As undergraduate students, one of the first things they teach us is that Friedel-Crafts alkylations can be performed in the presence of catalytic amounts of AlCl3, while Friedel-Crafts acylations, on the other hand, always require stochiometric amounts of AlCl3 (presumably because of complexation between the Lewis acid and the carbonyl oxygen of the product).

Every once in a while, from the 90’s and onwards, a new article surfaces, claiming to finally have overcome this limitation. They all have promising titles — but wait until you reach the fine-print — the experimental details. Just one example of many: Tetrahedron Lett. 1995, 36, 409-412. (available here.)

So, this specific reaction requires only 5 mol-% of Lewis acid, and the catalyst TON is around 250,000%.

Catalytic Friedel-Crafts acylation

Pretty awesome, huh? (For now, I’ll refrain from even commenting on the choice of Lewis acid and solvent: hafnium triflate and nitromethane.)

Just one little thing: Don’t you forget to add those 6 equivalents of lithium perchlorate


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