A Phosphine-Mediated Conversion of Azides into Diazo-Compounds

A Phosphine-Mediated Conversion of Azides into Diazo-Compounds

Eddie L. Myers and Ronald T. Raines

DOI: http://dx.doi.org/10.1002/anie.200804689

While searching for some new interesting stuff I found this one again in the Angewandte (what a great Journal, isn’t it?). I thought a bit about the conversion of azides by myself and found as the most useful application the Staudinger reaction and the catalytic hydrogenation both to yield amines.

But this publication deals with another sort of application. They found that on treatment of azides with a phosphinoester the azide could be high yielding converted into a diazo-compound. The conversion of an azide to a diazo-compund is not new at all but gives almost modest yields and is limited to electron deficient arenes (doi:10.1016/j.tet.2005.09.145).

Other ways of yielding diazo-compunds were summarized below (this scheme is also found in the publication):

general

The main step of this specific reaction looks like this:

overview

The “normal” way of an azide-phosphine reaction goes through a so called Staudinger-ligation. Herein the azide decomposes through an azido-phosphetane (similar to the oxaphosphetane in a Wittig-reaction) into nitrogen and an amino-compound.

But if you combine your phosphine with an “azide trap” you can overcome the decomposition and yield a diazo-compund.

And here it is:

key-steps

The phosphine attacks as usual the electron deficient end of the azide which in turn cyclises to give an acyl-triazeniumphosphonium salt. This intermediate is then hydrolysed to give an acyl triazene which decomposes under warming and after proton exchange give the α-diazocarbonyl-compound.

They explored the scope of this method onto diverse starting azido-compounds, all giving high yields of the product:


examples

I think it’s an interesting method and a cool application of an old reaction combined with good knowledge of the reaction mechanism.

Feel free to comment and let me know when some of you used this chemistry. Maybe I can try it some time by myself…

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2 Responses

  1. its nice..

  2. yeah, think so too… did you try it?? i didn’t found the time yet to employ it by myself …

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