Nitrogen bridgehead compounds. Part 85 . Synthesis and reactivity of 3,4‐dihydro‐1 H ,6 H [1,4]oxazino[3,4‐ b ]quinazolin‐6‐ones

3,4‐Dihydro‐1 H ,6 H ‐[1,4]oxazino[3,4‐ b ]quinazolin‐6‐one 3 and its 1‐methyl and 1‐hydroxy derivatives 8 and 13 were prepared by different routes. The active methylene group of compound 3 was reacted with electro‐hilic reagents (bromine, phenyldiazonium chloride, nitrous acid, a Vielsmeier‐Haack reagent, aromatic aldehydes and diethyl oxalate) to yield 1‐substituted‐3,4‐dihydro[1 H ,6 H )‐1,4‐oxazino[3,4‐ b ]quinazo‐lin‐6‐ones. The reactivity of 1‐hydroxy and 1‐bromo derivatives 13 and 15 were also investigated in some reactions. The 3,4‐dihydro‐l H ,6 H ‐[1,4]oxazino[3,4‐ b ]quinazolin‐6‐ones were characterized by means of uv, 1 H and 13 C nmr spectroscopy.