2.3- Dichloro-6- quinoxaline

Both 2-chloro- and 2,6-dichloro-quinoxalines can be made by ring expansion of 1-methylimidazole using trichloromethyl radicals (91MI5). 

Crude 2,3(1//, 4//)-Quinoxalinedithione [prepared by thiolysis of 2,3-dichloro-quinoxaline (see Section 3.2.3)] gave 2,3-bismethylthioquinoxaline (10)... 

Typical examples of dyes belonging to this group are dichlorotriazine, dichloro-quinoxaline, difluoropyrimidine and vinylsulphone dyes. 

Methylquinoxaline-2,3-dione (173) is oxidized with Co(OAc)2 Mn(OAc)2 in HBr/H20 to the 6-carboxylic acid (174),183 which on treatment with thionyl chloride is converted into 2,3-dichloro-quinoxaline-6-carbonyl chloride (175).184 The 6-sulfonyl chloride is obtained from quinoxaline-2,3-dione and chlorosulfonic acid and treatment of the resulting 6-chlorosulfonyl derivative with phosphoryl chloride and pyridine.185 Such derivatives are useful synthetic dye intermediates. 

Bredereck and Schmotzer (1044), from diaminomaleonitrile (DAMN hydrogen cyanide tetramer) and oxalyl chloride, prepared 2,3-dicyano-5,6-dihydroxy-pyrazine but Stetten and Fox (1049) could not prepare 23-diamino-5-hydroxy-pyrazine from glycine amide and oxamide. Section 11.3 lists preparations from a, -diamino or a, -diimino compounds and reagents other than a,0-dicarbonyl compounds (384) with additional data (1050) and oxidation of 23-dichloro-quinoxaline with hot aqueous potassium permanganate gave 23-dicarboxy-5,6-dihydroxypyrazine (1051). 

Benzoin undei goes a cyclocondensation with the aminothiolactam (11.4) to form a new thiadiazine ring while the reactive chlorine atoms of 2,3-dichloro-quinoxaline under mildly basic conditions react to form a doubly fused thiadiazine. 

There have been two reports of the oxidation of 2,3-dichloro-quinoxaline with potassium permanganate to give 2,3-dichloropyrazine-... 

The preparation of 15 has been reported by Sakata et al. (15). 2,6-Dichloro-quinoxaline 2 and a three fold excess hydroquinone were refluxed with potassitun carbonate in dimethylformamide. The bis-adduct 14 was formed as main product in an early stage and cleaved to 15 with the excess hydroquinone. 

Some representative backbone stmctures of PQs and PPQs and their T data are given in Table 1. As in other amorphous polymers, the Ts of PQs and PPQs are controlled essentially by the chemical stmcture, molecular weight, and thermal history. Several synthetic routes have been investigated to increase the T and also to improve the processibiUty of PPQ (71). Some properties of PPQ based on 2,3-di(3,4-diaminophenyl)quinoxaline and those of l,l-dichloro-2,2-bis(3,4-diaminophenyl)ethylene are summarized in Table 2. 

Treatment of bis-lactim ether 420 with BuLi, then with cw-l,4-dichloro-2-butene in the presence of Nal afforded 3,4,9,9n-tetrahydro-6//-pyrido[l,2-fl]pyrazin-4-one (421) with 96% diastereomeric excess (97TA1855). Reaction of l,2-diphenyl-6-methyl-quinoxaline with 1,4-dichlorobutane in THF in the presence of Na at —78°C afforded a 3 1 mixture of 4a,5-diphenyl-9-methyl-l,2,3,4-tetrahydro-4a//-pyrido[l,2-n]quinoxaline and 4-(4-chlorobutyl)-2,3-diphenyl-6-methyl-1,4-dihydroquinoxaline (98JHC1349). 

Dichloro-3-[p-(l-ethoxycarbonylethyl)phenoxy]quinoxaline (127) gave 7-chloro-3- [p-( 1 -ethoxycarbonylethyl)phenoxy] -2( l//)-quinoxalinone (128),... 

Chloro-2-hydrazinoquinoxaline (254) with mucochloric acid (255) gave 6-chloro-2-(4,5-dichloro-6-oxo-1,6-dihydropyridazin-1 -yl)quinoxaline (256) (AcOH, reflux, 5.5 h 87% analogs likewise). ... 

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