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

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 Cs₂CO₃ 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.