Azete intermediate

An alternative meehanism eould be proposed that proeeeded through an azete intermediate. In the formation of 28 from 26 and 27, initial rearrangement of 26 into 29... 

It was impossible to obtain naphtho[bc]azete on pyrolysis or on photolysis of N-substituted naphtho[coxygen analogs 13, i.e., a substituent label was not introduced in the naphthalene nuclei of the initial compounds 26 and 27. 

The isolation of a 45% yield of trichloroacrylonitrile (296) upon thermolysis (at 600 °C) of trichloro-l,2,4-triazine (295) may implicate an azete intermediate (Scheme 116). ... 

Ring transposition processes are well established in six-membered heteroaromatic systems. Recent studies have centered on perfluoro systems in which bicyclic and tricyclic intermediates are sufficiently stable to permit isolation or at least detection. Thus, on irradiation in CF2C1CFC12, the perfluoropyridine 207 is converted into the azabicyclo[2.2.0]hexa-2,5-diene 208 and the two azaprismanes 209 and 210.154 An azabicyclo[2.2.0]hexa-2,5-diene has also been shown to be an intermediate in the photorearrangement of substituted 2-methylpyridines to o-substituted anilines.155 Diaza-bicyclo[2.2.0]hexa-2,5-dienes have similarly been shown to be intermediates in the conversion of fluorinated pyridazines (211) into the corresponding pyrazines (212)156 the proposed pathway is outlined in Scheme 7. Photoproducts which are formally dimers of intermediate azetes have been obtained when analogous reactions are carried out in a flow system.157... 

While all the above results on the thermolysis and pyrolysis of fused triazinones can readily be accommodated on the basis of formation of a reactive species (146), it is only recently that unambiguous evidence for such intermediates has been provided. Ege et a/." found that photolysis of the naphthotriazinone 155, R = Ph, gives the N-phenylnaphth[2,3-Z ]azet-2(l//)-one (156, R = Ph) as an isolable, moderately stable solid. Bashir and Gilchrist have shown that photolysis... 

A review including the synthesis of 3-azetidinones has been published <03T7631>. Azacyclobutadiene (azete) is a highly reactive and unstable molecule. A base-induced novel condensation reaction of a-chloro oxime derivatives to furnish alkynyl oximes through an azacyclobutadiene intermediate has appeared <03AG(E)5613>. 

Despite all attempts to synthesize naphth[l,8-Z)c]azete or its derivatives 2 not a single example has been prepared and no traces of such compounds as intermediates in chemical reactions have been found in keeping with the theoretical analysis (Figure 4). 

Derivatives of azete are only known as unstable reaction intermediates. Oxetane and azetidine are considerably less reactive than their three-membered connterparts (oxetane reacts with hydroxide anion 10 times more slowly than does oxirane), but nonetheless do undergo similar ring-opening reactions, for example oxetane reacts with organolithium reagents in the presence of boron triflnoride, or with cuprates, and azetidine is opened on heating with concentrated hydrochloric acid. Azetidininm ions react mnch more easily with nucleophiles. ... 

The successful generation of azetes from perfluorinated derivatives of 1,2,3-triazines has recently been described. Irradiation of the perfluorodi-isopropyl-l,2,3-triazine (40) gave a dimer (41) of the intermediate azete (42) which was also... 

Monocyclic 1,2,3-triazines 1 behave like other six-membered heterocycles as dienes in Diels-Alder reactions with inverse-electron demand. Substrates are electron-rich dienes and acetylenes. 11 103, 284-290 jn mosl caseSi the formation of the isolated products can be explained by an attack of the dienophile at N1 and C4 or N3 and C6 of 1. In a few cases, products were obtained, the formation of which had to be explained by an intermediate formation of an azacyclobutadiene (azete) or by an N2 and C5 attack.284,285... 

In general, pyrolysis of monocyclic 1,2,3-triazines 1 leads to acetylenes, nitriles and nitrogen.46, 295 297 300 Heating simple 1,2,3-triazines in a sealed tube led to the isolation of pyridines, pyrimidines, pyrazoles, pyrroles, pyridazine, and indeno[3,2-/>]pyridine, depending on the substituents bound to the 1,2,3-triazine ring and the reaction conditions.46 A mechanism formulated for the formation of these products involves an azete as an intermediate. 

Photolysis (>270 nm) of oxazinone (70) at 7 K gives the -lactone (71), which undergoes further fragmentation to give MeCN, Bu CN, propyne, and t-butyl-acetylene. That such products can be isolated strongly suggests the intermediate formation of the azete (72), which undergoes spontaneous cycloreversion via the two modes indicated overleaf. ... 

---