Synthesis and reactions of methylbenzo[c]quinolizinium salts

Six isomers of the methylbenzoc]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)benzoc]quinolizinium salts 6 . The reactivity of 3 and methylbenzoa]quinolizinium salts 1 was discussed on the basis of their π-electron energy.