Aryl group

4 Further Carbon Functional Groups 3.2.3.4.1 Aryl groups 

Electrophilic substitution usually occurs preferentially in the aryl group. In compounds containing both an aryl group and a fused benzene ring, electrophiles usually attack the aryl group exclusively. 

8 Reactivity of Substituents Attached to Ring Nitrogen Atoms 4.01.8.1 Aryl Groups 

This section did not appear in CHEC-I(1984) and CHEC-II(1996) 1984CHEC(2)1, 1996CHEC-II(6)1 . Examples are the intramolecular Heck-type reaction of 2-benzyl-5-(2-bromophenyl)-4-phenylpyridazin-3(2//)-one and 5-(2-bromophenyl)-2-methyl-6-phenylpyridazin-3(2//)-one which yields 2-benzyldibenzo[/, ]phthalazin-l(2//)-one and 2-methyldibenzo[/,. ]cinnolin-3(270-one, respectively 2003T5919 . The same compounds were also obtained from the corresponding 2-aminophenyl (instead of 2-bromophenyl) derivatives via diazotization and subsequent Pschorr reaction. 

The (T and Tp coefficients of 3-methylpyrazole (0.161 and 0.083, respectively) have been determined by alkaline hydrolysis of the p-methoxycarbonyl esters 86CB1627 . 

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This rearrangement is general for i,2-diols of the type R2C(OH) C(OH) R2 where the groups R may be alike or different, and may be alkyl or aryl groups. 

This method has the great advantage over method (A) in that it can be applied in particular to those aromatic nitriles in which the aryl group is readily sulphonated clearly, it can also be applied to nitriles in which the alkyl or aryl portion contains groups which are in any other way affected by concentrated sulphuric acid, or by concentrated aqueous alkalis. 

Nitrous acid does not react with aliphatic tertiary amines, such as triethyl-amine, (CaHj)aN, nor does it usually react with aromatic tertiary amines such as triphenylamine, (CaHj)aN, which contain three aryl groups. 

If, however, a tertiary amine has two alkyl groups and also an aryl group having the para position unsubstituted, then the action of nitrous acid is to insert the nitroso group directly into this para position. Dimethylaniline, for example, when treated with nitrous acid readily gives p-nitrosodimethyl-... 

Tertiary amines containing one alkyl and two aryl groups, such as mono-I ncthyldiphenyhiniir.e, Cl l3(C, l l.diX , arc rarely encountered and arc unimportant. They usually react with nitrous acid with the insertion of a nitroso group into only one of the two available para positions monomethyl-diphenylamine thus gives monomethyl-mono - pnitroso-diphenylamine. Cl hj(C.ill .)N C l 1 jXO, or V-nicthyl-p-nitrosodiphcnylaniine. 

The synthesis will therefore normally produce a 2,4-substituted pyrrole, with in addition an ester group or an acyl group at the 3-position, if a keto ster or a diketone respectively has been employed, and an ester group or an alkyl (aryl) group at the 5-position, according to the nature of the amino-ketone. 

In the alkyl aryl ketones, the aryl groups migrate preferentially, yielding V-aryl amides. 

A cr-aryl-Pd bond is formed by the transfer of an aryl group even from arylphosphines to Pd and alkene insertion takes placefl 17-119], This reaction is slow and it is not a serious problem when triarylphosphine is used as a ligand. The cinnamate 149 is obtained by the reaction of PhsP with acrylate in the presence of Pd(OAc)2 in AcOH. 

When allene derivatives are treated with aryl halides in the presence of Pd(0), the aryl group is introduced to the central carbon by insertion of one of the allenic bonds to form the 7r-allylpalladium intermediate 271, which is attacked further by amine to give the allylic amine 272. A good ligand for the reaction is dppe[182]. Intramolecular reaction of the 7-aminoallene 273 affords the pyrrolidine derivative 274[183]. 

Tandem cyclization/3-substitution can be achieved starting with o-(trifluoro-acetamido)phenylacetylenes. Cyclization and coupling with cycloalkenyl trif-lates can be done with Pd(PPh3)4 as the catalyst[9]. The Pd presumably cycles between the (0) and (II) oxidation levels by oxidative addition with the triflate and the reductive elimination which completes the 3-alkenylation. The N-protecting group is removed by solvolysis under the reaction conditions, 3-Aryl groups can also be introduced using aryl iodides[9]. 

An original method has recently been developed starting either from 1.3-dithiolane (10) or from 1.3.4-thiadiazole-2-thione derivatives (11) (Scheme 4) (3). This method does not work when Ri is an aryl group. 

To sum up, spectroscopic data indicate the amino" form (10) is predominant when R is a hydrogen atom or an alkyl group, while the imino form (11) is predominant when R is an aryl group (Scheme 66). 

In 1880, Liebermann and Voltzkow (40), and then Voltzkow (41), condensing chloroacetic acid with both ethyl N-phenylthiocarbamate and p-tolylisothiocyanate obtained homologous compounds to which they attributed formulas 40 and 41, whereas their structure probably derives from that of 38 by substituting an aryl group on the cyclic nitrogen. 

Esters of 2-thiazole carboxylic acids (75) (383) are also prepared from ethyl monothiooxamate (74) (Scheme 34), and several compounds of this type with hydrogen, alkyl, or aryl groups in the 4- or 5-position (201, 209, 210, 242, 294) or a nitro group in the 5-position (674) have been reported. 

Table III-92 2-Aralkylthiazoles with one substituent on the aryl group...

Diaryifliiiizoies with Substituents on flie Aryl Groups... 

Table ITI-100 2,4-Diarylthiazoles with substituents on the aryl groups Table III-lOl 2,5-Diarylthiazoles with substituents on the aryl groups Table 111-102 4,5-Diarylthiazoles with substituents on the aryl groups...

TABLE in-92. 2-ARALKYLTHIAZOLES WITH ONE SUBSTITUENT ON THE ARYL GROUP... 

TABLE III-93. 4-ARALKYLTHlAZOLES WITH ONE SUBSTITUENT ON THE aryl group... 

TABLE m-100. 2.4-DIARYLTHIAZOLES WITH SUBSTITUENTS ON THE ARYL GROUPS... 

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