Synthesis and characterization of some novel polyfunctionally substituted indeno[2,1-b]thiophene compounds derived from indanones

Condensation of 3-dicyanovinylindan-1-one 3 with arylamines 5a–5c afforded 2-[3-(substituted-amino)-inden-1-ylidene]-malononitriles 7a–7c, which were converted to 2-amino-indeno[2,1-b]thiophene 8a–8c using the Gewald reaction. Cyclization of ethyl(1-indanylidene)-cyanoacetate 4 with elemental sulfur gave 2-amino-8H-indeno[2,1-b]thiophene-3-carboxylic acid ethyl ester 9. Acetylation of 9 with acetic anhydride afforded the 2-acetyl compound 11, which was condensed with arylaldehydes 12a–12c to yield the corresponding 2-amino-indeno[2,1-b]thiophene moiety 13a–13c containing a methine chromophore located at the 8-position using the Knoevenagel reaction. Compound 9 was condensed with N,N-dimethylaminobenzaldehyde 12d in piperidine to afford the corresponding 2-amino-indeno[2,1-b]thiophene compound 13d. Electronic absorption spectra of these compounds were discussed.