Facile access to novel 1,2,4-oxadiazinan-5-ones via [3 + 3] cycloaddition of in situ generated azaoxyallyl cations with nitrones

Azaoxyallyl cations represent a family of versatile and powerful synthetic synthons, which are generally in situ generated from a-halohydroxamates in the presence of organic or inorganic bases. Owing to the unique structural features and reactivities of azaoxyallyl cations, some various efforts have been made to enrich the synthetic methodology of azaoxyallyl cations (Scheme 1, 1). In 2011, Jeffrey and co-workers pioneeringly reported the [4 + 3] cycloaddition between azaoxyallyl cations and cyclic dienes (Scheme 1, 1a). Since then, the research groups of Jeffrey, Wu and Liao independently devised similar [3 + 2] cycloadditions of azaoxyallyl cations with differently substituted indoles for the preparation of pyrroloindolines (Scheme 1, 1b). Moreover, Chen's group discovered the [3 + 1] and [3 + 2] cycloadditions of azaoxyallyl cations with sulfur ylides delivering band g-lactams (Scheme 1, 1c). In 2016, Lin and Jeffrey's groups individually successfully applied the [3 + 2] cycloaddition of azaoxyallyl cations with aldehydes in the synthesis of oxazolidin-4-ones (Scheme 1, 1d). Additionally, in the same year, Wu and co-workers established the [3 + 3] cycloaddition of isoquinoline N-oxides as cyclic nitrones with azaoxyallyl cations (Scheme 1, 1e). Even though the important and elegant advances in the synthetic methodology of azaoxyallyl cations, it remains highly demanded to develop novel and efficient synthetic methodologies of azaoxyallyl cations for the synthesis of structurally diverse heterocycles.