A new and effective procedure was developed for the synthesis of 3-ethylquinoxalin-2(1H)-one from o-phenylenediamine and ethyl 2-oxobutanoate. The latter was prepared by the Grignard reaction of diethyl oxalate with ethylmagnesium bromide or iodide. 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. Replacement of the chlorine atom by appropriate groups gives rise to structural fragments necessary for the subsequent ring closure at the a or b side of the pyrazine ring in the initial quinoxaline.
The reactions of 3 acetylquinoxalin 2 one with methyl and benzylpyridines in the pres ence of iodine produce the corresponding 3 (2 alkylpyridinioacetyl)quinoxalin 2(1H ) one iodides. Treatment of the latter with triethylamine affords the corresponding 3 indolizin 2 ylquinoxalin 2 ones. Due to the presence of the endocyclic carbamoyl group, the reactions of these compounds with bisalkylating reagents give quinoxaline containing monopodands and monoalkylation products containing spacers with different lengths and of different nature.
The oxidative dehydrocyclization of the 3 (indolizin 2´ yl) 2 oxoquinoxaline monopodand performed either electrochemically or under the action of molecular iodine affords new redox active heterocyclophane consisting of the redox switchable biindolizine fragment combined with the polyether bridged π deficient quinoxaline systems. The single crystal X ray diffrac tion study showed that the trioxaundecane chain of heterocyclophane adopts an extended conformation, and one of the phenyl substituents of the molecule closes the pseudocavity formed by the spacer from one of the sides. The cyclic voltammetric study of heterocyclophane in MeCN and DMF showed the three step oxidation of the indolizine fragments accompanied by the single electron transfer in each step. The first and third steps are reversible, and the second step is irreversible. The oxidation at potentials of the first peak gives rise to stable radical cations detected by the ESR method (g = 2.0024, a 2N = 0.26 mT).In recent years, the synthesis of macrocyclic com pounds, which can reversibly respond to external actions (thermal, photochemical, electrochemical, pH, etc.) by changing important properties and characteristics (the cavity size, the surface shape, the electronic structure, the complexing ability, etc.) due to the specially introduced functional groups or fragments, has taken a special place in supramolecular chemistry. 1 Such "sensitive" hetero cyclophanes containing redox active biindolizine systems can serve as molecular switches 2 and membrane carriers 3 and are of great interest in the design of new sensors for modern technologies based on molecular processes. Un like redox active compounds (ferrocenes, 4,5 tetrathia fulvalenes, 6,7 and quaternized 4,4´ bipyridines 8,9 ), bi indolizines have found little use as active regions, which make cyclophanes able to respond to external actions, in spite of the fact that biindolizines are quite stable two step redox systems, whose electrochemical behavior has been studied in sufficient detail. 10-15Indolizines are π rich compounds, which are readily oxidized (~0.2-0.3 V relative to Fc 0/+ ) to form radical cations. 10-14 The stability and subsequent transforma tions of radical cations are determined primarily by the presence of hydrogen atoms in the pyrrole ring of the indolizine system. The radical cations and dications of 3,3´ biindolizines, in which all hydrogen atoms in the five membered ring are replaced by alkyl or aryl groups, are quite stable and can be isolated and characterized as perchlorates. 12 The electrochemical behavior of two dia stereomers of macrocyclic biindolizines, in which both heterofragments are linked at positions 3,3´ and, through a bridge, at positions 1,1´, is different. 13 Thus, the diaste reomer having the anti configuration is oxidized to form stable radical cations and dications, whereas the oxida tion of the diastereomer having the syn configuration is followed by the intramolecular cyclization with the in volvement of the C(5) and C(5´) atoms of the pyridine rings of...
The interaction of 3-alkanoylquinoxalin-2-ones with 1,2-phenylenediamines in boiling acetic acid led to the contraction of the pyrazine ring as the result of a quinoxaline-benzimidiazole rearrangement with the formation of 2-benzimidazolyl-substituted quinoxalines.
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