Sulfones reaction with quinoxaline

The formation of quinoxaline quaternary salts is often difficult. However, reaction of quinoxaline with ethyl iodide in boiling acetonitrile gives ethyl quinoxalinium iodide in 76% yield, and treatment of the parent base with methyl toluene-p-sulfonate at room temperature gives methyl quinoxalinium toluene-p-sulfonate in quantitative yield. ... 

Carbanions of a-haloalkyl aryl sulfones, sulfonates and sulfonamides react with quinoxalines according to two general pathways vicarious nucleophilic substitution of hydrogen and/or bis-annulation to bis(azirino)quinoxaline derivatives. The charge distribution in the anionic (T-adducts and reaction conditions influence the direction of these reactions. ... 

The lability of the bromine in l-bromopyrrolo[l,2-a]quinoxaline (101) makes the reaction of the nitrosulfonic acid 109 more complex in both concentrated hydrobromic acid and in DMF containing lithium bromide. In the reaction of 109 with lithium bromide the l-bromo-3-sulfonic acid 112 may be isolated after 10 min. However after 1 hr only the 3-bromo compound 100 is obtained. It was also shown that the intermediate 112, as well as the 1-bromo compound 101 and l,3-dibromopyrrolo[l,2-a]quinoxaline, form the 3-bromo compound 100 on reaction with lithium bromide in DMF. ... 

SCHEME 11.39 VNS versus aziridination of quinoxaline in the reaction with carbanion of chloromethyl phenyl sulfone [61]. 

The vicinal position of nucleophilic amino and strongly electrophilic nitroso groups makes A -aryl-2-nitrnsoanilines 413 (Wrobel and Kwast 2007, 2010) very interesting starting materials for domino reactions with properly eqmpped dipolar parmers, leading to a variety of heterocyclic systems. The reactions of these compounds with comparatively acidic sulfones (Scheme 2.75, route a) or acetates and phosphonoacetates (Scheme 2.75, route b) appeared to be efficient ways of the synthesis of benzimidazoles 414 (Wrobel et al. 2011) and quinoxalin-2(lff)-ones 415 (Wrobel et al. 2013). 

The second class of benzo-fused heterocycles accessible from benzofuroxans are benzimidazole oxides. In this case only one carbon from the co-reactant is incorporated in the product. With primary nitroalkanes 2-substituted l-hydroxybenzimidazole-3-oxides (46) are formed via displacement of nitrite, and / -sulfones behave similarly. The nitrile group of a-cyanoacetamides is likewise eliminated to alford 2-amide derivatives (46 R = CONRjX and the corresponding esters are formed in addition to the expected quinoxaline dioxides from acetoacetate esters. Under similar conditions secondary nitroalkyl compounds afford 2,2-disubstituted 2//-benzimidazole-1,3-dioxides (47). Benzimidazoles can also result from reaction of benzofuroxans with phosphorus ylides <86T3631>, nitrones (85H(23)1625>, and diazo compounds <75TL3577>. 

The second synthetic route to PAE containing quinoxaline units involved the reaction of an aromatic dihydroxy quinoxaline or aromatic bis(hydroxy-quinoxaline) with activated aromatic difluoro compounds (Eq. (3)) [15]. The dihydroxy quinoxaline and bis(hydroxyquinoxaline) monomers were readily prepared from the condensation of 1,2-diaminobenzene with 4,4 -dihydroxyben-zil and aromatic bis(o-diamines) with 4-hydroxybenzil, respectively. The Tgs of a series of PAE containing quinoxaline units are presented in Tables 3 and 4. For these polymers, the trend for the Tg is sulfone > carbonyl > terephthaloyl-> isophthaloyl. This trend holds for most polymer families when polymers of similar molecular weights are compared. Several polyphenylquinoxalines of the same chemical structure as those in Table 3 were also prepared by the poly-... 

Nitration of pyrrolo[l,2-a]quinoxaline by adding a mixture of the compound and potassium nitrate to concentrated sulfuric acid yields a mixture of 25% 1-nitro and 48% 3-nitro derivatives. No significant reaction was observed with potassium nitrate in trifluoroacetic acid, or in fuming nitric acid alone or fuming nitric acid and acetic anhydride." The attempts to avoid the use of sulfuric acid were made because of the ease with which the heterocycle undergoes sulfonation. Thus treatment with concentrated sulfuric acid at room temperature readily gave the 3-sulfonic acid. Apparently the electrophile is too large to allow formation of detectable amounts of the isomeric 1-sulfonic acid. The 1-methyl and... 

Azolopyridazines bearing no nitro substituent are, nevertheless, sufficiently active electrophiles to enter the VNS reaction. However, similar to the series of quinoxalines [127] and pyridazinones [67], in the reactions of azolopyridazines with the carbanion of bromomethyl phenyl sulfone, two ways for conversion of the intermediate adducts are observed, depending on the structure of these heterocyclic compounds - p-elimination, leading to the VNS product, or intramolecular substitution, resulting in formation of the cyclopropane ring (Scheme 34) [128]. 

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