Synlett 2006(1): 0124-0126  
DOI: 10.1055/s-2005-922769
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Anthraquinone Derivatives: Tandem Diels-Alder-Decarboxyl­ation-Oxidation Reaction of 3-Hydroxy-2-pyrone with 1,4-Naphthoquinone

Takuzo Komiyama, Yutaka Takaguchi, Sadao Tsuboi*
Department of Material and Energy Science, The Graduate School of Environmental Science, Okayama University, Okayama 700-8530, Japan
Fax: +81(86)2518898; e-Mail: stsuboi6@cc.okayama-u.ac.jp;
Further Information

Publication History

Received 3 October 2005
Publication Date:
16 December 2005 (online)

Abstract

In the presence of triethylamine, the Diels-Alder reaction of 3-hydroxy-2-pyrones with 1,4-naphthoquinones by a decarboxylation-oxidation process gave anthraquinone derivatives in good to excellent yields.

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Without triethylamine, the reaction of 1a and 2a gave only traces of desired compound 4a.

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Anthraquinone 4c; Typical Procedure. To a stirred solution of 1,4-naphthoquinone 2a (72 mg, 0.46 mmol) and 2-pyrone 1c (50 mg, 0.23 mmol) in toluene (5 mL) was added Et3N (2 mg, 0.02 mmol) and the reaction mixture was heated to reflux for 2 h. Then the reaction mixture was allowed to cool to r.t. After evaporation of the solvent, the crude product was purified by column chromatography (hexane-EtOAc, 50:1) to give anthraquinone 4c (70 mg, 93%) as an orange solid; mp 210-212 °C. IR (neat): 1662, 1630, 1591, 1424, 1349, 1285, 1217, 1126, 1017, 747, 708 cm-1. 1H NMR (300 MHz, CDCl3): δ = 7.07 (d, J = 8.1 Hz, 1 H), 7.47-7.49 (m, 3 H), 7.57-7.61 (m, 2 H), 7.67 (d, J = 8.1 Hz, 1 H), 7.80-7.85 (m, 2 H), 8.27-8.34 (m, 2 H), 13.3 (br, 1 H). Anal. Calcd for C20H12O3S: C, 72.27; H, 3.64. Found: C, 72.48; H, 3.66.