A study of the temperature effect on Hantzsch reaction selectivity using Mn and Ce oxides under solvent-free conditions
•Mn and Ce oxides are relevant catalysts in a Hantzsch reaction.•Reaction selectivity may change depending on the reaction temperature and catalyst composition.•The Hantzsch reaction was performed in solvent-free conditions using Ce, Mn and Cu oxides as catalysts.•Alternatively, 1,4-dihydropyridine or 2-arylpyridine can be obtained in very good yields.•The methodology represents a green alternative for the synthesis of Hantzsch derivatives that exhibit an important biological activity.
In this communication, four materials (CeO2, CeO2(Cu), MnOx, and MnOx(Cu)) were prepared, characterized and tested as catalysts, in solvent-free conditions, for the multicomponent Hantzsch reactions to obtain alternatively the 1,4-dihydropyridine or 2-phenylpyridine depending on the reaction conditions. 1,4-Dihydropyridine 4 was the main product formed at 80 °C (76%), and 2-phenylpyridine 7 was the main product at 40 °C (91%), in oxidant-free conditions, using CeO2 catalyst. It is the first report that shows that, not only the temperature but also the nature of the catalyst may change the product selectivity in Hantzsch reactions.
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Journal: Catalysis Communications - Volume 60, 5 February 2015, Pages 65–69