title: Competing amination and C-H arylation pathways in Pd/xantphos-catalyzed transformations of binaphthyl triflates: switchable routes to chiral amines and helicene derivatives.
abstract: A Pd(OAc)2/xantphos catalyst system was found effective for benzylaminations of binaphthyl 2-triflates bearing a variety of alkyl, benzyl, and substituted phenyl substituents at the 2'-position. With 2'-aryl substituents, an intramolecular Pd-catalyzed C-H arylation was observed as a competing side reaction under some conditions. By adjusting the solvent and quantity of the amine, the reaction was optimized to favor either the amination or the C-H arylation pathway, affording two distinct and potentially useful sets of products. The amines represent tunable chiral ligand precursors, while the C-H arylation pathway affords a series of benzofused [5]helicene derivatives. Kinetic studies and activation parameters for the C-H arylation pathway, supported by DFT calculations, are consistent with a concerted metalation-deprotonation (CMD) mechanism involving a Pd-bound carbonate as the base. Xantphos is proposed to facilitate the turnover-limiting inner-sphere CMD step by acting as a hemilabile ligand, while its wide bite angle engenders a low reductive elimination barrier.
authors: Department of Chemistry, University of North Texas, 1155 Union Circle #305070, Denton, Texas, USA. legrande@unt.edu.
authors: Aaron A
authors: AA
authors: Ruch
authors: Sachin
authors: S
authors: Handa
authors: Fanji
authors: F
authors: Kong
authors: Vladimir N
authors: VN
authors: Nesterov
authors: Dale R
authors: DR
authors: Pahls
authors: Thomas R
authors: TR
authors: Cundari
authors: LeGrande M
authors: LM
authors: Slaughter