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Synlett 2013; 24(9): 1137-1141
DOI: 10.1055/s-0032-1316915
letter
© Georg Thieme Verlag Stuttgart · New York

An Environmentally Benign Synthesis of Octahydro-2H-chromen-4-ols via Modified Montmorillonite K10 Catalyzed Prins Cyclization Reaction

Gakul Baishya*
Natural Products Chemistry Division, CSIR-North East Institute of Science & Technology, Jorhat-785006, Assam, India   Fax: +91(376)2370011   Email: b.gakul@gmail.com
,
Barnali Sarmah
Natural Products Chemistry Division, CSIR-North East Institute of Science & Technology, Jorhat-785006, Assam, India   Fax: +91(376)2370011   Email: b.gakul@gmail.com
,
Nabajyoti Hazarika
Natural Products Chemistry Division, CSIR-North East Institute of Science & Technology, Jorhat-785006, Assam, India   Fax: +91(376)2370011   Email: b.gakul@gmail.com
› Author Affiliations
Further Information

Publication History

Received: 22 January 2013

Accepted after revision: 20 March 2013

Publication Date:
16 April 2013 (online)

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Abstract

(–)-Isopulegol undergoes Prins cyclization reaction in the presence of 20 wt% of acid-treated montmorillonite K10 to produce octahydro-2H-chromen-4-ols in good yields and with high cis selectivities under solvent-free conditions. The solid-acid catalyst can be reused without loss of its activity.

Key words

(–)-isopulegol - Prins cyclization - H-K10 mont - octahydro-2H-chromen-4-ols - reusability

Supporting Information

    for this article is available online at http://www.thieme-connect.com/ejournals/toc/synlett.
  • Supporting Information
 

  • References

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  • 13 Experimental Procedure and Analytical Data Preparation of the Catalyst H-K10 Mont A slurry of commercially available montmorrilonite K10 (5 gm) in 1 M HCl (100 mL) was stirred vigorously at 80 °C for 6 h. The solid was filtered out and washed several times with deionized H2O to remove Cl– completely. The solid residue was then dried at 120 °C for 12 h to afford the catalyst. General Procedure for the Synthesis of Octahydro-2H-chromen-4-ol Derivatives A mixture of (–)-isopulegol (1, 1 mmol), an aldehyde 2 (1.2 mmol), and H-K10 mont [20% (wt/wt of 1] were irradiated in a closed vessel in the absence of any solvent in a Synthos 3000 microwave reactor at 360 W for 3 min. After 3 min of reaction time EtOAc was added to the crude reaction mixture, and the mixture was filtered. The residue was further washed with EtOAc to completely remove any product. The EtOAc layer was concentrated under reduced pressure, and the residue was purified by chromatography on silica gel using EtOAc–hexane (3:7) as the eluent to furnish pure the chromenol derivatives 3 and 4. The solid acid catalyst was dried under vacuum and kept in oven at 100 °C before its use for another cycle. The sturctures of the compounds 3a, 4a, 3c, 4c, 3e, 4e, 3f, 4f, 3h, 4h, 3r, 4r, 3s, and 4s were confirmed by comparison of their analytical data with those reported in the literature.7 The analytical data of all new compounds are given in the Supporting Information. Selected Analytical Data Compound 3g: viscous liquid. IR (CHCl3): 3376, 2949, 2924, 2869, 1590, 1562, 1473, 1455, 1377, 1092, 942, 824, 759 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.52 (d, 1 H, J = 8.4 Hz), 7.32 (d 1 H, J = 1.9 Hz), 7.24 (m, 1 H), 4.76 (dd, 1 H, J = 1.4, 11.4 Hz), 3.27 (dt, 1 H, J = 4.2, 10.4 Hz), 2.08–1.93 (m, 2 H), 1.75 (m, 1 H), 1.60 (br s, 1 H, OH), 1.45–1.30 (m, 3 H), 1.32 (s, 3 H), 1.27–0.98 (m, 4 H), 0.94 (d, 3 H, J = 6.4 Hz). 13C NMR (75 MHz, CDCl3): δ = 138.7, 133.3, 131.8, 128.8, 128.2, 127.4, 77.6, 73.0, 70.8, 52.1, 48.6, 41.4, 34.3, 31.4, 23.0, 22.2, 21.0. ESI-MS: m/z = 330 [M + 1]+. Anal. Calcd for C17H22Cl2O2: C, 62.01; H, 6.73. Found: C, 61.96; H, 6.80. Compound 4g: viscous liquid. IR (CHCl3): 3481, 2926, 2854, 1589, 1563, 1472, 1455, 1375, 1251, 1095, 777 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.50 (d, 1 H, J = 8.4 Hz), 7.31 (d 1 H, J = 2.0 Hz), 7.23 (d, 1 H, J = 1.9 Hz), 5.12 (dd, 1 H, J = 1.7, 11.4 Hz), 3.59 (dt, 1 H, J = 4.0, 11.0 Hz), 1.99–1.94 (m, 2 H), 1.85–1.65 (m, 2 H), 1.55 (br s, 1 H, OH), 1.50–1.40 (m, 2 H), 1.25 (s, 3 H), 1.23–0.96 (m, 4 H), 0.94 (d, 3 H, J = 6.5 Hz). 13C NMR (75 MHz, CDCl3): δ = 139.3, 133.1, 132.0, 128.8, 128.3, 127.3, 75.8, 71.2, 69.4, 49.5, 46.6, 41.3, 34.4, 31.2, 28.1, 22.5, 22.2. ESI-MS: m/z = 330 [M + 1]+. Compound 3i: white solid; mp 97 °C. IR (CHCl3): 3387, 2923, 2867, 1597, 1569, 1454, 1376, 1354, 1321, 1206, 1102, 1034, 781, 689 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.45 (s, 1 H), 7.32 (dd, 1 H, J = 1.4, 3.1 Hz), 7.18 (d, 1 H, J = 1.5 Hz), 7.10 (d, 1 H, J = 7.7 Hz), 4.33 (dd, 1 H, J = 2.0, 11.7 Hz), 3.53 (dt, 1 H, J = 4.2, 10.5 Hz), 1.84–1.96 (m, 1 H), 1.82 (dd, 1 H, J = 2.3, 12.8 Hz), 1.20–1.76 (m, 5 H), 1.23 (s, 3 H), 0.95–1.19 (m, 3 H), 0.87 (d, 3 H, J = 6.5 Hz). 13C NMR (75 MHz, CDCl3): δ = 145.3, 130.2, 129.8, 129.0, 124.6, 122.5, 75.6, 74.0, 69.4, 49.3, 48.1, 41.2, 34.4, 31.3, 28.2, 22.5, 22.2. ESI-MS: m/z = 362 [M + Na]+. Anal. Calcd for C17H23BrO2: C, 60.18; H, 6.83. Found: C, 60.14; H, 6.81. Compound 4i: semi-solid. IR (CHCl3): 3455, 2927, 2869, 1597, 1570, 1476, 1455, 1424, 1375, 1327, 1253, 1162, 1097, 1063, 1036, 901, 782, 757 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.53 (s, 1 H), 7.38 (dd, 1 H, J = 1.2, 2.9 Hz), 7.32 (d, 1 H, J = 1.5 Hz), 7.15 (d, 1 H, J = 7.7 Hz), 4.75 (dd, 1 H, J = 2.1, 11.6 Hz), 3.53 (dt, 1 H, J = 4.1, 11.0 Hz), 1.98 (m, 1 H), 1.70–1.80 (m, 1 H), 1.35–1.76 (m, 3 H), 1.24 (s, 3 H), 1.05–1.19 (m, 3 H), 0.96 (d, 3 H, J = 6.5 Hz). 13C NMR (75 MHz, CDCl3): δ = 145.3, 130.2, 129.8, 129.0, 124.6, 122.5, 75.6, 74.0, 69.4, 49.3, 48.1, 41.2, 34.4, 31.3, 28.2, 22.5, 22.2. ESI-MS: m/z = 362 [M + Na].