Syntheses of Strychnan- and Aspidospermatan-Type Alkaloids. 11. Total Syntheses of (−)-Lochneridine and (−)- and Racemic 20-epi-Lochneridine
摘要:
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).
Syntheses of Strychnan- and Aspidospermatan-Type Alkaloids. 11. Total Syntheses of (−)-Lochneridine and (−)- and Racemic 20-epi-Lochneridine
摘要:
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).
Catalytic Regioselective γ-Methylenation of α,β-Unsaturated Aldehydes Using Formaldehyde via Vinylogous Aldol Condensation
作者:Mahesh S. Kutwal、Sachin Dev、Chandrakumar Appayee
DOI:10.1021/acs.orglett.8b04110
日期:2019.4.19
first vinylogous aldol condensation of α,β-unsaturated aldehydes using aqueous formaldehyde is developed under mild reaction conditions to form the γ-methylenated products with excellent regioselectivity. Using this methodology, a short synthesis of α-triticene, an antifungal compound, is achieved in two steps. The practicality of this methodology is demonstrated by the gram-scale synthesis. Formation of