1,4-Oxazines and their Benzo Derivatives

Facile preparation of dihydro-1,4-benzothiazine derivatives via oxidative ring-expansion of 2-aminobenzothiazoles with olefins

“…1 Thus, the construction of 1,4-benzothiazine scaffolds in an efficient, concise, and green style under benign conditions is of importance and has attracted substantial interest from both academic communities and pharmaceutical industries. 2,3 In particular, for the synthesis of dihydro-1,4-benzothiazine derivatives, Jiang and co-workers 4 developed a Pd-catalyzed double C–S bond coupling reaction to prepare substituted dihydro-1,4-benzothiazine derivatives, in which Na 2 S 2 O 3 was employed as a sulfur source to avoid a thiol odor (Scheme 1a). Cossy et al 5 described a FeCl 3 -catalyzed intramolecular nucleophilic cyclization to construct the 1,4-benzothiazine skeleton via a carbocation intermediate (Scheme 1b).…”

1,4-Oxazine

“…Although a fair number of substituted and ring-fused 1,4-oxazines are known, the parent compound has never been prepared and work on it has so far been restricted to theoretical predictions of bond lengths and electron distribution. 5 Our long-standing interest in the area started with the unexpected formation of 1,4-dioxin in a retro-Diels-Alder reaction under conditions of flash vacuum pyrolysis (FVP), which allowed its NMR spectra to be recorded for the first time. 6 However numerous attempts to extend the retro-Diels-Alder approach to formation of 1,4-oxazine by pyrolysis of derivatives 2 or 3 failed.…”