Quinoline alkaloids. Part XIII. A convenient synthesis of furoquinoline alkaloids of the dictamnine type

Abstract

The furoquinoline alkaloids dictamnine, γ-fagarine. and skimmianine have been synthesised (48–66% yield) from 4-methoxy-3-(3-methylbut-2-enyl)-2-quinolones or from the corresponding 2,4-dimethoxy-derivatives by ozonolysis or by reaction with osmium tetroxide–periodate and cyclisation of the resultant aldehydes with polyphosphoric acid. The N-methyl-4-quinolone, isodictamnine, was prepared similarly. The starting isoprenyl derivatives were obtained by alkylation of 2,4-dimethoxyquinolines as well as by established methods. The rearrangement of linear into angular furoquinolines is discussed.