Tethering a metal complex to its phosphate counterion via a phosphine ligand enables a new strategy in asymmetric counteranion-directed catalysis (ACDC). A straightforward, scalable synthetic route gives access to the gold(I) complex of a phosphine displaying a chiral phosphoric acid function. The complex generates a catalytically active species with an unprecedented intramolecular relationship between the cationic Au(I) center and the phosphate counterion. The benefits of tethering the two functions of the catalyst are demonstrated here in a tandem cycloisomerization/nucleophilic addition reaction, by attaining high enantioselectivity levels (up to 97% ee) at an unusually low 0.2 mol % catalyst loading. Remarkably, the method is also compatible with a silver-free protocol.

A series of novel polyhydroxylated N-alkoxypiperidines has been synthesized by ring-closing double reductive amination (DRA) of highly functionalized 1,5-dialdehydes with various hydroxylamines. The required saccharide-based dialdehydes were prepared efficiently from sodium cyclopentadienylide in seven steps. A two-step protocol has been developed for the DRA; it led, after deprotection, to isofagomine, 3-deoxyisofagomine, and numerous other N-alkoxy analogues. The barrier to inversion in these polyhydroxylated N-alkoxypiperidine derivatives was found by variable-temperature NMR methods to be approximately 15 kcal mol(-1). With the exception of N-hydroxyisofagomine itself, none of the compounds prepared showed significant inhibitory activity against sweet almond β-glucosidase.