Temperature-controlled S vs N selective alkylation of 1-phenyl tetrazole-5-thione with α,β-unsaturated systems in solvent-free organic salt media

In this work, a novel series of N and S-alkylated derivatives of 1-phenyl tetrazole-5-thione were synthesized by Michael addition in organic salt media TBAB (Tetrabutylammonium bromide) using inorganic base K₂CO₃ under solvent-free conditions. The new and conveniently synthesized products showed unusual regioselectivity during the reaction. S-Michael adducts via reaction between 1-phenyl tetrazole-5-thione and acrylic esters as well as acrylonitrile were afforded at room temperature and N-Michael adducts obtained at 70°C. Both reactions occurred within 24 h. Surprisingly, using fumarate esters as Michael acceptor proceeded a S_N2 reaction at 100°C due to steric effects. The structures of products all were confirmed by ¹H and ¹³C NMR spectra and target compound yields were good to excellent.