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On the Mechanism of Phenolic Formylation Mediated by TiCl 4 Complexes: Existence of Diradical Intermediates Induced by Valence Tautomerism
Author(s) -
Heras Carlos,
RamosTomillero Iván,
Caballero Marc,
ParadísBas Marta,
Nicolás Ernesto,
Albericio Fernando,
de P. R. Moreira Ibério,
Bofill Josep Maria
Publication year - 2015
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201403548
Subject(s) - chemistry , diradical , formylation , tautomer , electrophile , intramolecular force , valence (chemistry) , nucleophile , phenylsilane , photochemistry , dehydrogenation , medicinal chemistry , computational chemistry , stereochemistry , singlet state , organic chemistry , catalysis , physics , nuclear physics , excited state
The conventional electrophilic intramolecular aromatic substitution pathway proposed by Cresp et al. [ J. Chem. Soc., Perkin Trans. 1 1973 , 340–345] is confirmed by the observed products of phenolic formylation mediated by TiCl 4 . However, when the nucleophilic path is quenched by appropriate ligand modification, the initial equilibria between the possible neutral complexes of TiCl 4 with 3,5‐dimethoxyphenol and/or diethyl ether lead to different stable diradical intermediates induced by valence tautomerism that provide valuable activated reagents. Some of these species have been detected by EPR, characterized theoretically and captured by TEMPO, thus providing a consistent mechanism for the reaction with one or more equivalents of TEMPO per phenol.