Catalytic Synthesis of 5-Substituted Tetrazoles: Unexpected Reactions and Products

Tetrazoles are incredibly useful organic molecules with a wide range of applications from medicinal chemistry as carboxylic acid isosteres to high energy density materials in space research. In an effort to develop an easy protocol for the synthesis of tetrazoles from nitriles, we used nano-Ag-TiO2 as an efficient heterogeneous catalyst for the reaction of various nitriles and sodium azide to afford 5-substituted tetrazoles in excellent yields. By this method, a wide variety of aryl nitriles underwent [3 + 2] cycloaddition to afford tetrazoles in excellent yields. Further reaction of tetrazoles with ethylchloroacetate resulted in the formation of expected products, except for a bis-tetrazole, which underwent ring opening and subsequent reaction to afford an unusual product. The bis-tetrazole also formed an unusual polymeric sodium complex in aq. NaOH solution. X-ray crystallography revealed a distorted octahedral geometry for the complex, which forms a three-dimensional network of chains interlinked by bis-tetrazole moieties through a network of H-bonds.