Alkylation 1,4-dibromobenzene

It can be applied generally homologous bromobenzenes such as dibromobenzene and all possible alkyl bromides come within its scope. The reaction takes place also, although less readily, between two molecules of aryl bromide ... 

The same procedure is useful for N-alkylation of aromatic amines.3 Thus N,N,N, N -tetraethyl-l,4-diamino-2,5-dibromobenzene (4) was obtained in this way from 1,4-diamino-2,5-dibromobenzene (3) in 49 % yield. 

This method is applicable to a variety of alkyl-substituted phenylene AB-type monomers [88]. The procedure was also extended to the condensation of AA and BB monomers [89]. Hereby, poly-p-phenylene polymers containing ether and carbonyl linkages in the polymer backbone are accessible. By polymerization of the AB2 monomer 3,5-dibromobenzene boronic acid in a biphasic aqueous/organic medium, Kim and Webster obtained hyperbranched polyphenylenes [90], Suzuki polycondensation in aqueous systems has proven to be a versatile method, which has been applied to the synthesis of a variety of different polymer types [91]. 

It has also been reported that 1,2-dibromobenzene can be sequentially aminated with two different amines.40 As before, the first animation of an aryl bromide with an alkyl amine is catalyzed by Pd/BINAP. The second amination of the product bromoaniline can then be catalyzed by either Pd/BINAP or Pd/L3 with a variety of cyclic secondary or primary amines. 

When dibromobenzene is used the halogen atoms are replaced by two alkyl groups. The method is of particular value, as by means of it compounds of definite structure may be prepared. Metadibrombenzene is converted, for example, into metaxylene when treated with methyl iodide and sodium. 

More generally, PPP derivatives 15 with solubihsing side chains, most commonly alkyl or alkyoxy groups, are prepared by transition metal catalysed polycondensations [56]. The main methods used are the Suzuki and Yamamoto polycondensations. Two variations of the Suzuki polycondensation can be used. The simpler, so-called AB coupling (Scheme 7), involves conversion of a dibromobenzene 16 into a bromoarylboronic acid 17, which is then homocoupled to give 15. Random copolymers can be made by using a mixture of monomers. 

Scheme 14. Syntheses of substituted o-dibromobenzenes [R = -alkoxymethyl (a), n-alkoxy (b), n-alkyl (c) or (2-n-alkoxypropyl)oxymethyl (d)]...

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