Deconjugated butenolide: a versatile building block for asymmetric catalysis

The wide abundance of γ-lactones in natural products and bioactive targets calls for suitable building blocks for their enantioselective synthesis. β,γ-Unsaturated γ-butenolides, commonly known as deconjugated butenolides, owing to their easy accessibility and highly reactive nature, have emerged as the synthon of choice during the past decade for the enantioselective synthesis of γ-lactones. Their compatibility under organocatalytic, metal-catalyzed as well as cooperative catalytic conditions has resulted in numerous enantioselective transformations involving deconjugated butenolides. These reactions not only led to enantioenriched γ-lactones, but also various other heterocycles and acyclic compounds through ring-opening and fragmentation of the parent butenolide ring. The purpose of this review is to provide a comprehensive treatise on the catalytic asymmetric reactions of deconjugated butenolides reported so far. This aspect is presented alongside the preparation and reactivity comparison of deconjugated butenolides with other competing synthons of γ-lactones. Limitations of the existing protocols and the possible scope for future development are also discussed. Deconjugated butenolides have emerged as a popular synthon for the enantioselective synthesis of γ-lactones. This review provides a comprehensive overview on the catalytic asymmetric reactions of deconjugated butenolides reported till date.