Azides, 1,2-dichloro synthesis

The 3-chloro-l,7-dimethylpyridazino[3,4-(7][l,3]oxazine-4,5-dione (149) was prepared in a four-step synthesis starting with (Z)-methyl-3-(3,6-dichloro-l-methyl-4-oxo-l,4-dihydropyridazin-5-yl)-2-methylacrylate (146) which is converted with sodium azide into the 6-azido compound (147). Heating in o-dichlorobenzene at 150°C results in cyclization to methyl 3-chloro-l,6-dimethyl-4-oxo-1,4-dihydro(7//)pyrrolo[2,3-c]pyridazine-5-carboxylate (148) via a nitrene intermediate. Ozonolysis effects ring-enlargement of the pyrrole ring into the 3-chloro-l,7-dimethylpyridazino[3,4-d][l,3]oxazine-4,5-dione (149) (Scheme 26) <79JHC1213>. 

Banks, R. E. Sparkes, G. R. Azide chanistiy. V. Synthesis of 4-azido-2,3,5,6-tetra-fluoro-, 4-azido-3-chloiD-2,5,6-trilluoro-, and 4-azido-3,5-dichloro-2,6-difluoiDpyridine,... 

Cyclic enol ethers are cleaved by bu l nitrite in acidic ethand, providing a useful synthesis of oxim-inomacrolides (Scheme 99). 1,2-Dichloroazides, from addition of chlorine azide to 1,2-dichloroal-... 

Benzofurazane synthesis." Benzofurazanes can be prepared by the spontaneous decomposition (100°) of o-nitrosophenylazides. Thus 1,3-dichloro-2-nitrosobenzene (2) reacts with sodium azide to give 4-chlorobenzofurazane (3), m.p. 84°. 

Cycloadditions of i) azides with acetylene equivalents N=N=N + C=C] or ii) diazoalkanes and amide equivalents [C=N=N + C=N] continue to be used for the synthesis of monowclic 1,2,3-triazoles. Notably, diazoalkanes add to 3,5-dichloro-2H-l,4-oxazin-2-ones (/8) and 3-chlorobenzoxazin-2-ones (81) to afford [l,2,3]triazolo[5,l-c]-[l,4]oxazin-4-ones (79) and [l,2,3]triazolo[5,l-c][l,4]benzoxazin-4-ones (82), respectively. These adducts are further modified to the triazoles (80, 82-83). The regioselectivity of this method is opposite to that for the azide addition to nonsymmetric acetylenic acceptors which give predominantly 4-substituted isomers. Addition of azide, in lieu of diazoalkanes, affords the corresponding 1,5-disubstituted tetrazoles [94TL(35)9767]. 

---