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2306
Banerjee, Vera, and Laya
added dropwise. The mixture was heated at 100–1108C for 2 hr, the resulting
material was cooled and poured on cold water, and extracted with ether several
times. The combined ethereal extracts were washed with saturated
aq.NaHCO3 and dried. Removal of solvent and subsequent distillation
afforded the reported[4] tetralone 2 (1.74 g, 96%); bp 136–1388C (2 mmHg)
(Ref.[4] 160–1628C/1595 Pa); nmax/cm21 1674 (CO); m/z 174 (Mþ, 88%);
dH 7.16 (1H, d, J ¼ 7.5 Hz), 6.97 (1H, d, J ¼ 7.5 Hz) (ArH), 2.87 (2H, t,
J ¼ 6 Hz, CH2CO), 2.59 (3H, s), 2.28 (3H, s), (5,8-Me), and 2.08–1.99
(2H, m, CH2) (Found: C, 82.98; H, 8.28. C12H14O requires C, 82.72; H,
8.10%). [(Lit.[4] d 200 MHz) 2.90 (2H, t, J ¼ 7 Hz, CH2CO), 2.60 (3H, s,
Me), 2.28 (3H, s, Me)].
5,8-Dimethyl-1,2-dihydronaphthalene 3. A solution of tetralone 2
(1.21 g, 6.91 mmol), p-toluenesulfonic acid (35 mg), 2,4-pentanediol (3 mL,
27.6 mmol) in dry toluene (60 mL) was refluxed in a Dean–Stark water
separator for 48 hr. The reaction mixture was cooled to room temperature
(258C) and poured into dilute sodium bicarbonate solution (50 mL, 5%)
and extracted with toluene. The organic extract was washed several times
with saturated sodium chloride solution, dried, evaporated, and the residue
was distilled to obtain the dihydronaphthalene 3 (981 mg, 90%); as an oil,
bp 96–988C (1 mmHg); nmax/cm21 3100–3001 (ArH) and 1600 (C55C);
m/z 158 (Mþ. 100%); d 6.89–6.85 (2H, m, ArH), 6.76–6.71 (1H, dt,
J ¼ 9.8 Hz and 1.6 Hz); 6.16–6.13 (1H, dt, J ¼ 9.8 Hz and 4.1 Hz) (olefinic
protons, 1-H and 2-H), 2.78 (2H, t, J ¼ 8 Hz, 4-H) 2.36 (3H, s), and 2.31
(3H, s) (ArCH3) (Found: C, 91.35; H, 9.14. C12H14 requires C, 91.08; H,
8.92%).
5,8-Dimethyl-2-tetralone 4. To a solution of m-chloroperbenzoic acid
(Aldrich, 79% purity) (6.39 g, 28.5 mmol) in dichloromethane (70 mL),
cooled to 0–58C, was added dropwise a solution of compound 3 (3.09 g,
18.9 mmol) dissolved in dichloromethane (20 mL). The resulting mixture
was stirred at 0–58C for 6 hr and then filtered. The filtrate was washed
with dilute sodium hydroxide solution (50 mL, 10%), dried and evaporated
to yield an oil which was dissolved in ethanol (25 mL), treated with aqueous
sulphuric acid (25 mL, 60%), and heated (608C) for 3 hr. The dark brown
solution was diluted with water and extracted with ether. The workup
followed by chromatographic purification (hexane : Et2O 9 : 1) yielded the
reported[1] tetralone 4 (1.57 g, 46%); nmax/cm21 1716 (CO); m/z 174
(Mþ, 100%); 132 (81); dH 6.93 (2H, bs) (ArH), 3.53–3.49 (2H, m),
3.05–3.02 (2H, m) (1-H and 4-H), 2.62–2.57 (2H, m, 3-H), 2.33 (3H, s),
and 2.24 (3H, s) (ArMe) (Found: C; 82.91; H, 8.02. C12H14O requires C,
82.72; H, 8.10%). [(Lit[1] nmax/cm21 1710(CO); d (90 MHz) 2.08 (s, 3H)
(ArMe), 2.22 (s,3H) (ArH), 6.82 (bs, 2H) (ArH)].