5-Fluoro-2- quinoxaline

Nucleophilic halogen exchange, using cesium fluoride and 18-crown-6 in tetrahydrofuran, gave high yields of 2-, 3-, and 2,3,-di-fluoroquinoxalines from the chloro analogues [87H)26)1215]. The Balz-Schiemann process has been used successfully to make 2-fluoro-quinoxaline (84MI8). 

The fluorine chemical shifts for fluoropyrimidines, 2-fluoropyrazine, 2-fluoro quinoxaline, 4-fluoroquinazaline, 5-fluorouracil, 5-fluoro-cytosine, and cyanuric fluoride are provided in Scheme 3.82. The fluorine of 2-fluoropyrimidine is considerably deshielded relative to... 

The progression from hydroxypyrazines/quinoxalines through the halo derivatives to the amines is a logical sequence in that, for practical purposes, this is the best method of synthesis of the amino compounds (see preceding Section). The ammonolysis proceeds most easily in the case of fluoro compounds. Fluoropyrazine reacts with aqueous ammonia at room temperature, whereas the reaction with chloropyrazine requires higher temperature and pressure. 

Reaction of ethyl 7-bromo-8-fluoro-l-(2-bromo-l-methylethyl)-4-oxo-l,4-dihydroquinoline-3-carboxylate with MeNH2 yielded 10-bromo-A, 1, 3-trimethyl-7-oxo-2,3-dihydro-7//-pyrido[l,2,3-<7e]quinoxaline-3-carboxamide (OOMIPIO). 

The synthesis of polyether quinoxaline by nucleophilic displacement discussed in Section 5.4.2.2 has also been used for the preparation of hyperbranched polyquinoxaline based on AB2 or A2B monomers. In the AB2 monomer the focal point is a single fluoro group (Fig. 5.42)172 in the A2B the focal point is a single... 

Indirect fluorination of quinoxaline gave a separable mixture of 2-fluoro- and 2,3-difluoroquinoxaline (I2, Et3N, CIP2CCP2CI, P2 -f N2i, 5°C, min 48%... 

Chloro-5-fluoroquinoxaline gave 5-fluoro-2-(piperazin-l-yl)quinoxaline (74) [neat HN(CH2CH2)2NH, 125°C, N2, 90 min 71%, as fumarate salt].708... 

Ethyl 3-bromomethyl-6,7-difluoro-2-quinoxalinecarboxylate 1,4-dioxide (84) gave 6-fluoro-2-methyl-7-methylamino-2,3-di hydro-1 //-pyrrolo 3,4-h]quinoxalin-l -... 

Acetyl-3-ethylthiomethylquinoxaline 1-oxide 2-(Acetylethynyl)quinoxaline 2-Acetyl-7-fluoro-3-methyl-6-morpholinoquinoxaline 2-Acetyl-7-fluoro-3-methyl-6-... 

Chloro-3-( 1-ethoxy carbonylpropyl)quinoxaline 2-Chloro-7-ethoxy-6-fluoro-3-methylquinoxaline... 

Chloro-2-fluoroquinoxaline 6-C hloro-7-fluoro-2,3( I //, 47/)-quinoxalincdionc 6-Chloro-2-(hex-1 -ynyl)quinoxaline 2-Chloro-3-hydrazino-6-methoxyquinoxaline 6-Chloro-2-hydrazino-3-methoxyquinoxaline 6-Chloro-3-hydrazino- l-mcthyl-2(l //)-... 

In a closely related study, Tung and Sun discussed the microwave-assisted liquid-phase synthesis of chiral quinoxalines [80], Various L-a-amino acid methyl ester hydrochlorides were coupled to MeOPEG-bound ortho-fluoronitrobenzene by the aforementioned ipso-fluoro displacement method. Reduction under microwave irradiation resulted in spontaneous synchronous intramolecular cyclization to the corresponding l,2,3,4-tetrahydroquinoxalin-2-ones (Scheme 7.71). Retention of the chiral moiety could not be monitored during the reaction, but after release of the desired products it was found that about 10% of the product had undergone racemization. 

The reaction of benzene-1,2-diamines with ethyl / -fIuoro-a-oxo esters affords 3-fluoro-alkylquinoxalin-2(l//)-ones in good yields. In the same manner, 3-fluoroalkylben-zo[g]quinoxalin-2(l//)-ones are prepared. ... 

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