1,3,4-Oxadiazine

The reaction of 2-aminothiazole derivatives with the 1,3,5-oxadiazine 2,4.6-trione shown leads to biuret derivatives (126) (Scheme 83) (287). 

Oxadiazines herbicidal activity, 3, 1085 reactions with bases, 3, 1060 ring contraction, 3, 1065 ring opening, 3, 1061... 

A variety of 2H- (121, X = O) and 4H- (122, X = O) 1,3,5-oxadiazines has been studied and eharaeterized, whereas 2//-l,3,5-thiadiazines 121 (X = S), unlike the 4H isomers 122 (X = S), are uneommon. The most eommon type of tautomerie intereonversions for sueh systems is ring-ehain tautomerism. A few studies on substituent tautomerism have also been earried out however, no data on annular tautomerism have yet appeared in the literature. 

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... 

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). 

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. 

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). 

Trifluoromethyl-substituted 1,3,5-oxadiazines behave similarly on thermolysis. Thus (122) extrudes hexafluoroacetone to generate (123), which may be in equilibrium with a 1,3-diazete, and the reaction follows a course exactly analogous to that in Scheme 5. In... 

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... 

Sulfonamides (253) react with formaldehyde to give fully saturated lV-sulfonyl-1,3,5-dioxazines, 1,3,5-oxadiazines or 1,3,5-triazines according to the relative quantities of reagents used (75JCS(P1)772). 

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)... 

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-... 

III.B.1. The products formed via cations 174-177. 179 and 180 are the same derivatives of 1,3,5-oxadiazine (i.e. 120) as well as 2-oxazoline (122 and 128) obtained earlier, except that the reactions are considerably faster (equation 56). 

The acid-catalyzed reaction of benzonitrile proceeds with formation of 1,3,5-oxadiazine 108a (256). 

---