[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.
regio-, diastereo-, and enantiocontrolled access to alpha,beta-unsaturated delta-lactones is described, based on the reaction of a silyl dienolate and an aldehyde in the presence of 10 % of Carreira's catalyst. The scope and limitations of this reaction, as well as mechanisticinsights concerning the reactivity of an allyl copper species, are discussed.
Catalytic Asymmetric Access to α,β Unsaturated δ-Lactones through a Vinylogous Aldol Reaction: Application to the Total Synthesis of the Prelog-Djerassi Lactone
[reaction--see text] A one-step catalyticasymmetric access to alpha,beta unsaturated delta-lactones is described, using a vinylogous Mukaiyama-aldol reaction between a gamma-substituted dienolate and various aldehydes in the presence of Carreira catalyst CuF.(S)-tolBinap. This methodology has been further applied to a straightforward access to the Prelog-Djerassi lactone.
Direct one-pot highly enantioselective assembly of polyketide and carbohydrate synthons
作者:Gui-Ling Zhao、Wei-Wei Liao、Armando Córdova
DOI:10.1016/j.tetlet.2006.05.018
日期:2006.7
short, direct, catalytic, enantioselective synthesis of polyketide segments and carbohydrates is presented. The novel, direct, one-pot, organocatalytic asymmetric tandem cross-aldol/Horner–Wittig–Emmons reactions assemble polyketide and carbohydrate derivatives in good yield with 93–98% ee. The one-pot catalytic asymmetric tandem reaction was applied to a highly enantioselective formal denovo synthesis