Pseudo-azulenes

Photolysis of the triazepine products produces 2,2-dimethylpropanenitrile and the corresponding pyrazole in quantitative yield <1997BSF927>. Reaction of sydnone 89 with fulvene 91 proceeds by [ji4s + jt6s]-cycloaddition followed by spontaneous loss of carbon dioxide and a molecule of dimethylamine or acetic acid from the pseudo-azulene , cyclopentaMpyridazine 92 (Equation 9) <1996CC1011, 1997T9921>. 

Table I, containing compounds 26-87, summarizes all pseudoazulenes known through July 1979, as well as the corresponding literature. Not included are hydroderivatives of known and hitherto unknown pseudo-azulene systems containing many oxo and thio compounds. Such pseudoazulenes are predominantly of the type produced by introduction of an NR group. Only one system (78) of pseudoazulenes containing a selenium group is known, whereas tellurium compounds are unknown because of difficulties...

By application of the analogy principle regarding azulene and pseudo-azulene, preparations for pseudoazulenes can be found. By analogy to... 

Only a few investigations of electrophilic substitution reactions of pseudo-azulenes containing a pyrrole-type nitrogen have been reported. There are many examples of alkylations (see Table VI). An alkylation always takes place at the nitrogen of the five-membered ring. For 7H-pyrrolo[2,3-b]-pyridine 68 azocoupling and reaction with dithiolium salts have been reported.166... 

Lithium alkyls or aryls add to pseudoazulenes 3398100 and 39.113-114 The carbanion always reacts with the carbon atom opposite the heteroatom in the six-membered ring (Scheme 16). After hydrolysis of primary intermediate 121 dihydro products (122) are formed, which can be transformed to pseudoazulenes in the usual manner (see Section III,A,2). The structure of primary intermediate 121 is confirmed by its alkylated (or acylated) products (123). Even these compounds can easily be dehydrogenated to pseudo-azulene. In this way. substituted pseudoazulenes can be formed that are not obtainable otherwise. The direction of addition to the pseudoazulenes is the same as in azulenes.241... 

Even these compounds can easily be dehydrogenated to pseudo-azulene. In this way, substituted pseudoazulenes can be formed that are not obtainable otherwise. The direction of addition to the pseudoazulenes is the same as in azulenes.-""... 

An interesting application with a methylene ketone was described by Boyd380 for the synthesis of pseudo azulenes from the oxalene381... 

A number of heterocyclic derivatives (27 X = S, O, or NR) and their benzologues have been synthesized in order to examine the involvement of the SOg group in the conjugation of the molecule. Investigation of their spectral and chemical properties led to the conclusion that these compounds (27) could not be considered as pseudo-azulenes, and that there was little interaction of the S—O bond with the conjugated system. 

Kato et al. (151,152) explored the chemistry of 2-ferf-butylMvenes with isomiinchnones, as well as with several other mesoionic compounds, in a novel approach to pseudo-hetero-azulenes. Thus, isomtinchnone 51a, generated as before in situ from A-benzoylphenylglyoxyanilide 253 with triethylphosphite, reacts with 2-ferf-butyl-6-(dimethylamino)fulvene to give the [47i+6ti] adduct diphenylcyclo-penta[c]pyran in low yield. Likewise, reaction of 51a with dimethylfulvene gave a mixture of two adducts, one of which arises from a [47i+2ti] cycloaddition. 

Kato and coworkers [61] reported that a sterically assisted [6-1-4]cycloaddition of 2-tert-butylfulvenes and to mesoionic compounds provides a route to pseudo-heteroazulenes (Scheme 7.55). The [6-i-4]adduct underwent further fragmentation, elimination or isomerization to yield a series of heterocycles isoelectronic with azulene. 

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