Axially Chiral N-Heterocyclic Carbene Gold(I) Complex Catalyzed Asymmetric Cycloisomerization of 1,6-Enynes

A new class of axially chiral NHC-Au(I) complexes (<b>1</b>–<b>11</b>) has been developed from optically active BINAM and fully characterized by NMR, ESI-MS, and IR spectroscopic data, where structures of complexes <b>1</b>, <b>2a</b>, and <b>6</b> have been further determined by X-ray diffraction studies of their single crystals, exhibiting a nearly linear coordination geometry around the gold(I) center. Within the carried out investigations herein, the sterically less hindered gold(I) complex (a<i>R</i>)-<b>6</b>, having a pyrrolidin-1-yl group, has been realized to be the best catalyst in gold(I)-catalyzed asymmetric acetoxycyclization of 1,6-enyne <b>52a</b>, giving product <b>53a</b> in >99% yield with −59% ee at 0 °C, and the sterically less hindered gold(I) catalyst (a<i>S</i>)-<b>2a</b> is the best catalyst in the asymmetric oxidative rearrangement of 1,6-enynes, affording the corresponding aldehydes <b>56a</b>,<b>c</b>–<b>h</b> in excellent yields (up to >99%) and modest enantioselectivities (3.1–70% ee) using PhCl as the solvent at 10 °C.