Rapid synthesis of the tetrahydroquinoline alkaloids: angustureine, cuspareine and galipinine

A one-pot method for the preparation of 1,2-substituted dihydroquinolines is described. This method features the C-2 addition of a range of organolithium reagents to quinoline followed by the in-situ addition of an electrophile. Standard palladium-catalysed hydrogenation, of the resultant 1,2-disubstituted dihydroquinoline adducts, generates the corresponding 1,2-disubstituted tetrahydroquinoline. A series of such compounds have been synthesised including the natural products; (±)-angustureine 1, cuspareine 2 and galipinine 3.