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-arylpropyamides. DMSO acts as both solvent and sulfur source, and use of DMSO-h6/d6, enables the incorporation of SCH3 or SCD3 moieties to the 3-position of the heterocyclic framework. Different para-substituents trigger strongly divergent reaction pathways, leading to the formation of quinolin-2-ones for mild-substituents, but to spiro[4,5]trienones for both electron-witdrawing and -donating substituents, respectively. We present a combination of experimental and quantum chemical data that outline the scope, robustness and mechanism behind this novel, fast, high-yielding, room-temperature reaction.

Surprising substituent effects in spiro-compound forming rearrangements: Synthesis of 3-(methylthio)quinolin-2-ones and 3-(methylthio)spiro[4,5]trienones via intramolecular cyclization of N-arylpropynamides.

ACS Spring Meeting 2021

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