Department of Chemistry, Hope College, 35 East 12th Street, Holland, Michigan 49423, United States.
J Org Chem. 2012 Oct 5;77(19):8689-95. doi: 10.1021/jo3016083. Epub 2012 Sep 20.
The spirocyclic oxazinoquinolinespirohexadienone (OSHD) "photochromes" are computationally predicted to be an attractive target as electron deficient analogues of the perimidinespirohexadienone (PSHD) photochromes, for eventual application as photochromic photooxidants. We have found the literature method for their preparation unsuitable and present an alternative synthesis. Unfortunately the product of this synthesis is the long wavelength (LW) ring-opened quinonimine isomer of the OSHD. We have found this isomer does not close to the spirocyclic short wavelength isomer (SW) upon prolonged standing in the dark, unlike other PSHD photochromes. The structure of this long wavelength isomer was found by NMR and X-ray crystallography to be exclusively the quinolinone (keto) tautomer, though experimental cyclic voltammetry supported by our computational methodology indicates that the quinolinol (enol) tautomer (not detected by other means) may be accessible through a fast equilibrium lying far toward the keto tautomer. Computations also support the relative stability order of keto LW over enol LW over SW.
螺环[4.5]噁嗪并喹啉螺[4.5]二烯酮（OSHD）“光致变色体”被计算预测为具有吸引力的目标，因为它们是缺电子的类似物，与过咪啶螺[4.5]二烯酮（PSHD）光致变色体相比，最终可作为光致变色光氧化剂。我们发现文献中的制备方法不适用，并提出了一种替代合成方法。不幸的是，该合成的产物是 OSHD 的长波长（LW）开环醌亚胺异构体。我们发现，与其他 PSHD 光致变色体不同，这种异构体在黑暗中长时间放置不会重新闭环为螺环的短波长异构体（SW）。这种长波长异构体的结构通过 NMR 和 X 射线晶体学确定为仅为喹啉酮（酮）互变异构体，尽管实验循环伏安法得到我们计算方法的支持，表明喹啉醇（烯醇）互变异构体（其他方法未检测到）可能通过快速平衡而变得容易，该平衡远离酮互变异构体。计算还支持酮 LW 相对于烯醇 LW 相对于 SW 的相对稳定性顺序。
