A new class of chiral ligand, bisulfoxime 1, is showing promise as a catalyst for hetero Diels-Alder reactions of dienes with activated aldehydes, Scheme 1.~1 The ligand is readily available in one step, large scale and high yield 70%, by the reaction of (S)-S-methyl-S-phenylsulfoxime with 1,2-dibromobenzene. The active catalyst is generated in situ by reaction of copper triflate with one molar equivalent of the ligand 1 in the presence of 4A molecular sieve. This copper catalyst shows both high reactivity and high enantioselectivity in Diels-Alder reactions Hence, reaction of 1,3-cyclohexadiene with ethyl glyoxalate in dichlormethane containing 0.5 mol% of the copper catalyst at room temperature for 6 h gave the cycloadduct 2 in 96% yield, endo-selectivity 99:1 and 98% ee. This catalyst is as good as the best catalysts reported to data for performing this reaction.
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