Reactions of Unsaturated Azides, 6. Synthesis of 1,2,3‐Triazoles from Propargyl Azides by Rearrangement of the Azido Group. – Indication of Short‐Lived Allenyl Azides and Triazafulvenes

Abstract

AbstractTreatment of 3‐bromo3‐methyl‐1‐butyne (1) or 1‐iodo‐3‐methyl‐1,2‐butadiene (3) with solutions of sodium azide affords 3‐azido‐3‐methyl‐1‐butyne (5) which reacts already at room temperature to 1,2,3‐triazoles 8–11. Structures of 5 and 8–11 are verified by independent syntheses and spectroscopic data although in part other assignments of structures have been published. The preparation of 1H‐1,2,3‐triazoles via propargyl azides is carried out in the presence of various nucleophiles and investigated by means of 15N‐labelled starting material as well as optically active 3‐azido‐1‐butyne (R‐21). The only mechanism compatible with all results includes short‐lived allenyl azides and triazafulvenes. Thus, propargyl azide 14 rearranges to allenyl azide 16 leading to triazafulvene 18 by rapid ring closure. Finally, 18 is trapped by nucleophiles to give triazole 17. The conversion of various propargyl compounds into N‐unsubstituted 1H‐1,2,3‐triazoles 23, 41, 44, 46, 50, and 51 is effected by a one‐pot procedure without isolation of 14 and turns out to be a convenient method to prepare these heterocycles.