Asymmetric Synthesis of Congested Spiro-cyclopentaneoxindoles via an Organocatalytic Cascade Reaction

Starting
from simple alkylidene oxindoles and nitroketones, a highly
stereoselective methodology was developed for the synthesis of spiro-cyclopentaneoxindoles
with four consecutive stereogenic centers. Using an organocatalytic
cascade of Michael and aldol reactions in the presence of a chiral
thiourea catalyst products were obtained in moderate to high yields
and excellent enantioselectivities. Nitro, ester, and hydroxyl groups
were introduced to the spiro ring, which could be used to facilitate
further functionalization of the products.