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Axially chiral enamides : substituent effects, rotation barriers, and implications for their cyclization reactions
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Clark, Andrew J., Curran, Dennis P., Fox, David J., Ghelfi, Franco, Guy, Collette S., Hay, Benjamin, James, Natalie, Phillips, Jessica M., Roncaglia, Fabrizio, Sellars, Philip B., Wilson, Paul and Zhang, Hanmo (2016) Axially chiral enamides : substituent effects, rotation barriers, and implications for their cyclization reactions. The Journal of Organic Chemistry, 81 (13). pp. 5547-5565. doi:10.1021/acs.joc.6b00889 ISSN 0022-3263.
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Official URL: http://dx.doi.org/10.1021/acs.joc.6b00889
Abstract
The barrier to rotation around the N-alkenyl bond of 38 N-alkenyl-N-alkylacetamide derivatives was measured (ΔG⧧ rotation varied between <8.0 and 31.0 kcal mol–1). The most important factor in controlling the rate of rotation was the level of alkene substitution, followed by the size of the nitrogen substituent and, finally, the size of the acyl substituent. Tertiary enamides with four alkenyl substituents exhibited half-lives for rotation between 5.5 days and 99 years at 298 K, sufficient to isolate enantiomerically enriched atropisomers. The radical cyclizations of a subset of N-alkenyl-N-benzyl-α-haloacetamides exhibiting relatively high barriers to rotation round the N-alkenyl bond (ΔG⧧ rotation >20 kcal mol–1) were studied to determine the regiochemistry of cyclization. Those with high barriers (>27 kcal mol–1) did not lead to cyclization, but those with lower values produced highly functionalized γ-lactams via a 5-endo-trig radical–polar crossover process that was terminated by reduction, an unusual cyclopropanation sequence, or trapping with H2O, depending upon the reaction conditions. Because elevated temperatures were necessary for cyclization, this precluded study of the asymmetric transfer in the reaction of individual atropisomers. However, enantiomerically enriched atropsiomeric enamides should be regarded as potential asymmetric building blocks for reactions that can be accomplished at room temperature.
Item Type: | Journal Article | ||||||||
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Subjects: | Q Science > QD Chemistry | ||||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Chemistry | ||||||||
Library of Congress Subject Headings (LCSH): | Anilides | ||||||||
Journal or Publication Title: | The Journal of Organic Chemistry | ||||||||
Publisher: | American Chemical Society | ||||||||
ISSN: | 0022-3263 | ||||||||
Official Date: | 6 June 2016 | ||||||||
Dates: |
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Volume: | 81 | ||||||||
Number: | 13 | ||||||||
Page Range: | pp. 5547-5565 | ||||||||
DOI: | 10.1021/acs.joc.6b00889 | ||||||||
Status: | Peer Reviewed | ||||||||
Publication Status: | Published | ||||||||
Access rights to Published version: | Open Access (Creative Commons) | ||||||||
Date of first compliant deposit: | 23 August 2016 | ||||||||
Date of first compliant Open Access: | 24 August 2016 | ||||||||
Funder: | National Science Foundation (U.S.) (NSF), Engineering and Physical Sciences Research Council (EPSRC), Advantage West Midlands (AWM), European Regional Development Fund (ERDF) | ||||||||
Grant number: | CHE 1265652 (NSF), EP/P502810/1, JMP EP/K503204/1, EP/L505110/1 (EPSRC) |
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