Synthesis and characterization of novel 4H-pyran-4-ylidene indole-based heterocyclic systems for several optical applications

Abstract

Two new quadrupolar 4H-pyran-4-ylidene fluorophores (3) derived from indole were prepared in good yields through condensation of 5-methyl-1H-indole-3-carbaldehyde with the acceptor precursors 2-(2,6-dimethyl-4H-pyran-4-ylidene)malononitrile (1) and 1,3-diethyl-dihydro-5-(2,6-dimethyl-4H-pyran-4-ylidene)-2-thiobarbituric (2), in the presence of a catalytic amount of piperidine. These building blocks were prepared by Knoevenagel condensation of the corresponding ketone precursor with malononitrile or 1,3-diethyl-dihydro-2-thiobarbituric acid. The new compounds were completely characterized by the usual spectroscopic techniques (UV-vis., FT-IR and multinuclear NMR - 1H, 13C).