Efficient construction of spirocyclopentane-1,3-dioxindoles via an annulation reaction of isocyanides and 3-methyleneoxindoles.

The DABCO-promoted annulation reaction of alkyl isocyanides with two 3-methyleneoxindole molecules in refluxing acetonitrile afforded functionalized dispiro[indoline-3,1'-cyclopentane-3',3''-indolines] in moderate yields and with a variety of diastereoselectivities through a cascade [2 + 2 + 1] cycloaddition reaction. However, the DABCO-promoted annulation reaction of 3-(2-isocyanoethyl)indole and 3-phenacylideneoxindoles gave unique polycyclic spiro[indoline-3,5'-pyrrolo[3',2':2,3]cyclopenta[1,2-b]indoles] in satisfactory yields and with high diastereoselectivity.