The reaction of 2-hydroxyindol-3-ones (1) with dimethyl acetylenedicarboxylate (2a, DMAD) in the presence of base (triethylamine or sodium carbonate) underwent Michael addition followed by cyclization to produce 3ahydroxyfuro[2,3-hlindoles (3). Compounds possessing furo[2,3-blindole skeleton are of interest in connection with their possible biological activities, represented by the Calabar bean alkaloid physovenine' and the akuammiline alkaloid aspidod a~~c a q i n e .~ A number of approaches to this skeleton are known: electrophilic addition-cyclization of tryptopholes,3 reductive cyclization of oxindole-ethanols and -acetates,4 Baeyer-Villiger oxidation of indol~butanone,~ reaction of indolylmagnesium bromides with ethylene oxide,6 reaction of 2-indolyl sulfoxide with ketene,7 reaction of indoles with dimethyl acetylenedicarboxylate (DMAD),' copper catalyzed reaction of isatin-3-hydrazone with DMAD? Knoevenagel reaction-cyclization of isatin,'' and others."-'3 The reaction of a-hydroxy ketones with acetylene compounds affords furan compounds.'4 In connection with our studies on the chemistry of indol-3-ones,'5 we here report the reactions of 2-hydroxyindol-3-ones (1) with acetylene compounds (2) by means of the addition-cyclization of l a , b with DMAD (2a) giving furo[2,3-blindole derivatives (3). 1 a : R'= AC, R' = ~h 2 a : R = C02Me, R'= Me b : R1= Ac. R 2 = Me b : R = H, R'= Et c : R'= Ac. R2 = H c : R = M e , R ' = E t d : R'= H. R2 = CH2CH=CH2
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.