Amination of N-heterocyclics

Amination of N-heterocycles (Chichibabin reaction) 87KGS1011 88AHC(44)1 90AHC(49)117. 

In the synthesis of N heterocycles, this technique also overcomes competitive retro Michael addition that lowers the yield of 1,4-adduct in the Michael addition of amines to nitro olefins. Thus, a toluene solution of nitro olefin 159 was treated with allylamine 160, EtgN, and TMSCI under nitrogen at ambient tern-... 

Singh and Han [60] have reported the preparation of another dihydropyrrole by using a N-Cbz derivative obtained by decarboxylative amidation (Scheme 9.27, results line 1) as starting material. N-Alkylation with allyl bromide followed by RCM (Grubbs II catalyst) furnished the dihydropyrrole in excellent yield (95%). Lee et al. have similarly transformed the amination product (Table 9.2, entry 21) into a variety of N-heterocycles [54]. 

They showed that use of the phosphonium IL resulted in milder conditions and yields comparable with conventional solvents. Both aliphatic and aromatic amines reacted well in presence of phosphonium ILs, in contrast with ammonium ILs where only aliphatic amines acted as Michael donors. Yang et al. demonstrated the use of aromatic amines and N-heterocycles as Michael donors in presence of a basic IL such as [emim]OH. They reacted cyclohexenone with aniline in presence of [emim]OH at room temperature to give the corresponding Michael adduct, Scheme 25. 

A very elegant approach has been developed by Kanerva et al. DKR of N-heterocyclic a-amino esters is achieved using CAL-A [29]. Racemization occurs when acetaldehyde is released in situ from the acyl donor. In this case, aldehyde-catalyzed racemization of the product cannot occur (Scheme 5.15). This is one of the few reported examples of DKR of secondary amines (see also Reference [69]). 

The kinetics and thermodynamics of the addition reactions of amine and N-heterocyclic ligands to [0s04] have been studied using UV/Vis and NMR spectroscopies. With py, 4-pic, and bpy, the kinetics are too fast to be studied without using stopped-flow techniques, whereas the... 

Hydrazone Dyes If the diazonium salts of aromatic amines are coupled with the methylene derivatives of N heterocycles, hydrazone dyes (i.e., the monoaza derivatives of the enamine dyes) are obtained. Paper and leather can be dyed in yellow to red shades with these dyes [23], They are moderately lightfast on polyacrylonitrile. If the diazo components contain substituents in the 2-position relative to the amino group that can form a hydrogen bond (e.g., 2-nitroaniline [24] or 1-ami-noanthraquinone [25]), lightfastness is improved considerably (10). 

Triazene Dyes. If diazonium salts of N-heterocyclic amines are coupled to A-alkyl anilines, e.g., diazotized 2-aminoinomethoxybenzothiazole to A-methyl-4-nitroaniline, a triazene is obtained. A cationic triazene dye (16, diazadimethine-hemicyanine dye) is formed by subsequent A-alkylation, and dyes polyacrylonitrile a very lightfast yellow shade [39],... 

The most important method for preparing apocyanine dyes is the reaction of N heterocycles containing 2- or 4-carbonyl groups with secondary or tertiary aromatic amines in the presence of dehydrating agents (e.g., phosphorus oxychloride or tin tetrachloride). 

With the application of N-heterocyclic carbene (NHC) ligands, the number of transition metal-catalyzed reactions has grown considerably in the past decade. The replacement of traditional amine or phosphine ligands with electron-rich NHC ligands has led to a substantial enhancement in catalytic activity. This chapter summarizes the recent impact that the use of NHC ligands has had in furthering the field of transition metal-mediated catalysis. 

Zeolites have also been shown to catalyze a variety of acid-promoted cyclizations. Many of these involve the formation of N-heterocycles via intramolecular amination reactions [75-77]. Some examples are shown in Fig. 2.24. 

The reaction is accelerated using a series of amines and N-heterocycles. SiH4 becomes the preferable product with increasing basicity of the ligands (Table 1). 

Others have investigated the kinetics of amination reactions mediated by catalyst systems employing the new electron-rich monodentate ligands. In particular, Hartwig has shown that for catalysis by a 1 1 palladium to Xn tert-butyl)phosphine system, a mechanism in which oxidative addition of aryl chlorides follows coordination of base to the palladium competes with the standard nonanionic pathway. Finally, Caddick, Cloke, and coworkers have studied amination reactions of aryl chlorides performed by palladium complexes of N-heterocyclic carbene ligands. They found the rate to be limited by the oxidative addition step, which occurs first through the dissociation of an NHC ligand. 

Reactions of epoxides with amines, azides, hydrazines, etc., formation of N-heterocycles by epoxide ring opening 04ZOR11. 

From the examples described in the preceding Sections and in Chapter 3, Section 3.3.2 (p. 84), it can be concluded that the hydrogenation of N-heterocyles is much more facile than C-N bond breaking reactions when soluble transition metal complexes are employed as models for HDN catalysis this is in parallel to what has been observed on metal sulfide surfaces. Indeed, while several examples of efficacious homogeneous catalysts for the hydrogenation of N-heterocycles to the corresponding cyclic amines (partially or fully saturated) are available (see Chapter 3), only one case of C-N bond hydrogenolysis promoted by a metal-complex in solution has been described so far. Moreover, the real nature of this process is not clearly defined. 

The formation of aminals via the Gabriel reaction can arise on changing the solvent from toluene to dimethylformamide, in the presence of sodium salts of N-heterocycles.31 In this unique example, 63 could be prepared in useful quantities in a more practical technique than with previous methods which required high heat and/or pressure conditions.32 - The required phthalimide derivatives 62 was also formed but in low yields. 

Because of their concerns about the mutagenicity of numerous commonly consumed heated foods, many of the studies of the isolation, identification, and estimation of N-heterocyclic amines in heated foodstuffs or heated food components, particularly amine-containing components such as amino acids, proteins, and peptides, were conducted by Japanese investigators. This becomes obvious from examination of the authors and coauthors of the references listed in Table XVII.F-3. 

Nitrenium ions and direct electrophilic aromatic amination (cyclic nitrenium ions, formation of N-heterocycles by intramolecular amination, N-aminopyridinium salts) 05ZOR487. 

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