Synthesis of gem-dibromo 1,3-oxazines by NBS-mediated electrophilic cyclization of propargylic amides

We present a highly efficient and practical method for synthesizing gem-dibromo 1,3-oxazines through 6-endo-dig cyclization of propargylic amides, using N-bromosuccinimide (NBS) as an electrophilic source. The metal-free reaction can be conducted under mild conditions with good functional group compatibility, delivering excellent yields of the desired products. Mechanistic studies suggest that the reaction proceeds via a double electrophilic attack by NBS on the propargylic amide substrate.

Automated summary

We introduce a highly efficient and practical method for synthesizing gem-dibromo 1,3-oxazines through 6-endo-dig cyclization of propargylic amides, using N-bromosuccinimide (NBS) as an electrophilic source. This metal-free reaction can be carried out under mild conditions, showing good compatibility with various functional groups and providing excellent yields of the desired products. Mechanistic studies indicate that the reaction proceeds through a double electrophilic attack of NBS on the propargylic amide substrate.