Unexpected photochemistry and charge-transfer complexes of [CB11H12]2 carborane

Although the [CB11H12]¯carborane does not exhibit an absorption band inUV, its triplet excited state can be generated upon 308 nm laser excitation; also unexpectedly carborane acts as electron donor forming a charge transfer complex with methylviologen that upon illumination gives rise to viologen radical cation.Galletero Pedroche, M.Sales, [email protected]

Cycloreversion of beta-lactams via photoinduced electron transfer

The radical anions of beta-lactams, photogenerated in the presence of DABCO as an electron donor, undergo cycloreversion via N-C4 bond cleavage, back electron transfer and final C2-C3 bond cleavage, leading to olefins. The involved intermediates are 1,4-radical anions and 1,4-biradicals. The experimental observations are consistent with the results of DFT calculations.Financial support from the Spanish Government (CTQ2013-47872-C2-1-P, SEV-2012-0267, BES-2011-043706, JCI-2010-06204), from CSIC (JAEDOC 101-2011 co-funded by FSE) and from the Generalitat Valenciana (PROMETEOII/2013/005) is gratefully acknowledged. J. A. S. acknowledges the computational facilities provided by the Theoretical Computational Chemistry Group of Prof. L. R. Domingo at the Universitat de Valencia.Pérez Ruiz, R.; Sáez Cases, JA.; Jiménez Molero, MC.; Miranda Alonso, MÁ. (2014). Cycloreversion of beta-lactams via photoinduced electron transfer. 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Design of β-Lactams with Mechanism Based Nonantibacterial Activities. Current Medicinal Chemistry, 10(17), 1741-1757. doi:10.2174/0929867033457089Chemistry and Biology of β-Lactam Antibiotics , ed. R. B. Morin and M. Gorman , Academic Press , New York , 1982 , pp. 1–3Nathwani, D., & Wood, M. J. (1993). Penicillins. Drugs, 45(6), 866-894. doi:10.2165/00003495-199345060-00002Fischer, M. (1968). Photochemische Reaktionen, IV. Photochemische Fragmentierungen von β-Lactamen. Chemische Berichte, 101(8), 2669-2678. doi:10.1002/cber.19681010809Fabre, H., Ibork, H., & Lerner, D. A. (1994). Photoisomerization Kinetics of Cefuroxime Axetil and Related Compounds. Journal of Pharmaceutical Sciences, 83(4), 553-558. doi:10.1002/jps.2600830422Rossi, E., Abbiati, G., & Pini, E. (1999). Substituted 1-benzyl-4-(benzylidenimino)-4-phenylazetidin-2-ones: Synthesis, thermal and photochemical reactions. 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Journal of Heterocyclic Chemistry, 34(5), 1559-1565. doi:10.1002/jhet.5570340529Andreu, I., Delgado, J., Espinós, A., Pérez-Ruiz, R., Jiménez, M. C., & Miranda, M. A. (2008). Cycloreversion of Azetidines via Oxidative Electron Transfer. Steady-State and Time-Resolved Studies. Organic Letters, 10(22), 5207-5210. doi:10.1021/ol802181uBelger, C., Neisius, N. M., & Plietker, B. (2010). A Selective Ru-Catalyzed Semireduction of Alkynes to Z Olefins under Transfer-Hydrogenation Conditions. Chemistry - A European Journal, 16(40), 12214-12220. doi:10.1002/chem.201001143Eicher, T., Böhm, S., Ehrhardt, H., Harth, R., & Lerch, D. (1981). Zur Reaktion von Diphenylcyclopropenon, seinen funktionellen Derivaten und Imoniumsalzen mit Aminen. Liebigs Annalen der Chemie, 1981(5), 765-788. doi:10.1002/jlac.198119810503Mazzocchi, P. H., & Thomas, J. J. (1972). Photolysis of N-methyl-2-pyrrolidone. Journal of the American Chemical Society, 94(23), 8281-8282. doi:10.1021/ja00778a085Platz, M. 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Metal-Free Photocatalytic Reductive Dehalogenation Using Visible-Light: A Time-Resolved Mechanistic Study

This is the peer reviewed version of the following article: Martínez-Haya, Rebeca, Miranda Alonso, Miguel Ángel, Marín García, Mª Luisa. (2017). Metal-Free Photocatalytic Reductive Dehalogenation Using Visible-Light: A Time-Resolved Mechanistic Study.European Journal of Organic Chemistry, 15, 2164-2169, which has been published in final form at http://doi.org/10.1002/ejoc.201601494. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving[EN] The reductive dehalogenation of organic bromides has been achieved in the presence of riboflavin (RF) as photocatalyst under visible-light irradiation. Specifically, benzyl bromide (2) and -bromoacetophenone (3) were quantitatively converted into toluene and acetophenone, respectively, by using amines as electron donors and iPrOH as hydrogen donor, whereas bromobenzene (1) did not react. The thermodynamics of the reduction of the radical anion of RF were evaluated by using the redox potentials of the species involved: The reaction was found to be thermodynamically exergonic for 2 and 3, but not expected to occur for bromobenzene (1). The viability of the different competing processes on the timescales of the corresponding singlet and triplet RF excited states ((RF)-R-1* and (RF)-R-3*) was analyzed by time-resolved techniques. The quenching of (RF)-R-1* by amines was very efficient, and comparison of the transient absorption spectra recorded in the absence and presence of amines additionally confirmed the efficient redox process between (RF)-R-1* and the amines. Moreover, RF- was quenched by bromides 2 and 3, but not by 1. Thus, a deeper understanding of the overall mechanism of the photocatalytic reductive reaction has been achieved, and the key role of the radical anion of the photocatalyst has been demonstrated.R. M.-H. acknowledges generous support from the Spanish Government (grant SEV-2012-0267). We also thank for support from the Ministerio de Economia y Competitividat (Project CTQ2012-38754-C03-03), the Generalitat Valenciana (Prometeo Program) and the VLC/Campus.Martínez-Haya, R.; Miranda Alonso, MÁ.; Marín García, ML. (2017). Metal-Free Photocatalytic Reductive Dehalogenation Using Visible-Light: A Time-Resolved Mechanistic Study. European Journal of Organic Chemistry. (15):2164-2169. https://doi.org/10.1002/ejoc.201601494S216421691

Recent visible light and metal free strategies in [2+2] and [4+2] photocycloadditions

When aiming to synthesize molecules with elevated molecular complexity starting from relatively simple starting materials, photochemical transformations represent an open avenue to circumvent analogous multistep procedures. Specifically, light-mediated cycloadditions remain as powerful tools to generate new bonds begotten from non-very intuitive disconnections, that alternative thermal protocols would not offer. In response to the current trend in both industrial and academic research pointing towards green and sustainable processes, several strategies that meet these requirements are currently available in the literature. This Minireview summarizes [2+2] and [4+2] photocycloadditions that do not require the use of metal photocatalysts by means of alternative strategies. It is segmented according to the cycloaddition type in order to give the reader a friendly approach and we primarily focus on the most recent developments in the field carried out using visible light, a general overview of the mechanism in each case is offered as wellFinancial support was provided by the European Research Council (ERC-CoG, Contract Number: 647550), the Spanish Government (RTI2018-095038-B-I00), the ‘Comunidad de Madrid’ and European Structural Funds (S2018/NMT-4367). R. I. R thanks Fundación Carolina for a graduate fellowshi

The photochemistry of N-p-toluenesulfonyl peptides: the peptide bond as an electron donor

The scope of photobiological processes that involve absorbers within a protein matrix may be limited by the vulnerability of the peptide group to attack by highly reactive redox centers consequent upon electronic excitation. We have explored the nature of this vulnerability by undertaking comprehensive product analyses of aqueous photolysates of 12 N-p-toluene-sulfonyl peptides with systematically selected structures. The results indicate that degradation includes a major pathway that is initiated by intramolecular electron transfer in which the peptide bond serves as electron donor, and the data support the likelihood of a relay process in dipeptide derivatives

Probing the interplay between factors determining reaction rates on silica gel using termolecular systems

This article was published in the journal, Photochemical and Photobiological Sciences [© Royal Society of Chemistry and Owner Societies]. The definitive version is available at: http://dx.doi.org/10.1039/c2pp25171jIn this study we have compared energy and electron transfer reactions in termolecular systems using a nanosecond diffuse reflectance laser flash photolysis technique. We have previously investigated these processes on silica gel surfaces for bimolecular systems and electron transfer in termolecular systems. The latter systems involved electron transfer between three arene molecules with azulene acting as a molecular shuttle. In this study we present an alternative electron transfer system using trans β-carotene as an electron donor in order to effectively immobilise all species except the shuttle, providing the first unambiguous evidence for radical ion mobility. In the energy transfer system we use naphthalene, a structural isomer of azulene, as the shuttle, facilitating energy transfer from a selectively excited benzophenone sensitiser to 9-cyanoanthracene. Bimolecular rate constants for all of these processes have been measured and new insights into the factors determining the rates of these reactions on silica gel have been obtained