Synthesis of pyrrolo[1,2-a]quinolines by formal 1,3-dipolar cycloaddition reactions of quinolinium salts

Quinolinium salts, Q(+)-CH(2)-CO(2)Me Br(−) and Q(+)-CH(2)-CONMe(2) Br(−) (where Q = quinoline), were prepared from quinolines. Deprotonation of these salts with triethylamine promoted the reaction of the resulting quinolinium ylides (formally azomethine ylides) with electron-poor alkenes by conjugate addition followed by cyclization or by [3 + 2] dipolar cycloaddition. The pyrroloquinoline products were formed as single regio- and stereoisomers. These could be converted to other derivatives by Suzuki–Miyaura coupling, reduction or oxidation reactions.