A catalytic route toward chiral Morita–Baylis–Hillman esters by asymmetric coupling between α,β‐acetylenic esters, aldehydes, and trimethylsilyl iodide has been developed (see scheme). The reaction proceeds with high to excellent enantioselectivities, and the products can be transformed into β‐branched derivatives in a single step and with excellent retention of configuration. TMS=trimethylsilyl
Broad-Spectrum Enantioselective Diels−Alder Catalysis by Chiral, Cationic Oxazaborolidines
作者:Do Hyun Ryu、Thomas W. Lee、E. J. Corey
DOI:10.1021/ja027468h
日期:2002.8.1
catalysts for Diels-Alder addition of cyclopentadiene to a wide variety of dienophiles. Adducts have been obtained in excellent yield and enantioselectivity from alpha,beta-unsaturated esters, lactones, and cyclic ketones. The absolute facial selectivity for each of these substrates follows a common pattern which differs from that observed with alpha,beta-enals. The different reaction channels can be
A novel, catalytic enantioselective route to synthesize a variety of a-tertiary aryl ketones via a boron Lewis acid promoted formal insertion of aryldiazoalkane into the C-H bond of both aromatic and aliphatic aldehydes is described. In the presence of chiral (S)-oxazaborolidinium ion catalyst 1, the reaction proceeded in good yields (up to 94%) with excellent enantioselectivities (up to 99% ee).
Triflimide Activation of a Chiral Oxazaborolidine Leads to a More General Catalytic System for Enantioselective Diels−Alder Addition
作者:Do Hyun Ryu、E. J. Corey
DOI:10.1021/ja035393r
日期:2003.5.1
The strong acid triflimide ((CF3SO2)2NH) protonates chiral oxazaborolidines to form superactive, stable, chiral Lewis acids which are highly effective catalysts for a wide variety of enantioselective Diels-Alder reactions, documented herein by more than 20 examples.
Enantioselective Cyclopropanation/[1,5]-Hydrogen Shift to Access Rauhut–Currier Product
A Michael addition initiated cyclopropanation/[1,5]-hydrogen shift has been developed for the enantioselective synthesis of Rauhut–Currier products. The reaction of α-alkyl diazoesters and in situ generated o-quinone methides proceeds in the presence of chiral oxazaborolidinium ion, providing Z-stereocontrolled Rauhut–Currier products in high yields (up to 96%) with excellent Z/E selectivities (>20:1)