✍ Scribed by Petr Šimůnek; Lucie Lusková; Markéta Svobodová; Valerio Bertolasi; Antonín Lyčka; Vladimír Macháček
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The reaction of 3‐phenylaminocyclopent‐2‐en‐1‐one with 4‐methyl, 4‐methoxy and 4‐chlorobenzenediazonium tetrafluoroborates was used to prepare the azo coupling products 3a‐c. It was found that these compounds are present in both CDCl~3~ solution and solid phase practically exclusively as (E)‐3‐phenylamino‐2‐(4‐subst.phenyldiazenyl)cyclopent‐2‐en‐1‐ones with NH···N intramolecular hydrogen bond. The substitution of the phenyl residue of the diazonium salt has no effect on the position of the tautomeric equilibrium. On the other hand, the compounds 4a, b formed by the reaction of 3‐phenylamino‐1__H__‐inden‐1‐one with 4‐methylbenzene‐ or benzenediazonium tetrafluoroborates exist in CDCl~3~ solution and in solid phase as hydrazone compounds. In the solution they occur as a mixture of three forms, out of which two were identified as E/Z isomers with different types of hydrogen bonds. Compound 5 formed by the reaction of 3‐amino‐5,5‐dimethylcyclohex‐2‐en‐1‐one with 4‐methoxybenzenediazonium tetrafluoroborate is converted into a stable hydrochloride 5·HCl on standing in CHCl~3~ solution; this product exhibits a high degree of delocalization of the positive charge. Its structure was studied by means of X‐ray. Copyright © 2007 John Wiley & Sons, Ltd.
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