Losing o-F in reductive amination

[clubcard]

Hi,

I've been performing a series of reductive aminations using refluxing toluene & toluenesulfonic acid and a Dean-Stark apparatus then reducing with NaBH4. So far it's worked with every example BUT this one has gone awry 3 times:

 

 

I'm guessing that the pi-bonds of the benzene and the enamine are reducing the stability of the -F (it only loses an o-F).

 

Would the use of a dehydrating agent like TICl4 prevent this? I only ask because I have to have the series ready so I'm going on with others while I ponder (and shout a plaintive help).

 

 

Any help would be gratefully received.

 

Thanks.

[Knumbnuts]

What about an F in the para position, does that vanish as well?

[spirochete27]

What Knumbnuts is getting at is that you possible have a case of nucleophilic aromatic subsitution going on, where an equivalent of nucleophilic "H minus" is displacing fluoride on the ring. This type of displacement usually only works when the halogen leaving group is ortho or para to an electron withdrawing group.

 

Have you tried using a weaker reducing agent? I know sodium cyanoborohydride is commonly used in reductive amination because it is easily strong enough to reduce an iminium, but less likely to reduce a ketone or aldehyde.

 

Another possibility would be to try using less sodium borohydride. I don't know how many equivalents you are using now.