Efficient synthesis of (-)-gamma-lycorane alkaloid by two Bu3SnH-mediated radical cyclisations.
An asymmetric induction using (S)-1-arylethylamine-based chiral auxiliary and two Bu(3)SnH-mediated radical cyclisations have been developed for a total synthesis of (-)-gamma-lycorane (1). The first cyclisation proceeded in 5-endo-trig manner with moderate diastereoselectivtiy to give (3aR,7aR)-octahydroindol-2-one 6b as the major product using alpha-iodo-N-(6-oxocyclohexen-1-yl)-N-[(S)-1-phenylethyl] acetamide (5b). In the second cyclisation, the radical precursor 8 was used as substrate to construct the optically active lycorane skeleton 15 which was reduced using LiAlH4 into (-)-gamma-lycorane (1).
Faculty of Pharmacy, Department of Pharmaceutical Organic Chemistry, University of Mansoura, Mansoura, Egypt. sbialy65@yahoo.com
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El Bialy
D000470:Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry*; D047151:Amaryllidaceae Alkaloids / Q000737:chemistry*; D003500:Cyclization; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure
D000470:Alkaloids; D047151:Amaryllidaceae Alkaloids; C412290:lycorane