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Regioselective Cyclometalation of Planar Chiral Pyridine and Oxazoline Derivatives: peri- versus ortho-C–H Functionalization

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posted on 22.07.2013, 00:00 by Audrey Mercier, Simon Wagschal, Laure Guénée, Céline Besnard, E. Peter Kündig
The cyclopalladation of highly enantioenriched cyclopentadienyl­(indenyl)­ruthenium complexes featuring pyridine or oxazoline functionalities as directing groups is detailed. Two competitive metalation sites inherent to the fused ring system were selectively activated after appropriate tuning of the reaction conditions, enabling the access to both six (peri)- and five-membered (ortho) membered chelates. A periortho isomerization was identified in the pyridine-based system, unveiling a kinetic preference for the peri-position and thermodynamic control for the ortho-cyclopalladation. In marked contrast, oxazoline derivatives incorporating a stereogenic center at C4 proved reluctant to form ortho-isomers and were exclusively converted into the corresponding peri-palladacyles at low temperatures.