Arnold, Remo (2024). Sulfone mediated olefination and allylation reactions. (Thesis). Universität Bern, Bern
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Abstract
In the first chapter a stepwise, Zweifel-type olefination reaction between alkenylboronic acid pinacol esters, alkyllithium (or alkyl Grignard) reagents and alkyl halides is reported. The reaction sequence involves a three-component coupling reaction, followed by an alkylation reaction under basic conditions and subsequent β-elimination triggered with a fluoride source. With the developed protocol, a variety of tri-substituted alkenes were prepared in high yield, possibly with a stereogenic centre at the allylic position and with high enantiomeric purity thanks to the robust chemistry of the organoboron species. Separation of the diastereomers of the alkylated intermediates allowed for the preparation of E- or Z-olefins with high levels of stereoselectivity, pointing at a stereospecific (anti)-elimination mechanism. The usefulness of the overall process was illustrated by the introduction of stereodefined olefin moieties on a short selection of natural products. The sequence can also be performed in a one pot protocol. In the second chapter, an olefination reaction is reported, which made it possible to use α-haloalkyl boronic acid esters as starting materials. Under basic conditions α-haloalkyl boronic esters were coupled with sulfones leading to β-borylated sulfones. These intermediates can be isolated or directly treated with TBAF to provide the desired alkenes. In most cases, Z-alkenes are preferentially formed and a particularly high Z stereoselectivity was achieved for arene substituted alkenes. In the last chapter, allylation reactions were investigated with complex α,β-disubstituted bicyclic allylic sulfones. Two different approaches were tested. In the first approach, triethylborane was used as an initiator and chain transfer reagent. In the second approach, photoredox catalysis was tested. Although the isomerisation of the allyl sulfone could not be completely avoided, the photoredox results with the model substrate are promising for future photoredox reactions with the bicyclic allyl sulfones.
| Item Type: | Thesis |
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| Dissertation Type: | Cumulative |
| Date of Defense: | 2 December 2024 |
| Subjects: | 500 Science > 540 Chemistry |
| Institute / Center: | 08 Faculty of Science > Department of Chemistry, Biochemistry and Pharmaceutical Sciences (DCBP) |
| Depositing User: | Hammer Igor |
| Date Deposited: | 25 Aug 2025 16:24 |
| Last Modified: | 25 Aug 2025 16:24 |
| URI: | https://boristheses.unibe.ch/id/eprint/6621 |
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