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August 17, 2011
New Ways to Fluorinate
There have been some neat ways to make fluorinated molecules reported recently, which I wanted to mention. We med-chemists just love our fluorines - as long as we don't have to use, like, fluorine itself to make them - because they armor-plate parts of our molecules against being metabolized and can change the binding profiles of the parent structures like nothing else can.
Over at New Reactions, there's a nice writeup on a new way to generate difluorocarbene, which (as it should) immediately adds to alkenes to give you difluorocyclopropanes. (It'll add to alkynes to give you the somewhat more exotic difluorocyclopropenes, too). This is from G. K. Surya Prakash and George Olah, and from the looks of it, it's simplicity itself: take your alkene and some TMS-CF3 in THF, and either run it hot with sodium iodide or in the cold with the anhydrous TBAF substitute TBAT. So there's what looks like a perfectly useful med-chem structural motif, suddenly made widely available.
The second paper is from the Baran and Blackmond labs at Scripps, and is a completely new way to introduce trifluoromethyl groups onto heterocyclic rings. This one generates trifluoromethyl radicals under very mild conditions, using the hitherto-obscure (but stable and relatively cheap) Langlois reagent as a source. You don't need any special group on the substrate to make this work - it charges right in and attacks the more active C-H bonds of the parent heterocycle. A wide variety of useful ring systems are shown to work, and it looks like you can change the regiochemistry by varying the solvent. I'm sure that people will think of other uses for the CF3 radical, now that it's much easier to get ahold of, but this one just by itself is going to be adopted very quickly.
These, I have to say, are just the kinds of new reactions that working chemists like to see: they make useful compounds that have been hard to access, they use commercial reagents, the conditions are not hideous and require no special equipment, and the authors have taken the time to demonstrate them on a very wide range of structures. The more things like this that get discovered, the better off we are.
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