safrole azide

[Rhodium]

Versatile Reagent for Reduction of Azides to Amines
B. Pal, P. Jaisankar, V. S. Giri
Synthetic Communications 34(7), 1317-1323 (2004)
DOI:

10.1081/SCC-120030322

Abstract
Triphenylphosphine in refluxing methanol effectively reduces a variety of azides to amines in very good yields.

Staudinger was the first to observe that TPP with azides form the phosphoazides, which spontaneously undergo nitrogen elimination resulting in iminophosphoranes. These iminophosphoranes on hydrolysis with water yield the corresponding amines and the TPP oxide. Drawbacks of Staudinger reaction being known, a few reagents were developed to expedite the reduction.  All those methods require dual steps, i.e., the formation of iminophosphoranes followed by hydrolysis with water. The method developed by us spontaneously results in the formation of amines when the azide is treated with TPP/methanol. Moreover, the amines could be directly precipitated out from the crude reaction mixture as hydrochloride salts. In our case the iminophosphoranes resulting from reaction of TPP with azides undergo methanolysis to yield the corresponding amines and TPP oxide. A comparison of literature data for reduction of azides to amines using PPh₃ reveals that TPP–MeOH is an ideal reagent for bringing about such a reduction. We also observed that the reduction takes place even if MeOH is replaced with EtOH or i-PrOH or n-BuOH, but MeOH appears to be a better solvent.


Reduction of Azides to Amines

Triphenylphosphine (1.5 mmol, 0.147 g) was added to a solution of azide (1 mmol) in dry methanol (10 mL). The reaction mixture was then refluxed at 80°C for 1 hr. After all the starting material had disappeared (monitored by TLC using 1:7 mixture of EtOAc–benzene solvent system), the reaction mixture was cooled to room temperature and the solvent was removed under reduced pressure to yield the crude amines.

The corresponding hydrochloride salts were obtained directly by the addition of few drops of hydrochloric acid to the solution of the crude reaction mixture in toluene (5 mL). The salts formed were filtered and recrystallized from chloroform–methanol (9:1) to afford the hydrochloride salts of the amines (85-94% yield).

_{Maybe someone could be kind enough to post the full paper?}