Convenient Synthesis of Dihydrobenzofuran‐Fused Spirocyclopentane‐1,2‐Diindolinone Scaffolds

Abstract The diverse functionalized dihydrobenzofuran‐fused spirocyclopentane‐1,2‐diindolin‐one scaffolds were conveniently synthesized by base promoted domino cyclization reaction of MBH (Morita‐Baylis‐Hillmann) carbonates of isatins and 3‐( o ‐hydroxybenzylidene)indolin‐2‐ones. The base promoted reactions of MBH maleimides of isatins and MBH formates of isatins with 3‐( o ‐hydroxybenzylidene)indolin‐2‐ones afforded polycyclic dispiro[indoline‐3,4′‐benzofuro[2′,3′:1,5]cyclopenta[1,2‐ c ]pyrrole‐5′,3′′‐indolines] and dispiro[indoline‐3,1′‐cyclopenta[ b ]benzofuran‐2′,3′′‐indolines] in good yields and with high diastereoselectivity. More importantly, DMAP facilitated annulation reaction of MBH nitriles of isatins and 3‐( o ‐hydroxybenzylidene)indolin‐2‐ones selectively resulted in dispiro[indoline‐3,1′‐cyclopentane‐2′,3′′‐indolines], while Cs 2 CO 3 promoted reaction gave dispiro[indoline‐3,1′‐cyclopenta[ b ]benzofuran‐2′,3′′‐indolines] in high yields and with high diastereoselectivity. The relative configurations of the various polycyclic compounds were clearly elucidated by determination several single crystal structures.