C,O-Chelated BINOL/Gold(III) complexes as efficient catalysts for enantioselective carboalkoxylation of ethynylbenzaldehydes Kwok-Heung Aries Chan, Wa-Yi O, Jia-Jun Jiang and Man-Kin Wong The Hong Kong Polytechnic University, Hong Kong Gold catalysis has been developed for a wide range of organic transformations with selective functionalization of C-C multiple bonds in the past decades [1-2] . With gold(I) and gold(III) as the common oxidation states, numerous chiral gold(I) complexes have been designed for asymmetric catalysis, while gold(III) catalysis remains largely unexplored. The instability towards reduction of the gold(III) complexes has significantly limited the design and synthesis of gold(III) catalysts [3-5] . Despite the difficulties in the development of gold(III) catalysts, enantioselective gold(III) catalysis offers a potential alternative to gold(I) catalysis. Gold(III) species with square planar geometry exhibit close proximity between ligands and substrates, facilitating better chiral induction than linear gold(I) species. However, examples of chiral gold(III) catalysts achieving high enantioselectivity are rare [6] . We have previously developed a series of novel C,O-chelated BINOL/cyclometallated gold(III) complexes [7] and chiral O,O’-chelated 4,4’-biphenol cyclometallated oxazoline gold(III) complexes achieving high enantioselectivity (up to 90% ee) in asymmetric carboalkoxylation of alkynes [8] . Here we present a new class of C,O-chelated chiral oxazoline-based C^N-cyclometalated gold(III) complexes with an easily accessible synthetic pathway. The chiral C,O-chelated BINOL/gold(III) complexes were synthesized from racemic C^N-cyclometalated dichloride gold(III) complexes and were easily isolated by simple filtration. The new synthetic approach overcomes the limitations of using expensive chiral source and chiral HPLC separation.These complexes were able to catalyze asymmetric carboalkoxylation of alkynes with excellent enantioselectivity of up to 99% ee.
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