Fe₃O₄@MCM-41-Cystine-ZnCl₂ nanocomposite in deep eutectic solvent: a sustainable and scalable catalytic system for three-component synthesis of triarylpyridines.

In this paper, we report a novel Fe₃O₄@MCM-41-Cystine-ZnCl₂ nanocatalyst as a highly active, recyclable, and sustainable platform for the synthesis of triarylpyridines. This catalyst integrates the benefits of a mesoporous MCM-41 support, magnetic Fe₃O₄ core, and ZnCl₂ Lewis acid centers stabilized by cystine linkers, resulting in high surface area, strong catalytic activity, and excellent stability. Under optimized conditions (100 °C, 2 h, 7 mol% catalyst) in a deep eutectic solvent (choline chloride-glycerol), twenty triarylpyridines were obtained in excellent yields (84-98%). The system exhibited broad substrate tolerance, efficiently converting electron-donating, electron-withdrawing, sterically hindered, and heteroaryl substrates with consistent turnover numbers (TON = 12.0-14.0) and turnover frequencies (TOF = 6.0-7.0 h⁻1). Compared to conventional catalysts, this method offers significantly shorter reaction times, higher yields, operation under air without oxidants, and facile magnetic recovery with reusability up to eight cycles. Thus, this approach provides a practical, eco-friendly, and scalable alternative for the synthesis of triarylpyridines, aligning efficiency with sustainability.