A continuing challenge: N-heterocyclic carbene-catalyzed syntheses of gamma-butyrolactones

Catalytic, stereoselective N-heterocyclic carbene-catalyzed reactions facilitate efficient construction of many different heterocyclic compounds, such as the enantioenriched 5-membered (gamma) lactones highlighted in this tutorial review. Herein, various strategies to enable formal [3+2] type annulations between electrophilic carbonyl equivalents and homoenolate nucleophiles for the synthesis of gamma-lactones are summarized.