A Tunable and Enantioselective Hetero-Diels-Alder Reaction Provides Access to Distinct Piperidinoyl Spirooxindoles

摘要

The active complexes of chiral N,N-dioxide ligands with dysprosium and magnesium salts catalyze the hetero-Diels-Alder reaction between 2-aza-3-silyloxy-butadienes and alkylidene oxindoles to selectively form 3,3- and 3,4-piperidinoyl spirooxindoles, respectively, in very high yields and with excellent enantioselectivities. The exo-selective asymmetric cycloaddition successfully regaled the construction of sp(3)-rich and highly substituted natural-product-based spirooxindoles supporting many chiral centers, including contiguous all-carbon quaternary centers.