A Photo-Favorskii Ring Contraction Reaction: The Effect of Ring Size

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• 作者：Viju Balachandran Kammath ; Tom谩拧 艩olomek ; Bokolombe Pitchou Ngoy ; Dominik Heger ; Petr Kl谩n ; Marina Rubina ; Richard S. Givens
• 刊名：The Journal of Organic Chemistry
• 出版年：2013
• 出版时间：March 1, 2013
• 年：2013
• 卷：78
• 期：5
• 页码：1718-1729
• 全文大小：492K
• 年卷期：v.78,no.5(March 1, 2013)
• ISSN：1520-6904

文摘

The effect of ring size on the photo-Favorskii induced ring-contraction reaction of the hydroxybenzocycloalkanonyl acetate and mesylate esters (7a鈥?b>d, 8a鈥?b>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 鈥淔avorskii intermediate 20鈥? 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.