Chlorination with convenience: Palau’chlor

I came across this article in JACS recently.  I remember using chlorine gas myself and being a little trepidacious with it.  It is a nasty gas to deal with.  I had to remember to clean out the regulator after every use so it didn’t corrode and make it difficult to close at the most inopportune time.  I used thionyl chloride a lot and that had a tendency to wreak havoc on my Rotovap at the time.  Not nice stuff.  Anyways.

What caught my eye with this article was that it was written by Phil Baran at Scripps and Martin Eastgate at Bristol-Myers Squibb in Chem. Dev., so it was worth a gander to take a look and see if this paper was a keeper for later use.  The article I am referring to is “Palau’chlor: A Practical and Reactive Chlorinating Reagent”, by Phil S. Baran et al, J. Am. Chem. Soc., 2014, 136 (19), pp 6908–6911. 

The Palau’chlor or CBMG (standing for chlorobis(methoxycarbonyl)guanidine) was synthesized in 3 quantitative steps.

Synthesis of Palau’chlor

 

Comparison of various chlorinating reagents on clotrimazole

This is already commercially-available through Sigma-Aldrich cat no. 792454.  It was pretty simple to synthesize in the lab, 3 steps.  It is an air-stable, free-flowing powder that is stable for up to a year at 25 C.   It is used in a slight excess (1.2 equivalents).

There is some extensive reactions of heterocycles being cleanly chlorinated as well as arenes and non-aromatic systems.  This is definitely a paper worth reading.

 

Comparison of chlorinating reagents and regioselectivity

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