Synthesis and substituent effects of some novel dyes derived from indeno[2,1-b]thiophene compounds

The synthesis and characteristic absorption spectra of 2,3,8-trisubstituted-indeno[2,1-b]thiophene compounds 5, 6 and 7 were reported. Cyclization of 3-dicyanovinyl-indan-1-one 3 with sulfur gave 2-amino-8-oxo-8H-indeno[2,1-b]thiophene-3-carbo-nitrile compound 5. The reaction of compound 5 with malononitrile and with ethyl cyanoacetate gave the indeno[2,1-b]thiophene derivatives 6 and 7, respectively. The absorption maxima of these compounds changed very significantly by the introduction of various substituents on the 8-position of indeno[2,1-b]thiophene ring system. The preparations of the corresponding azomethine dyes and azo disperse dyes were also reported. The azomethine dyes 10, 11 and 12 were prepared by condensation reaction of compounds 5, 6 and 7 with N,N-dimethylaminobenzaldehyde 8. Additionally, compounds 5, 6 and 7, as diazo components, were diazotized using sodium nitrite in concentrated sulfuric acid, and coupled to N,N-disubstituted anilines 9a–d to afford a series of novel azo disperse dyes 13a–d, 14a–d and 15a–d, respectively. The prepared products were confirmed by elemental analysis, IR, 1H NMR and MS spectral data. The substituent effects of these compounds and dyes on the electronic absorption properties in solvent are also evaluated.