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Open AccessFeature PaperReview

Riley Oxidation of Heterocyclic Intermediates on Paths to Hydroporphyrins—A Review

Department of Chemistry, North Carolina State University, Raleigh, NC 27695-8204, USA
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Academic Editors: M. Graça P. M. S. Neves, M. Amparo F. Faustino and Nuno M. M. Moura
Molecules 2020, 25(8), 1858; https://doi.org/10.3390/molecules25081858
Received: 22 March 2020 / Revised: 14 April 2020 / Accepted: 16 April 2020 / Published: 17 April 2020
Riley oxidation of advanced heterocyclic intermediates (dihydrodipyrrins and tetrahydrodipyrrins) is pivotal in routes to synthetic hydroporphyrins including chlorins, bacteriochlorins, and model (bacterio)chlorophylls. Such macrocycles find wide use in studies ranging from energy sciences to photomedicine. The key transformation (–CH3 → –CHO) is often inefficient, however, thereby crimping the synthesis of hydroporphyrins. The first part of the review summarizes 12 representative conditions for Riley oxidation across diverse (non-hydrodipyrrin) substrates. An interlude summarizes the proposed mechanisms and provides context concerning the nature of various selenium species other than SeO2. The second part of the review comprehensively reports the conditions and results upon Riley oxidation of 45 1-methyltetrahydrodipyrrins and 1-methyldihydrodipyrrins. A comparison of the results provides insights into the tolerable structural features for Riley oxidation of hydrodipyrrins. In general, Riley oxidation of dihydrodipyrrins has a broad scope toward substituents, but proceeds in only modest yield. Too few tetrahydrodipyrrins have been examined to draw conclusions concerning scope. New reaction conditions or approaches will be required to achieve high yields for this critical transformation in the synthesis of hydroporphyrins. View Full-Text
Keywords: aldehyde; bacteriochlorin; chlorin; dihydrodipyrrin; dipyrromethane; selenium dioxide; selenium reagent; tetrahydrodipyrrin aldehyde; bacteriochlorin; chlorin; dihydrodipyrrin; dipyrromethane; selenium dioxide; selenium reagent; tetrahydrodipyrrin
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MDPI and ACS Style

Wang, P.; Lindsey, J.S. Riley Oxidation of Heterocyclic Intermediates on Paths to Hydroporphyrins—A Review. Molecules 2020, 25, 1858.

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