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SM ISO690:2012 CAZACU, Cătălina, GÎRBU, Vladilena, KULCIŢKI, Veaceslav. Unprecedented atom transfer radical addition – hidrogen atom transfer sequence under visible light photoredox catalysis . In: Ecological and environmental chemistry : - 2022, Ed. 7, 3-4 martie 2022, Chișinău. Chisinau: Centrul Editorial-Poligrafic al USM, 2022, Ediția 7, Vol.1, pp. 67-68. ISBN 978-9975-159-07-4.. 10.19261/eec.2022.v1 |
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Ecological and environmental chemistry Ediția 7, Vol.1, 2022 |
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Conferința "Ecological and environmental chemistry 2022" 7, Chișinău, Moldova, 3-4 martie 2022 | |
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CZU: 54:[574+577] | |
Pag. 67-68 | |
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Rezumat | |
Green chemistry principles announced on the eve of the current century have set a clear strategic line for the global community of chemists. One of the essential elements of the Anastas‘ and Warner‘s paradigm represents the need to implement catalytic processes, which are more efficient, provide a better atom economy and diminish the negative impact on the environment that is characteristic for most stoichiometric transformations. In this line, the visible light photoredox catalysis has emerged in the last decade as an efficient synthetic tool, in particular for free radical mediated processes. Of those, atom transfer radical addition (ATRA) is a simple transformation that allows to achieve a simultaneous alkylation and heteroatom addition to an alkene. The aim of the current work was to investigate ATRA to manoyloxides 1, 2 under the conditions of visible light photoredox catalysis. The investigated substrates possess the carbon skeleton of forskolin – a well-known natural diterpenoid that increases the level of adenosine monophosphate in living cells. In our view, molecular editing of manoyloxides by functionalization with heteroatoms is the most convenient way to generate new derivatives with biological activity. This study established that ATRA of ethyliodoacetate to epimanoyloxide 2 under photochemical conditions takes place in a normal pathway, resulting in epimeric iodides 3, isolated with a very good yield. On the other hand, the manoyloxide 1 provided under similar reaction conditions a mixture of the expected 1,2-addition products 4, along with an unusual unsaturated compound 5. Formation of this product was interpreted on the basis of a hypothetical ATRA, followed by a hydrogen atom transfer (HAT) from the tertiary position of the neighbouring cycle which ends with an elimination and formation of olefin 5. The initiation of the free radical chain takes place on the single electron reduction of the R-I bond which is effected by the iridium catalyst [IrL6]X excited on blue LED irradiation and following reduction by a sacrificial reductant. Reaction conditions have been optimized for a better yield of olefin 5. Possible mechanistic pathways of the unprecedented ATRAHAT sequence will be under discussion. The obtained results represent the first example of triggering two simultaneous free radical processes under conditions of visible light photoredox catalysis. The unsaturated ester 5 represents a convenient substrate for the synthesis of manoyloxide functionalized derivatives, similar to forskolin. |
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