Reactions of Nitroheteroarenes with Carbanions: Bridging Aromatic, Heteroaromatic, and Vinylic Electrophilicity

• Published in: Chemistry : a European journal Vol. 14; no. 20; pp. 6108 - 6118
• Main Authors: Seeliger, Florian, Błażej, Sylwia, Bernhardt, Sebastian, Mąkosza, Mieczysław, Mayr, Herbert
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 07.07.2008; WILEY‐VCH Verlag; Wiley
• Subjects: aromatic vicarious nucleophilic substitution; Chemistry; Chemistry, Multidisciplinary; density functional calculations; heterocycles; kinetics; linear free energy relationships; Physical Sciences; Science & Technology; VICARIOUS NUCLEOPHILIC-SUBSTITUTION; ANIONS; PARAMETERS; aromatic vicarious nucleophilic substitution; linear free energy relationships; density functional calculations; HYDROGEN; NITROARENES; heterocycles; ORIENTATION; CHLOROMETHYL PHENYL SULFONE; kinetics; POLAR ORGANIC-REACTIVITY; DERIVATIVES
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200800329

The relative rate constants for the vicarious nucleophilic substitution (VNS) of the anion of chloromethyl phenyl sulfone (1−) with a variety of nitroheteroarenes, for example, nitropyridines, nitropyrroles, nitroimidazoles, 2‐nitrothiophene, and 4‐nitropyrazole, have been determined by competition experiments. It was shown that nitropyridines are approximately four orders of magnitude more reactive than nitrobenzene. Among the five‐membered heterocycles 2‐nitrothiophene is the most active followed by nitroimidazoles and 4‐nitropyrazole. Nitropyrroles are the least electrophilic nitroheteroarenes with reactivities comparable to nitrobenzene. Quantum chemically calculated methyl anion affinities (B3LYP/6–311G(d,p)//B3LYP/6–31G(d)) of the nitroarenes correlated only moderately with the partial relative rate constants. The correlation of these activities with the LUMO energies of nitroarenes is even worse. By measuring the second‐order rate constants of the addition of 1− to nitroarenes and to diethyl arylidenemalonates 10, it was possible to link the electrophilic reactivities of nitroheteroarenes with the comprehensive electrophilicity scale based on the linear‐free‐energy‐relationship log k(20 °C)=s(N + E). Extending the electrophilicity scale: The second‐order rate constants of vicarious nucleophilic substitution reactions of the anion of chloromethyl phenyl sulfone with nitroheteroarenes have been measured to define electrophilicity parameters E for electron‐deficient heteroarenes (see graphic) according to the correlation equation log k2(20 °C)=s(N + E).