Microenvironmental Control of Enantiodifferentiating Photocyclization of 5-Hydroxy-1,1-diphenylpentene through Selective Solvation
Microenvironmental Control of Enantiodifferentiating Photocyclization of 5-Hydroxy-1,1-diphenylpentene through Selective Solvation
复制标题
通过选择性溶剂化控制 5-羟基-1,1-二苯基戊烯对映分化光环化的微环境
作者：
Y. Nishiyama;T. Wada;K. Kakiuchi;Y. Inoue
为了阐明5-羟基-1，1-二苯基戊烯（1）光敏环化的机理，其甲基醚（4）被合成为非反应性的“虚拟”底物，并用作敏化剂荧光的猝灭剂，以揭示当反应性底物1用作猝灭剂/反应物时不能检测到的激基复合物中间体的干预。通过1，4-萘二甲酸酯的手性糖酯（3）敏化的（二苯基甲基）四氢呋喃（2），在25 ℃下在甲基环己烷（MCH）中获得的手性产物2的对映体过量（ee）在样品溶液用MCH稀释10倍后从20%显著提高至35%，其中降低的溶剂极性，阻碍插入的自由基离子激基复合物的解离，可能是原因。进一步尝试微环境控制光手性反应并通过极性共溶剂对非极性溶剂中的非对映体激基复合物对的选择性溶剂化来增强产物的ee没有成功，这可能是由于糖的激基复合物周围固有的高局部极性-附加有醇底物1.Chirality 24：400-405，2012。© 2012 Wiley Periodicals，Inc.
For mechanistic elucidation of the photosensitized cyclization of 5‐hydroxy‐1,1‐diphenylpentene (1), its methyl ether (4) was synthesized as an unreactive “dummy” substrate and used as a quencher of the sensitizer fluorescence to reveal the intervention of an exciplex intermediate that was unable to detect when reactive substrate1was used as a quencher/reactant In the enantiodifferentiating photocyclization of1to 2‐(diphenylmethyl)tetrahydrofuran (2) sensitized by a chiral saccharide ester of 1,4‐naphthalenedicarboxylate (3), the enantiomeric excess (ee) of chiral product2obtained in methylcyclohexane (MCH) at 25 °C was significantly enhanced from 20% to 35% upon 10‐fold dilution of the sample solution by MCH, for which the reduced solvent polarity, discouraging dissociation of the intervening radical ionic exciplex, is likely to be responsible. Further attempts to microenvironmentally control the photochirogenic reaction and enhance the product's ee through selective solvation of polar cosolvent to the diastereomeric exciplex pair in nonpolar solvent were not successful probably due to the inherently high local polarity around the exciplex of saccharide‐appended3with alcoholic substrate1.Chirality 24:400–405, 2012. © 2012 Wiley Periodicals, Inc.