Friday, February 1, 2013

Pd Bites Back! Isopropyl Surprise

Although we don't always admit it, we chemists love a good surprise.

That's the feeling I got reading through a recent JACS ASAP, from the Chen group at PSU. They've been playing with an easy-to-remove C-H activation auxiliary (PA) first developed by Daugulis back in 2005. They've taught it some pretty neat tricks thus far: C-H amination, alkoxylation, and even alkylation reactions using simple primary iodides.

Their latest extends the chemistry to methyl iodide, which, when combined with some silver salts and a phosphate additive, usually plunks a new CH3 on an unhindered, kinetically-accessible gamma-methyl (i.e. the chain grows by one). However, in the case of norbornene, something wild happens: the Pd catalyst activates a secondary C-H bond, sticks a methyl on, but doesn't stop there; it "bites" into the newly formed methyl and adds on two more, to produce an isopropyl group. Sweet!
       Source: JACS ASAP 2013 | Chen group, PSU
Chen's group shows that the position of the new i-Pr depends upon exo ("up") or endo ("down") relationships of the initial amine, but doesn't speculate much on mechanism.

O Norbornene Tree, O Norbornene Tree;
I do not grok your sterics.
Well, allow me! I wonder what happens if you keep feeding iodomethane into the system. I'm sure there's a limit (likely steric) that prohibits additional branching past a certain point, but currently nothing completely rules out a dendrimeric "norbornene tree" compound, right?

Readers, can someone disabuse me of this crazy notion?


  1. Norbornene or norbornane?

  2. Run it in iodomethane as solvent and let's see where it goes!