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      Organocatalytic synthesis of chiral tetrasubstituted allenes from racemic propargylic alcohols

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      1 , 2 , 1 , 1 , , 1 , 2 , 3 ,
      Nature Communications
      Nature Publishing Group UK

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          Abstract

          Although chiral allene preparation via formal S N2’ nucleophilic substitutions of enantioenriched propargylic derivatives or metal-catalyzed reactions of racemic propargylic derivatives has attracted considerable attention and found applications in many areas of research, direct use of propargylic alcohols instead of propargylic derivatives for catalytic asymmetric allene synthesis is unknown. Here, we show that a highly enantioselective synthesis of tetrasubstituted allenes from racemic propargylic alcohols has been realized by organocatalysis with good efficiency (up to 96% yield and 97% ee). The intermolecular C–C and C–S bond formation was achieved efficiently with simultaneous stereocontrol over the axial chirality. Furthermore, an adjacent quaternary stereocenter could also be constructed. Mechanistically, the reaction may involve efficient stereocontrol on the propargylic cation by its chiral counter anion or 1,8-conjugate addition of para-quinone methides. In sharp contrast to previous central chirality construction, this process employs quinone methides for axial chirality construction.

          Abstract

          Axially chiral allenes that are normally present in natural products, bioactive molecules, organocatalysts, and functional materials are usually produced from propargylic derivatives. Here, the authors show direct use of propargylic alcohols for catalytic asymmetric allene synthesis.

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          Complete field guide to asymmetric BINOL-phosphate derived Brønsted acid and metal catalysis: history and classification by mode of activation; Brønsted acidity, hydrogen bonding, ion pairing, and metal phosphates.

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            Enantioselective Mannich-Type Reaction Catalyzed by a Chiral Brønsted Acid

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              Chiral Brønsted acid-catalyzed direct Mannich reactions via electrophilic activation.

              It was found that the phosphoric acid derivatives of general structure 1 serve as highly effective catalysts for the direct addition of acetyl acetone to N-Boc-protected arylimines. The beneficial effects of the 3,3'-bisaryl substituents of the catalysts on the enantioselectivity are greatly appreciated, and thus 1d functions as an excellent catalyst. The Brønsted acid-catalyzed direct Mannich reactions presented herein provide an attractive way to construct beta-aminoketones under extremely mild conditions. The stereochemical course of this reaction was established through the synthesis of Boc-(S)-phenylglycine methylester. The transformation thus demonstrated is applicable to a useful method for the synthesis of various phenylglycine derivatives.
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                Author and article information

                Contributors
                chzlin@ust.hk
                sunjw@ust.hk
                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group UK (London )
                2041-1723
                18 September 2017
                18 September 2017
                2017
                : 8
                : 567
                Affiliations
                [1 ]Department of Chemistry, the Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong SAR, China
                [2 ]The Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, the Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong SAR, China
                [3 ]HKUST Shenzhen Research Institute, Shenzhen, 518057 China
                Article
                251
                10.1038/s41467-017-00251-x
                5603569
                28924216
                0b843c34-1f56-4284-8c04-b60b89b19156
                © The Author(s) 2017

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 30 March 2017
                : 9 June 2017
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