Synthesis and reactions of methylbenzo[c]quinolizinium salts

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 3g reacted with p ‐methoxybenzaldehyde in the presence of bis(l‐piperidino)‐( p ‐methoxyphenyl)‐methane 7 to yield trans ‐( p ‐methoxystyryl)benzo[ c ]quinolizinium salts 6 . The reactivity of 3 and methylbenzo[ a ]quinolizinium salts 1 was discussed on the basis of their π‐electron energy.