Enantioselective Organocatalytic Four-Atom Ring Expansion of Cyclobutanones: Synthesis of Benzazocinones
Résumé
An enantioselective Michael addition– four-atom ring expansion cascade reaction involving cyclobutanones activated by a N-aryl secondary amide group and ortho-amino nitrostyrenes has been developed for the preparation of functionalized eight-membered benzolactams using bifunc- tional aminocatalysts. Taking advantage of the secondary amide activating group, the eight-membered cyclic products could be further rearranged into their six-membered isomers having a glutarimide core under base catalysis conditions without erosion of optical purity, featuring an overall ring expansion– ring contraction strategy.