Direct and Facile Bromination at the 5- and 5′-Positions of (R)-6,6′-Dialkyl- and (R)-6,6′-Diaryl-2,2′-Binaphthols

Abstract

(R)-5,5′-Dibromo-6,6′-dibutyl-2,2′-binaphthol, (R)-5,5′-dibromo-6,6′-di(4-methylphenyl)-2,2′-binaphthol, (R)-5,5′-dibromo-6,6′-di(3,5-dimethylphenyl)-2,2′-binaphthol, and (R)-5,5′-dibromo-6,6′-di(4-trifluoromethylphenyl)-2,2′-binaphthol were synthesized from (R)-1,1′-bi-2-naphthol by a five-step reaction in excellent yields under mild conditions.

Key words

(R)-BINOL - bromination - five-step reaction

References and Notes

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10

General Procedure for Suzuki Reaction Method and Hydrolysis Reaction Method
(R)-6,6′-Dibromo-2,2′-bis(methoxymethoxy)-1,1′ -binaphthyl (1 equiv) is stirred with the corresponding boronic acid (2.5-3.5 equiv) and Pd(PPh₃)₄ (7-10 mol%) in a mixture solution of THF or DME and 2 M K₂CO₃ solution (referred to as solvent/base) overnight. The mixture was filtered through a short column of silica gel with EtOAc as an eluent. After removal of solvents under reduced pressure, the residue was extracted with CH₂Cl₂. The organic layer was washed with H₂O and brine, dried over anhyd Na₂SO₄ and concentrated. The crude product was purified by column chromatography on silica gel. The product was dissolved in THF. A mixture of MeOH and HCl (12 M) was added and stirred at r.t. for 12 h. The solvent was removed under reduced pressure, and the residue was extracted with EtOAc. The organic layer was washed with 2 M NaHCO₃ solution and brine twice, dried over anhyd Na₂SO₄, and concentrated. The crude product was purified by column chromatography on silica gel.
General Procedure for Brominated Reaction Method A solution of Br₂ (5 equiv in CH₂Cl₂) was slowly added to a solution of (R)-6,6′-diaryl-2,2′-binaphthol in CH₂Cl₂ at -15 °C or 0 °C over 1 h. The solution was stirred overnight and gradually warmed to r.t. The reaction was quenched with sat. NaHSO₃ solution and extracted with CH₂Cl₂. The combined organic layers were washed with H₂O and brine twice, and then dried over anhyd Na₂SO₄. After removal of solvent, the crude product was purified by column chromatography on silica gel
( R )-6,6′-Dibutyl-2,2′-binaphthol White solid (0.71 g, 93% yield); mp 72-74 °C. [α]_D -82.9 (c 0.31, CH₂Cl₂). ¹H NMR (300 MHz, CDCl₃): δ = 7.92 (d, 2 H, J = 9.0 Hz), 7.69 (s, 2 H), 7.36 (d, 2 H, J = 9.0 Hz), 7.19 (dd, 2 H, J = 8.4 Hz), 7.12 (d, 2 H, J = 8.4 Hz), 5.01 (s, 2 H), 2.76 (t, 4 H, J = 7.8 Hz), 1.74-1.64 (m, 4 H), 1.49-1.36 (m, 4 H), 0.97 (t, 6 H, J = 7.2 Hz). ¹³C NMR (75 MHz, CDCl₃): δ = 152.5, 139.0, 132.1, 131.2, 130.0, 129.4, 127.3, 124.6, 118.0, 111.3, 35.9, 33.9, 22.8, 14.4. FT-IR (KBr): 3503.4, 3421.9, 2950.1, 2921.8, 1598.1, 1507.3, 1474.1, 1363.7, 1214.1, 1142.6, 1124.5, 952.2, 880.6, 827.1, 684.0, 555.6 cm^-1.
( R )-6,6′-Di-(4-methylphenyl)-2,2′-binaphthol White solid (0.57 g, 93% yield); mp 113-116 °C; [α]_D
-288.2 (c 0.5, CH₂Cl₂). ¹H NMR (300 MHz, CDCl₃): δ = 8.08 (s, 2 H), 8.03 (d, 2 H, J = 8.9 Hz), 7.57 (d, 6 H, J = 8.0 Hz), 7.41 (d, 2 H, J = 8.9 Hz), 7.26-7.24 (m, 6 H), 5.12 (s, 2 H), 2.40 (s, 6 H). ¹³C NMR (75 MHz, CDCl₃): δ = 153.1, 138.3, 137.5, 137.3, 132.8, 132.1, 130.2, 130.0, 127.6, 127.5, 126.4, 125.1, 118.6, 111.1, 21.6. FT-IR (KBr): 3500.3, 3021.4, 2918.2, 1621.8, 1596.9, 1568.6, 1518.3, 1500.6, 1383.5, 1355.9, 1286.5, 1217.5, 1189.3, 1173.4, 1148.6, 1128.3, 935.3, 889.5, 812.5, 757.4, 525.4 cm^-1.
( R )-6,6′-Di-(3,5-dimethylphenyl)-2,2′-binaphthol White solid (1.07 g, 99% yield); mp 107-109 °C; [α]_D
-171.4 (c 0.1, CH₂Cl₂). ¹H NMR (300 MHz, CDCl₃): δ = 8.11 (s, 2 H), 8.06 (d, 2 H, J = 9.0 Hz), 7.60 (d, 2 H, J = 8.4 Hz), 7.45 (d, 2 H, J = 8.7 Hz), 7.32 (s, 4 H), 7.28 (d, 2 H, J = 9.0 Hz), 7.05 (s, 2 H), 5.16 (s, 2 H), 2.43 (s, 12 H). ¹³C NMR (75 MHz, CDCl₃): δ = 153.1, 141.2, 138.8, 137.6, 132.9, 132.1, 130.1, 129.4, 127.7, 126.7, 125.6, 125.1, 118.6, 111.2, 21.9. FT-IR (KBr): 3522.3, 3419.5, 3014.8, 2955.4, 2913.5, 1621.9, 1593.6, 1504.3, 1481.1, 1383.8, 1355.2, 1216.7, 1147.1, 1128.7, 945.0, 850.2, 824.1, 683.9, 572.9 cm^-1.
( R )-6,6′-Di-(4-trifluoromethylphenyl)-2,2′-binaphthol
White solid (1.25 g, 95% yield); mp 209-210 °C; [α]_D -225.2 (c 0.5, CH₂Cl₂). ¹H NMR (CDCl₃): δ = 8.16 (d, 2 H, J = 1.5 Hz), 8.10 (d, 2 H, J = 9.0 Hz), 7.80 (d, 4 H, J = 8.7 Hz), 7.74 (d, 4 H, J = 8.4 Hz), 7.60 (dd, 2 H, J = 8.7 Hz), 7.49 (d, 2 H, J = 9.0 Hz), 7.31 (d, 2 H, J = 8.7 Hz), 5.17 (s, 2 H). ¹³C NMR (CDCl₃): δ = 153.3, 144.3, 135.5, 133.1, 132.0, 129.7, 129.2, 127.5, 127.0, 126.9, 126.0, 125.9, 125.8, 118.6, 110.8. FT-IR (KBr): 3521.3, 3492.1, 3413.8, 1616.2, 1599.0, 1502.0, 1472.1, 1409.8, 1385.0, 1326.8, 1290.8, 1166.8, 1124.0, 1109.7, 1068.5, 1014.7, 849.2, 820.4, 778.3, 611.3 cm^-1.
Compound ( R )-1
Bromine (0.14 mL, 2.8 mmol in 5 mL CH₂Cl₂) was slowly added to a solution of (R)-6,6′-dibutyl-2,2′-binaphthol (0.52 g, 1.33 mmol) in CH₂Cl₂ (10 mL) at -78 °C over 1 h. The solution was stirred overnight and gradually warmed to r.t. After removal of solvent, a white solid product (R)-1 can directly be obtained in the yield of 99% (0.73 g) without further purification; mp 48-50 °C; [α]_D -13.3 (c 0.23, CH₂Cl₂). ¹H NMR (300 MHz, CDCl₃): δ = 8.52 (d, 2 H, J = 9.0 Hz), 7.46 (d, 2 H, J = 9.6 Hz), 7.17 (d, 2 H, J = 8.4 Hz), 7.01 (d, 2 H, J = 8.7 Hz), 5.04 (s, 2 H), 2.93-2.92 (m, 4 H), 1.67-1.62 (m, 4 H), 1.49-1.42 (m, 4 H), 0.99-0.94 (m, 6 H). ¹³C NMR (75 MHz, CDCl₃): δ = 153.1, 139.1, 133.4, 131.5, 130.2, 128.9, 124.6, 124.0, 119.2, 111.3, 37.3, 32.7, 23.0, 14.3. ESI-MS: m/z = 554.4 [M + 1]. Anal. Calcd for C₂₈H₂₈Br₂O₂: C, 60.45; H, 5.07. Found: C, 60.41; H, 5.11.
FT-IR (KBr): 3530.2, 3027.4, 2956.5, 2928.9, 1597.9, 1567.3, 1467.1, 1367.7, 1248.7, 1212.0, 1154.1, 1132.9, 970.7, 819.2, 709.0, 579.3 cm^-1.
Compound ( R )-2
White solid (600 mg, 83% yield); mp >250 °C; [α]_D -70.0 (c 0.5, CH₂Cl₂). ¹H NMR (300 MHz, CDCl₃): δ = 8.61 (d, 2 H, J = 9.3 Hz), 7.52 (d, 2 H, J = 9.3 Hz), 7.33 (d, 4 H, J = 8.1 Hz), 7.26 (d, 6 H, J = 7.2 Hz), 7.14 (d, 2 H, J = 8.7 Hz), 5.14 (s, 2 H), 2.42 (s, 6 H). ¹³C NMR (75 MHz, CDCl₃): δ = 153.7, 139.6, 139.5, 137.8, 134.0, 132.3, 130.8, 129.9, 129.2, 128.9, 124.0, 123.7, 119.7, 111.3, 21.7. ESI-MS:
m/z = 623.5 [(M + 1]. Anal. Calcd for C₃₄H₂₄Br₂O₂: C, 65.41; H, 3.87. Found: C, 65.46; H, 3.77. FT-IR (KBr): 3525.8, 3497.6, 3024.1, 2917.2, 1611.0, 1592.1, 1564.1, 1517.5, 1487.4, 1466.4, 1366.7, 1231.9, 1209.8, 1173.8, 1152.2, 1132.1, 955.3, 817.7, 810.9, 759.6, 546.7 cm^-1.
Compound ( R )-3 White solid (1.52 g, 77.1% yield); mp 184-186 °C; [α]_D
-69.57 (c 0.1, CH₂Cl₂). ¹H NMR (300 MHz, CDCl₃): δ = 8.63 (d, 2 H, J = 9.3 Hz), 7.55 (d, 2 H, J = 9.0 Hz), 7.27 (d, 2 H, J = 7.8 Hz), 7.23 (s, 2 H), 7.16 (s, 6 H), 5.18 (s, 2 H), 2.49 (s, 12 H). ¹³C NMR (75 MHz, CDCl₃): δ = 153.8, 140.8, 138.8, 138.4, 134.1, 132.4, 130.4, 129.7, 128.8, 127.5, 124.0, 123.5, 119.8, 111.3, 24.4. ESI-MS: m/z = 652.4 [M + 1]. Anal. Calcd for C₂₈H₂₈Br₂O₂: C, 66.27; H, 4.33. Found: C, 66.38; H, 4.21. FT-IR (KBr): 3520.2, 3029.7, 2951.2, 2920.7, 1600.1, 1566.2, 1473.2, 1369.0, 1305.5, 1208.9, 1151.7, 1134.2, 1027.9, 969.5, 820.3, 678.3, 567.5 cm^-1. Compound ( R )-4
White solid (503 mg, 79% yield); mp 152-154 °C; [α]_D -46.80 (c 0.5, CH₂Cl₂). ¹H NMR (300 MHz, CDCl₃): δ = 8.64 (d, 2 H, J = 9.3 Hz), 7.74 (d, 4 H, J = 8.1 Hz), 7.58 (d, 6 H, J = 9.0 Hz), 7.26 (d, 2 H, J = 9.6 Hz), 7.20 (d, 2 H, J = 8.7 Hz), 5.29 (s, 2 H). ¹³C NMR (CDCl₃): δ = 153.7, 145.5, 137.8, 134.1, 131.9, 130.0, 129.6, 128.4, 126.0, 125.2, 124.0, 123.2, 122.4, 120.0, 111.3. ESI-MS: m/z 731.7 [M + 1]. Anal. Calcd for C₂₈H₂₈Br₂O₂: C, 55.76; H, 2.48. Found: C, 56.12; H, 2.50. FT-IR (KBr): 3522.1, 3391.9, 1702.3, 1616.2, 1598.3, 1471.8, 1370.3, 1324.6, 1165.3, 1124.9, 1107.5, 1081.3, 1060.4, 1018.0, 819.6, 781.3, 610.0 cm^-1.