Evaluating the thermal vinylcyclopropane rearrangement (VCPR) as a practical method for the synthesis of difluorinated cyclopentenes : experimental and computational studies of rearrangement stereospecificity
Orr, David and Percy, Jonathan and Tuttle, Tell and Kennedy, Alan and Harrison, Zoe Alicia (2014) Evaluating the thermal vinylcyclopropane rearrangement (VCPR) as a practical method for the synthesis of difluorinated cyclopentenes : experimental and computational studies of rearrangement stereospecificity. Chemistry - A European Journal, 20 (44). 14305–14316. ISSN 0947-6539
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Abstract
Vinyl cyclopropane rearrangement (VCPR) has been utilised to synthesise a difluorinated cyclopentene stereospecifically and under mild thermal conditions. Difluorocyclopropanation chemistry afforded ethyl 3-(1'(2'2'-difluoro-3'-phenyl)cyclopropyl) propenoate as all four stereoisomers (18a, 18b, 22a, 22b) (all racemic). Trans-E isomer (18a), prepared in 70% yield over three steps, underwent near quantitative VCPR to difluorocyclopentene 23 (99%). Rearrangements were followed by 19F NMR (100-180 °C). While cis/trans cyclopropane stereoisomerisation was facile, favouring trans-isomers by a modest margin, no E/Z alkene isomerisation was observed even at higher temperatures. Neither cis nor trans Z-alkenoates underwent VCPR, even up to much higher temperatures (180 oC). Cis-cyclopropanes underwent [3,3]-rearrangement to afford benzocycloheptadiene species. The reaction stereospecificity was explored using electronic structure calculations and UB3LYP/6-31G* methodology allowed the energy barriers for cyclopropane stereoisomerisation, diastereoisomeric VCPR and [3,3]-rearrangement to be ranked in agreement with experiment.
Creators(s): |
Orr, David, Percy, Jonathan ![]() ![]() | Item type: | Article |
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ID code: | 50003 |
Keywords: | rearrangement, difluorocyclopentene, activation parameters, density functional calculations , stereoselectivity, Chemistry, Chemistry(all) |
Subjects: | Science > Chemistry |
Department: | Faculty of Science > Pure and Applied Chemistry Technology and Innovation Centre > Bionanotechnology |
Depositing user: | Pure Administrator |
Date deposited: | 23 Oct 2014 15:24 |
Last modified: | 23 Feb 2021 10:34 |
Related URLs: | |
URI: | https://strathprints.strath.ac.uk/id/eprint/50003 |
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