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Synlett 2010(16): 2493-2497  
DOI: 10.1055/s-0030-1258567
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Efficient Nucleophilic Substitution of α-Aryl Alcohols with 1,3-Dicarbonyl Compounds Catalyzed by Tin Ion-Exchanged Montmorillonite

Jiacheng Wang, Yoichi Masui, Makoto Onaka*
Department of Chemistry, Graduate School of Arts and Sciences, The University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan
e-Mail: conaka@mail.ecc.u-tokyo.ac.jp;
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Publikationsverlauf

Received 29 June 2010
Publikationsdatum:
10. September 2010 (online)

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Abstract

Tin ion-exchanged montmorillonite demonstrated the high catalytic activity for the direct nucleophilic substitution of a hydroxyl group in α-aryl alcohols with various 1,3-dicarbonyl compounds including less acidic 1,3-diesters in crude solvents to afford the benzylated products accompanied by water.

Key words

tin ion-exchanged montmorillonite - heterogeneous catalysis - nucleophilic substitution - α-aryl alcohols - 1,3-dicarbonyl compounds

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Masui, Y.; Wang, J. C.; Onaka, M. to be submitted.

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General Procedure for Sn-Mont-Catalyzed Nucleophilic Substitution of Alcohols with 1,3-Dicarbonyl Compounds: In a flask were placed Sn-Mont (25 mg, 4.75 mol%) which was activated at 120 ˚C for 1 h in a vacuum, 1,2-dichloroethane (2 mL), which was not required to be dehydrated, benzhydrol (1a; 1 mmol), and dimethyl malonate (2a; 1.5 mmol). The resultant mixture was stirred vigorously at 100 ˚C under reflux. After the completion of the reaction monitored with TLC, the catalyst was removed by filtration through a Celite plug, followed by being washed with CH2Cl2. The combined solution was evaporated under reduced pressure to give the crude product. Further purification was carried out by silica gel chromatography (eluting solvent: hexane-EtOAc, 8:1) to give the desired 3aa as a white solid in 90% yield.

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Spectroscopic data for selected products: 3-(Diphenylmethyl)-
pentane-2,4-dione (3aa): white solid; mp 112-114 ˚C. ¹H NMR (500 MHz, CDCl3): δ = 2.00 (s, 6 H), 4.73 (d, J = 12.3 Hz, 1 H), 4.81 (d, J = 12.3 Hz, 1 H), 7.10-7.20 (m, 2 H), 7.25-7.30 (m, 8 H). ¹³C NMR (126 MHz, CDCl3): δ = 29.7, 51.2, 74.5, 127.0, 127.7, 128.9, 141.2, 203.0. HRMS: m/z calcd for C18H18O2: 266.1307; found: 266.1312. Dimethyl 2-(Diphenylmethyl)malonate (3ac): white solid; mp 88-90 ˚C. ¹H NMR (500 MHz, CDCl3): δ = 3.54 (s, 6 H), 4.36 (d, J = 12.3 Hz, 1 H), 4.77 (d, J = 12.3 Hz, 1 H), 7.15-7.20 (m, 2 H), 7.24-7.30 (m, 8 H). ¹³C NMR (126 MHz, CDCl3): δ = 51.1, 52.6, 57.2, 126.9, 127.7, 128.6, 141.1, 168.0. HRMS: m/z calcd for C18H18O4: 298.1205; found: 298.1199. Ethyl 3-Oxo-2-(diphenylmethyl)butanoate (3af): white solid; mp 87-89 ˚C. ¹H NMR (500 MHz, CDCl3): δ = 1.00 (t, J = 7.1 Hz, 3 H), 2.09 (s, 3 H), 4.00 (q, J = 7.1 Hz, 2 H), 4.53 (d, J = 12.3 Hz, 1 H), 4.76 (d, J = 12.3 Hz, 1 H), 7.15-7.25 (m, 2 H), 7.24-7.35 (m, 8 H). ¹³C NMR (126 MHz, CDCl3): δ = 13.7, 30.0, 50.9, 61.5, 65.2, 126.8, 126.9, 127.7, 127.8, 128.6, 128.8, 141.2, 141.5, 167.6, 201.8. HRMS: m/z calcd for C19H20O3: 296.1412; found: 296.1423.