Fused polycyclic indoline skeletons are found in many natural productsa nd bioactive molecules.S everal approaches,i ncluding dearomative cyclization of functionalized indoles,h aveb eend eveloped for the rapid synthesis of these skeletons.A sa resulto fe xtensive research over the past few decades,n umerous elegant and efficient protocols for the transitionm etal-catalyzed dearomative cyclization of indoles to affordi ndolines have been reported, and recent developments in this area are discussed in detail in this review. Scheme 5. Gold-catalyzed intermolecular [2+ +2] cyclization reactionsofi ndoles with an allenyl amide. Scheme6.Gold-catalyzed intramolecular [2+ +2] cyclizations of indolyl-allenes. Scheme 10. Asymmetric rhodium-catalyzed intermolecular [3+ +2] cyclization reactions of indoles with vinylcarbenes.
Inverse‐electron‐demand Diels–Alder (IEDDA) reactions of electron‐poor 2‐pyrones as electrophilic dienes have been extensively studied in the past fifty years. These reactions provide an efficient access to bridged bicyclic lactones and their derivatives, such as densely functionalized 1,3‐cyclohexadienes after CO2 extrusion and polysubstituted aromatic compounds through elimination. This reaction has been used for the synthesis of many biologically active natural products and drug candidates. In this review, the developments of these IEDDA reactions including non‐catalytic, Lewis acid‐catalyzed and organocatalytic IEDDA reactions, and their applications in total synthesis are discussed in detail.
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