl group to 4-ethynyl-N,N-dialkylaniline derivatives and characterization of the resulting dyes

Electrophilic reactions of a strong acceptor, 3-chloro-1-butyl-4-cyano-5-dicyanomethylene-2-oxo-3-pyrroline, with 4-ethynylaniline derivatives were investigated. The major products were found to be the cis- or trans- monoadducts of the pyrroline-type acceptor, i.e., 4-(dialkylamino)phenylethene derivatives in which the ethene moiety is substituted by chlorine and 1-butyl-4-cyano-5-dicyanomethylene-2-oxo-3-pyrrolin-3-yl group. Their stereostructures depended on the substituent attached to the ethynyl group on the opposite side of aminophenyl group. The adducts with a chloroethylene linkage were able to convert to the ethynylene derivatives by triethylamine. Among the obtained D-pi-A molecules, the cis-compounds respect to the donor and acceptor groups showed the absorption maximum at longer wavelengths compared with the corresponding trans-compound. The calculation results suggested more polarized structures in the cis-forms, resulting in their bathochromic shift of the absorption.