From 1,3,5-Oxadiazines

Gambaryan and Zeifman synthesized l,4-dihydro-l,3,5-triazine (173) by reaction of 4,4-bis(trifluoromethyl)-2,6-diphenyl-l,3,5-oxadiazine (172) with 

Burger et al. have shown that upon thermolysis dihydro-l,3,5-oxadiazines (174) undergo a retro Diels-Alder reaction with elimination of hexaflu-oroacetone.269,270 The intermediate product, 4,4-bis(trifluoromethyl)-l,3-diaza-1,3-diene, was transformed to the corresponding 1,4-dihydro-1,3,5-triazine (173) [Eq. (83)]. 

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The 67T-cations (23) and (24) derived from 1,3,5-oxadiazines and thiadiazines undergo facile nucleophilic attack at the a-carbon by a variety of nucleophiles. These reactions result in the formation of other heterocyclic systems and some examples are presented in Scheme 3 (65CB334, 73BCJ3902, 80BCJ3369). 

The 8ir-electron anions derived from 1,3,5-oxadiazines (30) (75AG(E)581) are unstable and readily ring contract to give imidazolones (141 Scheme 9). The related anions from 1,3,5-thiadiazines (100 Scheme 1) also ring contract to give imidazoles in high yield... 

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) ... 

Folic acid models have been synthesised either from the bromomethylpteridine 104 or from the oxadiazine compound 105 (Scheme 17)<96IHC341 >. 

The reaction of acyclic ADC compounds with monoenes has already been discussed in Sections III,B and IV,B. In certain cases the major reaction pathway involves addition of the ADC compound as a 47r component, to the monoene to give 1,3,4-oxadiazines (Scheme 1). 1,3,4-Oxadiazines are the major or sole products from the reactions of ADC compounds with indene,80 and 4-nitrophenyl vinyl ether,90 and from the reaction of azodibenzoyl with enamines and enol ethers.91 93 Norbornadiene also gives a 1,3,4-oxadiazine (42) with ADC compounds.82 However, benzonorbornadiene behaves differently, and the major product from the reaction with PTAD has the structure 119.205 Other bicyclic monoenes react similarly.206 1,3,4-... 

Oxadiazines (120) are formed from ketene acetals and DMAZD in moderate yields.106... 

In certain cases the initial Diels-Alder adducts of ADC compounds are labile. For example, the adduct (121) from cyclopentadiene and azodibenzoyl rearranges in quantitative yield on heating in aqueous methanol to give the 1,3,4-oxadiazine 122.207 Solvent has little or no effect, and a concerted [3,3] rearrangement as shown in Scheme 17 seems the most likely explanation. The rearrangement has been extensively studied by Mackay and coworkers,208 and it shows great dependence on substitution effects. 

Ovine somatotropin (oST), effects on growth and gain in lambs, 13 llt Ovis aries, wool from, 11 173 Oxacarbocyanine sensitizers, 9 510 Oxacillin, 3 25 Oxacrown ethers, 24 44 Oxadiazine insecticides, 14 347 Oxadiazole (OXZ) dendrimers, 26 803 Oxafullerenes, 12 242, 243 Oxahomofullerenes, 12 243... 

Oxadiazine 370 was obtained from aziridinooxime 369 and concentrated HCl in 51% yield (equation 161) . CycUzation of acylated amidoxime 371 in the presence of K2CO3 in DMF also leads to formation of oxadiazine ring 372 (yield 12%), along with quinohne derivative 373 (equation 162) . 

Of particular note is the report by Butler et al. of the generation of 3,4-diarylfurazan 7V-methanides (92) <95JCS(P1)1083>. These were formed (Scheme 15) as transient intermediates by desilylation of 7V-trimethylsilylmethyl-l,2,5-oxadiazolium salts (93) using caesium fluoride, and subsequently underwent rapid ring expansion to 6//-1,2,4-oxadiazines. Methanide (92) also resulted from treatment of A-methylfurazan salt (94) with base. 

C- and H-NMR measurements350 have permitted a complete description of the conformational equilibria for 2,4-dimethyltetrahydro-l,2,4-oxadiazine (449), and this is summarized in Fig. 20. As expected from the... 

The only preparation of a ring system of this type from thioureas, which has been reported in the literature, is the tetrahydro-1,3,5-oxadiazine series of Seidel and Boettner,302 who synthesized compounds 171 by treating thioureas with formaldehyde in the presence of p-toluenesulfonic acid. 

Pyrimido[l,2-a][l,8]naphthyridines synthesis, 2, 599 Pyrimido[5,4-c]oxadiazine purine synthesis from, 5, 591 Pyrimido[4,5-6][ l,4]oxazine synthesis, 3, 312 Pyrimido[2,1 -6]pteridine structure, 3, 284 Pyrimido[5,4-g]pteridine structure, 3, 284 Pyrimidopurines, 5, 566 Pyrimido[4,5-c]pyridazine, aryl- H NMR, 3, 335... 

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... 

Oxadiazine (121) was treated with Raney nickel in ethanol to deliver compounds (125) (10%) and (126) (24%) via a common intermediate (124). The TV-ethyl group in compound (126) is derived from the solvent (Scheme 6) <82JOC523>. 

Reaction of the tertiary amine (390) with three equivalents of dibenzoyldiimide yielded the pyrido-1,3,4-oxadiazine (391) (65%) via the intermediacy of an enamine generated from the amine (390) <77 JCS(P2) 1977 >. 

Trimerization of methyl isocyanate (MeNCO) in the presence of tri- -butylphosphine gives a 1,3,5-oxadiazine 736 <1973CRC(277)795>. In the presence of carbon dioxide, the reaction leads to the 1,3,5-oxadiazinimine 737 derived from C02 (1 mol eq.) and the isocyanate (2 mol eq.) <1974BSF1497>. 

The analogous 1,3,5-oxadiazine 124 was obtained from 2,4-dichlorobenzaldehyde 123 (equation 42). However, neither the pivalophenone 125 nor the isobutyrophenone 129 react with benzonitrile in the presence of trifluoromethanesulfonic acid at room tempera-... 

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