“…While no heterocyclization occurs in the reaction of o -phenylenediamines and o -aminophenols with p -quinones, which stops at the stage of formation of quinoneimines, with 1,8-naphthylenediamines the reaction leads to derivatives of the spirocyclic system 5 (Y = CH). , With 2,6-di- tert -butyl-1,4-benzoquinone, the reaction proceeds smoothly under noncatalytic conditions when refluxing 1-propanol or toluene solutions of the components to give 2,3-dihydro-2-spiro-4‘-[2‘,6‘-di- tert -butylcyclohexadien-2‘,5‘-one]perimidines 30 in 40−70% yield. By contrast, catalysis with strong proton acids is necessary when 2,6-di- tert -butyl-1,4-benzoquinone is replaced in this reaction by 2- tert -butyl-1,4-naphthoquinone (Scheme ).…”
“…Similar photochromic transformations are also characteristic of the heteroanalogues 34 (Scheme ) as well as of perimidinespiro-4 H -naphthalenone 31 . 5 Changes in the UV−vis absorption spectrum of a perimidinespirocyclohexadienone 30 (R = CH 2 Ph, R 1 = H) on irradiation of its acetonitrile solution (25 °C, c = 5.15 × 10 -5 M) at the longest-wavelength band of the spirocyclic form (436 nm) with a time interval of 20 s. Data from refs a and a. 28 …”
“…Changes in the UV−vis absorption spectrum of a perimidinespirocyclohexadienone 30 (R = CH 2 Ph, R 1 = H) on irradiation of its acetonitrile solution (25 °C, c = 5.15 × 10 -5 M) at the longest-wavelength band of the spirocyclic form (436 nm) with a time interval of 20 s. Data from refs a and a.…”
“…The mechanism of the photochromic reaction (Scheme ) involves cleavage of a C−N bond in the first singlet excited state of 30 , followed by conformational rearrangement of the thus formed zwitterionic intermediate 30a that undergoes conformational rearrangement to its trans isomer 30b , which precedes the final step of the intramolecular proton transfer. Despite the complex character of the reaction, the initial spiro form 30 (R = CH 3 , R 1 = H) is fully transformed into the final quinoneimine photoproduct for about 40 ps 88c. For spiroperimidinecyclohexadienones 30 (R = Alk, CH 2 Ph), the quantum yields of the photoreaction measured in octane solution were found in the range 0.24−0.42 and are close to those typical of spiropyrans. 9b,d In polar solvents (acetonitrile), the quantum efficiency of the photocoloration reaction is substantially lower (Φ = 0.05−0.06 mol·einstein -1 ).…”
“…Some of the perimidinespirocyclohexadienones that exist in a solid as purely spirocyclic compounds, such as 30 (R, R 1 = 4,5-(CH 2 ) 2 , 34 ), fully convert to the quinoneimine form when dissolved in octane. 11a,, The position of the 30 ⇌ 29 equilibrium depends strongly on the solvent in use and the temperature of the solution, which defines respectively solvato- and thermochromic properties of perimidinespirocyclohexadienones. In proton donors and polar solvents (alcohols, acetonitrile, dimethylformamide), the equilibrium is shifted to the spirocyclic form, spirocyclic isomers of compounds 30 (R = Alk, R 1 = H, 5-Br) being the only isomers present in such solutions. 88a, …”
“…While no heterocyclization occurs in the reaction of o -phenylenediamines and o -aminophenols with p -quinones, which stops at the stage of formation of quinoneimines, with 1,8-naphthylenediamines the reaction leads to derivatives of the spirocyclic system 5 (Y = CH). , With 2,6-di- tert -butyl-1,4-benzoquinone, the reaction proceeds smoothly under noncatalytic conditions when refluxing 1-propanol or toluene solutions of the components to give 2,3-dihydro-2-spiro-4‘-[2‘,6‘-di- tert -butylcyclohexadien-2‘,5‘-one]perimidines 30 in 40−70% yield. By contrast, catalysis with strong proton acids is necessary when 2,6-di- tert -butyl-1,4-benzoquinone is replaced in this reaction by 2- tert -butyl-1,4-naphthoquinone (Scheme ).…”
“…Similar photochromic transformations are also characteristic of the heteroanalogues 34 (Scheme ) as well as of perimidinespiro-4 H -naphthalenone 31 . 5 Changes in the UV−vis absorption spectrum of a perimidinespirocyclohexadienone 30 (R = CH 2 Ph, R 1 = H) on irradiation of its acetonitrile solution (25 °C, c = 5.15 × 10 -5 M) at the longest-wavelength band of the spirocyclic form (436 nm) with a time interval of 20 s. Data from refs a and a. 28 …”
“…Changes in the UV−vis absorption spectrum of a perimidinespirocyclohexadienone 30 (R = CH 2 Ph, R 1 = H) on irradiation of its acetonitrile solution (25 °C, c = 5.15 × 10 -5 M) at the longest-wavelength band of the spirocyclic form (436 nm) with a time interval of 20 s. Data from refs a and a.…”
“…The mechanism of the photochromic reaction (Scheme ) involves cleavage of a C−N bond in the first singlet excited state of 30 , followed by conformational rearrangement of the thus formed zwitterionic intermediate 30a that undergoes conformational rearrangement to its trans isomer 30b , which precedes the final step of the intramolecular proton transfer. Despite the complex character of the reaction, the initial spiro form 30 (R = CH 3 , R 1 = H) is fully transformed into the final quinoneimine photoproduct for about 40 ps 88c. For spiroperimidinecyclohexadienones 30 (R = Alk, CH 2 Ph), the quantum yields of the photoreaction measured in octane solution were found in the range 0.24−0.42 and are close to those typical of spiropyrans. 9b,d In polar solvents (acetonitrile), the quantum efficiency of the photocoloration reaction is substantially lower (Φ = 0.05−0.06 mol·einstein -1 ).…”
“…Some of the perimidinespirocyclohexadienones that exist in a solid as purely spirocyclic compounds, such as 30 (R, R 1 = 4,5-(CH 2 ) 2 , 34 ), fully convert to the quinoneimine form when dissolved in octane. 11a,, The position of the 30 ⇌ 29 equilibrium depends strongly on the solvent in use and the temperature of the solution, which defines respectively solvato- and thermochromic properties of perimidinespirocyclohexadienones. In proton donors and polar solvents (alcohols, acetonitrile, dimethylformamide), the equilibrium is shifted to the spirocyclic form, spirocyclic isomers of compounds 30 (R = Alk, R 1 = H, 5-Br) being the only isomers present in such solutions. 88a, …”
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