Chiral synthesis via organoboranes. 11. Hydroboration. 82. Asymmetric hydroboration of 1-heteroarylcycloalkenes with monoisopinocampheylborane. Synthesis of trans-2-heteroarylcycloalkyl boronates and derived alcohols of very high enantiomeric purity.

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概要

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• The hydroboration of representative 1-heteroarylcycloalkenes with monoisopinocampheylborane (IpcBH<SUB>2</SUB>) was investigated systematically to establish the degree of asymmetric induction during hydroboration. The hydroboration of 1-heteroarylcyclopentene with IpcBH<SUB>2</SUB> at −25 °C proceeded cleanly to afford the corresponding dialkylboranes. These dialkylboranes, upon treatment with acetaldehyde and then oxidation, afforded the corresponding <I>trans</I>-2-heteroarylcycloalkanols of 85–86% ee. Similarly, 1-heteroarylcyclohexenes, upon hydroboration with IpcBH<SUB>2</SUB>, followed by acetaldehyde treatment and oxidation, gave the corresponding alcohols in ca. 90% ee. The dialkylboranes or alkylboronic acids derived from 1-heteroarylcyclopentenes and IpcBH<SUB>2</SUB> can be recrystallized to furnish materials approaching 100% ee. From such dialkylboranes or alkylboronic acids, the corresponding boronates of ca. 100% ee were prepared and isolated. These are proving to be highly versatile synthetic intermediates for organic synthesis.

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著者

• Brown Herbert

  H. C. Brown and R. B. Wetherill Laboratories of Chemistry, Purdue University

• Gupta Ashok

  H. C. Brown and R. B. Wetherill Laboratories of Chemistry, Purdue University

• Vara Prasad

  H. C. Brown and R. B. Wetherill Laboratories of Chemistry, Purdue University

関連論文

• Chiral synthesis via organoboranes. 11. Hydroboration. 82. Asymmetric hydroboration of 1-heteroarylcycloalkenes with monoisopinocampheylborane. Synthesis of trans-2-heteroarylcycloalkyl boronates and derived alcohols of very high enantiomeric purity.

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