Novel Polyfunctional Tautomeric Systems Containing Salicylideneamino and Proton Sponge Moieties

• Published in: European Journal of Organic Chemistry 2006-02, Vol.2006 (3), p.782-790
• Main Authors: Ozeryanskii, Valery A., Pozharskii, Alexander F., Schilf, Wojciech, Kamieński, Bohdan, Sawka-Dobrowolska, Wanda, Sobczyk, Lucjan, Grech, Eugeniusz
• Format: Article
• Language: English
• Subjects: Hydrogen transfer; Intramolecular hydrogen bonding; Proton sponge; Schiff bases; Tautomerism
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.200500574

The first salicylidenearylamines containing a proton sponge residue with 5′‐bromo (6), 5′‐nitro (7), and 3′,5′‐dinitro (8) substituents have been synthesized. X‐ray diffraction and 1H, 13C, and 15N NMR and infrared spectra revealed that 6 and 7 contain very strong OHN bridges typical of o‐hydroxy Schiff bases. Additional π‐electron coupling with the dimethylaminonaphthyl ring is manifested both in geometrical and infrared parameters. In the case of 7, proton transfer to the imine nitrogen atom occurs in the solid state, accompanied by a remarkable shortening of the OHN bridge (2.553 Å). In dinitro derivative 8, the OH proton jumps to the dimethylamino groups, giving a new tautomeric form with the formation of a homoconjugated [NHN]+ cation. Protonation of 6 and 7, affecting the (dimethylamino)naphthyl moiety, disrupts the π‐coupling and makes these molecules, unlike common aromatic Schiff bases, highly sensitive to hydrolysis, while 8, being already self‐protonated, equilibrates in wet DMSO with the corresponding salicylaldehyde and arylamine in a ca. 1:1 ratio at room temperature.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)