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The reaction of 3-alkyl(aryl)imidazo[1,5- a ]pyridines ( 1 ) with ninhydrin in dichloromethane at room temperature delivered good yields of the respective 2-hydroxy-2-(imidazo[1,5- a ]pyridine-1-yl)indene-1,3-diones. In the presence of dimethyl acetylenedicarboxylate (DMAD), this uncatalyzed electrophilic substitution reaction, involving C-1 (in  1 ) and the central C=O (in ninhydrin), takes precedence over the three-component 1,4-dipolar cycloaddition reaction. This selectivity is probably due to the higher electrophilicity of the carbonyl carbon-2 in ninhydrin as compared to that of the  sp -carbon atoms in DMAD, augmented with the high nucleophilicity of carbon-1 in  1 .

A study on the reaction of 3-alkyl(aryl)imidazo[1,5- a ]pyridines with ninhydrin