Transient Protection of Organic Azides from Click Reactions with Alkynes by Phosphazide Formation

A method for protecting organic azides from click reactions with alkynes is reported. Treatment of azides with Amphos affords phosphazides, which are stable under click reaction conditions and are easily converted back to azides by treatment with elemental sulfur. Thus, the method allows for facile modification of azide compounds via site-selective click reactions.