Synthesis and regioselective cycloaddition reactions of 2,4,6-triazido-3,5-dichloropyridine

2,4,6-Triazido-3,5-dichloropyridine, obtained by the reaction of pentachloropyridine with sodium azide, readily adds two molecules of dimethyl acetylenedicarboxylate to the azide groups at the 2- and 6-positions, whereas, in the reaction with norbornene, it forms a cycloadduct only at the azido group in the 4-position.