Diastereoselective Heteroatom-Directed Conjugate Addition of Silylcuprate Reagents to Unsaturated Carbonyls. A Stereoselective Route to .beta.-Carbonyl Siloxanes1
摘要:
Directed conjugate addition of the silylcuprate reagent lithium bis[diphenyl(diethylamino)silyl]-cuprate ((Ph(2)(Et(2)N)Si)(2)CuLi) to unsaturated esters and ketones is reported. The stereochemical course of the reaction can be-controlled by the presence of an appropriately disposed internal Lewis basic functionality, affording the corresponding beta-hydroxysilyl carbonyls with good to excellent levels of diastereoselection (e.g., 3b --> 4b).
[reaction: see text]. The use of the Z-configured vinylogous silyl ketene acetals in Mukaiyamaaldolreactions is described. Isopropyl alcohol as scavanger and the use of tris(pentafluorophenyl)borane as the Lewisacid are required for obtaining the gamma-alkylated syn-product selectively. In cases of alpha-chiral aldehydes, Felkin-Anh selectivity was observed.