A highly efficient iridium-catalyzed asymmetric hydrogenation of tetrasubstituted cyclicenones has been developed for the enantioselective synthesis of chiral cycloalkanols with three contiguous stereocenters. The C═O and C═C bonds of the enone substrates were hydrogenated sequentially in one pot with excellent enantioselectivity (92 to >99% ee) and diastereoselectivity (dr 95:5 to >99:1). The reaction
The organocatalytic enantio- and diastereoselective cycloetherification of 1,3-cyclohexanedione-bearing enones involving the in situ generation of chiral cyanohydrins was developed. This transformation offers the first catalytic asymmetric approach to oxadecalin derivatives containing contiguous tetrasubstituted chiral carbons at the bridge heads of the fused ring systems. Depending on substituents
Enantioselective Synthesis of Indolizidines Bearing Quaternary Substituted Stereocenters via Rhodium-Catalyzed [2 + 2 + 2] Cycloaddition of Alkenyl Isocyanates and Terminal Alkynes
作者:Ernest E. Lee、Tomislav Rovis
DOI:10.1021/ol800086s
日期:2008.3.1
An enantioselectivesynthesis of indolizidines bearing quaternary substituted stereocenters by way of a rhodium-catalyzed [2+2+2] cycloaddition of substituted alkenyl isocyanates and terminal alkynes is described. The reaction provides lactam products using aliphatic alkynes, whereas aryl alkynes give rise to vinylogous amide products. Through modification of the phosphoramidite ligand, high levels