New four-component reactions in water: a convergent approach to the metal-free synthesis of spiro[indoline/acenaphthylene-3,4′-pyrazolo[3,4-b]pyridine derivatives

New four-component domino reactions are described that allow the one-pot synthesis of spiro[indoline/acenaphthylene-3,4'-pyrazolo[3,4-b]pyridine derivatives from the reaction of phenylhydrazine, 3-aminocrotononitrile, isatin/acenaphthylene-1,2-dione, and cyclic 1,3-dicarbonyl compounds, including cyclohexane-1,3-diones, barbituric acid, and 2-thioxodihydropyrimidine-4,6(1H,5H)-dione, in the presence of (+/-)-camphor-10-sulfonic acid (CSA). These processes take place in water and involve the generation of two rings and five new bonds (two C-C, two C-N and one C = N) in a single synthetic operation, with expedient work-up and diminished waste generation due to the absence of extraction and purification steps. (C) 2011 Elsevier Ltd. All rights reserved.