Axially Chiral N-Heterocyclic Carbene Gold(I) Complex Catalyzed Asymmetric Cycloisomerization of 1,6-Enynes
journal contributionposted on 25.07.2011 by Wenfeng Wang, Jinming Yang, Feijun Wang, Min Shi
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A new class of axially chiral NHC-Au(I) complexes (1–11) has been developed from optically active BINAM and fully characterized by NMR, ESI-MS, and IR spectroscopic data, where structures of complexes 1, 2a, and 6 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 (aR)-6, having a pyrrolidin-1-yl group, has been realized to be the best catalyst in gold(I)-catalyzed asymmetric acetoxycyclization of 1,6-enyne 52a, giving product 53a in >99% yield with −59% ee at 0 °C, and the sterically less hindered gold(I) catalyst (aS)-2a is the best catalyst in the asymmetric oxidative rearrangement of 1,6-enynes, affording the corresponding aldehydes 56a,c–h in excellent yields (up to >99%) and modest enantioselectivities (3.1–70% ee) using PhCl as the solvent at 10 °C.