A magnetically recoverable copper nanocatalyst for tandem tetrazole synthesis and regioselective N-functionalization

A magnetically recoverable copper nanocatalyst supported on silica-coated maghemite (CuNPs/MagSilica) was developed and applied in the tandem synthesis and regioselective N-functionalization of tetrazoles. The catalyst was comprehensively characterized by FTIR, AAS, TEM, SEM-EDS, VSM, XPS, and XRD analyses, revealing highly dispersed copper nanoparticles stabilised on a magnetic core-shell support with suitable magnetic response for efficient recovery. The catalytic activity of CuNPs/MagSilica was evaluated in the [3 + 2] cycloaddition of aryl nitriles with sodium azide, affording 5-aryl-1H-tetrazoles in good to excellent yields under ligand- and base-free conditions. The methodology was further extended to a tandem one-pot sequential N-functionalization process with different electrophiles, providing 2,5-disubstituted tetrazoles with excellent regioselectivity toward the N-2-substituted isomer. The protocol operates under simple conditions, avoids chromatographic purification in the cycloaddition step, and can be scaled up successfully. In addition, the catalyst was magnetically recovered and reused for at least three consecutive cycles with minimal loss of activity. High catalytic efficiency was achieved at very low copper loading (0.1 mol%), reaching TON and TOF values of 935 and 58 h^-1, respectively.