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Synlett 2008(7): 1091-1095  
DOI: 10.1055/s-2008-1042921
LETTER
© Georg Thieme Verlag Stuttgart · New York

Microwave-Assisted One-Pot Synthesis of Dihydrocoumarins from Phenols and Cinnamoyl Chloride

Zhen Zhang, Yuan Ma*, Yufen Zhao
Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology, Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, P. R. of China
Fax: +86(10)62792673; e-Mail: mayuan@mail.tsinghua.edu.cn;
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Publication History

Received 10 December 2007
Publication Date:
17 March 2008 (online)

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Abstract

A facile approach has been developed for the synthesis of dihydrocoumarin derivatives through the reaction of phenols and cinnamoyl chloride in the presence of ecofriendly solid-acid catalyst montmorillonite K-10 via a tandem esterification-Friedel-Crafts alkylation process under microwave irradiation. The catalyst could be easily recovered and recycled.

Key words

microwave-assisted synthesis - dihydrocoumarins - phenols - cinnamoyl chloride - montmorillonite K-10

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General Procedure for the Synthesis of Dihydrocoumarins
A solution of phenol (2 mmol), cinnamoyl chloride (2 mmol, 0.33 g), and montmorillonite K-10 (1.0 g) in dried chlorobenzene (4 mL) was added to a sealed microwave tube. The reaction mixture was irradiated at a set temperature of 160 °C for 5 min with stirring using a CEM Discover microwave reactor in the closed-vessel mode. The reaction mixture was filtered and the catalyst montmorillonite K-10 was washed with EtOAc. The organic filtrates were combined. After removal of solvent, the residue was separated on a silica gel column with a mixture of hexane and CH2Cl2 (3:1 to 2:1, v/v) as eluent to afford the desired pure dihydrocoumarin as product. For dihydrocoumarins 3c and 3c′ (also for 3e and 3e′), another silica gel column chromatography (hexane-EtOAc, 20:1) was conducted to separate the isomeric products.

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Analytic Data for Unknown Products 3c′ and 3e′
3,4-Dihydro-5,6-dimethyl-4-phenylcoumarin (3c′): yellowish crystals, mp 118-120 °C. 1H NMR (300 MHz, CDCl3): δ = 2.08 (s, 3 H), 2.25 (s, 3 H), 3.01 (dd, J = 15.8, 3.5 Hz, 1 H), 3.03 (dd, J = 15.8, 5.5 Hz, 1 H), 4.47 (dd, J = 5.3, 3.4 Hz, 1 H), 6.93 (d, J = 8.2 Hz, 1 H), 7.04 (d, J = 6.2 Hz, 2 H), 7.13 (d, J = 8.2 Hz, 1 H), 7.20-7.29 (m, 3 H). 13C NMR (75 MHz, CDCl3): δ = 15.1, 20.0, 37.7, 38.7, 114.4, 123.1, 127.1, 127.4, 129.1, 130.0, 133.2, 135.1, 140.3, 150.5, 167.4. ESI-MS: m/z = 274.9 [M + Na]+. HRMS (EI): m/z calcd for C17H16O2: 252.1150; found: 252.1153.
3,4-Dihydro-5-methyl-4-phenylcoumarin (3e′): yellowish crystals, mp 110-112 °C. 1H NMR (300 MHz, CDCl3): δ = 2.19 (s, 3 H), 3.04 (dd, J = 15.8, 3.1 Hz, 1 H), 3.06 (dd, J = 15.8, 5.9 Hz, 1 H), 4.41 (dd, J = 5.9, 3.1 Hz, 1 H), 7.00 (d, J = 7.6 Hz, 1 H), 7.03-7.06 (m, 3 H), 7.19-7.30 (m, 4 H). 13C NMR (75 MHz, CDCl3): δ = 18.7, 37.6, 38.2, 115.1, 123.2, 126.4, 126.9, 127.5, 128.6, 129.1, 137.0, 140.0, 152.2, 167.2; ESI-MS: m/z = 260.8 [M + Na]+. HRMS (EI): m/z calcd for C16H14O2: 238.0994; found: 238.0997.