Asymmetric Diels–Alder reactions of N-sulfinyl dienophiles using chiral Ti(IV) Lewis acids
作者:Annette Bayer、Lars K. Hansen、Odd R. Gautun
DOI:10.1016/s0957-4166(02)00661-4
日期:2002.11
Enantioselective hetero Diels–Alder (HDA) reactions of 1,3-cyclohexadiene with benzyl N-sulfinylcarbamate 1a and with N-sulfinyl-p-toluensulfonamide 1b promoted by chiral Ti(IV)-based Lewis acids are reported. The obtained yields and enantiomeric excesses obtained are heavily dependant on the mode of catalyst preparation. Acceptable reproducibility was obtained with Ti(IV)-catalysts prepared from Me2TiCl2
对映选择性杂狄尔斯-阿尔德(HDA)用苄基1,3-环己二烯的反应Ñ -sulfinylcarbamate 1A和与Ñ -sulfinyl- p -toluensulfonamide 1b中报道通过手性钛(IV)的基于提升的路易斯酸。获得的产率和获得的对映体过量在很大程度上取决于催化剂的制备方式。使用由Me 2 TiCl 2和手性二醇制得的Ti(IV)催化剂可获得可接受的重现性。测试各种手性二醇得到内加合物,收率高达69%,ee为76%。HDA产品的绝对构型通过化学相关性确定,并通过X射线晶体学验证。
Highly enantioselective hetero Diels–Alder reactions of N-sulfinyl dienophiles promoted by copper(II)- and zinc(II)-chiral bis(oxazoline) complexes
作者:Annette Bayer、Odd R. Gautun
DOI:10.1016/s0957-4166(01)00525-0
日期:2001.11
Hetero Diels-Alder reactions of 1,3-cyclohexadiene with N-sulfinyl dienophiles 1a or 1b, promoted by Cu(II)- or Zn(II)-chiral bis(oxazoline) complexes, afforded endo adducts in high yields (up to 85%) and enantiomeric excess (e.e. of up to >98%) under stoichiometric conditions. With 10 mol% loading of the Zn(II) catalyst up to 75% e.e. was obtained for the endo adduct (endo:exo=10:1, total yield 68%). (C) 2002 Elsevier Science Ltd. All rights reserved.
Asymmetric Hetero-Diels−Alder Reactions of <i>N</i>-Sulfinyl Dienophiles Using Chiral Bis(oxazoline)−Copper(II) and −Zinc(II) Triflates
作者:Annette Bayer、Molla Mellese Endeshaw、Odd R. Gautun
DOI:10.1021/jo0490245
日期:2004.10.1
transformed into N-protected α-amino acid methyl esters, amino alcohols, and homoallylic amines. A stereochemical model, which accounts for the enantiofacial selectivity of the HDA reaction by a tetrahedral metal center, has been proposed. Mechanistic studies revealed positive nonlinear effects, assumed to arise from the formation of less-reactive heterochiral complexes. Investigation of the temperature