合成路线1

Stereoselective ketone (XVII) reduction with NaBH4, and then silylation with tert-butyldimethylsilyl chloride and KH furnished bis(silyl) ether (XVIII). The ester group of (XVIII) was converted to aldehyde (XX) via reduction to alcohol (XIX) with DIBAL and further oxidation with the Dess-Martin reagent. Reductive coupling of (XX) with indoline (XXI) was performed by formation of an intermediate imine using TiCl4 as the dehydrating reagent and then reduction with NaBH3CN to afford (XXII). Removal of all silyl groups from the N-alkylated indoline (XXII) with tetrabutylammonium fluoride and then selective silylation of the primary hydroxyl group with triethylsilyl chloride provided diol (XXIII). Oxidation of both secondary hydroxyl groups to ketone and indoline ring to the corresponding indole was performed by treatment with MnO2. Acid desilylation then yielded tryptophol (XXIV). Finally, oxidative ring closure of (XXIV) under Sharpless epoxidation conditions furnished the desired furoindoline system as a mixture of isomers. End product, identical with the natural (+)-madindoline A, was obtained as the major isomer using (+)-diethyl tartrate as the chiral catalyst.