Quinoxaline Synthesis from α-Hydroxy Ketones via a Tandem Oxidation Process Using Catalysed Aerobic Oxidation

Abstract

The direct conversion of α-hydroxy ketones into quinoxalines via metal-catalysed aerobic oxidation followed by in situ trapping with aromatic 1,2-diamines is reported. Catalyst screening indicated that these transformations could be carried out efficiently using 2 mol% Pd(OAc)₂ or RuCl₂(PPh₃)₃-TEMPO; the palladium system was utilised for a range of transformations.

direct conversion - α-hydroxy ketones - quinoxalines

References

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Permanent address: Department of Chemistry, University of KwaZulu-Natal , Private Bag XO1, Scottsville, Pieter­maritzburg, South Africa, 3209.

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2-Hydroxyacetophenone 1a (0.136 g, 1 mmol) was added to a 25 mL round bottomed flask containing toluene (4 mL, dried over activated 3 Å MS), Et₃N (0.01 mL) and dry THF (0.6 mL). This solution was stirred and o-phenylenediamine (0.108 g, 1 mmol) was added followed by Pd(OAc)₂ (4.5 mg, 2 mol%) and the mixture was boiled under reflux for 3 h. The mixture was then filtered through a silica plug and the solvent removed in vacuo to afford a crude product which was purified using column chromatography (petroleum ether-EtOAc, 3:1) to afford 2-phenylquinoxaline 4a (0.1703 g, 83%) as an orange solid: R _f = 0.35 (petroleum ether-EtOAc, 2:1); mp 79-80 °C (lit.^11a) mp 79-80 °C); spectroscopic data consistent with those published (ref. 10b).

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