Aliphatic azidonitriles separated by three or four carbon atoms undergo facile Lewis acid-induced cycloadditions to give bicyclic tetrazoles, even at 0 degrees C. Extension to 3-azido-2-aryl-1,3-dioxolanes and the corresponding 1,3-dioxanes in the presence of TMSCN and BF3.OEt2 leads to a series of diversely functionalized novel oxabicyclic tetrazoles. The reactions represent new aspects of proximity-assisted dipolar cycloadditions that afford thermodynamically controlled enantiopure products proceeding through discrete oxocarbenium ion intermediates.