Stereoselective, Ruthenium-Photocatalyzed Synthesis of 1,2-Diaminotruxinic Bis-amino Acids from 4-Arylidene-5(4H)-oxazolones

Autor: Sonia Sierra, M. Victoria Gomez, Ana I. Jiménez, Alexandra Pop, Cristian Silvestru, Maria Luisa Marín, Francisco Boscá, Germán Sastre, Enrique Gómez-Bengoa, Esteban P. Urriolabeitia
Přispěvatelé: Ministerio de Ciencia, Innovación y Universidades (España), Agencia Estatal de Investigación (España), European Commission, Gobierno de Aragón, Consejo Superior de Investigaciones Científicas (España), Universidad Politécnica de Valencia, Universidad del País Vasco, Ministry of Education and Scientific Research (Romania)
Jazyk: angličtina
Rok vydání: 2022
Předmět:
Zdroj: Digital.CSIC. Repositorio Institucional del CSIC
instname
Addi. Archivo Digital para la Docencia y la Investigación
Popis: The irradiation of (Z)-2-phenyl-4-aryliden-5(4H)-oxazolones 1 in deoxygenated CH2Cl2 at 25 °C with blue light (465 nm) in the presence of [Ru(bpy)3](BF4)2 (5% mole ratio) as a triplet photocatalyst promotes the [2+2] photocycloaddition of the C═C bonds of the 4-arylidene moiety, thus allowing the completely regio- and stereoselective formation of cyclobutane-bis(oxazolone)s 2 as single stereoisomers. Cyclobutanes 2 have been unambiguously characterized as the μ-isomers and contain two E-oxazolones coupled in an anti-head-to-head form. The use of continuous-flow techniques in microreactors allows the synthesis of cyclobutanes 2 in only 60 min, compared with the 24–48 h required in batch mode. Ring opening of the oxazolone heterocycle in 2 with a base affords the corresponding 1,2-diaminotruxinic bis-amino esters 3, which are also obtained selectively as μ-isomers. The ruthenium complex behaves as a triplet photocatalyst, generating the reactive excited state of the oxazolone via an energy-transfer process. This reactive excited state has been characterized as a triplet diradical 3(E/Z)-1* by laser flash photolysis (transient absorption spectroscopy). This technique also shows that this excited state is the same when starting from either (Z)- or (E)-oxazolones. Density functional theory calculations show that the first step of the [2+2] cycloaddition between 3(E/Z)-1* and (Z)-1 is formation of the C(H)–C(H) bond and that (Z) to (E) isomerization takes place at the 1,4-diradical thus formed.
The authors thank the Spanish Government for funding: Project PID2020-119636GB-I00, funded by MCIN/AEI/10.13039/501100011033; Projects PID2019-106394GB-I00/AEI/10.13039/501100011033, PID2019-110441RB-C33/AEI/10.13039/501100011033, and PID2019-110008GB-I00/AEI/10.13039/501100011033, funded by MCIN/AEI/10.13039/501100011033; Projects RTI2018-101784-B-I00, RTI2018-101033-B-I00, and CTQ2017-84825-R, funded by MCIN/AEI/10.13039/501100011033 and FEDER Una manera de hacer Europa. E.P.U., A.I.J., and S.S. thank Gobierno de Aragón-FSE (Spain, research group Aminoácidos y Péptidos E19_20R) for funding. G.S. thanks CTI-CSIC and ASIC-UPV for the use of computational facilities. E.G.-B. thanks SGIker (UPV/EHU) for providing human and computational resources. A.P. is grateful for the financial support of the Romanian Ministry of Education and Research through Grant PN-III-P1-1.1-MC-2018-2580. S.S. thanks Gobierno de Aragón-FSE for a Ph.D. fellowship.
Databáze: OpenAIRE
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