"Crystalline" CO - Saccharin's New Trick

Seems I'm posting an awful lot about artificial sweeteners these days!

This latest example, from the always entertaining and informative folks at Angewandte Chemie, employs our old friend N-formylsaccharin* as a carbon monoxide "equivalent" for Pd-catalyzed addition reactions:

Credit: Manabe Group | ACIEE

Quite a few benefits accrue: No pressure equipment. 'Medium' heat. Relatively low catalyst loading.  Cheap, off-shelf reagents. If they could figure out a slightly less exotic reductant, I'd use this all the time!

So, how does it work, anyway? The researchers confirm CO release by treating formylsaccharin with several bases and observing CO evolution.** The standard (boring) formylation model might be operative here - Pd oxidative addition, CO insertion, reductive cleavage (rinse, repeat). 

OR (more excitingly), the authors note that they detect a transient "acylsaccharin" by HRMS. This might imply that the formylsaccharin reacts directly with the palladated arene, or that the sodium saccharine byproduct plays a role in stabilizing / promoting reduction of the insertion intermediate.

Sweet.

*OK, so it's not saccharin itself, but pretty darn close. First developed by Cossy in 2011 for formylating amines.
**A great mechanism for those looking for cume questions!