Highly diastereoselective nitroaldol reactions with chiral derivatives of glyoxylic acid (original) (raw)
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Chemical Communications, 1998
S2 1. General Information 1 H NMR (400 MHz) and 13 C NMR (100 MHz) spectra were recorded on a Varian MERCURY plus-400 spectrometer with TMS as an internal standard. HRMS was performed at the Analysis Center of Shanghai Jiao Tong University. Enantioselectivity was measured by high performance liquid chromatography (HPLC) using Daicel Chiralcel ASH , OD-H and IC-3 columns with hexane / i-PrOH as a eluent. Column chromatography was performed using 100-200 mesh silica gel. Melting points were measured with SGW X-4 micro melting point apparatus. All commercially available substrates were used as received.
Beilstein Journal of Organic Chemistry, 2013
Chiral nonracemic aminated nitroso acetals were synthesized via diastereoselective multicomponent [4 + 2]/[3 + 2] cycloadditions employing new (S,E)-γ-nitrogenated nitroalkenes 5a–c as heterodienes, ethyl vinyl ether (EVE) as a dienophile, and selected electron-deficient alkenes as 1,3-dipolarophiles. The employment of different organic solutions of LiClO4 or LiCl as promoter systems provided the respective nitroso acetals with yields from 34–72% and good levels of diastereoselectivity. In addition, the nitroso acetal 9c was transformed to the pyrrolizidin-3-one derivative 14c, proving the usefulness of the route in the synthesis of an interesting chiral compound. The elucidation of the stereostructures was based on 2D COSY, NOESY and HSQC NMR experiments as well as an X-ray diffraction experiment.
Diastereoselective alkylation of chiral glycinate derivatives containing the a-phenylethyl group
2011
Novel chiral glycinate derivatives (S)-6 and (S)-7 contain- ing the a-phenylethyl group, were prepared and studied as potential precursors of enantiopure a-substituted-a-amino acids. In particu- lar, the alkylation of enolate (S)-7-Li showed substantial (78:22 dr) stereoinduction by the N-(1-phenylethyl)benzamide chiral auxiliary. Addition of DMPU showed no appreciable effect upon the diastere- oselectivity.
Stereoselective opening of chiral dioxane acetals. Nucleophile dependence
The Journal of Organic Chemistry, 1991
product, the expected product, 14, in which five contiguous chiral centers are present, was obtained in 95% yield. 21 We also examined the reaction of substrates that bear no ether oxygen atom at the t or f position (Scheme II).9 Such compounds reacted much more slowly than epoxy acrylates, which bear an ether oxygen atom a t the 6 or t position (e.g., 1,3,4,7, 9, 11, and 13) and gave mixtures of regioisomeric products. For example, the reaction of methyl (4R,5R)-4,5-epoxy-2-heptenoate (16) with (CH,),Al required more than 6 h a t -15 to -10 "C to go to completion and gave an 80🔞2 mixture of 16, 17, and 18, in (21) The MPM protective group was concomitantly removed under the conditions. 85% combined yield? Similarly, the reaction of ethyl 4,5-epoxy-2-pentadecenoate (19) (-15 to -10 "C, 6 h) gave a 78:21:1 mixture of 20, 21, and 22 in 79% yield. The results suggest that chelation of the aluminum reagent by the oxygen atoms of the epoxide and the ether moiety at the t or { position is important for the achievement of extremely high regioselectivity, as is seen in the reactions of , and 13.*
Synthesis, 2016
Ethynylation and propargylation of chiral nonracemic polyhydroxylated cyclic nitrones with Grignard reagents are efficient methods for preparing building blocks containing an alkyne moiety to be used in copper-catalyzed azide alkyne cycloaddition click chemistry. Whereas ethynylation takes place with excellent diastereoselectivity, propargylation afforded mixtures of diastereomers in some cases. The use of (trimethylsilyl)propargyl bromide as precursor of the Grignard reagent is necessary to avoid the formation of undesired allene derivatives. DFT calculations explain, within the experimental error, the observed behavior. Cycloaddition of the obtained pyrrolidinyl alkynes with sugar azides derived from β-(1,3)-glucans provides glycomimetics suitable to be used against fungal transglycosylases.