Abstract
A highly substituent-dependent rearrangement allows for the novel and SOCl2 -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 SCH3 or SCD3 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.