Aryl leaving groups

Dienes and allylarcncs can be prepared by the Pd-catalyzcd coupling of allylic compounds with hard carbon nucleophiles derived from alkenyl and aryl compounds of main group metals. Allylic compounds with various leaving groups can be used. Some of them are unreactive with soft nucleophiles, but... 

The generally accepted mechanism for nucleophilic aromatic substitution m nitro substituted aryl halides illustrated for the reaction of p fluoromtrobenzene with sodium methoxide is outlined m Figure 23 3 It is a two step addition-elimination mechanism, m which addition of the nucleophile to the aryl halide is followed by elimination of the halide leaving group Figure 23 4 shows the structure of the key intermediate The mech anism is consistent with the following experimental observations... 

Synthesis. The first hiUy alkyl/aryl-substituted polymers were reported in 1980 via a condensation—polymeri2ation route. The method involves, first, the synthesis of organophosphine-containing alkyl or aryl substituents, followed by the ready oxidation of the phosphine to a phosphorane with leaving groups suitable for a 1,2-elimination reaction. This phosphorane is then thermally condensed to polymers in which all phosphoms atoms bear alkyl or aryl substituents. This condensation synthesis is depicted in Eigure 2 (5—7,64). 

If the fV-aryl group is strongly activated, then it can be removed in nucleophilic substitution reactions in which the azole anion acts as leaving group. Thus l-t2,4-dinitrophenyl)pyrazole reacts with N2H4 or NaOMe. 

Detailed mechanistic studies have been carried out on aminolysis of substituted aryl acetates and aryl carbonates. Aryl esters are considerably more reactive than alkyl esters because the phenoxide ions are better leaving groups than alkoxide ions. The tetrahedral intermediate formed in aminolysis can exist in several forms which differ in extent and site of protonation ... 

Leaving-group effects Because aryl fluorides have the strongest carbon-halogen... 

Much less work has been done on the arylation of enamino ketones. The enamino ketone (49) has been allowed to react with 2,4,6-trinitrochloro-benzene. In this instance the latter reacts as the acid chloride of an acid the anion of which is a good leaving group (46). This type of reaction will be discussed in Section IV.A. 

Arylthio but not 2-arylthio groups in quinazolines can be replaced with hydroxide ion or alkylamines. 4-Alkylthio-2-alkyl (or aryl)-quinazolines are readily alkoxylated (65°, 1 hr, 80-90% yield) at the 4-position. Arylthio and alkylthio groups have been found to be poorer leaving groups than chloro in several azines. 

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