Brønsted acid and Pd-PHOX dual-catalysed enantioselective addition of activated C-pronucleophiles to internal dienes.

We describe the development of Pd-PHOX-catalysed enantioselective couplings of internal dienes with malononitrile and other activated C-pronucleophiles. Reactions are dramatically accelerated by the addition of Et3N·HBArF 4 as a Brønsted acid co-catalyst, enabling a suite of products bearing a variety of alkyl substituents at the stereogenic carbon to be prepared. A series of mechanism-oriented experiments reveal key aspects of the catalytic cycle and the importance of the non-coordinating BArF 4 counterion in not only promoting reactions of internal dienes but also additions of previously unreactive nucleophiles towards terminal dienes.