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Atropselective Dibrominations of a 1,1′‐Disubstituted 2,2′‐Biindolyl with Diverging Point‐to‐Axial Asymmetric Inductions. Deriving 2,2′‐Biindolyl‐3,3′‐diphosphane Ligands...
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Titel: |
Atropselective Dibrominations of a 1,1′‐Disubstituted 2,2′‐Biindolyl with Diverging Point‐to‐Axial Asymmetric Inductions. Deriving 2,2′‐Biindolyl‐3,3′‐diphosphane Ligands for Asymmetric Catalysis |
In: | Angewandte Chemie International Edition, 58, 2019, 14, S. 4714-4719 |
veröffentlicht: |
Wiley
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Umfang: | 4714-4719 |
ISSN: |
1433-7851 1521-3773 |
DOI: | 10.1002/anie.201806294 |
Zusammenfassung: | <jats:title>Abstract</jats:title><jats:p>On the <jats:sup>1</jats:sup>H NMR timescale, 2,2′‐biindolyls with (<jats:italic>R</jats:italic>)‐configured (1‐alkoxyprop)‐2‐yl, (1‐hydroxyprop)‐2‐yl, or (1‐siloxyprop)‐2‐yl substituents at C‐1 and C‐1′ are atropisomerically stable at <0 °C and interconvert at >30 °C. A 2,2′‐biindolyl (<jats:italic>R</jats:italic>,<jats:italic>R</jats:italic>)‐<jats:bold>17 a</jats:bold> of that kind and achiral (!) brominating reagents gave the atropisomerically stable 3,3′‐dibromobiindolyls (M)‐ and/or (P)‐<jats:bold>18 a</jats:bold> at best atropselectively—because of point‐to‐axial asymmetric inductions—and atropdivergently, exhibiting up to 95 % (M)‐ and as much (P)‐atropselectivity. This route to atropisomerically pure biaryls is novel and should extend to other substrates and/or different functionalizations. The dibromobiindolyls (M)‐ and (P)‐<jats:bold>18 a</jats:bold> furnished the biindolyldiphosphanes (M)‐ and (P)‐<jats:bold>14</jats:bold> without atropisomerization. These syntheses did not require the resolution of a racemic mixture, which distinguishes them from virtually all biaryldiphosphane syntheses known to date. (M)‐ and (P)‐<jats:bold>14</jats:bold> acted as ligands in catalytic asymmetric allylations and hydrogenations. Remarkably, the β‐ketoester <jats:italic>rac</jats:italic>‐<jats:bold>25 c</jats:bold> was hydrogenated <jats:italic>trans</jats:italic>‐selectively with 98 % <jats:italic>ee</jats:italic>; this included a dynamic kinetic resolution.</jats:p> |
Format: | E-Article |
Quelle: | Wiley (CrossRef) |
Sprache: | Englisch |