Synthesis and Structural Investigation of an \u27Oxazinoquinolinespirohexadienone\u27 That Only Exists as Its Long-Wavelength Ring-Opened Quinonimine Isomer

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

Synthesis and Photochemistry of Two Quinoline Analogs of the Perimidinespirohexadienone Family of Photochromes

We report the detailed synthesis and photochemistry of two analogs (specifically 35-di-tert-butyl-7\u27-methyl- and 3,5-di-tert-butyl-7\u27,9\u27-dimethyl-1\u27,3\u27-dihydrospirocyclohexa[2.5]diene-1,2\u27-pyrido[4,3,2-de]quinazolin-4-one) of the perimidinespirohexadienone (3,5-di-tert-butyl-1\u27,3\u27-dihydrospirocyclohexa[2,5]diene-1,2\u27-perimidin-4-one) family of photochromes in which the naphthalene moiety of the parent is replaced by a quinoline, and compare them to the parent compound. Molar absorptivities of both the short wavelength spirocyclic isomer (SW) and long wavelength quinonimine isomer (LW) of each were determined by a combination of proton NMR and UV-vis spectroscopy in solvents of varying polarity. Quantum yield measurements for photoisomerization of SW to LW are reported in those same solvents, with qualitative extrapolation to additional solvents. The position and rate of the thermal equilibrium reverting LW to SW is estimated for these compounds. The 9\u27-methyl in SW (6-methyl in LW) is found to be essential for complete reversion of LW to SW in the dark. Finally one-dimensional NOE NMR spectroscopy was used to conclusively determine the structure of LW for the quinoline analogs as the 4-(5-aminoquinolin-4-ylimino)-2,6-di-tert-butylcyclohexa-2,5-dienone resulting from opening toward the quinoline nitrogen, rather than the 4-(4-aminoquinolin-5-ylimino) structure that would result from spirocyclic ring opening away from the quinoline nitrogen which had been initially proposed by Minkin et al. for very similar compounds [V.I. Minkin, V.N. Komissarov, V.A. Kharlanov, Perimidinespirocyclohexadienones, in: J.C. Crano, RJ. Guglielmetti (Eds.), Organic Photochromic and Thermochromic Compounds, vol. 1, Plenum Press, New York, 1999, pp. 315-340, and references therein]

Synthesis and Structural Investigation of an “Oxazinoquinolinespirohexadienone” That Only Exists as Its Long-Wavelength Ring-Opened Quinonimine Isomer

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

Synthesis and Structural Investigation of an “Oxazinoquinolinespirohexadienone” That Only Exists as Its Long-Wavelength Ring-Opened Quinonimine Isomer

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

Synthesis and Structural Investigation of an “Oxazinoquinolinespirohexadienone” That Only Exists as Its Long-Wavelength Ring-Opened Quinonimine Isomer

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