Arenes cine-tele substitution

There is an alternative mechanism for halide replacement, following the sequence of nucleophile addition, protonation, and elimination of HX. In this pathway, the addition of the nucleophile need not be at the ipso position it can be ortho to halide leading to cine substitution or it can be at the meta or para positions, leading to tele substitution. The processes depend on the formation of the cyclohexadienyl anion intermediates in a favorable equilibrium (carbon nucleophiles from carbon acids with P a > 22 or so), protonation (which can occur at low temperature with even weak acids such as acetic acid), and hydrogen shifts in the proposed diene-chromium intermediates. Hydrogen shifts lead to an isomer that allows elimination of HX and regeneration of an arene chromium complex, now with the carbanion unit indirectly substituted for X (Scheme 40). ... [Pg.3317]

Arasabenzene, with chromium, 5, 339 Arcyriacyanin A, via Heck couplings, 11, 320 Arduengo-type carbenes with titanium(IV), 4, 366 with vanadium, 5, 10 (Arene(chromium carbonyls analytical applications, 5, 261 benzyl cation stabilization, 5, 245 biomedical applications, 5, 260 chiral, as asymmetric catalysis ligands, 5, 241 chromatographic separation, 5, 239 cine and tele nucleophilic substitutions, 5, 236 kinetic and mechanistic studies, 5, 257 liquid crystalline behaviour, 5, 262 lithiations and electrophile reactions, 5, 236 as main polymer chain unit, 5, 251 mass spectroscopic studies, 5, 256 miscellaneous compounds, 5, 258 NMR studies, 5, 255 palladium coupling, 5, 239 polymer-bound complexes, 5, 250 spectroscopic studies, 5, 256 X-ray data analysis, 5, 257... [Pg.55]