DFT studies of unique stereoelectronic effects of substituents on divergent reaction pathways of methylenecyclobutanone radical cations

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• 作者：Yusuke Kano^a ; Futoshi Tanaka^b ; Eisuke Ohta^a ; ^c ; Kazuhiko Mizuno^a ; ^c ; Hiroshi Ikeda^a ; ^c ; ^{ikeda@chem.osakafu-u.ac.jp}
• 刊名：Tetrahedron
• 出版年：2012
• 期刊代码：107_00404020
• 类别：ch
• 出版时间：8 July, 2012
• 卷：68
• 期：27-28
• 页码：5564-5571
• 文件大小：1170 K

摘要

The results of DFT investigation suggest that C2-C3 bond cleavage of the 2,2-dianisyl-3,3-dimethyl-4-methylenecyclobutanone radical cation (2b⁺) is preferred from both a thermodynamic and a kinetic perspective while C1-C2 bond cleavage is both thermodynamically and kinetically favored in the parent聽methylenecyclobutanone radical cation (MCB⁺) and the 2,2-diphenyl- and 2,2-dianisyl-4-isopropylidenecyclobutanone radical cations (1a-b⁺). The DFT calculations also suggest that a bonding character exists in C2-C3 bond of the 2,2-diphenyl-3,3-dimethyl-4-methylenecyclobutanone radical cation (2a⁺) but not in that of 2b⁺. Consequently, the unique reactivity of 2b⁺ can be accounted for by the existence of the steric hindrance between methyl and anisyl substituents, which favors C2-C3 bond cleavage, and the absence of C2-C3 bonding character. Those results support that the previous experimental results of photoinduced electron-transfer reactions of 1 and 2. The combined factors comprise stereoelectronic substituent effects that lead to a drastic change in the reaction pathways followed by 2b⁺ relative to that of other methylenecyclobutanone-type radical cations.