1,4,23-Dioxadiazines

Symmetrical 1,2,4,5-dioxadiazines are formed by [3 + 3] dimerization of arene nitrile oxides in the presence of pyridine (74JCS(Pl)l95l). The sulfonylsulfur diimide (579) cyclizes to the 1,3,2,4,6-dithia-triazine (580) on heating in DMF (71AG(E)264). 

Dehydrochlonnation of cnfluoroacetohydroxamyl chlonde yields tnfluoro-acetorutnle oxide that dimenzes depending on the dehydrochlormatmg agents either to bis(trifluoromethyl)-l,l,2,5-dioxadiazine or to 3,4 bis(tn-fluoromethyl)furoxan [7] (equation 8)... 

The literature on benzofuroxans is considerably complicated by uncertainties concerning their structure, which were resolved only in 1960. Thus, Beilstein s Hauptwerk includes them in Volume 7 (as derivatives of o-quinones, depicted as dioxadiazines, and named as... 

Trifluoroacetonitrile oxide has been used in the synthesis of trifluoro-methyl isoxazoles and isoxazolines (84BCJ2184 86BCJ2631). In the presence of a base it dimerizes to a dioxadiazine (84JOC919). 

Diazotization and nitration provide a synthetic approach to furazan azides and nitroamino derivatives. For example, 3,6-bis(4-amino-l,2,5-oxadiazol-3-yl)-l,4,2,5-dioxadiazine 172 gave 3,6-bis(4-azido-l,2,5-oxadiazol-3-yl)-l,4,2,5-... 

These routes are dimerization to furoxans 2 proceeding at ambient and lower temperatures for all nitrile oxides excluding those, in which the fulmido group is sterically shielded, isomerization to isocyanates 3, which proceeds at elevated temperature, is practically the only reaction of sterically stabilized nitrile oxides. Dimerizations to 1,2,4-oxadiazole 4-oxides 4 in the presence of trimethylamine (4) or BF3 (1 BF3 = 2 1) (24) and to 1,4,2,5-dioxadiazines 5 in excess BF3 (1, 24) or in the presence of pyridine (4) are of lesser importance. Strong reactivity of nitrile oxides is based mainly on their ability to add nucleophiles and particularly enter 1,3-dipolar cycloaddition reactions with various dipolarophiles (see Sections 1.3 and 1.4). 

Diphenylacrylonitrile oxide, exhibiting unexpected stability, presumably due to delocalization, dimerized to furoxan 20 or 1,4,2,5-dioxadiazine 21 (22). 

Dioxadiazine ring 377 was successfully obtained by dimerization of the corresponding hydroximoyl chloride 376 in the presence of EtsN (equation 164). ... 

Dehydrochlorinationof trifluoro-IV-hydroxyacetimidyl chloride (46) yields trill uoroacetonitrile oxide (47) that dimerizes, depending on the dehydrochlorination agents, either to 3,6-bis(tri-fluoroniethyl)- , 4.2,5-dioxadiazine (48) or to 3,4-bis(trifluoromethyl)furazan 2-oxide (49).142... 

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