Pd-PEPPSI-IPentCl : A Useful Catalyst for the Coupling of 2-Aminopyridine Derivatives
Abir Khadra1, Stanislas Mayer2, Michael G Organ1,3
1Department of Chemistry, York University, 4700 Keele Street, Toronto, Ontario, M3J1P3, Canada.
Abstract:
The Pd-PEPPSI-IPentCl precatalyst (PEPPSI=pyridine-enhanced precatalyst preparation stabilisation initiation) has been demonstrated to be highly effective in the coupling of hetero(aryl)chlorides to free 2-aminopyridine substrates to produce N-(hetero)aryl-2-aminopyridine derivatives. The catalyst has proven to be competent in a number of other difficult cross-coupling reactions owing to the combination of the 3-pentyl-substituted N-aryl groups and the chlorines on the backbone of the N-heterocyclic carbene (NHC) core. This same reactivity here allows couplings to take place under very mild conditions (e.g., NaBHT (BHT=2,6-di-tert-butyl-4-methylphenol) or carbonate base) such that sensitive functional groups including esters, ketones and nitriles are tolerated. Key is that the same bulk that drives the cross-coupling also mitigates poisoning of the Pd centre with the 2-aminopyridine functionality in the starting materials and/or products, which forces the catalyst into inactive, stable resting states.
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