Enantioselective Approach to (−)-Hamigeran B and (−)-4-Bromohamigeran B via Catalytic Asymmetric Hydrogenation of Racemic Ketone To Assemble the Chiral Core Framework

A new
strategy featuring an iridium-catalyzed asymmetric hydrogenation
of a racemic ketone via dynamic kinetic resolution to generate a cyclopentanol
with three contiguous stereocenters and a SmI2-promoted
pinacol coupling to install the six-membered ring with correct stereochemistry
has been described for the enantioselective total synthesis of (−)-hamigeran
B (19 steps, 10.6% overall yield) and (−)-4-bromohamigeran
B (19 steps, 12.3% overall yield).