Harnessing Gold(I)-Catalyzed Hydroamination/1,3-Sulfonyl Migration Cascade for Divergent Synthesis of Isoxazolidine and Isoxazoline from -Alkynyl Hydroxylamine.

Gold-catalyzed 5- hydroamination on -homopropargylic hydroxylamine gave expeditious access to methylene isoxazolidine. Excess catalyst loading led to facile 1,3-sulfonyl migration in a cascade fashion to furnish the isoxazoline. Mechanistic studies using react-IR and NMR as well as crossover experiments indicated that 1,3-sulfonyl group migration is an intramolecular concerted process. The ene-hydroxylamine moiety also underwent dipolar cycloaddition reactions with nitrile oxide and nitrones leading to the first examples of spirocyclic -isoxazolidine derivatives.