Oxazine, nitrogen-oxygen bond

In a similar manner, imines 50 with various ancillary groups X, such as ethoxy-carbonyl, 2-pyridyl, or 2-thiazolyl, are also converted into lactams 51 in mod-erate-to-good yields (Eq. 24) [38]. The [2+2+1] lactam formation using a chiral substrate 52, ethylene, and CO quantitatively furnished the spiro lactam 53 (Eq. 25) [39]. The cycloaddition exclusively took place at the carbon-nitrogen double bond next to the oxazine oxygen atom, although 53 was obtained as a diastereomeric mixture. 

A bond between nitrogen and oxygen was hydrogenolyzed in a cyclic derivative of hydroxylamine, 2-methyl-6-[ -pyridyl]-l,2-oxazine, which on treatment with zinc dust in acetic acid gave, on ring cleavage, 84.5% of 1-hydroxy-4-methylamino-1 -[ -pyridyl]butane [739]. 

---