Synthesis of 7,8-Dimethoxytetralin-2-one
2375
acetate–hexane 10 : 1) Rf 0.7. IR (KBr) 3430, 2950, 1700, 1640, 1595, 1495,
1
1270, 1085, 800 cm21. H NMR (300 MHz, CDCl3) 2.30 (s, 3H, CH3), 3.71
(s, 3H, OCH3), 3.82 (s, 3H, OCH3), 6.2 (d, J ¼ 15.9 Hz, 1H, 55CH–), 6.73
(d, J ¼ 8.7 Hz, 1H, ArH), 7.35 (d, J ¼ 8.7 Hz, 1H, ArH), 7.94
(d, J ¼ 15.9 Hz, 1H, –CH55) ppm. Anal. calcd. for C12H14O4: C, 64.85; H,
6.35: Found C, 64.64; H, 6.31.
Ethyl 3-(3,4-Dimethoxy-2-methylphenyl)-2-propenoate (4)
Carboxylic acid (3) (10.37g, 46.7mmol) was dissolved in ethanol (155ml) and
1.5 ml of cc. H2SO4 was added. The reaction mixture was refluxed for 2 h,
solvent was evaporated to dryness under reduced pressure, and the residue
was shared between saturated aqueous sodium hydrogencarbonate solution
(70ml) and dichloromethane (100ml). The aqueous layer was extracted with
dichloromethane (100ml), the combined organic layers were washed with
water (3 ꢀ 100 ml), and after drying (MgSO4) was evaporated to dryness
under vacuum. Product (4) (10.86g, 93%) was obtained as a crystallizable oil,
used in the next bromination step without any purification. TLC (benzene–
MeOH 14: 3) Rf 0.8. IR (KBr) 2990, 2940, 1720, 1640, 1600, 1500, 1260,
1
1180, 1080, 870, 820 cm21. H NMR (300 MHz, CDCl3) 1.33 (t, J ¼ 7.0 Hz,
3H, OCH2CH3), 2.36 (s, 3H, CH3), 3.78 (s, 3H, OCH3), 3.87 (s, 3H, OCH3),
4.25 (q, J ¼ 7.0 Hz, 2H, OCH2CH3), 6.25 (d, J ¼ 15.6Hz, 1H, 55CH–), 6.77
(d, J ¼ 8.7 Hz, 1H, ArH), 7.33 (d, J ¼ 8.7 Hz, 1H, ArH), 7.92 (d, J ¼ 15.6Hz,
1H, –CH55) ppm. HRMS: calcd. 250.1200, found 250.1201 (delta: 0.7 ppm).
Ethyl 3-(2-Bromomethyl-3,4-dimethoxyphenyl)-2-propenoate (5)
To a solution of ester (4) (7.27 g, 29.1mmol) in carbon tetrachloride (180 ml),
200 mg of benzoyl peroxide and 7.87g (44.2 mmol) of N-bromosuccinimide
was added. After refluxing the reaction mixture for 8 h with stirring, precipitate
was filtered off and the filtrate was evaporated to dryness under reduced pressure.
The residue was recrystallized from ethanol, and from the ethanolic mother
liquor another part of product was isolated by column chromatography on
silica gel (dichloromethane) and by preparative layer chromatography (silica,
dichloromethane). Yield: 6.22g (65%). Mp 93–948C. TLC (dichloromethane)
Rf 0.65. IR (KBr) 2990, 2936, 1720, 1640, 1600, 1500, 1280, 1190, 1090,
1040, 820 cm21
.
1H NMR (300MHz, CDCl3) 1.35 (t, J ¼ 7.2 Hz, 3H,
OCH2CH3), 3.90 (s, 3H, OCH3), 3.96 (s, 3H, OCH3), 4.27 (q, J ¼ 7.2 Hz, 2H,
OCH2CH3), 4.71 (s, 2H, CH2Br), 6.35 (d, J ¼ 15.6Hz, 1H, 55CH–), 6.90
(d, J ¼ 8.7 Hz, 1H, ArH), 7.35 (d, J ¼ 8.7 Hz, 1H, ArH), 7.95 (d, J ¼ 15.6Hz,
1H, –CH55) ppm. Anal. calcd. for C14H17BrO4: Br, 24.27. Found: Br, 24.20.