Syntheses of Strychnan- and Aspidospermatan-Type Alkaloids. 11. Total Syntheses of (−)-Lochneridine and (−)- and Racemic 20-<i>epi</i>-Lochneridine
作者:Martin E. Kuehne、Feng Xu
DOI:10.1021/jo981401o
日期:1998.12.1
Enantioselective syntheses of (-)-lochneridine (1) and (-)-epi-lochneridine (2) were obtained by two alternative C-20 diastereoselective syntheses of the respective pentacyclic (3aS,5S,11bR)-methyl 12-oxo-3,5-ethano-2,3,3a,4,5,7-hexahydro-3H-pyrrolo[2,3-d]carbazole-6-carboxylate ((-)-8) and tetracyclic methyl (2S,3aS,5R,11bR))-3-benzyl-2,3,3a,4,5,7-hexahydro-5-(2-(1-butenyl))-1H-pyrrolo[2,3d]carbazole-6-carboxylate ((-)-12b) precursors from tryptophan derived 2-[(methoxycarbonyl)methyl]3-[2(S)-(methoxy or benzyloxycarbonyl)-2-(N-b-benzyl)aminoethyl]indole (15 or 16). While a modified Grignard reaction of the ketone (-)-8 provided (-)-lochneridine (1), dihydroxylation and cyclization of the olefin (-)-12b gave its C-20 epimer (2).