Abstract Six isomers of the methylbenzo [c] quinolizinium salt 3 including four new monomethyl derivatives were synthesized by thermal-intramolecular quaternization of the cis-methyl-substituted 2-[2-(2-chlorophenyl)-vinyl] pyridines 4 or by the irradiation of trans-4 with selected wavelengths (290< λ< 340 nm and λ> 400 nm) in acetonitrile. Among the regioisomeric monomethyl derivatives 3, the 1-, 3-, and 6-methyl derivatives 3b, 3d, and ...