Synthesis of diastereomeric 2,4-disubstituted pyrano[2,3-b]quinolines from 3-formyl-2-quinolones through O–C bond formation via intramolecular electrophilic cyclization

A number of 3-homoallyl-2-quinolones have been synthesized from 3-formyl-2-quinolones by reaction with allylindium bromide in aqueous DMF. Intramolecular electrophilic cyclization of these quinolones with iodine afforded either exclusively, or predominantly, racemic cis-diastereoisomers. Nucleophilic substitution reactions at the iodomethyl group afforded a mixture of tetracyclic products and unreacted racemic trans-diastereoisomer.