DBU-Mediated Dimerization: Facile Access to 9,9′-Bifluorenylidenes and Isoindigos

Abstract The present work describes the 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-promoted self-dimerization of 9-chlorofluorenes and 3-chlorooxindoles for the preparation of the corresponding 9,9′-bifluorenylidene and isoindigo derivatives in moderate to good yields of 29–97%. The reactions proceed readily in a short reaction time under mild and metal-free conditions. Scale-up syntheses (5.0 mmol) of selected 9,9′-bifluorenylidene derivatives proceed in decent yields, highlighting the synthetic utility of the reported protocol.