“…Among the pyridooxazine derivatives, most of the synthetic studies are focused on pyrido [2,3-b][1,4] oxazines, 10,11 pyrido[2,1-b][1,3]oxazines, 12 pyrido [3,2-b][1,4] oxazines, 13,14 pyrido[4,3-b][1,4]oxazines, 15 and pyrido [3,2-b][1,2]oxazines. 16 However, several reports are available on the synthesis of pyrido [4,3-d][1,3]oxazine derivatives.…”