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Buttressing Effects on Haloarene Deprotonation: A Merely Kinetic or Also Thermodynamic Phenomenon?

2004; American Chemical Society; Volume: 6; Issue: 24 Linguagem: Inglês

10.1021/ol0480022

1523-7060

Joanna Gorecka, Christophe Heiss, Rosario Scopelliti, Manfred Schlosser,

Chemical Reaction Mechanisms

(2,6-Dichlorophenyl)- and (2,6-dibromophenyl)trialkylsilanes undergo hydrogen/metal interconversion preferentially at the 4- rather than 3-position. However, the organometallic species generated by such a "meta metalation" are thermodynamically less stable (i.e., more basic) than those that would result from an ordinary "ortho metalation". This was demonstrated by equilibration experiments based on permutational halogen/metal interconversion. A new buttressing effect can explain the unprecedented regioselectivity. It is supported by X-ray structures that reveal marked deformations of the benzene ring in halophenylsilanes. [structure: see text]