Controllable selectivity in Biginelli and Hantzsch reactions using nanoZnO as a structure base catalyst

Preparative nanoZnO and ZnO have been found as reusable catalysts for either condensation or dissociation of urea to ammonia and controllable selectivity in the Biginelli and Hantzsch reactions. The feasibility of urea dissociation to ammonia and switching of the selectivity of heterocyclization for DHPMs to DHPs over various metal oxides has been comparatively investigated. In the presence of nanoZnO and ZnO, direction of the MCR reaction in either Biginelli or Hantzsch way is possible by choice of the reaction conditions. Biginelli reaction occurs at 60 °C under solvent-free conditions, while Hantzsch reaction occurs in water at ∼120–140 °C or under microwave irradiation using 5 mol% nanoZnO or 10 mol% ZnO.

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► NanoZnO show high activity toward MCRs for the synthesis of DHPMs and DHPs.
► Selectivity is controllable by choice of the reaction conditions.
► NanoZnO and ZnO are reusable and catalyze the Biginelli reaction at ∼60 °C.
► Dissociation of urea over ZnO results in the Biginelli/Hantzsch switching under MW irradiation.