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

作者：Kammath Viju Balachandran; Solomek Tomas; Ngoy Bokolombe Pitchou; Heger Dominik; Klan Petr^*; Rubina Marina; Givens Richard S

来源：Journal of Organic Chemistry, 2013, 78(5): 1718-1729.

DOI：10.1021/jo300850a

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. Cyclo-alkanones of seven or eight carbons undergo a highly efficient photo-Favorskii rearrangement with ring contraction paralleling the photo-chemistry 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 %26quot;Favorskii intermediate 20%26quot;. The six carbon analogue demonstrates the bifurcation in reaction channels, yielding a solvent sensitive mixture of both. Employing a combination of tune 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.

• 出版日期2013-3-1