Expedient approach for the synthesis of novel indenothiophene derivatives

Gewald reaction of 2-(2,3-dihydro-5,6-dimethoxy-1 H -inden-1-ylidene)malononitrile, elemental sulfur, and a catalytic amount of triethylamine furnished the new synthon 2-aminoindenothiophene-3-carbonitrile. Its reaction with conc. H 2 SO 4 furnished the expected 2-amino-3-carboxamide derivative instead of the corresponding carboxylic acid. The key intermediates 2-aminoindenothiophene-3-carbonitrile and -3-carboxamide were used for the synthesis of tetracyclic indenothienopyrimidine derivatives by cyclocondensation reaction with acid chlorides, amides, formic acid, or hydrazine hydrate. Neat reactions of the carbonitrile with cyclic and aliphatic ketones in the presence of anhydrous ZnCl 2 furnished pentacyclic and tetracyclic indenothienopyridine derivatives, respectively, in good yields. All new compounds were characterized by spectroscopic and analytical data. Graphical abstract