First report of syn isomers in the diastereoselective synthesis of highly functionalized piperidines catalysed by wet picric acid: factors influencing the syn–anti ratios

This is the first report of the formation of a syn-diastereoisomer in the diastereoselective synthesis of highly functionalized piperidines catalysed by wet picric acid via a one-pot, step-economic condensation of aromatic aldehydes, 1,3-dicarbonyl compounds and aromatic amines. DFT calculation shows that anti isomers are more stable compared to the syn. The syn–anti ratio of the products depends on the temperature and the nature of substitution on both the aromatic aldehydes and aromatic amines. Conditions for getting pure anti and pure syn compounds have been studied.