5,7-dibromo-2-tetralone synthesis

Yield:144066-44-4 10% ，1131456-53-5 6%

Reaction Conditions:

Stage #1: 1,2,3,4-tetrahydronaphthalen-2-one;aluminum (III) chloride at 0 - 90; for 0.666667 h;
Stage #2: with bromine at 85; for 1 h;

Steps:

III

,7-Dibromo-2-tetralone and 6,8-dibromo-2-tetralone. Into a round bottom flask kept at 0° C., AlCl₃ (2.26 g, 16.9 mmol) was added and the reaction system was put under nitrogen. 1 mL of β-tetralone (1.08 g, 7.37 mmol) were added during a 10-minute period, at which point, the reaction mixture was heated in an oil bath at 90° C. for about 30 minutes before adding 0.45 mL of Br₂ (1.41 g, 8.82 mmol). The reaction mixture was stirred at 85° C. for an hour before 15 mL of ice-water and 8 mL of NaHCO₃ were added. The product was extracted twice from the aqueous phase with Et₂O and, the resultant organic phase was washed once with NaHCO₃, once with brine and dried under Na₂SO₄. The crude reaction mixture was purified by flash chromatography (10% EtOAc/90% hex) which afforded 2 major compounds. 0.110 g (0.362 mmol) of 6,8-dibromo-2-tetralone (less polar compound) was obtained in a 6% yield.¹H NMR (300 MHz, CDCl₃, δ): 7.34 (s, ArH, 2H), 3.66 (s, CH₂, 2H), 3.24 (t, J=6.8, CH₂, 2H), 2.60 (t, J=6.9, CH₂, 2H).¹³C NMR (75 MHz, CDCl₃): δ 207.8, 137.9, 135.1, 131.93, 131.90, 123.2, 122.9, 44.6, 37.9, 29.4.Dept 135 NMR (75 MHz, CDCl₃): δ 131.99 (CH), 131.95 (CH), 44.7 (CH₂), 38.0 (CH₂), 29.5 (CH₂).The more polar compound was recrystallized (MeOH-hex) to yield 0.2602 g (0.856 mmol) of 5,7-dibromo-2-tetralone in a 10% yield.¹H NMR (300 MHz, CDCl₃, δ): 7.64 (d, J=1.8, ArH, 1H), 7.34 (d, J=1.8, ArH, 1H), 3.58 (s, CH₂, 2H), 3.06 (t, J=6.5, CH₂, 2H), 2.57 (t, J=6.7, CH₂, 2H).¹³C NMR (75 MHz, CDCl₃): δ 207.9, 140.1, 133.3, 133.2, 130.4, 124.7, 120.6, 44.1, 38.1, 29.0.Dept 135 NMR (75 MHz, CDCl₃): δ 133.2 (CH), 130.1 (CH), 44.1 (CH₂), 38.1 (CH₂), 29.0 (CH₂).

References:

US2009/76076,2009,A1 Location in patent:Page/Page column 21