Hydrogenation of ortho-nitrochalcones over Pd/C as simple access to 2-substituted 1,2,3,4-tetrahydroquinolines

The preparation of some 2-substituted-1,2,3,4-tetrahydroquinoline has been achieved by the one-pot reductive intramolecular cyclization of ortho-nitrochalcones with gaseous hydrogen in the presence of a Pd/C catalyst and the best selectivity was observed using CH2Cl2 as solvent. The method is operationally simple and versatile since ortho-nitrocalchones are easily accessible by Claisen-Schmidt condensation of 2-nitrobenzaldehydes and enolizable ketones. Selected examples on structurally different substrates have been considered and a novel tetrahydroquinoline and a benzo[h]tetrahydroquinoline were prepared and characterised.