Synlett 2019; 30(15): 1840-1842
DOI: 10.1055/s-0039-1690106
letter
© Georg Thieme Verlag Stuttgart · New York

Base-Promoted Reactions of Hydroxyquinones with Pyrones: A Direct and Sustainable Entry to Anthraquinones and Naphthoquinones

Huangchao Yu
,
George A. Kraus
Department of Chemistry, Iowa State University, Ames, Iowa 50010, USA   Email: gakraus@iastate.edu
› Author Affiliations
We thank the NSF Engineering Center for Biorenewable Chemicals (CBiRC) which awarded NSF grant EEC-0813570 for support of this research.
Further Information

Publication History

Received: 11 April 2019

Accepted after revision: 07 June 2019

Publication Date:
08 July 2019 (online)


Abstract

Hydroxybenzoquinones and hydroxynaphthoquinones react with methyl coumalate and 5-cyanopyrone to generate anthraquinones and naphthoquinones in good to excellent yields.

Supporting Information

 
  • References and Notes

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  • 8 Diels–Alder Reaction of Methyl Coumalate with Hydroxyquinone; Typical Procedure for Methyl 6-Methoxy-5,8-dioxo-5,8-dihydronaphthalene-2-carboxylate (9a) To a solution of methyl coumalate (555 mg, 3.6 mmol, 0.9 equiv) and hydroxyquinone 8 (552 mg, 4.0 mmol, 1.0 equiv) in acetonitrile (20 mL), triethylamine (405 mg, 4.0 mmol, 1.0 equiv) was added, and the solution turned dark-red immediately. The mixture was stirred under argon at 45 °C for 24 hours (monitored by 1H NMR) then was cooled to ambient temperature. 0.5 M HCl solution was added, and the mixture was extracted with ethyl acetate three times. The organic phase was washed with brine and was dried over Na2SO4. Purification by column chromatography gave the product 9a (45% yield) as a light-brown solid. 1H NMR (400 MHz, CDCl3): δ = 8.75 (d, J = 1.6 Hz, 1 H), 8.39 (dd, J = 8.0, 1.5 Hz, 1 H), 8.16 (d, J = 8.1 Hz, 1 H), 6.23 (s, 1 H), 3.98 (s, 3 H), 3.93 (s, 3 H). 13C NMR (101 MHz, CDCl3): δ = 184.2, 179.5, 165.6, 160.9, 135.2, 134.9, 134.8, 131.3, 128.2, 126.8, 110.4, 56.8, 53.0. HRMS (ESI-QTOF): m/z [M + H]+ calcd for C13H10O5: 247.0601; found: 247.0600. Synthesis of Tomichaedin Methyl Ester Methyl 7-Hydroxy-5,8-dioxo-5,8-dihydronaphthalene-2-carboxylate (12) Under argon, a suspension of methoxy quinone 9a (180 mg, 0.73 mmol, 1.0 equiv) and AlCl3 (195 mg, 1.46 mmol, 2.0 equiv) in DCE (5 mL) was stirred under reflux for 1 hour. The reaction mixture was allowed to cool, 0.5 M HCl was added, and the mixture was extracted with ethyl acetate three times, and the organic phase was dried over Na2SO4. Filtration through a thin silica pad followed by removal of solvent afforded the product 12 as a solid, which was pure enough to use in the next step. 1H NMR (400 MHz, CDCl3): δ = 8.75 (d, J = 1.7 Hz, 1 H), 8.44 (dd, J = 8.0, 1.7 Hz, 1 H), 8.20 (d, J = 8.0 Hz, 1 H), 7.39 (s, 1 H), 6.43 (s, 1 H), 4.00 (s, 3 H). 13C NMR (101 MHz, CDCl3): δ = 184.3, 181.4, 165.4, 156.9, 136.1, 135.7, 134.7, 129.7, 128.0, 127.3, 111.4, 53.1. HRMS (ESI-QTOF): m/z [M] calcd for C12H8O5: 232.0370; found: 232.0323. Tomichaedin Methyl Ester (13) To a stainless-steel reactor, hydroxy quinone 12 (68 mg, 0.3 mmol, 1.0 equiv) was dissolved in a mixture of ethanol/water (1:1 ratio, 2 mL), and paraformaldehyde (40 mg, 1.2 mmol, 4.0 equiv) was added. The reactor was sealed under air, and was heated to 200 °C for 3 hours. After cooling, the mixture was diluted with 0.5 M HCl, and extracted with ethyl acetate. Filtration through a thin silica pad (the compound was found to be unstable on silica) afforded tomichaedin methyl ester 13 (40% over two steps) as a light-yellow solid. 1H NMR (400 MHz, CDCl3): δ = 8.71 (d, J = 1.7 Hz, 1 H), 8.39 (dd, J = 8.0, 1.8 Hz, 1 H), 8.20 (d, J = 8.0 Hz, 1 H), 3.99 (s, 3 H), 2.13 (s, 3 H). 13C NMR (101 MHz, CDCl3): δ = 184.5, 180.6, 165.5, 153.7, 135.8, 135.7, 134.5, 129.7, 127.6, 127.3, 121.5, 53.0, 9.0. HRMS (ESI-QTOF): m/z [M – H] calcd for C13H9O5: 245.0455; found: 245.0456