[Mitch]

http://pubs.acs.org/doi/abs/10.1021/jo100276m



Pyridine derivatives and dichloromethane (DCM) are commonly used together in a variety of different applications. However, DCM slowly reacts with pyridine and a variety of other representative pyridine derivatives to form methylenebispyridinium dichloride compounds under ambient conditions. The proposed mechanism (two consecutive SN2 reactions) was studied by evaluating the kinetics of the reaction between 4-(dimethylamino)pyridine and DCM. The second-order rate constants for the first (k1) and second (k2) substitutions were found to be 2.56(±0.06) × 10−8 and 4.29(±0.01) × 10−4 M−1 s−1, respectively. Because the second substitution is so much faster than the first, the monosubstitution product could not be isolated or detected during the reaction; it was synthesized independently in order to observe its kinetics.

[Doc Oc]

This is very surprising.  The whole point of using DMAP in coupling is that it's supposed to be a great leaving group because it wants to rearomatize.  This is showing that not only does it add and not leave, but it's able to displace Cl, which isn't a great leaving group.  Twice!  So much about this is backwards from what I would expect.

[g-bones]

looks like i will start running most of my acylations in neat pyridine then 

[democanarchis]

Bet they had a bottle of pyridine/dcm soln sitting at the back of the press for a few months 

[Mitch]

Why are there two -bones on the forum? Is there a pop cultural reference I'm unfamiliar with?

[Doc Oc]

No, you didn't miss the bandwagon on some new fad.  Just coincidence I suppose.