doi:10.1039/d3ob00284eengSierra, SoniaLópez, RosaGómez-Bengoa, EnriqueFalvello, Larry R.Urriolabeitia, Esteban P.Synthesis of 1,2-diaminotruxinic d-cyclobutanes by BF₃-controlled [2 + 2]-photocycloaddition of 5(4<i>H</i>)-oxazolones and stereoselective expansion of d-cyclobutanes to give highly substituted pyrrolidine-2,5-dicarboxylatesART-2023-133629The irradiation of (Z)-4-arylidene-5(4H)-oxazolones 1a–1u with blue light (465 nm) in the presence of the photosensitizer [Ru(bpy)3](BF4)2 (2.5 mol%) and the Lewis acid BF3·OEt2 (2 equiv.) in deoxygenated methanol at room temperature affords the corresponding 1,2-diaminotruxinic cyclobutane bis-amino esters 2a–2u stereoselectively as the δ-isomer. Characterization of cyclobutanes 2 shows that the photocycloaddition takes place by the coupling of two Z-oxazolones in a head-to-head 1,2-anti way. This change in the orientation of the coupling is promoted by O- or/and N-bonding of the BF3 additive. The δ-cyclobutanes 2 undergo a ring expansion when heated in methanol in the presence of NaOMe (1/1 molar ratio) to give densely substituted pyrrolidine-2,5-dicarboxylates 3 in a regio- and stereoselective way. The mechanism of the cyclobutane-to-pyrrolidine ring expansion has been elucidated using DFT methods.2023http://zaguan.unizar.es/record/12631010.1039/d3ob00284ehttp://zaguan.unizar.es/record/126310oai:zaguan.unizar.es:126310info:eu-repo/grantAgreement/ES/DGA/E11-20Rinfo:eu-repo/grantAgreement/ES/DGA/E19-20Rinfo:eu-repo/grantAgreement/ES/MCINN-FEDER/PGC2018-093451-B-I00info:eu-repo/grantAgreement/ES/MICINN AEI PID2019-110008GB-I00info:eu-repo/grantAgreement/ES/MICINN/PID2019-106394GB-I00Organic & Biomolecular Chemistry 21, 15 (2023), 3203-3213by-nchttp://creativecommons.org/licenses/by-nc/3.0/es/info:eu-repo/semantics/openAccess