Acid fluorides are enigmatic compounds that can often withstand aqueous conditions. This happens to a certain degree, of course. Relative rates kick in at some point and reactions with nucleophiles do take place. Heck, this is why we love these intermediates, not to mention the corresponding acid chlorides. Acid chlorides partake in the best organic reaction I know – the Schötten-Baumann process. The fact that the classic version of this reaction is carried out in water/dichloromethane is one of the best ways to illustrate to virtues of kinetics in chemistry, especially when you also teach that acid chlorides are hydrolytically unstable. Organic chemistry is indeed a study of contrasts.
But let’s get back to acid fluorides. The following molecule, made by Lavilla and co-workers from Barcelona, Spain, is one of the most bizarre acid fluorides I have ever come across. I heard Professor Lavilla speak about this chemistry last week in Brazil. The synthesis is pretty fascinating and hinges on El Kaïm’s finding from many years ago. That report documented some peculiar reactivity between isocyanides and fluorinated acid anhydrides. The mechanism proposed by Lavilla hinges on destroying the CF3 group. As someone who worked on trifluoromethylation in the past, I cannot say that I know many good methods of monofluorination that have CF3-containing starting materials. There is a neat application of Lavilla’s zwitterionic heterocycle as a sensor of histamine. It is remarkable that the compound works well in cells. Histamine Blue (the name of this new dye) shows good selectivity over a range of metabolites in live RBL-2H3 basophils.