Selective oxidations by nitrosating agents in liquid and solid acid catalysts

Ethylene glycol and H2SO4 / SiO2 as a green medium for the preparation of quinoxaline derivatives at room temperature

“…5 Most of the existing methodologies suffer from disadvantages such as the use of volatile organic solvents, unsatisfactory product yields, critical product isolation procedures, expensive and detrimental metal precursors and harsh reaction conditions, which limit their use under the aspect of environmentally benign processes. Also silicasupported reagent, H2SO4 / SiO2 for its ease of preparation, low cost, high efficiency and environmental benignness, 6 has already been used in cylcoadditions, 7 Beckmann rearrangements, 8 glycosylations, 9 condensations, 10 esterification, 11 acetylation of (+)cedrol compound, 12 synthesis of 2,4,5-triaryl-1H-imidazoles, 13 and as catalyst in organic transformations: a comprehensive review. 14 On the other hand, during our continuing efforts to develop convenient approaches to synthesize heterocycle compounds, 15 we revealed that H2SO4/SiO2 was a high-efficient and recyclable catalyst for preparing the quinoxaline derivatives in a synthetically practical procedure (stoichiometric ratios of starting materials and short reaction times) with relatively widely functional group compatibility in ethylene glycol at ambient temperature (Scheme 1).…”