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
✍ Scribed by Banert, Klaus
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1989
- Tongue
- English
- Weight
- 850 KB
- Volume
- 122
- Category
- Article
- ISSN
- 0009-2940
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✦ Synopsis
Triazoles, preparation of
Treatment of 3-bromo-3-methyl-I-butyne (1) or 1 4odo-3-methyl-13-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-tn'azoles 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 1 H-1,2,3-triazoles via propargyl azides is carried out in the presence of various nucleophiles and investigated by means of "N-labelled starting material as well as optically active 3-azido-I-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 lH-1,2,3-triazoles 23,41,44,46, 17 1 1 8 1 S-20 prepared from S-( -)-19 (83% ee)") can be converted to R-21. With methanol this optically active propargyl azide furnishes the triazole 23 with > 99.97% racemization. Hydrogenation of R-21 to the known R-( -)-24'6) indicates the optical activity of the azide. If S-( -)-19 is transformedz4) to S-22 and subsequently treated with trimethylsilyl azide the resulting S-( -)-23 shows a high rotation value. These results Chem. Ber. 122 (1989) 911 -918