This title appears in the Scientific Report :
2015
Investigation of Differently Substituted Allylboronic Esters in Allylation Reactions
Investigation of Differently Substituted Allylboronic Esters in Allylation Reactions
One of the most attractive reactions in the field of asymmetric synthesis is the aldehydeallylation by using allylic boronates as reagents. Due to their efficiency, non-toxicity as well as their high predictability concerning the stereochemical outcome, they have been the focus of the research of ma...
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Personal Name(s): | Vahabi, Roza (Corresponding author) |
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Contributing Institute: |
Institut für Bioorganische Chemie (HHUD); IBOC |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2015
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Physical Description: |
288 |
Dissertation Note: |
Dissertation, Heinrich-Heine-Universität Düsseldorf, 2015 |
ISBN: |
978-3-95806-102-6 |
Document Type: |
Book Dissertation / PhD Thesis |
Research Program: |
Biotechnology |
Series Title: |
Bioorganische Chemie an der Heinrich-Heine-Universität im Forschungszentrum Jülich
20 |
Subject (ZB): | |
Publikationsportal JuSER |
One of the most attractive reactions in the field of asymmetric synthesis is the aldehydeallylation by using allylic boronates as reagents. Due to their efficiency, non-toxicity as well as their high predictability concerning the stereochemical outcome, they have been the focus of the research of many groups, including Hoffmann et al.,[2,3] Roush et al.,[4] Corey et al.,[5] and Brown et al.[6] The reaction was explained to proceed via a closed six-membered chair-like transition state,[7-9] resulting in chiral homoallylic alcohols, which are valuable building blocks for the synthesis of many natural products. Moreover, it has been shown that reagents presenting a stereogenic centre at the $\alpha$-position with respect to the boronic ester provide increased chirality transfer. The resulting absolute configuration has been demonstrated to be dependenton two principle factors: the steric bulk of the boronic esters protecting group and the presence of a substituent exercising an electronic effect in the molecule.[10] In the past years Pietruszkaet al. have developed a tartrate derived chiral auxiliary[11] diol 1, which was used as a protective group for boronic acids, and allowed the formation of stable $\alpha$-substituted alkenyl boronic esters. Their addition to aldehydes led to the formation of enantiomerically pure Z-homoallylicalcohols, as the reagents possessed an important factor improving the Z selectivity: a sterically demanding diol covering the boronic acid.[12] Differently substituted diastereomerically pure allylboronic esters were synthesized in this work, and their addition to aldehydes was investigated in detail. The resulting enantio-enriched homoallylic alcohols were then applied in the attempt towards the synthesis of a natural product. Highly substituted allylboronic esters 2 and 4 were synthesized by two different methods (Scheme 1). Starting from the protected alkyne 3c, a one-pot hydroboration, oxidation, and transesterification sequence, followed by deprotection of the silyl group furnished 2 in a good yield. On the other hand, the haloboration reaction of protected propargyl alcohol 5 and subsequent esterification with diol 1 proceeded via an intermediate haloalkenyl boronate. Next, a Negishi coupling reaction took place in the presence of palladium catalyst and dimethyl zinc. Subsequent deprotection of the alcohol group yielded 4 in 29% over 4 steps |