Synthesis of Thiomorpholin-3-ones by a Gold-Catalysed Oxidative Cyclisation-Rearrangement Cascade from Ynamides

A gold-catalyzed oxidative N-cyclisation strategy allows for the preparation of alpha-aryl thiomorpholin-3-ones from readily assembled ynamides bearing tethered thioethers. A cascade of oxidation, cyclisation and then [2,3]- or [1,2]-sigmatropic rearrangement of the resulting sulfonium ylide proceeds under mild reaction conditions. Cyclisation and intermolecular oxidation are in competition at two different stages of the reaction. The required switch in selectivity between these processes can be managed by combining pyridine N-oxide oxidant with an IPrAuCl-derived catalyst.