Meta-substituted anilines synthesis

FrielA,nderSynthesis. The methods cited thus far all suffer from the mixtures which usually result with meta-substituted anilines. The use of an ortho-disubstituted benzene for the subsequent constmction of the quinoline avoids the problem. In the FrieWider synthesis (52) a starting material like 2-aminoben2aldehyde reacts with an CX-methyleneketone ia the presence of base. The difficulty of preparing the required anilines is a limitation ia this approach, but 2-nitrocarbonyl compounds and the subsequent reduction of the nitro group present a usehil modification (53). 

Other Type B Syntheses.—The prolonged interaction of 2-picoline with meta-substituted anilines in the presence of sulphur at 170 °C under Wiligerodt-Kindler conditions gives, apart from the thioanilides (18), only one of the two possible isomers, namely 5-substituted benzothiazoles (19), the structure of which was confirmed by their unequivocal synthesis from (20). In contrast, both isomers (19) and (21) are obtained by the oxidative cyclization of the thioanilides (18) by the modified Jacobson reaction the two reactions clearly occur by distinct mechanisms. ... 

Good yields of 10-aryl-3,6-dinitroacridones were obtained merely by heating 2,2, 4,4 -tetranitrobenzophenone (419) with an excess of the corresponding aryl amines at 125°C. For example, aniline provided 420 in 80% yield (Eq. 38). The reaction is fairly general for meta- and para-substituted anilines, though it proceeds less readily with orf/io-substituted compounds (79JCS(P1)1364). A method of isolation of the intermediate diarylamine in the synthesis of certain 10-aryl-3,6-dinitroacridones from 2,2, 4,4 -tetranitrobenzophenone has also been described (93JCR(M)2779). 

The first, path (1), was straightforward since all N-aminohet-erocycles used in this work (Table V) were known, and methods for their preparation have been published. The majority of the sub-stituted-benzaldehydes used in this method were prepared according to the Beech (17) method as described (18) for the conversion of 2-bromo-4-toluidine into 2-bromo-4-methylbenzaldehyde. The method is of wide application and gave substituted benzaldehydes in 50-75% yield. The unavailability of certain (polyfluoroalkoxy)anilines precluded synthesis of corresponding aldehydes via this method. These were prepared from anisic acids (Chart III) or reduction of nitro-phenols. For example, conversion of meta-anisic acid into 3-(tri-... 

Aryldiazonium ions are important synthetic intermediates because they provide a means of modifying substituents already located at specific positions on the ring. The synthesis of an aryldia-zonium ion on a multiply substituted aromatic ring allows us to make compounds that sequential electrophilic aromatic substitution could not produce. For example, bromination of aniline yields tribromoanihne. Diazotization of the product followed by treatment with hypophosphorous acid removes the amino group. The three bromine groups are located meta to one another. Direct bromination of benzene would not produce this compound because bromine is an ortho-para director. 

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