I want to talk about two user-friendly aromatic substitutions today. While the mechanisms are entirely different, there is a common link. Both of these reactions made a difference in our approaches to either making or modifying halogenated aromatics. The first reaction is the aromatic bromination process that requires a curious combination of triphenylphosphine sulfide catalyst, an aromatic compound, and N-bromosuccinimide. My PhD student Sean Liew found this remarkably mild process in Gustafson’s Org Lett paper. I can highly recommend this reaction, whose only downfall is the production of phosphorous-based by-products. I don’t think that the role of triphenylphosphine sulfide has been fully delineated, if that is what you are interested in.
The other process is separated from the one above by 8 years. This is when Lilu Yu was doing her Masters degree in my lab and was in need of a mild method to replace aromatic fluorine by the hydroxyl group. I remember this process to be an excellent way to deliver the hydroxide nucleophile, although in a somewhat convoluted way. We used this chemistry, originally described by Green, when nothing else worked, so I would highly recommend this process.
both reactions are very nice and practical – than you! (I think another good hydroxide equivalent that instantly deprotects itself is TMS-ONa.)
The phosphine-sulfide halogenation catalyst: Me3P 1M in THF or toluene is affordable, and maybe Me3P=S would leave less phosphine-related stuff behind (Me3PO is water soluble).
I think you are making a good point. It is indeed a great idea to go to Me3P… Solubility will be enhanced (we are in fact trying to make some reagents based on it, perhaps we should try with “S” too).
They sell Me3P 1M in toluene and S8 has a decent enough solubility in toluene, maybe one could just dump in sulfur, stir, filter and apply the filtrates directly on a silica column, toluene is quite good for loading poorly hexane-soluble material on a column, and one could nicely see the translucent toluenic front coming through, the marker to start collecting the fractions…