Enantioselective Intramolecular Michael Addition of Nitronates onto Conjugated Esters: Access to Cyclic γ-Amino Acids with up to Three Stereocenters

摘要

The asymmetric Michael reaction is one of the most powerful carbon-carbon bond-forming reactions available to the organic chemist and remains an important challenge within organic synthesis.Since the start of the new millenium, much work has focused on asymmetric organocatalytic processes.In most cases, the Michael acceptor is almost always a conjugated enone, enal, or nitroalkene variant.Very few examples of other Michael acceptors exist, in particular the conjugated ester, which is surprising given its synthetic utility. Within our laboratory, we were particularly drawn to the use of nitronates in the intramolecular Michael addition to conjugated esters as an entry to cyclically constrained y-amino acids (Scheme 1).