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Arene C−H Activation at Aluminium(I): meta Selectivity Driven by the Electronics of S N Ar Chemistry
Author(s) -
Hicks Jamie,
Vasko Petra,
Heilmann Andreas,
Goicoechea Jose M.,
Aldridge Simon
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.202008557
Subject(s) - chemistry , substituent , reactivity (psychology) , toluene , selectivity , destabilisation , medicinal chemistry , stereochemistry , photochemistry , catalysis , organic chemistry , medicine , psychology , social psychology , alternative medicine , pathology
The reactivity of the electron‐rich anionic Al I aluminyl compound K 2 [(NON)Al] 2 (NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐ tert ‐butyl‐9,9‐dimethylxanthene) towards mono‐ and disubstituted arenes is reported. C−H activation chemistry with n ‐butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer‐type transition state. Selectivity is therefore based on similar electronic factors to classical S N Ar chemistry, which implies the destabilisation of transition states featuring electron‐donating groups in either ortho or para positions. In the cases of toluene and the three isomers of xylene, benzylic C−H activation is also possible, with the product(s) formed reflecting the feasibility (or otherwise) of competing arene C−H activation at a site which is neither ortho nor para to a methyl substituent.