Cyclic Azo Compounds

Thermal decomposition of cis- and frans-3,6-dimethyl-3,4,5,6-tetrahydropyridazines affords propene, cis- and frans-l,2-dimethylcyclobutanes and 1-hexene. The stereochemistry of the products is consistent with the intermediacy of the 1,4-biradical 2,5-hexadienyl. The results indicate that thermal reactions of cyclic azo compounds and cyclobutanes of similar substitution proceed with similar stereospecificity when compared at similar temperatures 79JA2069). 

Hydroxyhexahydropyridazine was freed from the polymer (168) by hydrolysis (Scheme 91) (79TL1333). Cyclic azo compounds may also be employed for example with 1,2,4-triazole-3,5-dione, adducts (169,170) are formed first and these are subsequently transfor-... 

The most common example is decomposition of azo compounds, where —X—Y— is -N=N-.311 The elimination of nitrogen from cyclic azo compounds can be carried... 

The photolysis reactions of some other cyclic azo compounds are shown below(1B-18) ... 

Many reports concerning the direct and sensitized photolysis of cyclic azo compounds have appeared/11 Photolysis of meso and d,l forms of azo compound (2) results in varying mixtures of products (3), (4), and (5) ... 

Novel steroidal pyridazines are readily prepared from ADC compounds and steroidal A2,4-dienes,163 A14,1 -dienes,164 and A16,20-dienes.165 ADC compounds are also commonly used in the protection of the steroid 5,7-diene system (see Section V,A). These Diels-Alder adducts of steroidal dienes and azo dienophiles should not be confused with the so-called azasteroids, which are also prepared from ADC compounds. Cyclic ADC compounds such as the pyrazole-3,5-diones (7), and the diazaquinones 12 and 13 readily add to dienes to give bicyclic pyridazine derivatives,166168 and these reactions have been adapted to the synthesis of 5,10-diazasteroids (106).42 Similarly, the 13,14-diaza- (107) and 13,14,16-triazasteroid (108) ring systems have been prepared.169... 

Diazirine and several of its 3-substituted homologues, formally cyclic azo compounds, are explosive on heating or impact [1]. The shock-sensitivity of all diazirine compounds and the inadvisability of their handling in the undiluted state have again been stressed [2], In a description of the synthesis of 27 3-(4-substituted)halodiazirines, the need is stressed to handle the compounds at below 30°C to prevent thermal decomposition, or, for the pure compounds, explosion [3],... 

The most widely studied example is decomposition of azo compounds, where —X—Y— is —N=N—,220 The elimination of nitrogen from cyclic azo compounds can be carried out either photochemically or thermally. Although the reaction generally does not proceed by a concerted mechanism, there are some special cases in which concerted elimination is possible. We will consider some of these cases first and then consider the more general case. 

A cyclic silyl hydrazone derivative <83ZAAC(50i)57> as well as azo compounds isomeric to hydrazones <74PS197> have also been used for the synthesis of 2//-1,2,3-diazaphospholes by the PCI3 condensation. 2,4,5-Triphenyl-l,2,3-diazaphosphole is best prepared from the respective azoalkene and a fused benzothiadiphosphole as phosphorus donating reagent <95TL447>. 

The behavior of cyclic azo compounds differs considerably from that of the acyclic ones in that spin correlation effects have been seen in several cases. Since singlet decomposition gives a different product distribution than triplet sensitization, these cases provide an elegant test of the sensitization mechanism. 

Another cyclic azo compound which shows a spin correlation effect is the pyrazoline 44201 (Fig. 6). The product distribution under various conditions... 

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). 

The most extensively investigated 1,2-diazocines are 3,4,5,6,7,8-hexahydro derivatives, of interest in connection with studies on the properties of cyclic azo compounds. These compounds are obtained from the hydrazines (159) usually not isolated, by oxidation with yellow mercury(II) oxide. 3,8-Diaryloctahydrodiazocines are prepared by reduction of the azines dialkyl and unsubstituted derivatives are obtained by hydrolysis of the N,N-bis(ethoxycarbonyl) compounds (69JA3226,70JA4922). Cyclization of 2,7-diaminooctane with IFs gave the 3,3,8,8-tetramethyl compound (78CB596). 

Olefins have been added to diazoalkanes to prepare 1-pyrazolines, a class of cyclic azo compounds. 

Intramolecular coupling of diazonium salts with ortho substituents bearing an active methylene grouping or its equivalent gives rise to cinnolines, which may be considered a class of cyclic azo compounds. Three name reactions are cited here for reference only. 

In the course of an extensive study of the chemistry of azo compounds, Overberger et al. [47a] prepared 1-pyrazolines, which may be considered cyclic azo compounds, by the addition of diazoalkanes to styrene. The reaction is considered a stereospecific 1,3-dipolar addition and, in the reaction between />-methoxyphenyldiazomethane and />-methoxystyrene both trans-3,5-bis-(p-methoxyphenyl)pyrazoline (m.p. 129°C, dec.) and c/s-3,5-bis(/>-methoxy-phenyl)pyrazoline were prepared and separated [47b]. 

Azoalkanes have also been produced by oxidation with mercuric oxide. This reagent is considered the reagent of choice for azoalkanes [76, 87, 93], as well as for the preparation of cyclic azo compounds [94], and 1-pyrazolines [95a]. When used in the preparation of a-carbonyl azo compounds, evidently mercury complexes are formed with the diacylhydrazine starting materials. These complexes are then treated with halogens (iodine or chlorine) to produce the azo compounds [92]. 

Evidence has been presented that a genuine equilibrium exists between azo compounds and hydrazones, at least in the case of aliphatic cyclic compounds [106] (Eq. 46). The proposed mechanism was assumed to involve anion... 

Bicyclobutanes also undergo thermal and photochemical cycloaddition reactions with cyclic azo compounds to form 2,3-diazabicyclo[2.1.1]hexanes 31.45,46 Some typical examples are shown. 

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