Abstract
Synthesis of racemic and optically active cispentacin ((-)-1) is described. Intramolecular nitrone-olefin cycloaddition of the alkenyl nitrone 7 gave cis-isoxazolidine (±)-8, which was transformed into (±)-1 by sequential reactions involving catalytic hydrogenolysis and oxidation. Similarly, the optically active nitrone (R)-22, which was derived from the ketone 15 via lipase-catalyzed hydrolysis of the acetate (±)-17, underwent intramolecular cycloaddition to give (+)-25 with high stereoselectivity (15 : 1). The cycloadduct (+)-25 was transformed in 4 steps into optically active natural cispentacin.
