Synthesis

More Stahl Aerobics

“Highly Practical Copper(I)/TEMPO Catalyst System for Chemoselective Aerobic Oxidation of Primary Alcohols” Hoover, J. M.,; Stahl, S. S.  J. Am. Chem. Soc. 2011. ASAP. DOI: 10.1021/ja206230h

To quickly follow up yesterday’s post on aerobic alcohol oxidation, I thought that this new paper from the Stahl lab on the same topic was worth mentioning.  While their continuous flow process for alcohol oxidation was a pretty big improvement over many existing methods, the reagents necessary were not ideal.  Toluene and pyridine are both toxic, and palladium is not extremely abundant, especially compared to 1st row transition metals.  So there was plenty of room for improvement, which is why I was really psyched to see this new catalyst system for primary alcohol oxidation that was published a few days ago. Virtually all of the reaction components have been replaced by greener reagents:  acetonitrile instead of toluene, N-methylimidazole instead of pyridine, and catalytic TEMPO/(bpy)Cu(I) instead of palladium acetate.  Unlike most aerobic alcohol oxidations, an atmosphere of pure oxygen was not necessary – the oxygen present in ambient air was enough for the reaction to run efficiently.  And the reaction is run at room temperature to boot.  It’s hard to imagine that this reaction would be more difficult to scale up using their flow reactor than the Pd-catalyzed version, although you never know I suppose.

There’s loads more in the paper on their catalyst development studies, and on the chemoselectivity of this process for primary alcohols versus secondary ones – definitely worth reading!

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