Amination preferential

Alkylpyridines are aminated preferentially at the 2-position, but reaction is slower than in the parent system. Quinoline is difficult to aminate and only a low yield of 2-aminoquinoline (32%) is obtained from reaction with sodamide in toluene. When dimethylaniline is employed as solvent, 2-amino-3,4-dihydroquinoline (24%) becomes the major product, and the yield of 2-aminoquinoline drops to 7%. The best yields of 2-aminoquinoline (53-69%) have been obtained by using barium or potassium amide in liquid ammonia. Use of the potassium salt also produces a 10% yield of the 4-amino isomer. The... 

Thus the halogens preferentially cause the loss of the radical X through a cleavage of the adjacent bond, whereas the amines preferentially lose a radical through a cleavage of the alpha bond. 

The snbstitntion chemistry of 3,5-dichloro-2,4-p3Troledicarboxaldehydes has been investigated with different amine nncleophiles <05T5831>. Secondary amines preferentially form addncts with the formyl gronps, while primary amines replace the 5-chloro group. 

Disubstituted 2,4-dithiohydantoins (75) react with ammonia or amines preferentially at the 4-position to give imino derivatives (76) which can be hydrolyzed by acid to 2-thiohydantoins (77). Carrington46 found ethanol-amine convenient for this purpose. Acid hydrolysis of the methylthio... 

Y. -L. Zhong, et al.. Tetrahedron Lett., 50, 2293-2297 (2009). These Merck researchers were evaluating a series of compounds for antiviral activity. They performed nucleophilic aromatic substitution with a hindered amine preferentially at the less hindered aryl fluoride followed by a second nucleophilic aromatic substitution at the hindered aryl fluoride. After condensation and loss of water, the product is formed. Draw the product. 

Friedel-Crafts acylation follows the established activation-orientation rules of electrophilic aromatic substitution. However, the acylation of some highly activated aromatic compounds such as phenols and aromatic amines preferentially occurs at the substituent heteroatom, affording esters or amides instead of the more valuable aromatic ketones. These ort/io-hydroxy- or... 

PaUadium-carbonIbenzylamine Stereospecific reductive amination Preferential formation of amines from ketones and a,/ -ethyleneketones... 

The nonexchanging groups, the nature of which is critical to activity, should be relatively inert amines, preferentially primary. 

Ring hydrogenation of isocyclic amines preferential s. 12, 106 Ring hydrogenation of steroids... 

There also exists an acidregioselective condensation of the aldol type, namely the Mannich reaction (B. Reichert, 1959 H. Hellmann, 1960 see also p. 291f.). The condensation of secondary amines with aldehydes yields Immonium salts, which react with ketones to give 3-amino ketones (=Mannich bases). Ketones with two enolizable CHj-groupings may form 1,5-diamino-3-pentanones, but monosubstitution products can always be obtained in high yield. Unsymmetrical ketones react preferentially at the most highly substituted carbon atom. Sterical hindrance can reverse this regioselectivity. Thermal elimination of amines leads to the a,)3-unsaturated ketone. Another efficient pathway to vinyl ketones starts with the addition of terminal alkynes to immonium salts. On mercury(ll) catalyzed hydration the product is converted to the Mannich base (H. Smith, 1964). 

If a bromomethyl- or vinyl-substituted cyclopropane carbon atom bears a hydroxy group, the homoallyiic rearrangement leads preferentially to cyclobutanone derivatives (J. Sa-laun, 1974). Addition of amines to cydopropanone (N. J. Turro, 1966) yields S-lactams after successive treatment with tert-butyl hypochlorite and silver(I) salts (H.H. Wasserman, 1975). For intramolecular cyclopropane formation see section 1.16. 

The principle of solvent extraction in refining is as follows when a dilute aqueous metal solution is contacted with a suitable extractant, often an amine or oxime, dissolved in a water-immiscible organic solvent, the metal ion is complexed by the extractant and becomes preferentially soluble in the organic phase. The organic and aqueous phases are then separated. By adding another aqueous component, the metal ions can be stripped back into the aqueous phase and hence recovered. Upon the identification of suitable extractants, and using a multistage process, solvent extraction can be used to extract individual metals from a mixture. 

Secondary and tertiary amines are preferentially produced when rhodium or palladium are chosen as catalyst. As in Method 3, reforming reactions do not normally compete with the hydrogenation reaction and high selectivities to the desired product are possible. 

Experimental results are consistent with this representation nucleophilic reagents always attack B in amine—borane complexes, electrophilic reagents preferentially attack N. 

Primary and secondary aliphatic and aromatic amines react readily with thiiranes to give 2-mercaptoethylamine derivatives (Scheme 76) (76RCR25, 66CRV297). The reaction fails or gives poor yields with amines which are sterically hindered e.g. N,iV-dicyclohexylamine) or whose nitrogen atom is weakly basic e.g. N,A/ -diphenylamine). Aromatic amines are less reactive and higher reaction temperatures are usually required for them. The reaction mechanism is Sn2 and substituted thiiranes are attacked preferentially at the least hindered... 

The oxidation of amines by mercuric acetate is an old reaction (54) which up until recent years was employed primarily to modify alkaloid structures (55). A systemic study of the oxidizing action of mercuric acetate by Leonard and co-workers led to the development of a general method for the synthesis of enamines from cyclic tertiary amines. An observation made after a large number of compounds were oxidized, but which is worth noting at the onset, is that a tertiary hydrogen alpha to the nitrogen atom is removed preferentially to a secondary a-hydrogen. 

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