6H-l,2-oxazines

H-1,2-Oxazine, 3,6-dihydro-6-(2-pyridyl)-mass spectra, 2, 529 2H-1,2-Oxazine, tetrahydro-synthesis, 2, 92 4H-l,2-Oxazine, 5,6-dihydro-pyrolysis, 3, 999 synthesis, 3, 1017 tautomerism, 3, 999 4H-1,2-Oxazine, 5,6-dihydro-3-methyl-metallation, 1, 484 4H-l,2-Oxazine, 5,6-dihydro-3-nitro-reactions, 3, 1000 6H-l,2-Oxazine, 3,5-diphenyl-stability, 3, 997 synthesis, 3, 1014... 

Nitrosoalkenes 192, generated in situ from a-halo oximes, reacted with methox-yallene in a [4+ 2] fashion to give 6H-l,2-oxazines [156]. 

The array of dienophiles amenable to these hetero Diels-Alder reactions is not limited to enol ethers and enamines since allylsilanes and simple alkenes have also been successfully employed [370, 371]. More recently, it has been shown that methoxy allenes such as 4-41 undergo formation of 6H-l,2-oxazines 4-43 upon cycloaddition to nitrosoalkenes such as 4-34 and subsequent tauto-merisation of the intermediate exo-methylene compound 4-42 (Fig. 4-9) [372, 373]. In these studies, 4-43 proved to be a versatile synthetical intermediate allowing oxidative demethylation or reductive removal of the methoxy group as well as nucleophilic substitutions after the generation of an azapyrylium ion [372 - 374]. Furthermore, ring contraction reactions of these oxazines leading to pyrroles [373] and y-lactames [375] are known. 

H-l,2-Oxazine 6-Methoxy-5-methylen-3-trifluormethyl-5,6-dihydro- E9a, 99 (1-CF3 — 1-NO —ethen + Methoxy-allen) 6H-l,2-Oxazine 6-Methoxy-5-methyl-3-trifluormethyl- E9a, 99 (Methylen - En —CH3)... 

H-l,2-Oxazin 3-Ethoxycarbonyl-6-methoxy-5-methyl- E9a, 99 (Methylen -+ En —CH3) 2H-l,3-Oxazin 3-Butyl-2,4-dioxo-6-methyl-3,4-dihydro- E15/2, 2418 (4-Oxo — 4H-1,3-dioxin/A + R-NCO)... 

H-l,2-Oxazine 5-(Deuterooxy-methyl)-6-methoxy-3-phenyl-E9a, 102f. (6-OR —3-Ar — 5-methylen — 5,6-H2 —... 

Under catalysis by mercuric sulfate, the reagent adds 1,4 to a conjugated diene to give a C-nitroso sulfate (1) which cyclizes spontaneously to a 6H-l,2-oxazine (3) and this on pyrolysis gives a pyrrole (4). ... 

Oxazabicyclo[4.1.0]heptanes from 4,5-dihydro-6H-l,2-oxazine 2[Pg.169]

Carbomethoxy-4,5-dihydro-6H-l,2-oxazine N-oxide dissolved with stirring and cooling in methyl propiolate, allowed to stand 24 hrs. at ca. 20°, and excess methyl propiolate removed by vacuum distillation product. Y 92%. F. e. s. I. E. Chlenov et al., Izvest. 1973, 473 C. A. 79, 5304. 

---