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September 21, 2010
Want To Make an Amide? Have I Got Good News For You!
Y'know, this is what I call an incremental improvement in the synthetic repetoire. I noticed this new paper in Tetrahedron Letters by its title, and read the whole thing just to make sure that I wasn't missing something.
Yep, that's right: someone has come up with a new way to form amides by reacting acid chlorides and amines. "But hold on," you say, "I thought that acid chlorides and amines form amides like an unstoppable juggernaut, which grinds to a halt only when enough HCl is given off to take the remaining amine out of contention". Well, you'd be right about that: but that's because you didn't think of using samarium metal as an acid scavenger.
Because that's what it seems to be here. The authors report that you have to pretty much use a full equivalent of samarium to get the high yields - control experiments with only 1/3 equivalent didn't work so well. What I wish they'd done is run the freaking control experiments with triethylamine. Or Hünig's base. Or pyridine. Or potassium carbonate, or aqueous 0.1N NaOH, or resin-bound nanocrystalline cesium complexes prepared in ionic liquids through renewable green chemistry whatchamacallits - in fact, with damn near anything else except stoichiometric metallic samarium, of all things. Well, OK: zinc and indium didn't work. I stand corrected. Give these folks another four or five Tet Lett papers, and they'll work their way back to baking soda. Only it'll be samarium bicarbonate, with any luck.
Perhaps I'm being unfair here. But really, amide formation is not a problem that is crying out for a new solution. It's really very, very, well worked out, and the number of options available for the experimentalist are nearly beyond counting. But now there's samarium metal. So if you're looking for the most expensive way you can think of to react an acid chloride with an amine, one that will make your labmates question your sanity and a reaction that will probably be a separate item all on its own come your next annual performance review, then go to it.
Oh, and one more thing: if you bother to read the experimental section, which apparently no one did, the procedure is titled: "General procedure for the homocoupling of terminal alkynes". Wrong samarium reaction, guys.
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