Preparation and rearrangement of N-vinyl nitrones: synthesis of spiroisoxazolines and fluorene-tethered isoxazoles.

N-Vinyl nitrones derived from fluorenone have been prepared via a copper-mediated coupling between fluorenone oxime and vinyl boronic acids. These compounds undergo subsequent rearrangement and addition reactions that are distinct from the traditional [3 + 2] cycloaddition reactivity of nitrones. Thermal rearrangements of fluorenone N-vinyl nitrones give spiroisoxazolines, while treatment with alkynes provides fluorene-tethered isoxazoles. The scope and limitations of the preparation of fluorenone N-vinyl nitrones and their subsequent rearrangement and addition reactions are discussed.