Unexpected Formation of OpticallyActive 4-Substituted 5-Hydroxy-γ-lactams by OrganocatalyzedReaction of 3-Substituted Cyclobutanones with Nitrosobenzene

An organocatalyzed enantioselective desymmetrization reaction for converting 3-substituted cyclobutanones into 4-substituted 5-hydroxy-γ-lactams is presented. This involves a ring-expanding O-nitroso aldol―cyclization domino sequence. This synthetic protocol provides access to five-membered ring systems in good yields with the generation of two new stereogenic centers.