Strategic and Tactical Approaches to the Synthesis of 5,6-Dihydro-[1,2,4]oxadiazines

Three methods were developed for the synthesis of substituted 5,6-dihydro-4H-[1,2,4]oxadiazines. The desired oxadiazine rings were synthesised via reductive amination, addition to an iminium ion intermediate and by condensation of a diamine with an imidate. For all methods the scope with respect to the substituents that could be introduced was explored. It was found that the imidate condensation route was the most versatile and the products could be isolated in yields up to 91%. This route is also suitable for the introduction of chirality on the C5 and C6 position of the oxadiazine rings.