Asymmetric Syntheses of Amaryllidaceae Alkaloids (−)-Crinane and (+)-4a-Dehydroxycrinamabine

A palladium-catalyzed
asymmetric allyl–allyl cross-coupling
reaction to construct the chiral quaternary carbon center of crinane
alkaloids has been developed. On the basis of an efficient approach,
the enantioselective synthesis of (−)-crinane (1) is presented, and the first asymmetric total synthesis of (+)-4a-dehydroxycrinamabine
(2) was achieved by subsequent oxidation, 1,4-conjugate
addition, RCM reaction, reductive amination, and Pictet–Spengler
reaction. The method provided an alternative strategy for the syntheses
of crinane alkaloids and other Amaryllidaceae natural products.