Experimental and Computational Study of the 1,5‑O → N Carbamoyl Snieckus–Fries-Type Rearrangement

The
reactions of o-lithiated O-aryl N,N-diethylcarbamates with different C–N multiple
bond electrophiles have been thoroughly studied. A 1,5-O →
N carbamoyl shift, a new variation of the anionic Fries-type rearrangement,
takes place when nitriles, imines, or alkylcarbodiimides are employed.
In these cases, the carbamoyl group plays a dual role as a directing
group, building up a variety of functional groups through the 1,5-O
→ N carbamoyl migration. On the other hand, the use of iso­(thio)­cyanates
and arylcarbodiimides led to non-rearranged o-functionalized O-arylcarbamates. This reactivity was further computationally
explored, and the governing factor could be traced back to the relative
basicity of the alternative products (migrated vs nonmigrated substrates).
This exploration also provided interesting insights about the degree
of complexation of the lithium cations onto these substrates. A new
access to useful 2-hydroxybenzophenone derivatives has also been developed.