Regiodivergent Synthesis of 4‐ and 5‐Sulfenyl Oxazoles from Alkynyl Thioethers.

The regiodivergent synthesis of 4‐ and 5‐sulfenyl oxazoles from 1,4,2‐dioxazoles and alkynyl thioethers has been achieved. Gold‐catalysed conditions are used to favour the formation of 5‐sulfenyl oxazoles via β‐selective attack of the nitrenoid relative to the sulfenyl group. In contrast, 4‐sulfenyl oxazoles are formed by α‐selective reaction under Brønsted acid conditions from the same substrates. The nature of stabilising gold‐sulfur interactions have been investigated by natural bond orbital analysis, showing that the S→Au interactions are significantly stronger in the intermediate that favours the 5‐sulfenyl oxazoles. A kinetic survey identifies catalyst inhibition processes. This study into the regiodivergent methods includes the development of telescoped annulation‐oxidation protocols for regioselective access to oxazole sulfoxides and sulfones. [ABSTRACT FROM AUTHOR]