1.2- Diazetines

Diazetidinones carbonyl derivatives nucleophilic reactions, 7, 462 A -1,2-Diazetine, c/s-3,4-diethyl-3,4-dimethyl-decomposition, 7, 456-457, 483 A -1,2-Diazetine, tetrafluoro-thermolysis, 7, 456 A -l,2-Diazetine, tetramethyl-thermolysis, 7, 456 A -1,2-Diazetine, 3,3,4,4-tetramethyl-properties, 7, 483... 

Photoelimination of nitrogen from 3,3,4,4-tetramethyldiazetine has been shown to proceed with a quantum efficiency of 0.52,332 but no systematic study of the photodecomposition of such compounds has been undertaken. The fused diazetine 403 is converted on irradiation into norbornadiene (404).333... 

The simple 3,4-dihydro-l,2-diazete 1,2-dioxide (1,2-diazetine 1,2-dioxide, DD) system 53 is unknown. 3,3,4,4-Tetramethyl derivative 54 was the first compound of the class to be synthesised [50]. It has an unusually low triplet energy and is a useful triple quencer [51, 52]. Many other derivatives of 53 have recently been prepared in view of their NO-donor properties. 

Other heterocyclic N-oxides have been found to display biological activities that may depend on their proven or hypothesised ability to release NO these include 4/ /-pyrazol-4-oTie 1,2-dioxides 71, 2H-1,2,3-triazole 1-oxides 72, benzotetrazine 1,3-dioxides 73 and 1,2,3-benzotriazine 3-oxides 74. These systems have been less extensively studied than the furoxan and 1,2-diazetine dioxide systems discussed above. 

G ) [89JMS(201)17], thus emphasizing the role of ring strain in the destabilization of 1,2-diazetine structure (180). The energy of planar structure (184) is higher by 13.1 kcal/mol than that of (205) [89JMS(201)17]. 

Die iiber 2-(2,4-Dioxo-1-phenyl-diazetin-l-yl)-l,3,4-oxadiazole beschriebenc Umsetzung mit Aminen zu 5-(3-Aminocarbonyl-ureido)-2-phenyl-l, 3,4-oxadiazolen656 kann auch problemlos ausgehend von 5,7-Dioxo-5,7-dihydro-6H-[Pg.607]

The most characteristic spectral detail for AM -diazetines is the fine structure in the UV spectrum around 350 nm. This is not typical, as other cyclic azo compounds usually show unstructured broad absorptions at 360 nm (62JCS3276, 78TL2469, 75JOC1409>. The PE spectrum of the tetramethyl derivative is also unique and shows an inversion in the normal n+,Tr,n energy level for cyclic azo compounds with the tt and n + levels inverted (77JOC609). 

Oxidative closure of dioximes leads to diazetine dioxides which can be further reduced in two steps to A -l -diazetines (Scheme 56) (75JOC1409,75KGS748). 

One example of direct conversion to diazetines is known (Scheme 57) (62JCS3276, 4840). 

Several workers have made use of the ability of cyclobutadiene to add [2 + 2] to azodicarboxylates (72CC818, 75JA918, 78TL2469, 79AJC2659) to make fused diazetine compounds (Scheme 76). 

The mode of decomposition of diazetines, diradical or concerted, has been probed by using cz s-3,4-diethyl-3,4-dimethyl-A1-l,2-diazetine as a model. The stereospecificity of product formation would imply a formally disallowed decomposition, but it is also conceivable that a short lived diradical intermediate is involved (Scheme 127) (78JA6760). 

The corresponding tetramethyl N,N-dioxide, actually a precursor to the diazetine, has an interesting property in that it is an efficient triplet state quencher. For example, it inhibits the photopinacolization of benzophenone and can be used instead of dienes where wavelengths above 300 nm are employed (72JA5077). 

Cyclodehydration of m-phenylglyoxal-2-phenylhydrazone with anhydrous AlCl3-NaCl, at 150°-160° yields some 2-phenyl-quinoxaline, together with 4-phenylcinnoline.38 The same workers prepared 2-(o-hydroxyphenyl)quinoxaline (34) from o-hydroxyphenyl-glyoxal-2-phenylhydrazone (33) under similar conditions. Quinoxaline formation is thought to proceed through a diazetine intermediate as shown.39... 

---