Synthesis of 1,2-diaminotruxinic δ-cyclobutanes by BF3-controlled [2 + 2]-photocycloaddition of 5(4H)-oxazolones and stereoselective expansion of δ-cyclobutanes to give highly substituted pyrrolidine-2,5-dicarboxylates
The 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-amin...
| Autores: | , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2023 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/344556 |
| Acceso en línea: | http://hdl.handle.net/10261/344556 |
| Access Level: | acceso abierto |
| Sumario: | The 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. |
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