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Synlett 2004(13): 2429-2433  
DOI: 10.1055/s-2004-832824
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© Georg Thieme Verlag Stuttgart · New York

(R)-1,1′-Binaphthyl-2-bis(pentafluorophenyl)borane Lewis Acids

Darryl J. Morrison, Warren E. Piers*, Masood Parvez
Department of Chemistry, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, T2N 1N4, Canada
Fax: +1(403)2899488; e-Mail: wpiers@ucalgary.ca;
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Publication History

Received 18 June 2004
Publication Date:
24 September 2004 (online)

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Abstract

A practical and high yielding synthetic route was developed for the preparation of optically pure (R)-(+)-2-bis(pentafluorophenyl)boryl-, (R)-(+)-1a,b, and (R)-2-difluoroboryl-1,1′-binaphthyls, (R)-5a,b. Chiral boranes (R)-1a and (R)-5a are active catalysts for the allylstannation of aromatic aldehydes although enantioselectivities for R products were low. A structural investigation of the adduct (±)-1a·o-anisaldehyde suggested that substituents in the 2′-position of the binaphthyl backbone could increase enantiofacial discrimination. Consistent with this structural study, the 2′-Me derivative (R)-1b gave slightly higher enantioselectivities and opposite configuration S of homoallylic alcohol products.

Key words

Lewis acids - boron - asymmetric synthesis - asymmetric catalysis - allylations

    References

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    1-Phenyl-3-buten-1-ol: t R (R)-(+), 13.7 min; t R (S)-(-), 14.8 min (Daicel Chiralcel OD, hexane-2-PrOH = 19:1, 1 mL/min) [lit.: [18d] t R (R)-(+), 15.2 min; t R (S)-(-), 16.5 min, Daicel Chiralcel OD-H, hexane-2-PrOH = 19:1, 0.5 mL/min]

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    1-(2-Methoxyphenyl)-3-buten-1-ol: t R (S)-(-), 16.9 min; t R (R)-(+), 18.9 min, (Daicel Chiralcel OD, hexane-2-PrOH = 49:1, 1 mL/min) [lit.: [18d] t R (S)-(-), 15.6 min; t R (R)-(+), 16.7 min, Daicel Chiralcel OD-H, hexane-2-PrOH = 9:1, 0.5 mL/min]

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11

(R)-3a: The 1H NMR and 11B NMR spectral data matched that reported by Yamamoto and co-workers. [6] (R)-3b: 11B NMR (128.2 MHz, CDCl3 + D2O): δ = 28.8 (s).

13

(R)-(-)-4a: 19F NMR (282.4 MHz, acetone-d 6): δ = -137.5 (m). 11B NMR (128.2 MHz, acetone-d 6): δ = 2.8 (s). [α]D 20 -100.0 (c 0.011, acetone). (R)-(-)-4b: 19F NMR (282.4 MHz, acetone-d 6): δ = -137.5 (m). 11B NMR (128.2 MHz, acetone-d 6): δ = 2.7 (s). [α]D 21 = -4.8 (c 0.0080, acetone).

14

(R)-5a: 19F NMR (282.4 MHz, CD2Cl2): δ = -82.2, (s). 11B NMR (128.2 MHz, CD2Cl2): δ = 24.0, (s). (R)-5b: 19F NMR (282.4 MHz, CDCl3): δ = -82.7, (s). 11B NMR (128.3 MHz, CDCl3): δ = 23.6 (s).

15

Complete characterization data and experimental procedures for all new compounds will be reported elsewhere. (R)-(+)-1a: yield: 82% [60% overall yield over 5 steps from (R)-(+)-DBBN]. 1H NMR (399.9 MHz, CDCl3): δ = 8.00 (app. t, J = 8.08 Hz, 2 H), 7.76-7.73 (m, 2 H), 7.61-7.58 (m, 2 H), 7.52 (dm, J = 7.68 Hz, 1 H), 7.44-7.32 (m, 6 H); (300.1 MHz, C6D6): δ = 7.77 (d, J = 8.21 Hz, 1 H), 7.68 (d, J = 8.21 Hz, 1 H), 7.47-7.41 (m, 3 H), 7.39-7.35 (m, 3 H), 7.21 (m, 1 H), 7.13 (m, 1 H), 7.06 (m, 1 H), 6.96 (m, 1 H), 6.92 (m, 1 H). 13C NMR (100.6 MHz, CDCl3; aryl-CFs, aryl-CB, and one other aromatic carbon resonance not located): δ = 145.8, 140.2, 135.4, 132.7, 132.5, 132.4, 130.2, 129.4, 128.9, 128.5, 128.4, 128.3, 128.0, 127.63, 127.56, 127.0, 126.7, 126.6, 125.5. 19F NMR (282.4 MHz, C6D6): δ = -127.5 (m, 4 F, ortho-F), -148.3 (app. t, J = 19.7 Hz, 2 F, para-F), -161.3 (m, 4 F, meta-F). 11B NMR (128.2 MHz, CD2Cl2): δ = 62.7 (br s). [α]D 22 +610.0 (c 0.0070, CH2Cl2). Analytically pure samples of (±)-1a were obtained by recrystallization from pentane. Anal. Calcd for C32H13BF10: C, 64.25%; H, 2.19%. Found: C, 64.85%; H, 2.28%. X-ray quality single crystals of (±)-1a were obtained by cooling a saturated pentane solution of (±)-1a to -30 °C to yield yellow blocks. (R)-(+)-1b: yield: 84% [62% overall yield over 5 steps from (R)-(+)-DBBN]. 1H NMR (399.7 MHz, CD2Cl2): δ = 8.05 (d, J = 8.44 Hz, 1 H), 8.02 (d, J = 8.27 Hz, 1 H), 7.75 (d, J = 8.42 Hz, 1 H), 7.70 (m, 2 H), 7.63 (m, 1 H), 7.36-7.31 (m, 4 H), 7.22 (m, 1 H), 7.00 (d, J = 8.51 Hz, 1 H), 2.08 (s, 3 H). 13C NMR (100.5 MHz, CD2Cl2; aryl-CFs, aryl-CB, and one other aromatic carbon resonance not located): δ = 148.4, 136.9, 136.8, 136.1, 134.0, 133.0, 131.9, 131.6, 129.6, 129.0, 128.8, 128.5, 128.0, 127.64, 127.57, 127.5, 126.7, 125.6, 20.7. 19F NMR (282.4 MHz, CD2Cl2): δ = -128.3 (m, 4 F, ortho-F), -150.3 (app. t, J = 19.5 Hz, 2 F, para-F), -162.2 (m, 4 F, meta-F). 11B NMR (128.2 MHz, CD2Cl2): δ = 64.6 (br s). [α]D 21 +450.0 (c 0.0080, CH2Cl2). Anal. Calcd for C33H15BF10: C, 64.74%; H, 2.47%. Found: C, 63.68%; H, 2.32%.

16

Crystallographic data for (±)-1a: yellow plate, C32H13BF10, FW = 598.23, monoclinic, space group C2/c, radiation MoKα (λ = 0.71073 Å), a = 40.833 (16) Å, b = 8.717 (4) Å, c = 14.386 (7) Å, β = 93.60 (2)°, V = 5110 (4) Å3, ρ calc = 1.555 gcm-3, Z = 8, absorption coefficient 0.141 mm-1, F(000) = 2400, crystal size 0.18 × 0.16 × 0.07 mm3, T = 173 (2) K, θ range for data collection 3.4-25.0°, index ranges -47 ≤ h ≤ 48, -10 ≤ k ≤ 8, -16 ≤ l ≤ 16, 7363 reflections collected, 4414 independent reflections (R ( int) = 0.029), completeness to θ = 25.0° 97.7%, absorption correction multi-scan method, refinement method full-matrix least-squares on F 2, number of data/restraints/parameters 4414/0/388, goodness of fit on F 2 1.000, final R indices [I > 2σ(I)] R1 = 0.0431 and wR2 = 0.1001, final R indices (all data) R1 = 0.0802 and wR2 = 0.1180, largest difference peak and hole 0.179 and -0.189 eÅ-3.

19

Crystallographic data for (±)-1a·o-anisaldehyde: orange prism, C40H21BF10O2·0.25C6H14, FW = 755.92, triclinic, space group P-1, radiation MoKα (λ = 0.71073 Å), a = 11.064 (2) Å, b = 12.839 (3) Å, c = 14.902 (3) Å, α = 89.906 (12)°, β = 106.060 (14)°, γ = 115.233 (8)°, V = 1823.6 (7) Å3, ρ calc = 1.377 gcm-3, Z = 2, absorption coefficient 0.118 mm-1, F(000) = 769, crystal size 0.20 × 0.16 × 0.15 mm3, T = 173 (2) K, θ range for data collection 3.1-27.4°, index ranges -14 ≤ h ≤ 14, -16 ≤k ≤ 16, -19 ≤ l ≤ 19, 15455 reflections collected, 8226 independent reflections (R ( int) = 0.039), completeness to θ = 27.4° 99.0%, absorption correction multi-scan method, refinement method full-matrix least-squares on F 2, number of data/restraints/parameters 8226/0/506, goodness of fit on F 2 1.037, final R indices [I > 2σ(I)] R1 = 0.0582 and wR2 = 0.1663, final R indices (all data) R1 = 0.1188 and wR2 = 0.1989, largest difference peak and hole 0.673 and
-0.255 eÅ-3.