Sierra Sonia, López Rosa, Gómez-Bengoa Enrique, Falvello Larry R, Urriolabeitia Esteban P
Instituto de Síntesis Química y Catálisis Homogénea, ISQCH (CSIC - Universidad de Zaragoza), 50009 Zaragoza, Spain.
Departamento de Química Orgánica I, Universidad del País Vasco, UPV-EHU, CP-20080 Donostia-San Sebastián, Spain.
Org Biomol Chem. 2023 Apr 12;21(15):3203-3213. doi: 10.1039/d3ob00284e.
The irradiation of ()-4-arylidene-5(4)-oxazolones 1a-1u with blue light (465 nm) in the presence of the photosensitizer Ru(bpy) (2.5 mol%) and the Lewis acid BF·OEt (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 -oxazolones in a head-to-head 1,2- way. This change in the orientation of the coupling is promoted by O- or/and N-bonding of the BF 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.
在室温下，将（）-4-亚芳基-5（4）-恶唑酮1a - 1u在光敏剂Ru（bpy）（2.5摩尔％）和路易斯酸BF·OEt（2当量）存在下，于脱氧甲醇中用蓝光（465 nm）照射，可立体选择性地得到相应的1,2-二氨基曲昔环丁烷双氨基酯2a - 2u作为δ-异构体。环丁烷2的表征表明，光环加成反应是通过两个-恶唑酮以头对头的1,2方式偶联发生的。BF添加剂的O-或/和N键促进了偶联方向的这种变化。当δ-环丁烷2在NaOMe（1/1摩尔比）存在下于甲醇中加热时，会发生扩环反应，以区域和立体选择性的方式得到高度取代的吡咯烷-2,5-二羧酸酯3。已使用密度泛函理论（DFT）方法阐明了环丁烷到吡咯烷的扩环机理。
