Photooxidation of Methylnaphthalenes
material by preparative thin-layer chromatography (C6H6,
silica gel). Photooxidation at -78 °C of 203 mg (1.3 mmol) of
1,8-dimethylnaphthalene in CH2Cl2 (20 mL) resulted in the
isolation of pure 1,8-dimethylnaphthalene-1,4-endoperoxide
after recrystallization at -78 °C from pentane: yield 0.202 g,
oxide was isolated as a white crystalline solid: yield 0.541 g,
83%; 1H NMR (CDCl3) δ 7.20 (s, 4H, arom.); 1.76 (s, 6H, CH3);
1.74 (s, 6H, CH3). Anal. Calcd for C14H16O2: C, 77.75; H, 7.46.
Found: C, 77.53; H, 7.47.
Calculations. The ab initio calculations were carried out
1
using Gaussian 99.16
83%; H NMR (CDCl3) δ 7.20-7.01 (m, 3H, arom); 6.90 (dd,
1H, J ) 5.5, 8.0, alkenyl); 6.59 (dd, 1H, J ) 1.8, 8.0, alkenyl);
5.42 (dd, 1H, J ) 1.8, 5.5, alkenyl); 2.48 (s, 3H, CH3); 1.98 (s,
3H, CH3). Anal. Calcd for C12H12O2: C, 76.57; H, 6.43. Found:
C, 76.47; H, 6.55.
1,2,4-Trimethylnaphthalene-1,4-endoperoxide (3). A
sample of 1,2,4-trimethylnaphthalene (1.13 g, 6.65 mmol) in
CH2Cl2 (60 mL) was photooxidized at 20 °C. After 15 min. the
theoretical volume of oxygen was absorbed. On workup, a pale
orange solid was isolated: yield 1.24 g, 93%; 1H NMR (CDCl3)
δ 7.20 (bs, 4H, arom.); 6.25 (s, 1H, alkenyl); 1.86 (s, 3H,
CH3)1.80 (s, 6H, CH3). Anal. Calcd for C13H14O2: C, 77.20; H,
6.98. Found: C, 77.21; H, 6.92.
1,4,5-Trimethylnaphthalene-1,4-endoperoxide (4). A
sample of 1,4,5-trimethylnaphthalene (1.2 g, 7.1 mmol) in CH2-
Cl2 (10 mL) was photooxidized at 15 °C. Oxygen uptake was
rapid, and the theoretical volume was absorbed in a short time.
After standard workup, the crude product was dissolved in
ether and passed through a short silica gel column. After
removal of solvent by evaporation, 1,4,5-trimethylnaphthalene-
1,4-endoperoxide was isolated as a fluffy white crystalline
solid: yield 0.678 g, 54%; 1H NMR (CDCl3) δ 7.00 (m, 3 H,
arom.); 6.53 (s, 2 H, arom.); 6.53 (s, 2H); 2.48 (s, 3H, CH3);
1.95 (s, 3H, CH3); 1.80 (s, 3H, CH3). Anal. Calcd for C13H14O2:
C, 77.20; H, 6.98. Found: C, 77.45; H, 6.81.
1,2,3,4-Tetramethylnaphthalene-1,4-endoperoxide (5).
A sample of 1,2,3,4-tetramethylnaphthalene (564 mg, 3 mmol)
in CH2Cl2 (70 mL) was photooxidized at 15 °C. Oxygen was
absorbed rapidly until 3 mmol (70 mL) was consumed. After
normal workup 1,2,3,4-tetramethylnaphthalene-1,4-endoper-
Acknowledgment. This study was supported by
grants from the National Institutes of Health and the
National Science Foundation. We thank Professor Nicho-
las Turro, Columbia University, for helpful discussions.
Supporting Information Available: General and pho-
tooxidation experimental details, experimental tables of total
energies and other energy quantities for the substituted
naphthalenes and their endoperoxides, and tables of calculated
energies and geometries for the compounds in this report. This
material is available free of charge via the Internet at
JO040228V
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