Reactions of N-arylamides of acetoacetic acid with ninhydrin in the presence of piperidine

We have earlier discovered that the interaction of arylamides of acetoacetic acid with aromatic aldehydes under basic catalysis results in the formation of N,N',2triaryl-6-hydroxy-6-methyl-4-oxocyclohexane-1,3-dicarboxamides, including compounds with antimicrobial activity [16–18]. Further developing our studies on the synthesis of novel biologically active compounds, herein we report the reaction of arylamides of acetoacetic acid with ninhydrin as the carbonyl component. We found that the reactions of N-arylamidoacetoacetates with ninhydrin occurred in ethanol at room temperature in the presence of piperidine to form piperidinium 1-{1-aryl-3a,8b-dihydroxy-2,4-dioxo-1,2,3а,4tetrahydroindeno[1,2-b]pyrrol-3(8bH)ylidene}ethenolates 1a and 1b (Scheme 1).