Arenes from amines

The photolability of nitrobenzenes has previously received comment, and reactions in the presence of carbon tetrachloride and diethanolamine have now been studied. In the former system the main products are chlorobenzene and hexachloroethane, with smaller amounts of CHCh, COCI2, and C2CI4. Nitrobenzene is photoreduced in the presence of the amine to give phenyl-hydroxylamine. The reaction is enhanced six-fold in the presence of 0.1 M benzophenone and is considered to proceed by way of hydrogen abstraction by the triplet nitro-arene from diethanolamine (which is degraded to glyoxal). 

Notes Half-wave oxidaiion potentials for amines and arenes from Ref. IS ind fbr tryl oldlns from Ref. 9. Ionization potentials for amines from Ref. 20c and for arenes ftom Ref 20d,... 

The reactions of (arene)Cr(CO)j, (arene)Mn(CO)j and [(arene)MCp] (M = Fe or Ru) complexes have been studied extensively. Many of these arene compoimds have been prepared by heating the arene with Cr(CO)y but because dissociations of amines, nitriles or arenes from Cr(0) fragments are typically faster than dissociation of CO (see Chapter 5), reactions of arenes with Cr(CO)j(L)3 (L = NH or NCMej) or with (naphthalene) Cr(CO)j are milder than reactions with Cr(CO). Manganese-arene complexes [(arene) Mn(CO)3] - are typically generated from (CO)5MnBr, AgBF and arene, while the iron-and ruthenium-arene complexes [(arene)MCp] are typically generated by addition of arenes to [CpM(NCMe)3] (M = Fe or Ru). " ... 

The preparation of radioiodinated arenes from aryl amines by means of the Sandmeyer reaction has proven to be impractical. The unstable diazonium compounds, however, may be converted into stable pyrrolidine triazenes or dialkyltriazenes and used as precursors for labeling. The reaction sequence using pyrrolidine is shown in Pig. 44.8. 

TABLE III. Equilibria data for the proton-transfer reaction from p-rerr-butylcalix[4]arene and amines in benzonitrile at 298.15 K. Derived Gibbs energies (molar scale). 

NMR signals of the amino acid ligand that are induced by the ring current of the diamine ligand" ". From the temperature dependence of the stability constants of a number of ternary palladium complexes involving dipeptides and aromatic amines, the arene - arene interaction enthalpies and entropies have been determined" ". It turned out that the interaction is generally enthalpy-driven and counteracted by entropy. Yamauchi et al. hold a charge transfer interaction responsible for this effect. 

Addition of methyllithium to the enantiomerically pure arene dicarbonylchromium chelate 2, prepared by irradiation of imine l52 [derived from ( 1 )-(S)-tricarbonyl(2-methylbenzalde-hyde)chromium53] and subsequent removal of the chromium moiety provides amine 3 in 72% yield and 94% ee54. Interestingly, addition of methyllithium to imine 1 affords only racemic 3. 

Asymmetric induction may also derive from chirality in the amine part of the enamine. The reaction of the enamine (S)-l-(l-cyclohexenyl)-2-(methoxymethyl)pyrrolidine with ( )-(2-ni-troethenyl)arenes gives, after hydrolysis, a single diastereomeric product in >90% ee30. 

Noyori and coworkers reported well-defined ruthenium(II) catalyst systems of the type RuH( 76-arene)(NH2CHPhCHPhNTs) for the asymmetric transfer hydrogenation of ketones and imines [94]. These also act via an outer-sphere hydride transfer mechanism shown in Scheme 3.12. The hydride transfer from ruthenium and proton transfer from the amino group to the C=0 bond of a ketone or C=N bond of an imine produces the alcohol or amine product, respectively. The amido complex that is produced is unreactive to H2 (except at high pressures), but readily reacts with iPrOH or formate to regenerate the hydride catalyst. 

Tert-butyl calix[4]arene possessing four antennary amine groups (7) were initially synthesized from commercially available phenolic tert-butyl calix[4]arene according to a published procedure [13]. After derivatization of the phenolic group by alkylation with ethyl bromoacetate, hydrolysis, acid... 

Success was obtained with Ru3(CO)i2 as catalyst precursor [6], but the most efficient catalysts were found in the RuCl2(arene)(phosphine) series. These complexes are known to produce ruthenium vinylidene spedes upon reaction with terminal alkynes under stoichiometric conditions, and thus are able to generate potential catalysts active for anti-Markovnikov addition [7]. Similar results were obtained by using Ru(r]" -cyclooctadiene)(ri -cyclooctatriene)/PR3 as catalyst precursor [8]. (Z)-Dienylcarba-mates were also regio- and stereo-selectively prepared from conjugated enynes and secondary aliphatic amines (diethylamine, piperidine, morpholine, pyrrolidine) but, in this case, RuCl2(arene) (phosphine) complexes were not very efficient and the best catalyst precursor was Ru(methallyl)2(diphenylphosphinoethane) [9] (Scheme 10.1). 

Figure 14. Potentiometric responses to simple amine guests (33-37) by PVC matrix liquid membranes, (a) Membrane based on calix[6]arene hexaester (29 (R = H)/DOS/PVC = 5 68 27 wt%). (b) Membrane based on dibenzo-18-crown-6 (32/DOS/PVC = 2 66 32 wt%). Measured in 0.1 M Tris-HCI buffer (pH 7.0) at room temperature (ca. 20 °C) (reproduced with permission of American Chemical Society from Anal. Chem. 1993, 65,1079).

Support-bound triazenes, which can be prepared from resin-bound secondary aliphatic amines and aromatic diazonium salts [455], undergo cleavage upon treatment with acids, leading to regeneration of the aromatic diazonium salts. In cross-linked polystyrene, these decompose to yield nitrogen and, preferentially, radical-derived products. If the acidolysis of polystyrene-bound triazenes is conducted in the presence of hydrogen-atom donors (e.g. THF), unsubstituted arenes can be obtained (Entries 8 and 9, Table 3.47). In the presence of alkenes or alkynes and Pd(OAc)2, the initially formed diazonium salts undergo Heck reaction to yield vinylated or alkynylated arenes (Entry 10, Table 3.47). Similarly, unsubstituted arenes can be obtained by oxida-... 

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