Benzoxazines as Substrates

This synthetic route to phthalazines has proved reasonably useful, as indicated in the following examples. 

In contrast, 5,6,7,8-tetrabromo-4-p-tolyl-177-2,3-benzoxazin-l-one (187) with hydrazine gave 2-amino-5,6,7,8-tetrabromo-4-p-tolyl-l(277)-phthalazinone (188) (H2NNH2 H2O, BuOH, reflux, 6h 85% analogs likewise). 

The presence or absence of an iV-amino group in the foregoing products clearly depends on the mechanism involved, but the reason for such a difference is not evident. 

---