4.5- Dihydro-1,3,4-oxadiazines

Phenyl-3,6-dihydro-l,3,4-oxadiazin-2-one (50) is a high temperature blowing agent used primarily for polycarbonates (qv). It is prepared by the reaction of a-hydroxyacetophenone and methyl carbazate (52), made from hydrazine and dimethyl carbonate (175) ... 

Fully saturated and 5,6-dihydro-4//-l,2,5-oxadiazines 106 (X = O) have been reported (96MI3), whereas the 2H- and 4//-l,2,5-oxadiazines 107a and 107b are still unknown. 

The l,3,4-oxadiazin-6-one (240) undergoes cycloaddition followed by a remarkable rearrangement to give the triazole A(-imine 241 and an open-chain product (136). Cycloadditions have also been carried out with the following ring systems 1,2-dihydroisoquinoline (242) (137) dihydro-1,3-oxazine (243) (138,139), 2H-, 3-benzothiazine (244) (140,141), and 27/-l-pyran-2-thione (245) (142). 

The conformational equilibrium (Fig. 23) for N,N-dimethyltetrahydro-1,3,5-oxadiazine (457) is suggested by a priori considerations similar to those discussed above (Section III,G,1) for the dihydro-1,3,5-dioxazine system to... 

The 1,2-bishydroxylamine (494) with phosgene gives the 5-hydroxy-1,2,5-oxadiazine (495) (80AP35). Acid-catalyzed dehydration of A-(2-hydroxyethyl)-A -acylhydrazines (496) is a general route to 4,5-dihydro-1,3,4-oxadiazines (497) (64JOC668). 

Treatment of TV.A -disubstituted ureas with methanal followed by cyclodehydration of the resulting Ar,Ar -bis(hydroxymethyl)ureas (531) with P205 furnishes 3,5-dialkyl-5,6-dihydro-2H-1,3,5-oxadiazin-4(3//)-ones (532) in high yields (85JAP(K)6067471, 85JAP(K)6067472, 85JAP(K)60104075, 85JAP(K)60104076). 

Cyclonite Oxide or 3,5-Dinitro-dihydro 1,3,5 -oxadiazine (names given by Blatt) l-Oxa-3, 5-dinitro-3,5-diazacyclohexane (name given by Jones Thorne) and 3,5-Dinitro-tetra-hydro-2H-l,3,5-oxad iazine (name given in CA) (called Oxyhexogene in Fr)... 

Thus, ketenes (2) can react as dienophiles with (E)-l,3-diazabuta-l,3-dienes (E)-(25) to yield either [4 + 2] cycloaducts (26) or (27) depending on the participation of the C = C or C = O moieties of the ketenes (Scheme 7). Claisen rearrangement of 3,6-dihydro-2-methylene-2//-l,3,5-oxadiazines (27) yields the p-lactams (28). Alternatively, reaction between ketenes (2) and (Z)-l,3-diaza-buta-1,3-dienes (Z)-(25) leads to the usual zwitterionic intermediates (29), whose conrotatory electrocyclation leads to p-lactams (28). No computational data including solvent effects have been reported for these reactions. 

Reaction of coumarinoyl hydrazides 213 and 3-methyl-2,3-dihydro-7-oxo-7H-pyrido[l,2,3-de][l,4]benzoxazine-5-carboxylic chlorides 212 in the presence of H2NS03H in DMF at 125 °C for 4-5 h, or under microwave irradiation for 4-5 min afforded 2,5-diaryl-l,3,4-oxadiazines 214 in excellent yields (09JHC289). 

A [1,5]-sigmatropic shift of hydrogen from an A-methyl group to the carbonyl carbon atom in protonated 3-(A,A-dialkylhydrazono)-l,l,l-trifluoroalkan-2-ones has been found to be a key step for the acid-catalysed cyclization of these ketones to 6-trifluoromethyl-3,6-dihydro-2//-[l,3,4]oxadiazines.58 Gas-phase kinetic studies on interconversions of monodeuterocyclohexadienes have given activation parameters in reasonable agreement with previous experimental and theoretical data.59... 

New fused 6,8a-dihydro-4/7-pyrrolo[l,2- ][l,2,5]oxadiazines 1176 and 5,7a-dihydro-37/-pyrrolo[l,2- ]imidazole 1-oxides 1177 were obtained via hetero-Diels-Alder reactions ([4-1-2] and 1,3-dipolar) adding 277-pyrrole 1174 to substituted nitrosoalkenes [CH2=C(R)N=0], generated in situ thorough base-mediated dehydrohalogenations of ot-bromooximes 1175 (Equation 268) <2002T1507>. 

S)-Methyl 7-chloro-2,5-dihydro-2- [methoxycarbonyl)(4-(trifluoromethoxy)Phenyl]amino)Carbonyl Indenol[l,2-e][l,3 4]Oxadiazine-4a(3/y)-carboxylate... 

Diazetidines and/or 5,6-dihydro-4//-l,3,4-oxadiazines are produced by cycloaddition reactions of alkenes and acyl or diacyldiazenes, depending on the structure of both the reaction partners, but the synthetic application of this cycloaddition is seriously limited by the occurrence of the ene reaction (Section 7.2.10.1.). 

The oxadiazine 1, previously believed to be a diazetidine2, is obtained from indene and dialkyl diazenedicarboxylate1,3. The oxadiazine ring is cleaved by lithium aluminum hydride to afford the cw-(l,2-dihydro-3-hydroxy-2-indenyl)hydrazine 21,3, which is successively converted to hydroxyamine 3 by hydrogenolysis3. 

Diazetidines and/or oxadiazines are obtained from cnol ethers and acyclic diacyldiazenes depending on the structure and the substitution pattern of the alkene (Section 7.2.10.1.). For 3,4-dihydro-2//-pyran (12) and certain glycals it has been found that the cycloaddition of dibenzyl di-azenedicarboxylate 13 to give oxadiazines is favored over the ene products by carrying out the reactions at lower concentration of dihydropyran and under irradiation, which converts ( )-13 to (Z)-1312. 

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