Asymmetric ring opening of meso-epoxides with B-halobis(2-isocaranyl)boranes 2-dIcr2BX |
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| Institution: | 1. Argenta, Early Discovery, Charles River, 7-9 Spire Green Centre, Flex Meadow, Harlow, Essex CM19 5TR, United Kingdom;2. Genentech, Inc., 1 DNA Way, South San Francisco, CA 94080, USA;1. Institute of Chemistry, Academia Sinica, Taipei, 11529, Taiwan, ROC;2. Department of Engineering and System Science, National Tsing Hua University, Hsinchu, 300, Taiwan, ROC;3. Nano Science and Technology Program, Taiwan International Graduate Program, Academia Sinica and National Tsing Hua University, Taiwan, ROC;4. Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, 19716, USA;5. Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300, Taiwan, ROC;1. Chemistry Department, G. N. Khalsa College, Matunga, Mumbai 400019, India;2. Department of Chemistry, University of Mumbai, Santacruz E, Mumbai 400098, India |
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| Abstract: | Hydroboration of commercially available (+)-2-carene (96% ee) with either BH2Cl·SMe2 or BCl3/Me3SiH, provides chemically pure B-chlorobis(2-isocaranyl)borane (2-dIcr2BCl) whereas B-bromobis(2-isocaranyl)borane (2-dIcr2BBr) could only be prepared by Matteson’s BBr3/Me3SiH procedure in high chemical yield and purity. The enantiomeric excess achieved with 2-dIcr2BCl (78%), was significantly higher than those realized with the previously explored reagent, dIpc2BCl (41%), especially for meso-cyclohexene oxide. The new reagent, 2-dIcr2BBr also 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 the previously reported reagent, dIpc2BBr (57% and 61%, respectively). |
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