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Chiral Brønsted Acid Catalysed Synthesis of Tetrahydropyrans and Tetrahydrofurans.

nannapaneni, Sai pavan chakravarthy (2018) Chiral Brønsted Acid Catalysed Synthesis of Tetrahydropyrans and Tetrahydrofurans. MSc by research thesis, University of York.

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Abstract

Tetrahydropyrans are important structural motifs, present in various natural products with significant biological and pharmacological properties. During previous efforts into the synthesis of the C20-C32 core of phorboxazoles, a stereodivergent oxa-Michael reaction was encountered and investigated computationally. TFA and CSA have been shown to act as proton shuttles in the cyclisation. The TFA mediated cyclisation doesn’t depend on inherent structural features and the use of chiral phosphoric acids, with acidities in the range of TFA and CSA, instead of TFA should make the reaction enantiodivergent. This means that with chiral phosphoric acid and it’s (ent) form giving the enantiomers from the same cyclisation precursor. This was shown to be feasible by computational analysis, with the mesityl tetrahydropyran cyclisation precursor more enantioselective than the tolyl precursor. To this end, the chiral brønsted acid catalysed cyclisation of the mesityl and tolyl tetrahydropyran and tetrahydrofuran precursors have been carried out under various solvent, catalyst and temperature conditions. For the tetrahydrofuran precursors, the tolyl substrate shows greater enantioselectivity, with the highest ee being 60% using (R)-TIPSY. For the tetrahydropyran precursors, the mesityl shows greater enantioselectivity, with the highest ee being 69% using (R)-TRIP. Finally, a kinetic resolution of the mesityl tetrahydropyran precursor has been carried out using optimised conditions, resulting in the enantioenrichment of the product at 95%ee and the starting material at 96%ee.

Item Type: Thesis (MSc by research)
Academic Units: The University of York > Chemistry (York)
Depositing User: Mr Sai pavan chakravarthy nannapaneni
Date Deposited: 31 Jul 2018 13:31
Last Modified: 31 Jul 2018 13:31
URI: http://etheses.whiterose.ac.uk/id/eprint/20986

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