The Kemp elimination is a well-studied reaction that involves base-catalyzed proton abstraction from the C3 of benzisoxazoles with concurrent ring opening due to the cleavage of the labile O-N bond. The reaction is concerted, with no intermediate detected, and greatly accelerated by polar, aprotic solvents and by the presence of electron-withdrawing groups on the benzisoxazole ring. Benzisothiazoles are more resistant to the Kemp elimination, but their reactivity has not been studied in detail. We found that benzisothiazoles also undergo Kemp elimination, and that reactions are greatly accelerated by dimethylsulfoxide (DMSO), a polar and aprotic solvent, relative to water. Extrapolations suggest the reaction of benzoisothiazoles in water is at least seven orders of magnitude slower than the corresponding reaction of benzisoxazoles. We are currently investigating the mechanism of the reaction of this alternative substrate.

Kemp elimination of benzisothiazoles

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