Stereochemie der Ringöffnung der σ‐Komplexe von 2‐Naphtol‐1‐sulfonsäure mit Diazoniumsalzen und der anschliessenden Phtalazinbildung: Eine fragmentierung als konkurrenzreaktion der abspaltung der abgangsgruppe bei der elektrophilen substitution 25. Mitteilung zur Kenntnis der Azokupplung

Abstract

AbstractThe reaction of 2‐naphthol‐1‐sulfonic acid with diazonium salts was investigated in the pH range 10 to 15. The structures postulated for the reaction products by Rowe et al. [3] and by Koller [4] were proved by instrumental analysis. In alkaline solutions, instead of the usual diazodesulfonation reaction, addition of an hydroxyl ion to the σ‐complex formed from 2‐naphthol‐l‐ sulfonic acid and substituted diazonium salts takes place. The resulting intermediates undergo heterolytic fragmentation leading to substituted o‐(phenylhydrazono‐sulfo‐methy1)‐cinnamicacids 7. The kinetic measurements prove that one equivalent of water is added during this fragmentation. 7 is produced by a conrotatory ringopening of the σ‐complex. An intramolecular ring closure in the formation of 8 from 7, results from studies of NMR. spectra, and molecular models show that both exocyclic double bonds in 7 have cis‐configuration. Kinetic measurements demonstrate that it is the anion 11 which enters the ring closure reaction: After intramolecular nucleophilic attack of the anionic nitrogen upon the double bond of the cinnamic group, a proton is added stereospecifically. The fragmentation of the σ‐complex is a competitive reaction to the release of the elctrofngal leaving group in electrophilic aromatic substitution. The fragmentation is dominant in this case because the electrofugal leaving group is not a proton but a SO, molecule. The conditions (constitution of reagents, catalysts, etc.) which influence the ratio of the two competitive reactions of cyclohexadienone‐type σ‐complexes are discussed.