Bimetallic Catalytic Asymmetric Tandem Reaction of β-Alkynyl Ketones to Synthesize 6,6-Spiroketals

The enantioselective tandem reaction of beta,gamma-unsaturated alpha-ketoesters with beta-alkynyl ketones was realized by a bimetallic catalytic system of achiral Au-III salt and chiral N,N'-dioxide-Mg-II complex. The cycloisomerization of beta-alkynyl ketone and asymmetric intermolecular [4+2] cycloaddition with beta,gamma-unsaturated alpha-ketoesters subsequently occurred, providing an efficient and straightforward access to chiral multifunctional 6,6-spiroketals in up to 97% yield, 94 % ee and >19/1 d.r. Besides, a catalytic cycle was proposed based on the results of control experiments.