A highly substituent-dependent
rearrangement allows for the novel and SOCl
2
-induced divergent
synthesis of 3-methylthioquinolin-2-ones and 3-methylthiospiro[4.5]trienones
through intramolecular electrophilic cyclization of
N
-aryl propyamides. DMSO acts as both solvent and sulfur source, and
use of DMSO-
h
6
/
d
6
enables the incorporation of SCH
3
or SCD
3
moieties to the 3-position of the heterocyclic framework. Different
para
-substituents trigger divergent reaction pathways leading
to the formation of quinolin-2-ones for mild substituents and spiro[4,5]trienones
for both electron-withdrawing and -donating substituents, respectively.
On the basis of both computational and experimental results, a new
mechanism has been put forward that accounts for the exclusive spirolization/defluorination
process and the surprising substituent effects.