RESUMEN
An asymmetric one-pot hydrocyanation/Michael reaction of α-aryl diazoacetates with trimethylsilyl cyanide, tert-butanol, and N-phenylmaleimides has been realized. Using a chiral guanidinium salt/CuBr catalyst, a series of cyanide-containing pyrrolidine-2,5-diones could be obtained in good yields with excellent diastereo- and enantioselectivities.
RESUMEN
The investigation of diverse reactivity of ß,γ-unsaturated carbonyl compounds is of great value in asymmetric catalytic synthesis. Numerous enantioselective transformations have been well developed with ß,γ-unsaturated carbonyl compounds as nucleophiles, however, few example were realized by utilizing them as not only nucleophiles but also electrophiles under a same catalytic system. Here we report a regioselective catalytic asymmetric tandem isomerization/α-Michael addition of ß,γ-unsaturated 2-acyl imidazoles in the presence of chiral N,N'-dioxide metal complexes, delivering a broad range of optically pure 1,5-dicarbonyl compounds with two vicinal tertiary carbon stereocenters in up to >99% ee under mild conditions. Meanwhile, stereodivergent synthesis is disclosed to yield all four stereoisomers of products. Control experiments suggest an isomerization process involved in the reaction and give an insight into the role of NEt3. In addition, Mannich reaction and sulfur-Michael addition of ß,γ-unsaturated 2-acyl imidazoles proceed smoothly as well under the same catalytic system.
RESUMEN
An efficient kinetic resolution of racemic oxaziridines has been realized via catalytic asymmetric α-hydroxylation of available ß-keto esters. In the presence of a chiral bifunctional guanidine catalyst, a variety of optically active oxaziridines and chiral α-hydroxy ß-keto esters were generated with excellent results (ee's of up to 99% and 97% and yields of up to 44% and 54%, respectively).