Gold(I)-Catalyzed Enantioselective Hydroamination of Allenes

The authors report a gold(I)-xylyl-BINAP system whose catalytic as well as enantio­selective efficiency is highly dependent upon the coordinating counteranion. The isolable, bench-stable (R)-xylyl-BINAP(AuOPNB)2 (OPNB = p-nitro­benzoate) catalyzes the intramolecular hydroamination of a variety of alkyl- and aryl-substituted allenes in high yield and ee. The authors believe the electronic nature of the nitrobenzoate anion confers reactivity, favoring complex B, while its steric bulk induces asymmetry. Notably, when 3 mol% of AgBF4 are used, forming complex B with one chloride counteranion, product with only 51% ee is obtained, providing support for the role of the counteranion in chiral induction.