Development of a New Chiral
Spiro Oxazolinylpyridine Ligand (Spymox) for Asymmetric
Catalysis

Kazutaka Shibatomi; Tsubasa Muto; Yusuke Sumikawa; Akira Narayama; Seiji Iwasa

doi:10.1055/s-0028-1087675

LETTER

Development of a New Chiral Spiro Oxazolinylpyridine Ligand (Spymox) for Asymmetric Catalysis

Kazutaka Shibatomi*, Tsubasa Muto, Yusuke Sumikawa, Akira Narayama, Seiji Iwasa*
Department of Materials Science, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580, Japan
Fax: +81(532)48 5833; e-Mail: shiba@tutms.tut.ac.jp; e-Mail: iwasa@tutms.tut.ac.jp;

Abstract

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Abstract

A novel optically active 2-(oxazolinyl)pyridine ligand (Spymox) having a spiro binaphthyl backbone was synthesized from an α,α-disubstituted α-amino acid (H-Bin-OH), and successfully used in palladium-catalyzed asymmetric allylic alkylations to afford the corresponding alkylated products with 99% ee.

Key words

ligand design - α-amino acid - spiro compounds - asymmetric catalysis - allylic substitution

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References

References and Notes

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Most of the reported efficient spiro chiral ligands have a 1,1′-spirobiindane backbone. For examples, see:

<A NAME="RU10808ST-2A">2a</A> Birman VB. Rheingold AL. Lam K.-C. Tetrahedron: Asymmetry 1999, 10: 125

<A NAME="RU10808ST-2B">2b</A> Hu A.-G. Fu Y. Xie J.-H. Zhou H. Wang L.-X. Zhou Q.-L. Angew. Chem. Int. Ed. 2002, 41: 2348

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Examples of spiro chiral ligands other than those listed in ref. 2:

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Synthesis of H-Bin-OR and their application to peptide chemistry:

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Palladium-catalyzed asymmetric allylic alkylation using a spiro chiral ligand having a 1,1′-spirobiindane backbone (SDP) has been reported, see ref. [²d] .

A previous report on asymmetric allylic alkylation using pymox-Pd complex also shows moderate enantioselectivity (50% ee): Nordström K., Macedo E., Moberg C.; J. Org. Chem.; 1997, 62: 1604

Palladium-catalyzed asymmetric allylic alkylations with fluorinated carbanion:

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Compound 1: ^¹H NMR (300 MHz, CDCl₃): δ = 8.71 (m, 1 H), 8.08 (m, 1 H), 7.95 (m, 4 H), 7.77 (m, 1 H), 7.65 (d, J = 8.0 Hz, 1 H), 7.50 (d, J = 8.4 Hz, 1 H), 7.46-7.38 (m, 4 H), 7.33 (d, J = 8.8 Hz, 1 H), 7.27-7.20 (m, 2 H), 4.65 (d, J = 8.8 Hz, 1 H), 3.95 (d, J = 8.8 Hz, 1 H), 2.94 (d, J = 13.1 Hz, 1 H), 2.88 (d, J = 13.3 Hz, 1 H), 2.72 (d, J = 13.3 Hz, 1 H), 2.65 (d, J = 13.1 Hz, 1 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 162.1, 149.8, 147.0, 136.7, 135.4, 134.7, 134.5, 133.7, 133.1, 133.0, 132.1, 131.9, 128.7, 128.5, 128.4, 128.4, 128.3, 127.5, 127.4, 127.2, 126.0, 125.7, 125.4, 125.1, 124.4, 82.5, 77.3, 44.4, 43.5. IR (neat): 3847, 3741, 3475, 3053, 2938, 1635, 1577, 1469, 1361, 1302, 1092, 968, 813, 751, 696, 615 cm^-¹. Anal. Calcd (%) for C₃₀H₂₂N₂O: C, 84.48; H, 5.20; N, 6.57. Found: C, 84.67; H, 5.15; N, 6.36. [α]_D -72.4 (c 1.25, CHCl₃).

Compound 4: ^¹H NMR (300 MHz, CDCl₃): δ = 8.45 (m, 1 H), 8.23 (m, 2 H), 7.96-7.86 (m, 5 H), 7.55 (m, 1 H), 7.48-7.37 (m, 6 H), 7.29-7.23 (m, 2 H), 5.19 (dd, J = 5.2, 8.0 Hz, 1 H), 4.01 (dd, J = 8.0, 11.5 Hz, 1 H), 3.83 (dd, J = 5.2, 11.5 Hz, 1 H), 3.23 (d, J = 13.7 Hz, 1 H), 3.11 (d, J = 12.4 Hz, 1 H), 2.54 (d, J = 13.7 Hz, 1 H), 2.45 (d, J = 12.4 Hz, 1 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 165.0, 149.6, 148.2, 137.8, 135.4, 135.4, 134.8, 134.6, 134.4, 133.2, 133.2, 133.1, 132.0, 132.0, 128.6, 128.4, 128.4, 128.1, 128.1, 127.4, 126.6, 126.1, 126.0, 125.6, 125.4, 122.3, 70.2, 66.9, 41.0, 38.9. IR (neat): 3846, 3343, 3053, 2928, 1667, 1525, 1457, 1324, 1245, 1058, 817, 752, 697, 621, 436 cm^-¹. Anal. Calcd (%) for C₃₀H₂₄N₂O₂: C, 80.06; H, 5.44; N, 6.30. Found: C, 81.34; H, 5.74; N, 6.03. [α]_D -90.5 (c 1.0, CHCl₃).

Compound 5e: ^¹H NMR (300 MHz, CDCl₃): δ = 7.29-7.05 (m, 8 H), 6.60 (d, J = 15.3 Hz, 1 H), 6.41-6.28 (m, 2 H), 2.36 (s, 3 H), 2.32 (s, 3 H), 2.13 (s, 3 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 170.2, 139.3, 138.4, 138.2, 136.2, 132.6, 129.0, 128.9, 128.63, 128.57, 127.8, 127.5, 124.2, 124.0, 76.4, 21.6, 21.49, 21.45. Anal. Calcd (%) for C₁₉H₂₀O₂: C, 81.40; H, 7.19; O, 11.41. Found: C, 81.06; H, 6.62.

Compound 6e: ^¹H NMR (300 MHz, CDCl₃): δ = 7.26-7.00 (m, 8 H), 6.44 (d, J = 15.6 Hz, 1 H), 6.29 (dd, J = 15.6 Hz, 1 H), 4.21 (dd, J = 10.8, 8.4 Hz, 1 H), 3.94 (d, J = 10.8 Hz, 1 H), 3.70 (s, 3 H), 3.53 (s, 3 H), 2.33 (s, 3 H), 2.31 (s, 3 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 168.4, 168.0, 140.3, 138.4, 138.1, 136.9, 131.9, 129.1, 128.7, 128.5, 128.0, 127.2, 124.8, 123.7, 57.7, 52.76, 52.74, 52.60, 52.57, 49.3. Anal. Calcd (%) for C₂₂H₂₄O₄: C, 74.98; H, 6.86; O, 18.16. Found: C, 74.69; H, 6.86. [α]_D +24.1 (c 0.63, CHCl₃). The er was determined by HPLC [hexane-2-PrOH (96:4), 0.5 mL/min] using a CHIRALPAK AD column (0.46 cm × 25 cm): t _R (major isomer) = 23.0 min; t _R (minor isomer) = 26.5 min.