Arylamine reactions dimerization

Dimerization of arylamine cation-radicals is a prominent example of the product s steric hindrance effects on the reaction course. Although stable in AN, the A,A-dimethyl-p-toluidine dimerizes if its uncharged counterpart is present in the solution (Goto et al. 2002, Oyama and Goto 2003). The cation-radical loses a proton, and the parent amine reacts as a base, accepting this proton. Coupling of benzylic radicals is an understandable result of the following reaction ... 

An extensive series of neutral macrocyclic complexes, mainly of nickel(II), copper(II), platinum(II) and palladium(II), has been developed by Dziomko and coworkers. The cyclization step in the template reaction is a nucleophilic aromatic substitution of an arylamine on to a haloaryl azo compound. A variety of aryl and heteroaryl rings can be incorporated in different combinations. For instance, a diaminoazo compound can be combined with a dihaloazo compound (Scheme 58).246 247 Another synthetic strategy involves the dimerization of an aminohaloazo compound and leads to more symmetrical macrocyclic complexes (Scheme 59).248 249 Most recently, dihalodiazo compounds have been synthesized from dihydrazines and pyrazolinediones and undergo template reactions with simple 1,2-diamines (Scheme 60).249 250... 

The one-electron oxidation of a secondary amine results in the formation of a secondary aminium ion which on deprotonation gives an aminyl radical (Scheme 1). The nature of the final products derived from these intermediates dqiends very much on the structure of the substrate and the reaction conditions. If the amine has a hydrogen atom on the a-carbon atom the major products usually result from deprotonation at this a-position. With aromatic secondary amines, products can result from coupling of the delocalized radicals at a ring carbon atom. The formal dimerization of aminyl radicals shown in Scheme 21 is therefore not often a useful method of preparation of hydrazines. Nickel peroxide has been used to oxidize diphenylamine to tetraphenylhydrazine in moderate yield, and other secondary arylamines also give... 

Vilar and coworkers reported the isolation of two new dinuclear Pd(I) dimers containing P(Bu-f)2Bph (Bph = biphenyl) (equation 48) as ligand168. The complexes were prepared by the same conproportionation used to prepare the palladium dimers with trialkylphosphines. The complexes contain a single phosphine, and both metals are coordinated to the terminal phenyl group of the biphenyl unit in a p2 — rf -iy fashion. These complexes were tested for the animation of aryl halides with arylamines. The reaction of 4-chlorotoluene with p-tolylamine catalyzed by 52a or 52b formed di-p-tolylamine in 78 to 81% yield within 3 h at room temperature, whereas the same reaction conducted with a mixture of Pd2(dba)3 and P(Bu-f)2Bph required 80 °C to obtain 90% yield. 

Goodin, 1970). Thus, there is no point in searching for the esr spectrum of the pyridine cation radical. Probably the same situation prevails in reactions of other amines with TCNE. For example, a variety of arylamines react with TCNE and form, finally, tricyano-vinyl derivatives (Foster, 1974). The reaction is thought to involve complex formation first (Isaacs, 1966). The TCNE - is produced over a period of minutes, while the other anticipated radical, presumed to be an aminium ion, is not observed. Its absence is attributed to dimerization and proton loss, although the anticipated products (hydrazobenzene and its isomers) are not found. In these reactions, therefore, there can be little doubt that the TCNE" - arises from reactions of TCNE with hydroxide ion and/or cyanide ion (formed in the tricyanovinylation reaction). Thus, in these cases the formation of an anion radical is not linked to electron transfer from an organic donor (Isaacs, 1966). 

Fluoroalkylquinolines can also be obtained from iV-arylfluoroalkylketenimines generated by treating hexafluoropropene dimer with primary arylamines indeed, the intermediate ketenimines can be isolated only if the aryl group possesses no available o-hydrogens (see Scheme 20). The extension of this reaction to heterocyclic synthesis is discussed in detail elsewhere (see p. 464). 

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