Indolopyridines with an angular heteroatom. 11. Synthesis of 12-arylidenindolo-[2,1-a]isoquinolinium salts

The condensation of aromatic aldehydes with indolo[2,1-a]isoquinoline in a solution of trifluoroacetic acid yielded a series of 12-arylidenindolo[2,1-a]isoquinolinium trifluoroacetates. Analogous quaternary salts are formed with trichloroacetic and acetic acids as well as upon the reaction of indoloisoquinolinium hydrochloride with p-nitrobenzaldehyde or with p-nitrophenyldiazonium chloride in ethanol.