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Synthesis and Functionalization of 3-Ethylquinoxalin-2(1H)-one

“…The 1 H NMR spectra of α-substituted 3-ethylquinoxalin-2-one derivatives VI-VIII contained signals from the CH and CH 3 protons of the substituent in position 3, which appeared as a quartet and doublet, Having such derivatives as 3-(1-bromoethyl), 3-(1-thiocyanatoethyl), and 3-(1-azidoethyl) (compounds III, VI, and VII) at our disposal, it seemed reasonable to obtain a more promising (from the synthetic viewpoint) quinoxaline derivative, namely 3-acetylquinoxalin-2(1H)-one (IXa) [5]. It can be prepared by analogy with 3-(α-X-benzyl) derivatives, or from bromo and thiocyanato derivatives III and VI by the Kornblum reaction, or by acid hydrolysis of azido derivative VII.…”

“…Thiourea, 0.06 g (0.79 mmol), was added to a solution of 0.20 g (0.75 mmol) of compound Xa in 10 ml of methanol, and the mixture was heated for 1. 5 …”

“…The ethyl group in 3-ethylquinoxalin-2(1H)-one can readily be converted into various functional groups: α-bromoethyl, α-thiocyanato, α-azidoethyl, α-phenylaminoethyl, acetyl, and bromoacetyl. The reaction of 3-(bromoacetyl)quinoxalin-2(1H)-one with thiourea and hydrazine-1,2-dicarbothioamide gives the corresponding 3-(2-amino-4-thiazolyl) derivatives.We previously showed that 3-(α-chlorobenzyl)-quinoxalin-2(1H)-one (I), which is readily available via reaction of 3-chloro-3-phenyl-2-oxopropionates with o-phenylenediamine, is a convenient polyfunctional reagent for the synthesis of various fused quinoxaline derivatives, such as thiazolo[3,4-a]-, imidazo-[1,5-a]-, pyrrolo[1,2-a]-, pyrazolo[3,4-b]-, pyrano-[5,6-b]-, and indolizino[2,3-b]quinoxalines [1][2][3][4][5]. The key factor in the formation of all these compounds is favorable arrangement of the α-chlorobenzyl group with respect to the endocyclic imino and carbamoyl moieties.…”

Synthesis of (E)‐1,1‐Diethoxy‐3‐(3‐hydroxy‐3‐arylfuro[2,3‐b]quinoxalin‐2(3H)‐ylidene)propan‐2‐ones via Acid‐Catalyzed, Stereoselective 5‐Exo‐Dig Cyclization

“…Common reagents and solvents were purchased from commercial suppliers and used without further purification. 3‐Aroylquinoxalin‐2(1 H )‐ones 1a , 1b , 1c , 1d , 1e , 1f , 1g were prepared from the arylhalopyruvates according to the literature , whereas TEB (3,3,4,4‐tetraethoxybut‐1‐yne) was synthesized from ethyl vinyl ether following a four‐step procedure published in the literature .…”

Spirothiazolo[4?,2]- and thiazolo-[3,4-a]quinoxalines based on 3-(?-bromoethyl)quinoxalin-2-ones and thiourea

“…We have observed that 3-(α-bromoethyl)quinoxalin-2-ones 1a,b [1], when reacted with thiourea, form spirothiazoloquinoxalines 2a,b which, when briefly heated in acetic anhydride, are converted to thiazolo- [3,4-a]quinoxalines 3a,b [2]. Formation of the thiazolo [3,4-a] Judging from the IR and 1 H NMR spectra, spirothiazoloquinoxalines 2 are also mixtures of tautomers, the ratio of which depends on the nature of the substituent R. When treated with acetic anhydride, they all are converted to thiazolo [3,4-a] Evidence in favor of the formation of spirothiazoloquinoxalines comes from the ~1 ppm upfield shift of the signals from the benzo moiety of the quinoxaline system in the 1 H NMR spectra and the presence in the 13 C NMR spectra of a signal at 89 ppm which is typical for a spiro atom [3], and the signal for the H-9 proton in the 1 H NMR spectrum, which resonates relatively downfield (9.9 ppm) [2,4] compared with other aromatic protons and is diagnostic for azolo[a]annelation of quinoxalines, indicates formation of a 1-iminothiazolo- [3,4-a]quinoxaline system.…”