Asymmetric Synthesis using Organoboranes. Relative Effectiveness of the B-Halobis(terpenyl)boranes for the Enantioselective Halogenative Cleavage of Representative meso-Epoxides*

Chandra D. Roy; Herbert C. Brown

doi:10.1071/CH07118

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Asymmetric Synthesis using Organoboranes. Relative Effectiveness of the B-Halobis(terpenyl)boranes for the Enantioselective Halogenative Cleavage of Representative meso-Epoxides^*

Chandra D. Roy ^A ^B ^C and Herbert C. Brown ^A

+ Author Affiliations

- Author Affiliations

^A Department of Chemistry, Herbert C. Brown Center for Borane Research, Purdue University, West Lafayette, IN 47907-2084, USA.

^B Present address: EMD Biosciences, Inc., 10394 Pacific Center Court, San Diego, CA 92121, USA.

^C Corresponding author. Email: chandra0919@gmail.com

Australian Journal of Chemistry 60(11) 835-842 https://doi.org/10.1071/CH07118
Submitted: 20 April 2007 Accepted: 13 May 2007 Published: 1 November 2007

Abstract

A comparative study of the relative effectiveness of various Ter₂BX, such as ^dEap₂BX, ^lEap₂BX, 2-^dIcr₂BX, 4-^dIcr₂BX, and ^lCleap₂BX along with ^dIpc₂BX for the asymmetric ring opening of three representative meso-epoxides (cyclohexene, cyclopentene, and cis-2,3-butene oxides) is reported. Among all the reagents studied, 2-^dIcr₂BCl (78–80%) demonstrated significant improvement in enantiomeric excess over a previously explored reagent, ^dIpc₂BCl (41%), especially for meso-cyclohexene oxide. Although all these three reagents, ^dIpc₂BBr, ^dEap₂BBr, and 2-^dIcr₂BBr provided comparable enantiomerically enriched 2-bromocyclohexan-1-ol (76–86%) from meso-cyclohexene oxide, the carene-based reagent, 2-^dIcr₂BBr showed considerable improvements in enantiomeric excesses in the cases of meso-cyclopentene oxide (67%) and meso-cis-2,3-butene oxide (78%) than those achieved with previously reported reagent, ^dIpc₂BBr (57 and 61% respectively). The enantioselectivity of the reaction was observed to be highly substrate dependent. The present study represents a significant advance in asymmetric synthesis using the chiral organoborane chemistry.

Acknowledgments

This work was supported by grants from the Office of Naval Research and the Purdue Borane Research Fund.

References

^* This paper is dedicated to the memory of my mentor, the late Professor Herbert C. Brown (1912–2004). The work described herein was carried out at Purdue University as a post-doctoral research associate.

Asymmetric Synthesis using Organoboranes. Relative Effectiveness of the B-Halobis(terpenyl)boranes for the Enantioselective Halogenative Cleavage of Representative meso-Epoxides*

Abstract

Acknowledgments

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Asymmetric Synthesis using Organoboranes. Relative Effectiveness of the B-Halobis(terpenyl)boranes for the Enantioselective Halogenative Cleavage of Representative meso-Epoxides^*