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Synlett 2023; 34(09): 1068-1074
DOI: 10.1055/a-2002-4122
letter

Gold-Catalyzed Formal (3+2) Cycloaddition in an Ionic Liquid: Environmentally Friendly and Stereoselective Synthesis of Polysubstituted Indanes from Benzylic Alcohols and 1-Phenylpropenes

Nobuyoshi Morita∗
,
Hitomi Chiaki
,
Kanae Ikeda
,
Kosaku Tanaka III
,
Yoshimitsu Hashimoto
,
Osamu Tamura∗
This work was financially supported by the JSPS KAKENHI (grant number 20 K05517).
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Abstract

A gold-catalyzed formal (3+2) cycloaddition of benzylic alcohols with 1-phenylpropenes in an ionic liquid permits the environmentally friendly stereoselective synthesis of polysubstituted indanes in good yields and with high selectivity. The gold catalyst can be recycled at least five times.

Key words

gold catalysis - ionic liquids - (3+2) cycloaddition - indanes - benzylic alcohols - propenylbenzenes

Supporting Information

    Supporting information for this article is available online at https://doi.org/10.1055/a-2002-4122.
  • Supporting Information


Publication History

Received: 30 November 2022

Accepted after revision: 20 December 2022

Accepted Manuscript online:
21 December 2022

Article published online:
19 January 2023

© 2022. Thieme. All rights reserved

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  • References and Notes

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  • 19 Ethyl (1R*,2S*,3S*)- and (1R*,2R*,3R*)-1-Ethyl-5,6-dimethoxy-3-(4-methoxyphenyl)indane-2-carboxylate (4gg and 4′gg) 1 mol% AuCl (1.2 mg, 0.0051 mmol) was added at rt to a solution of benzylic alcohol 1g (100 mg, 0.51 mmol) and ethyl trans-p-methoxycinnamate (2g) (315 mg, 1.53 mmol) in [EMIM][NTf2] (1 mL). When benzylic alcohol 1g was completely consumed (TLC; usually <30 min), the product was extracted with Et2O and the solvent was removed in vacuo. The crude product was purified by column chromatography (silica gel, hexane–EtOAc) to give 4gg and 4′gg as a colorless oil; yield: 158 mg (81%, 4:1). IR (KBr): 2958, 2933, 2833, 1728, 1609, 1510, 1500, 1463 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.18 (d, J = 8.7 Hz, 2 H × 4/5)*, 7.13 (d, J = 8.7 Hz, 2 H × 1/5), 6.88 (d, J = 8.7 Hz, 2 H × 1/5), 6.86 (d, J = 8.7 Hz, 2 H × 4/5)*, 6.78 (s, 1 H × 4/5)*, 6.75 (s, 1 H × 1/5), 6.41 (s, 1 H × 4/5)*, 6.38 (s, 1 H × 1/5), 4.75 (d, J = 9.9 Hz, 1 H × 4/5)*, 4.52 (d, J = 9.3 Hz, 1 H × 1/5), 4.16 (q, J = 7.2 Hz, 2 H × 4/5)*, 4.14 (q, J = 7.2 Hz, 2 H × 1/5), 3.91 (s, 3 H × 4/5)*, 3.91 (s, 3 H × 1/5), 3.83 (s, 3 H × 1/5), 3.81 (s, 3 H × 4/5)*, 3.74 (s, 3 H × 4/5)*, 3.73 (s, 3 H × 1/5), 3.52–3.45 (m, 1 H × 1/5), 3.41 (t, J = 8.1 Hz, 1 H × 4/5)*, 3.41–3.34 (m, 1 H × 4/5)*, 2.86 (t, J = 9.0 Hz, 1 H × 1/5), 2.09–1.98 (m, 1 H × 1/5), 1.80–1.50 (m, 2 H × 4/5)*, 1.27 (t, J = 7.2 Hz, 3 H × 4/5)*, 1.23 (t, J = 7.2 Hz, 3 H × 1/5), 0.99 (t, J = 7.5 Hz, 3 H × 1/5), 0.96 (t, J = 7.5 Hz, 3 H × 4/5)*. 13C NMR (75 MHz, CDCl3): δ = 175.0, 172.6*, 158.5, 158.4*, 148.8, 148.7*, 148.1*, 136.71*, 136.67*, 136.6, 136.2, 135.8, 135.5*, 129.7*, 129.3, 113.9, 113.8*, 108.1*, 107.8*, 107.7, 106.3, 60.7, 60.5, 60.3*, 60.2*, 56.1*, 56.0*, 55.2*, 53.9, 50.7*, 48.8, 47.7*, 26.5, 24.6*, 14.3*, 11.7*, 10.6. HRMS (EI): m/z [M+] calcd for C23H28O5: 384.1937; found: 384.1935.
  • 20 CCDC 2223279 contains the supplementary crystallographic data for compound 4gg. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures
  • 21 5,6-Dimethoxy-1-(4-methoxyphenyl)-2-methylindane (3aa); Enlarged-Scale Procedure 1 mol% AuCl (14 mg, 0.060 mmol) was added at rt to a solution of benzylic alcohol 1a (1.0 g, 6.0 mmol) and ethyl trans-anethole (2a) (0.88 g, 6.0 mmol) in [EMIM][NTf2] (5 mL). When benzylic alcohol 1a was completely consumed (TLC; usually <30 min), the product was extracted with Et2O and the solvent was removed in vacuo. The crude product was purified by column chromatography (silica gel, hexane–EtOAc) to give a colorless oil; yield: 1.3 g (73%). IR (KBr): 3033, 299, 2931, 2837, 1614, 1512, 1472, 1446, 1512, 1471, 1445, 1410, 1313, 1213, 1173, 1088, 1028, 995, 856, 820, 804, 764 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.11 (d, J = 8.7 Hz, 2 H), 6.87 (d, J = 8.7 Hz, 2 H), 6.79 (s, 1 H), 6.39 (s, 1 H), 3.88 (s, 3 H), 3.81 (s, 3 H), 3.72 (s, 3 H), 3.70 (d, J = 9.5 Hz, 1 H), 3.06 (dd, J = 14.9, 7.5 Hz, 1 H), 2.55 (dd, J = 14.9, 9.5 Hz, 1 H), 2.42–2.30 (m, 1 H), 1.17 (d, J = 6.6 Hz, 3 H). 13C NMR (75 MHz, CDCl3): δ = 158.2, 148.14, 148.07, 138.3, 136.4, 135.2, 129.4, 113.8, 108.1, 107.4, 58.9, 56.1, 56.1, 55.2, 46.9, 40.1, 18.4. HRMS (EI): m/z [M+] calcd for C19H22O3: 298.1569; found: 298.1569.
  • 22 In the recycling of the gold catalyst in this reaction, the reaction time was prolonged after the first cycle. The cause is assumed to be imidazole, which is a decomposition product generated when water produced during the reaction reacts with the ionic liquid in the presence of the gold catalyst.23 The generated imidazole might coordinate to the gold catalyst, significantly reducing its activity and prolonging the reaction time; however, this has not been confirmed.
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