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.