合成路线1

The oxidative cyclization of the formamide derivative (I) with iodosobenzene bis(trifluoroacetate) (PIFA) gives the tricyclic semiquinone (II), which is debenzylated by means of TFA and Me2S and cyclized with Ms-OH to yield the tetracyclic ketone (III). Elimination of the extra OH group of (III) by means of Tf2O, Pd(OAc)2 and TEA affords the intermediate (IV), which is reduced by means of L-Selectride and LiAlH4 to provide racemic galanthamine (V). Finally, this compound is submitted to optical resolution to furnish the target (-)-galanthamine. Alternatively, the protection of the ketonic group of (IV) with ethyleneglycol and PPTS gives the spiroketal (VI), which is selectively reduced with LiAlH4 and hydrolyzed with HCl to yield racemic narwedine (VII). Finally, the reduction of (VII) with L-Selectride affords the already described racemic galanthamine.