NiFe2O4@SiO2@PrNH2–DPA–CeCl3: a cerium-based magnetic nano dual-acid catalyst with high efficacy and recyclability for domino sequential synthesis of lactam ring-fused 1,5-benzodiazepines

Abstract

A cerium-based magnetic nano dual-acid catalyst (NiFe₂O₄@SiO₂@PrNH₂–DPA–CeCl₃) was successfully designed and prepared. It was characterized and confirmed by distinct techniques such as FTIR, XRD, XPS, SEM, TEM, BET, EDS, ICP-AES, TGA/DTA and VSM. The high efficacy and recyclability of the catalyst was identified via domino sequential reaction to synthesize aryl/carboxyl-substituted lactam ring-fused 1,5-benzodiazepines (20 examples, 85–98% yields) with a high TON (up to 124 841) and TOF (up to 124 841 h⁻¹). Functional NiFe₂O₄@SiO₂ supported with Brønsted acid (2,6-pyridinedicarboxylic acid (DPA)) and Lewis acid (CeCl₃·7H₂O) has been used to doubly and synergistically activate carbonyl and imine bonds. The 1,5-benzodiazepines were fused with a lactam ring in one-pot. A speculated reaction mechanism for the synergistic synthesis of aryl/carboxyl-substituted lactam ring-fused 1,5-benzodiazepines by the magnetic nano dual-acid catalyst was proposed. The catalyst engaged in six repeated rounds without obvious decline of catalytic proficiency. Given its facile recycling, repetitive use, high catalytic efficacy, mild conditions and wide substrate suitability, the applicability of the magnetic nano dual-acid catalyst in this protocol conforms to the principal aim of environmental friendliness and cost-effective chemistry.