Synthesis of dispirocyclopentyl-3,3′-bisoxindoles via base promoted cyclization reaction of 3-phenacylideneoxindoles with nitromethane

A special kind of dispirocyclopentyl-3,3′-bisoxindoles, in which the two oxindole units exist at 1,2-positions of the newly formed cyclopentyl ring, were conveniently prepared in 49–86% yields by cyclization reaction of nitromethane with two molecules of 3-phenacylideneoxindoles in refluxing ethanol in the presence of DBU as base. The reaction has the advantages of readily available starting materials, operational simplicity, good yields, and high diastereoselectivity. [Display omitted]