Unsubstituted aromatic rings, arylation reactions

Arylation Reactions with Unsubstituted Aromatic Rings... 

Organomagnesium compounds add to unsubstituted arenes only under forcing or Barbier conditions [1], On the other hand, aromatic rings substituted by electron-withdrawing groups are surprisingly susceptible to attack by organomagnesium compounds. The early work on reactions of hindered aryl ketones [2] has been little further developed [3], despite some reports which should surely be followed up, e.g. [4],... 

The major pathways for the anodic oxidation of diarylamines are N,N- or aryl,aryl-coupling, A,aryl-coupling, and nucleophilic substitution in the aromatic ring. Which pathway actually will be followed depends on the reaction conditions and the substitution pattern of the substrate. With regard to the latter, one has to distinguish between p-unsubstituted, p-mono- and / -disubstituted diphenylamines. 

Although it is known that the presence of electron-donor substituents on the aromatic ring greatly enhances the efficiency of the transposition leading to 2-arylpropanoates, we have chosen for our study the unsubstituted phenyl group, which shows a low migratory aptitude. This will provide us a deeper understanding of the influence of the physicochemical parameters of the zeolite on the side reactions competitive to the 1,2-aryl shift. 

In general, nucleophilic aromatic substitution reactions are rather difficult with unsubstituted aryl derivatives or when the aromatic ring contains a strongly electron-releasing group. Formation of the chromium complex activates such aromatic compounds to nucleophilic substitution. Since the nucleophiles are carbon nucleophiles, this technique offers a route to carbon bonds that would be very difficult to form by other methods. 

The fully aromatic and unsubstituted pyrimido[ 1,2-6 ]pyridazinium perchlorate (171) has been prepared by the condensation of 3-aminopyridazine (170) with 1,1,3,3-tetraethoxypropane in the presence of polyphosphoric acid. The product was precipitated from the reaction mixture by treatment with perchloric acid and ice. Several alkyl, aryl and halogenated derivatives of this ring system have also been prepared (71JOC2457). 

To exploit the synthetic versatility of aryl diazonium salts, be prepared to reason backward. When you see a fluorine attached to a benzene ring, for example, realize that it probably will have to be introduced by a Schiemann reaction of an arylamine realize that the required arylamine is derived from a nitroarene, and that the nitro group is introduced by nitration. Be aware that an unsubstituted position of a benzene ring need not have always been that way. It might once have borne an amino group that was used to control the orientation of electrophilic aromatic substitution reactions before being removed by reductive deamination. The strategy... 

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