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Synlett 2009(15): 2542-2544  
DOI: 10.1055/s-0029-1217736
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

An Efficient and Direct Solvent-Free Synthesis of Naphtho[1,2-b]furans, Naphtho[2,1-b]furans, and Furo[3,2-c]chromenes

Mehdi Adib*a, Mohammad Mahdavia, Sharareh Bagherzadeha, Hamid Reza Bijanzadehb
a School of Chemistry, University College of Science, University of Tehran, PO Box 14155-6455, Tehran, Iran
Fax: +98(21)66495291; e-Mail: madib@khayam.ut.ac.ir;
b Department of Chemistry, Tarbiat Modarres University, PO Box 14115-175, Tehran, Iran
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Publication History

Received 9 February 2009
Publication Date:
27 August 2009 (online)

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Abstract

An efficient and direct synthesis of naphtho[1,2-b]furans, naphtho[2,1-b]furans, and furo[3,2-c]chromenes is described. Heating a mixture of a naphthol or 4-hydroxycoumarin, an isocyanide, and an aldehyde under an argon atmosphere and solvent-free conditions afforded the title compounds in excellent yields.

Key words

naphtho[1,2-b]furans - naphtho[2,1-b]furans - furo[3,2-c]chromenes - isocyanides - three-component reactions - solvent-free synthesis - cyclizations - heterocycles

17

Typical Procedure: Preparation of N - tert -Butyl-3-phenylnaphtho[1,2- b ]furan-2-amine (7b)
A mixture of α-naphthol (0.288 g, 2 mmol), tert-butyl isocyanide (0.166 g, 2 mmol), and benzaldehyde (0.212 g, 2 mmol) was stirred at 180 ˚C in a sealed glass vial under an argon atmosphere for 1.5 h. Then the reaction mixture was cooled to r.t., and the residue was purified by column chromatography using 4:1 n-hexane-EtOAc as eluent.
The solvent was removed under argon atmosphere, and the product was obtained as colorless crystals. Yield 0.58 g (93%); mp 145 ˚C. ¹H NMR (500.1 MHz, CDCl3): δ = 1.62 [s, 9 H, C(CH3)3], 4.49 (br s, 1 H, NH), 7.47 (t, J = 7.1 Hz, 1 H, CH), 7.54 (t, J = 7.1 Hz, 1 H, CH), 7.65 (dd, J = 7.7, 7.8 Hz, 2 H, 2 × CH), 7.71 (t, J = 7.9 Hz, 1 H, CH), 7.77 (dd, J = 0.9, 7.9 Hz, 2 H, 2 × CH), 7.79 (d, J = 8.6 Hz, 1 H, CH), 7.83 (d, J = 8.5 Hz, 1 H, CH), 8.04 (d, J = 8.2 Hz, 1 H, CH), 8.42 (d, J = 8.2 Hz, 1 H, CH). ¹³C NMR (125.8 MHz, CDCl3): δ = 30.71 [C(CH3)3], 53.81 [C(CH3)3], 100.58 (ONC=C), 117.68, 119.33 (2 × CH), 121.06 (C), 123.37 and 123.66 (2 × CH), 125.03 (C), 126.29, 126.35, 128.21, 128.62, 129.36 (5 × CH), 130.17, 133.89, 144.96, 154.67 (4 × C). Anal. Calcd for C22H21NO (315.41): C, 83.78; H, 6.71; N, 4.44. Found: C, 83.7; H, 6.8; N, 4.2.
2-( tert -Butylamino)-3-(4-methylphenyl)-4 H -furo[3,2- c ]chromen-4-one (7o)
Yield 0.66 g (95%); yellow crystals; mp 140-141 ˚C. ¹H NMR (500.1 MHz, CDCl3): δ = 1.39 [s, 9 H, C(CH3)3], 2.40 (s, 3 H, CH3), 4.20 (br s, 1 H, NH), 7.27 (d, J = 7.9 Hz, 2 H, 2 × CH), 7.28-7.30 (m, 1 H, CH), 7.38-7.41 (m, 2 H, 2 × CH), 7.43 (d, J = 7.9 Hz, 2 H, 2 × CH), 7.77 (d, J = 7.8 Hz, 1 H, CH). ¹³C NMR (125.8 MHz, CDCl3): δ = 21.28 (CH3), 30.44 [C(CH3)3], 53.98 [C(CH3)3], 103.28 (ONC=C), 110.39, 112.88 (2 × C), 116.89, 119.71, 124.19 (3 × CH), 127.59 (C), 128.93, 129.26, 129.34 (3 × CH), 136.80, 150.77, 151.56, 154.81, 157.76 (5 × C). Anal. Calcd for C22H21NO3 (347.41): C, 76.06; H, 6.09; N, 4.03. Found: C, 76.1; H, 6.1; N, 4.0.