Construction of the Erythrinane Core Skeleton via Asymmetric Catalytic Cascade Reaction of Tertiary Enamides

We
report herein an efficient cascade strategy for the rapid construction
of a highly enantioenriched erythrinane core skeleton. Under the sequential
catalysis of a chiral Cr­(III)­(salen)Cl and InCl3, cyclohexanone-derived
tertiary enamides undergo an intramolecular enantioselective nucleophilic
addition followed by diastereoselective Pictet–Spengler cyclization.
This method is highly enantio- and diastereoselective, leading to
diverse erythrina alkaloid derivatives as the sole diastereoisomer
with up to 98% ee.