2-Hydroxylation of 1,3-Diketones with Atmospheric Oxygen

Abstract

An efficient method for the 2-hydroxylation of 1,3-diketones by using atmospheric oxygen as an oxidant under transition-metal-free condition is described. The protocol has the advantages of using an inexpensive and stable oxidant, producing high yields, and requiring ecofriendly conditions.

Key words

diketones - hydroxylations - oxidations - green chemistry

• References and Notes

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• 13 2-Hydroxy-1,3-diketones 2; General Procedure A mixture of 1,3-diketone 1 (1.0 mmol), KF (0.1 mmol), and NaOH (0.2 mmol) in DMF (4.8 mL) and H₂O (0.2 mL) was stirred at 120 °C under air for 12 h. When the reaction was complete (TLC), the mixture was cooled to r.t., diluted with EtOAc, and washed with sat. aq Na₂CO₃. The resulting organic phase was dried (MgSO₄) and concentrated under reduced pressure. The residue was purified by column chromatography [silica gel, PE–EtOAc (20:1)]. Analytical data for representative products are given below. 2-Hydroxy-1,3-diphenylpropane-1,3-dione (2a) White solid; yield: 95%; mp 92–94 °C. ¹H NMR (600 MHz, CDCl₃): δ = 7.99 (d, J = 7.8 Hz, 4 H, ArH), 7.47–7.55 (m, 6 H, ArH), 6.86 (s, 1 H, CH). ¹³C NMR (150 MHz, CDCl₃): δ = 185.7, 135.5, 132.4, 126.7, 127.1, 93.1. Anal. Calcd for C₁₅H₁₂O₃: C, 74.99; H, 5.03. Found: C, 74.86; H, 5.05. 1-(2-Furyl)-2-hydroxy-3-phenylpropane-1,3-dione (2n) White solid; yield: 80%; mp 76–78 °C. ¹H NMR (600 MHz, CDCl₃) δ = 7.96 (d, J = 7.2 Hz, 2 H, ArH), 7.47–7.62 (m, 4 H, ArH and FuH), 7.23–7.27 (m, 2 H, ArH and FuH), 6.77 (s, 1 H, CH). ¹³C NMR (150 MHz, CDCl₃): δ = 182.5, 177.7, 151.0, 146.1, 134.7, 132.4, 128.7, 127.0, 115.8, 112.7, 92.7. Anal. Calcd for C₁₃H₁₀O₄: C, 67.82; H, 4.38. Found: C, 67.74; H, 4.39.