A photo-Favorskii ring contraction reaction: the effect of ring size.
A photo-Favorskii ring contraction reaction: the effect of ring size.
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DOI：
10.1021/jo300850a
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发表时间：
2013-03-01
期刊：
影响因子：
--
通讯作者：
Givens RS
中科院分区：
文献类型：
--
作者：
Kammath VB;Šolomek T;Ngoy BP;Heger D;Klán P;Rubina M;Givens RS
环大小对羟基苯并环烷酮乙酸酯和甲磺酸酯（7a-d，8a-c）的光Favorskii诱导的缩环反应的影响为重排机理提供了新的见解。通过单调地减小这些环状衍生物中的环尺寸，施加于形成难以捉摸的双环螺环丙酮20的增加的环张力导致偏离重排并朝向溶剂分解。七或八个碳的环烷酮经历高效的光-Favorskii重排，其环收缩与对羟基苯甲酰甲基酯的光化学平行。相比之下，五碳环不重排，而是转向到光溶剂解通道，避免了伴随螺双环酮（“Favorskii中间体20”）形成的应变能增加。六碳类似物展示了反应通道的分叉，产生了两者的溶剂敏感性混合物。采用时间分辨吸收测量，量子产率测定，同位素标记，溶剂变化的研究加上理论治疗相结合，一个更全面的机制描述的重排已经出现。
The effect of ring size on the photo-Favorskii induced ring-contraction reaction of the hydroxybenzocycloalkanonyl acetate and mesylate esters (7a–d, 8a–c) has provided new insight into the mechanism of the rearrangement. By monotonically decreasing the ring size in these cyclic derivatives, the increasing ring strain imposed on the formation of the elusive bicyclic spirocyclopropanone 20 results in a divergence away from rearrangement and toward solvolysis. Cycloalkanones of seven or eight carbons undergo a highly efficient photo-Favorskii rearrangement with ring contraction paralleling the photochemistry of p-hydroxyphenacyl esters. In contrast, the five-carbon ring does not rearrange but is diverted to the photosolvolysis channel avoiding the increased strain energy that would accompany the formation of the spirobicyclic ketone, the “Favorskii intermediate 20”. The six-carbon analogue demonstrates the bifurcation in reaction channels, yielding a solvent-sensitive mixture of both. Employing a combination of time-resolved absorption measurements, quantum yield determinations, isotopic labeling, and solvent variation studies coupled with theoretical treatment, a more comprehensive mechanistic description of the rearrangement has emerged.
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