Concerning the Stereochemical Course and Mechanism of the Photochemical 1,3-Acetyl Shift in a ?,?-Unsaturated Ketone. Preliminary Communication
作者:David E. Sadler、Knut Hildenbrand、Kurt Schaffner
DOI:10.1002/hlca.19820650714
日期:1982.11.3
Enantiomerically enriched samples of 1,2-dimethyl-3-(2H3)methyl-2-cyclopentenyl (1) and 1-(2H3)methyl-2,3-dimethyl-2-cyclopentenyl methyl ketones (2) have been irradiated at 313 nm in methanol in the temperature range +50 to −45°. The 1,3-acetyl shift, which interconverts the two isomeric ketones, occurs with a small change in the enantiomeric composition and independently of temperature in the range
对映体富集的1,2-二甲基-3-(2 H 3)甲基-2-环戊烯基(1)和1-(2 H 3)甲基-2,3-二甲基-2-环戊烯基甲基酮(2)的样品具有在+50至-45°的温度范围内,在313 nm的甲醇中进行辐照。相互转化两个异构酮的1,3-乙酰基转移发生时,对映体组成的变化很小,并且与所研究范围内的温度无关。该变化对应于外消旋反应的大约20%的上限。建议从S 1(n,π*)和T 2(n,π*)的激发态在整个温度范围内均以S 1的立体定向反应为主(单峰自由基对的快速初次geminate重组,可能通过协调的1,3位移做出贡献),但反应的比例却来自T 2随着温度的降低而增加。外消旋作用是由于单线态和三线态自由基对的二次重叠重组和自由基的随机重组所致。提出了粘度效应来解释外消旋作用对温度的独立性。