5-Membered rings nitro derivatives, reactions

The intramolecular cyclization of a nitro group with a triple bond has been extended to the synthesis of six- and seven-membered ring compounds analogous to isatogens. Thus, the reaction of the acetylene group with the nitro group in 39 yields 2-phenyl-3-oxobenzo[prepared from the corresponding biphenyl derivative.19... 

Conversion of the nitro compound to the ketone by hydrolysis of the enol derivative is followed J- Froborg and G. Magnusson, J. by an extremely good intramolecular aldol reaction giving the fused five-membered ring. 1978,100, 6728. 

The normal mode of reaction of cycloproparenes with electrophiles involves opening of the three-membered ring and leads to benzylic derivatives (see Section 3.B.3.). The bis(triiso-propylsilyl) group offers efficient protection of the cyclopropene moiety, so that electrophilic attack of the protected benzocyclopropene occurs at the aromatic ring. Reaction of 1,1-bis(triisopropylsilyl)benzocyclopropene with 67% nitric acid gave the 3-nitro derivative 1 in 58% yield. Electrophilic attack on the cycloproparene occurs at C3 and this is consistent with theoretical calculations. A variety of substituted derivatives of benzocyclopropene are available from the nitro compound (see Section 3.5.). 

Heterocyclic aromatic derivatives also undergo electrophilic aromatic substitution reactions. Pyrrole, for example, reacts with nitric acid in acetic anhydride, at 0°C, to give 509r of 2-nitropyrrole and 15% of 3-nitro-pyrrole. Pyrrole is more reactive in these reactions when compared to benzene, and the mild reaction conditions described are sufficient. One caution is that the products may decompose with prolonged exposure to a powerful Lewis acid. The preference for substitution at C2 in pyrrole is seen in other five-membered ring... 

In some cases the reaction is accompanied by a five-membered heterocyclic ring closure. For example, l-nitro-4-methoxynaphthalene 265 reacts with p-tolylpro-penylsulfone to give benzo[/z]quinoline 266 (35%) together with A-hydroxybenzo-pyrrole derivative 267 (14%) (Scheme 77) (00EJO521). Annulation of the pyridine ring may proceed via anion 268, whereas the formation of benzoindole 267 occurs via neutral alkene 269. 

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