Convenient Synthetic Protocols for Diverse Functionalized Dihydrobenzofuran-Fused Spiro-indanedione-oxindole Scaffolds.

Diverse functionalized dihydrobenzofuran spiro-indanedione-oxindole scaffolds were conveniently synthesized by base-promoted cyclization reaction of Morita-Baylis-Hillman (MBH) carbonates of isatins and 2-(-hydroxybenzylidene)-1,3-indanediones. The two diastereomeric dispiro[indene-2,1'-cyclopenta[]benzofuran-2',3″'-indolines] could be selectively synthesized by using DABCO or DMAP as a base promoter. More importantly, DABCO or DMAP facilitated the annulation reaction of MBH formates of isatins and 2-(-hydroxybenzylidene)-1,3-indanediones selectively, resulting in spiro[cyclopropa[]chromene-1,2'-indene]-1',3'-diones or dispiro[indene-2,1'-cyclopenta[]benzofuran-2',3″'-indolines]. Additionally, a similar reaction with MBH maleimides of isatins afforded dispiro[indene-2,5'-benzofuro[2',3':1,5]cyclopenta[1,2-]pyrrole-4',3″'-indolines] in high yields and with high diastereoselectivity.