Synthesis and Application of 3,3′-Diarylmethyl BINOLs

Abstract

A new class of 3,3′-diarylmethyl BINOL derivatives were synthesized and applied to the catalytic asymmetric addition of diethylzinc to aldehydes. These chiral diol auxiliaries could be used as catalysts without the addition of Ti(i-PrO)₄ and showed unprecedented catalytic activities and enantioselectivities (up to 94% ee, 5 mol% catalyst loading).

Key words

1,1′-binaphthyls - asymmetric catalysis - diethylzinc ­additions

References and Notes

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• Other methods for the synthesis of compound 10a, see:
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10

BINOL 9a: To a stirred solution of MOM-protected BINOL 8 (2.83 g, 5.30 mmol) in THF (20 mL) was added n-BuLi (1.60 M in hexane; 19.0 mmol) at r.t. The mixture was stirred for 2 h at the same temperature. After cooling to -78 °C, benzophenone (4.08 g, 22.4 mmol) in THF (10 mL) was added slowly. The reaction mixture was stirred for 2 h at
-78 °C and then at r.t. for 2 h. After addition of aq NH₄Cl (5%; 20 mL), the organic phase was extracted with Et₂O, dried over Na₂SO₄, and concentrated. Column chromatography on silica gel (PE-EtOAc, 6:1) afforded 9a (3.56 g, 91% yield) as a white solid. ¹H NMR (300 MHz, CDCl₃): δ = 2.81 (s, 6 H), 3.77-3.83 (m, 4 H), 5.79 (s, 2 H), 7.15-7.45 (m, 28 H), 7.62 (d, J = 7.74 Hz, 2 H).

13

Compound 9e was synthesized by using the same procedure for 9a except half the amount of n-BuLi and benzophenone was used.

14

Catalysts 7a-e; General Procedure: To a solution of 9 (4.07 mmol) in CH₂Cl₂ (150 mL) was added CF₃COOH (14.0 mmol). The reaction mixture was stirred for 24 h at r.t. After neutralization with sat. aq NaHCO₃ (20 mL), the organic layer was separated, dried over Na₂SO₄, and concentrated. Column chromatography on silica gel (PE-EtOAC,15:1) afforded catalysts 7 (82-90% yield) as white powders.
3,3′-Diphenylmethyl-2,2′-dihydroxyl-1,1′-binaphthalene ( 7a) Mp 153-155 °C; [α]_D ²⁰ -132 (c 1.11, THF). ¹H NMR (300 MHz, CDCl₃): δ = 5.04 (s, 2 H, OH), 5.95 (s, 2 H), 7.00 (d, J = 8.00 Hz, 2 H), 7.11-7.28 (m, 24 H), 7.35 (s, 2 H), 7.61 (d, J = 7.32 Hz, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 50.93, 111.14, 123.87, 124.03, 126.44, 126.54, 127.03, 128.35, 128.41, 128.49, 129.04, 129.34, 129.52, 131.40, 132.24, 132.99, 142.92, 143.12, 151.23. HRMS (FT-ICRMS): m/z calcd for C₄₆H₃₄O₂ [M]⁺: 618.2559; found: 618.2548.
3,3′-Di(4-methylphenyl)methyl-2,2′-dihydroxyl-1,1′-binaphthalene ( 7b) Mp 309-311 °C; [α]_D ²⁰ -113.8 (c 1.13, THF). ¹H NMR (300 MHz, CDCl₃): δ = 2.25 (s, 6 H), 2.27 (s, 6 H), 5.03 (s, 2 H, OH), 5.86 (s, 2 H), 6.96-7.20 (m, 22 H), 7.34 (s, 2 H), 7.62 (d, J = 7.46 Hz, 2 H). ¹³C NMR (75M Hz, CDCl₃): δ = 21.11, 21.12, 50.20, 111.17, 123.92, 123.95, 126.90, 128.38, 129.08, 129.16, 129.21, 129.32, 131.35, 132.29, 133.26, 135.86, 135.97, 140.13, 140.33, 151.26. HRMS (FT-ICRMS): m/z calcd for C₅₀H₄₂O₂ [M]⁺: 674.3185; found: 674.3180.
3,3′-Di(2,5-dimethylphenyl)methyl-2,2′-dihydroxyl-1,1′-binaphthalene ( 7c) Mp 314-315 °C; [α]_D ²⁰ -126.6 (c 0.89, THF). ¹H NMR (300 MHz, CDCl₃): δ = 2.07 (s, 6 H), 2.11 (s, 6 H), 2.16 (s, 6 H), 2.19 (s, 6 H), 5.03 (s, 2 H, OH), 5.97 (s, 2 H), 6.59 (s, 4 H), 6.88-7.24 (m, 20 H), 7.63 (d, J = 7.48 Hz, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 19.07, 19.24, 21.32, 21.38, 44.54, 111.02, 123.66, 123.87, 126.82, 127.09, 127.30, 128.48, 129.12, 129.17, 129.75, 130.30, 131.03, 132.29, 132.36, 133.56, 133.70, 134.94, 135.25, 140.10, 141.25, 151.50. HRMS (FT-ICRMS): m/z calcd for C₅₄H₅₀O₂ [M]⁺: 730.3812; found: 730.3811.
3,3′-Di(2,3,5-trimethylphenyl)methyl-2,2′-dihydroxyl-1,1′-binaphthalene ( 7d) Mp 328-331 °C; [α]_D ²⁰ -109.2 (c 1.14, THF). ¹H NMR (300 MHz, CDCl₃): δ = 2.03 (s, 6 H), 2.05 (s, 6 H), 2.07 (s, 6 H), 2.08 (s, 6 H), 2.13 (s, 6 H), 2.17 (s, 6 H), 5.02 (s, 2 H, OH), 5.90 (s, 2 H), 6.54 (d, J = 3.86 Hz, 4 H), 6.85-7.22 (m, 12 H), 7.62 (d, J = 7.47 Hz, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 18.90, 19.06, 19.30, 19.35, 19.51, 19.62, 43.94, 111.11, 123.71, 126.64, 128.43, 129.19, 129.70, 130.36, 130.86, 131.86, 131.90, 132.37, 132.69, 133.36, 133.68, 133.72, 133.86, 134.15, 134.36, 137.64, 138.80, 151.52. HRMS (FT-ICRMS): m/z calcd for C₅₈H₅₈O₂ [M]⁺: 786.4413; found: 786.4437.
3-Phenylmethyl-2,2′-dihydroxyl-1,1′-binaphthalene ( 7e) Mp 219-220 °C; [α]_D ²⁰ -127.7 (c 1.00, THF). ¹H NMR (300 MHz, CDCl₃): δ = 4.96 (s, 1 H, OH), 5.03 (s, 1 H, OH), 5.98 (s, 1 H), 7.05 (d, J = 8.09 Hz, 2 H), 7.10-7.32 (m, 15 H), 7.43 (s, 1 H), 7.66 (d, J = 7.42 Hz, 1 H), 7.79 (d, J = 7.70 Hz, 1 H), 7.87 (d, J = 8.95 Hz, 1 H). ¹³C NMR (75 MHz, DMSO): δ = 51.00, 110.95, 110.99, 117.70, 123.92, 124.02, 124.10, 124.15, 126.48, 126.57, 127.09, 127.49, 128.39, 128.43, 128.49, 129.05, 129.40, 129.45, 129.51, 131.37, 131.46, 132.31, 133.12, 133.26, 142.97, 143.05, 151.28, 152.72. HRMS (FT-ICRMS): m/z calcd for C₃₃H₂₄O₂ [M]⁺: 452.1771; found: 452.1776.

15

For detailed X-ray structure data for 7c, see: CCDC 291165, which can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB21EZ, UK; fax: [phone]; or [e-mail]].

18

Asymmetric Addition of Diethylzinc to Aldehydes; Typical Procedure: To an ice-cooled solution of chiral ligand (0.025 mmol) in anhyd toluene (1 mL) was added Et₂Zn (1.0 M solution in toluene; 0.375 mmol) over a period of 10 min. The mixture was stirred at r.t. for 30 min and then aldehyde (0.125 mmol) was added at 0 °C. The reaction mixture was stirred for 24 h at r.t. and HCl (2.0 M) was added to quench the reaction. The mixture was extracted with EtOAc, the organic extract was washed with aq NaHCO₃ and brine in sequence, dried over anhyd Na₂SO₄, and the solvent was evaporated under reduced pressure. The conversion and ee were determined by chiral GC on a Chirasil-Dex CP 7502 (30 µ × 0.25 mm) column.