Visible light‐induced diastereoselectiveE/Z‐photoisomerization equilibrium of the C=C benzofuran‐3‐one‐hydantoin dyad. (20th July 2014)

• Record Type: Journal Article
• Authors: Talhi, Oualid; Lopes, Guido R.; Santos, Sérgio M.; Pinto, Diana C. G. A.; Silva, Artur M. S.
• Is Part Of: Journal of physical organic chemistry. Volume 27:Number 9(2014:Sep.)
• Page Start: 756
• Page End: 763
• Publication Date: 2014-07-20
• Subjects: Chemistry, Physical organic -- Periodicals; 547.1
• DOI: 10.1002/poc.3335
• Languages: English
• ISSNs: 0894-3230

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>The <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">diastereoselective</named-content> photodependent <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">isomerization</named-content> equilibrium of <italic>E</italic>/<italic>Z</italic>‐1, 3‐ditolyl‐5‐[3‐oxobenzofuran‐2(3<italic>H</italic>)‐ylidene]imidazolidine‐2, 4‐dione (<bold>5</bold>) is reported. Both diastereomers <bold>E-5</bold> and <bold>Z-5</bold> are stereochemically stable in solid state but show significant photosensibility in solutions of halogenated solvent. The photoisomerization equilibrium of <italic>E</italic>/<italic>Z</italic>‐<bold>5</bold> is therefore deduced from the <sup>1</sup>H NMR profile after visible‐light irradiation of both <bold>E-5</bold> and <bold>Z-5</bold> samples. The results of the kinetic study, monitored by UV‐HPLC, reveal that the <italic>E/Z</italic> equilibrium is <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">diastereoselective</named-content> and photodependent, being the transformation <italic>E</italic> ➔ <italic>Z</italic> proceeding faster than that of <italic>Z</italic> ➔ <italic>E</italic>, and the <italic>E</italic>/<italic>Z</italic> ratio at the equilibrium depends on the used solvent, light source, and temperature. Both diastereomers are visible‐light photosensitive tending to coexist together in equilibrium solutions at a determined ratio, which is always in favor of the <italic>Z</italic>‐product assuming a minimum thermodynamic energy and an increased entropy of the system. Time‐dependent density functional theory calculations suggest that the photoisomerization mechanism proceeds via a conical intersection involving the first‐excited state: Upon irradiation, the <bold>E-5</bold> isomer is excited to the S1 potential energy surface, where it relaxes through rotation of the C=C bond and reaches a conical intersection with the ground‐state potential energy surface, thus yielding the <bold>Z-5</bold> isomer. Copyright © 2014 John Wiley & Sons, Ltd.</p> </abstract>