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Synlett 2021; 32(05): 532-538
DOI: 10.1055/s-0039-1690901
cluster
The Power of Transition Metals: An Unending Well-Spring of New Reactivity
© Georg Thieme Verlag Stuttgart · New York

Chiral P,Olefin Ligands with Rotamers for Palladium-Catalyzed Asymmetric Allylic Substitution Reactions

Takashi Mino∗
a   Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
b   Molecular Chirality Research Center, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
c   Soft Molecular Activation Research Center, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan   eMail: tmino@faculty.chiba-u.jp
,
Daiki Yamaguchi
a   Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
,
Manami Kumada
a   Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
,
Junpei Youda
a   Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
,
Hironori Saito
a   Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
,
Junya Tanaka
a   Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
,
Yasushi Yoshida
a   Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
b   Molecular Chirality Research Center, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
c   Soft Molecular Activation Research Center, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan   eMail: tmino@faculty.chiba-u.jp
,
Masami Sakamoto
a   Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
b   Molecular Chirality Research Center, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
› InstitutsangabenThis work was supported by Grants-in-Aid for Scientific Research (C) (Nos. 26410109 and 18K05117) from the Japan Society for the Promotion of Science (JSPS).
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Publikationsverlauf

Received: 16. März 2020

Accepted after revision: 29. März 2020

Publikationsdatum:
16. April 2020 (online)

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Abstract

We synthesized a series of phosphine–olefin-type chiral aminophosphines, and we confirmed that these each exists as two rotamers at the C(aryl)–N(amine) bond. We also investigated the ability of these aminophosphines to act as chiral ligands for Pd-catalyzed asymmetric allylic substitution reactions, such as the alkylation of allylic acetates with malonates or indoles, and we found they gave high enantio­selectivities (up to 98% ee).

Key words

phosphines - ligands - rotamers - asymmetric catalysis - palladium catalysis - allylic acetates

Supporting Information

    Supporting information for this article is available online at https://doi.org/10.1055/s-0039-1690901.
  • Supporting Information
 

  • References and Notes

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  • 9 [2-(Diphenylphosphoryl)-6-methoxyphenyl][(1S)-1-phenylethyl]amine [(S)-8a] A 1.6 M solution of BuLi in hexane (9.4 mL, 15.0 mmol) was slowly added to a solution of [(1S)-1-phenylethyl]amine (1.82 g, 15.0 mmol) in THF (35 mL) at –80 °C. Phosphine oxide 7a (1.69 g, 5.0 mmol) was added at r.t., and the mixture was stirred for 21 h at r.t. The mixture was then diluted with Et2O, and the reaction was quenched with sat. aq NH4Cl. The organic layer was washed with brine, dried (MgSO4), and concentrated under reduced pressure. The residue was purified by chromatography [silica gel, hexane–EtOAc (2:1)] to give a beige solid; yield: 1.60 g (75%, 3.74 mmol); mp 124–126 °C; [α]D 20 +99.1 (c 0.50, CHCl3). 1H NMR (300 MHz, CDCl3): δ = 7.68–7.53 (m, 6 H), 7.50–7.41 (m, 4 H), 7.36 (br s, 1 H), 7.15–7.12 (m, 2 H), 7.06–7.03 (m, 3 H), 6.79 (d, J = 7.1 Hz, 1 H), 6.56 (dt, J = 3.6 and 7.8 Hz, 1 H), 6.42 (ddd, J = 1.4, 7.7, 14.0 Hz, 1 H), 5.10 (t, J = 6.1 Hz, 1 H), 3.69 (s, 3 H), 1.33 (d, J = 6.8 Hz, 3 H). 13C NMR (75 MHz, CDCl3): δ = 150.7 (d, JCP = 11.6 Hz), 146.4, 144.1 (d, JCP = 5.5 Hz), 133.0 (d, JCP = 103.9 Hz), 132.6 (d, JCP = 104.5 Hz), 132.2 (d, JCP = 10.1 Hz) (2 C), 132.0 (d, JCP = 9.9 Hz) (2 C), 131.8 (d, JCP = 2.5 Hz), 131.7 (d, JCP = 2.5 Hz), 128.4 (d, JCP = 12.2 Hz) (4 C), 127.9 (2 C), 126.2 (2 C), 126.0, 125.6 (d, JCP = 11.0 Hz), 117.5 (d, JCP = 15.5), 115.6 (d, JCP = 2.5 Hz), 115.5 (d, JCP = 104.2 Hz), 55.5, 55.4, 24.6. 31P NMR (121 MHz, CDCl3): δ = 37.5. EI-MS: m/z (%): 427 (M+, 30), 412 (100). HRMS (ESI-Orbitrap): m/z [M + H]+ calcd for C27H27NO2P: 428.1774; found: 428.1766. [2-(Diphenylphosphoryl)-6-methoxyphenyl][(1S)-1-phenylethyl][(2E)-3-phenylprop-2-en-1-yl]amine [(S)-9a] To the solution of the phosphine oxide (S)-8a (2.14 g, 5.0 mmol) in MeCN (50 mL) at r.t. were added K2CO3 (3.46 g, 25 mmol) and cinnamyl bromide (1.18 g, 6.0 mmol) in MeCN (20 mL), and the mixture was stirred at 60 °C for 22 h. The mixture was then filtered and concentrated under reduced pressure. The residue was purified by chromatography [silica gel, hexane–EtOAc (5:1)] to give a white solid; yield: 2.29 g (84%, 4.22 mmol); mp 169–171 °C; [α]D 20 +53.1 (c 0.36, CHCl3). 1H NMR (300 MHz, CDCl3): δ = 7.84–7.73 (m, 4 H), 7.47–7.38 (m, 8 H), 7.24–7.01 (m, 10 H), 6.66 (ddd, J = 1.2, 7.7, 13.9 Hz, 1 H), 5.83 (d, J = 15.9 Hz, 1 H), 5.33 (ddd, J = 7.0, 7.0, 15.9 Hz, 1 H), 4.67 (q, J = 6.0 Hz, 1 H), 3.73 (dd, J = 7.5, 7.6 Hz, 1 H), 3.67 (s, 3 H), 3.26 (dd, J = 6.5, 15.1 Hz, 1 H), 1.11 (d, J = 6.7 Hz, 3 H). 13C NMR (75 MHz, CDCl3): δ = 160.1 (d, JCP = 11.5 Hz), 145.3, 143.8 (d, JCP = 4.4 Hz), 137.8, 134.7 (d, JCP = 106.6 Hz), 134.0 (d, JCP = 105.3 Hz), 133.0 (d, JCP = 103.8 Hz), 132.1 (d, JCP = 9.0 Hz) (2 C), 131.1(931) (d, JCP = 2.6 Hz), 131.1(925) (d, JCP = 9.4 Hz) (2 C), 131.0 (d, JCP = 2.8 Hz), 129.5, 128.9, 128.5 (2 C), 128.2 (d, JCP = 12.2 Hz) (2 C), 128.1 (d, JCP = 11.7 Hz) (2 C), 128.0 (2 C), 127.6 (2 C), 126.7 (d, JCP = 12.4 Hz), 126.4, 126.3, 126.2 (d, JCP = 3.3 Hz), 126.0 (2 C), 115.6 (d, JCP = 2.3 Hz), 62.3, 56.9, 55.1, 22.4. 31P NMR (121 MHz, CDCl3): δ = 27.5. EI-MS: m/z (%) = 543 (M+, 0.15), 438 (100). HRMS (ESI-Orbitrap): m/z [M + H]+ calcd for C36H35NO2P: 544.2400; found: 544.2388. X-ray diffraction analysis: Colorless plate crystals (0.20 × 0.10 × 0.020 mm3) from hexane–CHCl3; monoclinic space group P21, a = 12.4152(3) Å, b = 8.9538(2) Å, c = 13.5274(3) Å, β = 103.4670(10)°, V = 1462.40(6) Å3, Z = 2, ρ = 1.235 g/cm3, μ (Cu Kα) = 1.54178 mm–1. The structure was solved by the direct method of full-matrix least–squares, where the final R and Rw were 0.0327, 0.0875, respectively, for 4982 reflections. [2-(Diphenylphosphino)-6-methoxyphenyl][(1S)-1-phenylethyl][(2E)-3-phenylprop-2-en-1-yl]amine [(S)-6a] To a mixture of phosphine oxide (S)-9a (1.09 g, 2.0 mmol) and Et3N (3.1 mL, 22 mmol) in m-xylene (10 mL) was added HSiCl3 (2.0 mL, 20 mmol) at 0 °C under Ar. The mixture was stirred at 120 °C for 24 h then cooled to r.t. and diluted with Et2O. The reaction was quenched with 2 M aq NaOH, and the organic layer was washed with brine, dried (MgSO4), and concentrated under reduced pressure. The residue was purified by chromatography [silica gel, hexane–EtOAc (50:1)]. to give a white solid; yield 0.530 g (50%. 1.0 mmol); mp 55–56 °C; [α]D 20 +59.6 (c 0.51, CHCl3); rotamer ratio = 20:1. 1H NMR (300 MHz, CDCl3): δ (major rotamer) = 7.66 (d, J = 8.0 Hz, 2 H), 7.37–7.04 (m, 19 H), 6.86 (dd, J = 1.0, 8.1 Hz, 1 H), 6.53 (ddd, J = 1.3, 2.8, 7.6 Hz, 1 H), 6.04–5.94 (m, 1 H), 5.85 (d, J = 15.9 Hz, 1 H), 4.59 (q, J = 6.5 Hz, 1 H), 3.83 (s, 3 H), 3.58–3.42 (m, 2 H), 0.89 (d, J = 6.7 Hz, 3 H); δ (minor rotamer) = 7.66 (d, J = 7.4 Hz, 2 H), 7.37–7.04 (m, 19 H), 6.64 (dd, J = 1.0, 8.1 Hz, 1 H), 6.42–6.39 (m, 1 H), 6.09 (d, J = 16.1 Hz, 1 H), 5.76–5.68 (m, 1 H), 4.81 (q, J = 6.5 Hz, 1 H), 3.75 (s, 3 H), 3.58–3.42 (m, 2 H), 1.50 (d, J = 6.9 Hz, 3 H). 13C NMR (75 MHz, CDCl3): δ = 159.3 (d, JCP = 3.9 Hz), 147.1, 141.9 (d, JCP = 4.2 Hz), 141.1 (d, JCP = 22.0 Hz), 138.7 (d, JCP = 14.4 Hz), 138.5 (d, JCP = 15.1 Hz), 137.6, 134.2 (d, JCP = 20.5 Hz) (2 C), 134.0 (d, JCP = 20.5 Hz) (2 C), 130.1, 129.0, 128.2(8) (d, JCP = 2.0 Hz) (2 C), 128.2(6), 128.2(2) (d, JCP = 1.0 Hz) (2 C), 128.1(4) (2 C), 128.0(9) (d, JCP = 1.0 Hz) (2 C), 128.0(3), 128.0(1) (2 C), 126.9, 126.6, 126.4 (2 C), 126.1 (2 C), 111.9, 61.6, 56.3, 55.1, 23.5. 31P NMR (121 MHz, CDCl3): δ (major rotamer) = −16.0; δ (minor rotamer) = −14.1. EI-MS: m/z (%) = 527 (M+, 8.2), 422 (100). HRMS (ESI-Orbitrap): m/z [M + H]+ calcd for C36H35NOP: 528.2451; found: 528.2441.
  • 11 Palladium-Catalyzed Allylic Alkylation of Malonates; General Procedure BSA (0.15 mL, 0.60 mmol) and the appropriate allylic ester (0.20 mmol) were added to a mixture of [Pd(C3H5)Cl]2 (1.48 mg, 4 μmol), (S)-6d (4.64 mg, 8 μmol), and NaOAc (1.64 mg, 20 μmol) in PhCF3 (0.4 mL) at r.t. under Ar, and the mixture was stirred for 10 min. A dialkyl malonate (0.60 mmol) was added, and stirring was continued for 24 h at r.t. The mixture was then diluted with Et2O and water. The organic layer was washed with brine then dried (MgSO4), filtered, and concentrated in a rotary evaporator. The residue was purified by column chromatography [silica gel, hexane–EtOAc (10:1)]. Dimethyl [(1S,2E)-1,3-Diphenylprop-2-en-1-yl]malonate [(S)-10a]16 Colorless oil; yield: 55.7 mg (86%, 0.172 mmol, 94% ee); [α]D 20 –21.6 (c 0.51, CHCl3). HPLC [Daicel CHIRALPAK AD-H, 0.46 × 25 cm, λ = 254 nm, hexane–i-PrOH (90:10), 0.5 mL/min]: t R = 26.3 min (minor), 33.3 min (major). 1H NMR (400 MHz, CDCl3): δ = 7.34–7.18 (m, 10 H), 6.48 (d, J = 15.8 Hz, 1 H), 6.33 (dd, J = 8.4, 15.7 Hz, 1 H), 4.27 (dd, J = 8.1, 8.6 Hz, 1 H), 3.95 (d, J = 10.8 Hz, 1 H), 3.70 (s, 3 H), 3.52 (s, 3 H). 13C NMR (101 MHz, CDCl3): δ = 168.2, 167.8, 140.2, 136.8, 131.9, 129.1, 128.7, 128.5, 127.9, 127.6, 127.2, 126.4, 57.7, 52.7, 52.5, 49.2. EI-MS: m/z (%) = 324 (M+, 13).
  • 13 Palladium-Catalyzed Allylic Alkylation of Indoles; General Procedure PhMe (0.2 mL) was added to a mixture of indole or a substituted indole (0.2 mmol), the appropriate 1,3-diarylprop-2-enyl acetate (60.6 mg, 0.24 mmol), (S)-6a (6.3 mg, 12 μmol), [Pd(C3H5)Cl]2 (2.2 mg, 6 μmol), and KOAc (39.3 mg, 0.4 mol) at r.t. under Ar, and the mixture was stirred for 18 h at 40 °C. The reaction was quenched with H2O, and the mixture was diluted with Et2O. The organic layer was washed with H2O and brine then dried (MgSO4), filtered, and concentrated in a rotary evaporator. The residue was purified by column chromatography [silica gel, hexane–EtOAc–Et3N (20:2:1)]. 3-[(1R,2E)-1,3-Diphenylprop-2-en-1-yl]-1H-indole [(R)-11a]4 Yellow solid; yield: 48.0 mg (74%, 0.146 mmol, 97% ee); mp 118–120 °C; [α]D 20 –35.3 (c 0.19, CHCl3). HPLC [Daicel CHIRALPAKIB, 0.46 × 25 cm, λ = 254 nm, hexane–EtOH (99:1), 0.7 mL/min]: t R = 56.3 min (major), 63.9 min (minor). 1H NMR (400 MHz, CDCl3): δ = 7.98 (br s, 1 H), 7.43–7.15 (m, 13 H), 7.04–7.00 (m, 1 H), 6.90 (d, J = 2.4 Hz, 1 H), 6.73 (dd, J = 7.4, 15.8 Hz, 1 H), 6.43 (d, J = 15.9 Hz, 1 H), 5.12 (d, J = 7.3 Hz, 1 H). 13C NMR (101 MHz, CDCl3): δ = 143.3, 137.5, 136.6, 132.5, 130.5, 128.5 (2 C), 128.4, 127.1, 126.8, 126.4, 126.3, 122.6, 122.1, 119.9, 119.4, 118.7, 111.1, 46.2. EI-MS: m/z (%) 309 (M+, 100).
  • 14 CCDC 1938333 contains the supplementary crystallographic data for compound (S)-9a. The data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.