108666-00-8Relevant articles and documents
The Selective Cross-Coupling of Secondary Alkyl Zinc Reagents to Five-Membered-Ring Heterocycles Using Pd-PEPPSI-IHeptCl
Atwater, Bruce,Chandrasoma, Nalin,Mitchell, David,Rodriguez, Michael J.,Pompeo, Matthew,Froese, Robert D. J.,Organ, Michael G.
supporting information, p. 9502 - 9506 (2015/08/11)
The ability to cross-couple secondary alkyl centers is fraught with a number of problems, including difficult reductive elimination, which often leads to β-hydride elimination. Whereas catalysts have been reported that provide decent selectivity for the expected (non-rearranged) cross-coupled product with aryl or heteroaryl oxidative-addition partners, none have shown reliable selectivity with five-membered-ring heterocycles. In this report, a new, rationally designed catalyst, Pd-PEPPSI-IHeptCl, is demonstrated to be effective in selective cross-coupling reactions with secondary alkyl reagents across an impressive variety of furans, thiophenes, and benzo-fused derivatives (e.g., indoles, benzofurans), in most instances producing clean products with minimal, if any, migratory insertion for the first time. A wide variety of five-membered-ring heterocycles were successfully cross-coupled to secondary alkyl zinc reagents with the new precatalyst Pd-PEPPSI-IHeptCl, which features a bulky N-heterocyclic carbene ligand. This catalyst suppresses migratory-insertion (rearrangement) pathways, and the desired products are thus formed with high selectivity.
