Condensations with Amines

The mechanism of the original Knorr pyrrole synthesis entails in situ reduction of the oxime moiety to an amine, condensation with the second carbonyl compound, and cyclization with loss of a second molecule of water to give a pyrrole for example, 10 + 11 to 12. Several studies have demonstrated that different pathways and pyrrole products obtain depending on the substrates. 

In 1911, Ame Pictet and Theodor Spengler reported that P-arylethyl amines condensed with aldehydes in the presence of acid to give tetrahydroisoquinolines. Phenethylamine 6 was combined with dimethoxymethane 7 and HCl at elevated temperatures to give tetrahydroisoquinoline 8. Soon after, the Pictet-Spengler reaction became the standard method for the formation of tetrahydroisoquinolines. 

Like alcohols, amines condense with carboxylic acids ... 

The initiating reaction between aldoses and amines, or amino acids, appears to involve a reversible formation of an N-substituted aldosyl-amine (75) see Scheme 14. Without an acidic catalyst, hexoses form the aldosylamine condensation-product in 80-90% yield. An acidic catalyst raises the reaction rate and yet, too much acid rapidly promotes the formation of 1-amino-l-deoxy-2-ketoses. Amino acids act in an autocat-alytic manner, and the condensation proceeds even in the absence of additional acid. A considerable number of glycosylamines have been prepared by heating the saccharides and an amine in anhydrous ethanol in the presence of an acidic catalyst. N.m.r. spectroscopy has been used to show that primary amines condense with D-ribose to give D-ribopyrano-sylamines. ... 

Amines, Condensation With Aromatic Chlorine Compounds. Amines can be condensed with aromatic Cl den vs and the resulting compds... 

Similar to the Combe synthesis, primary aromatic amines condense with alkyl acetoacetates at lower temperatures to give / -anilinocrotonates, which can be used as precursors for cyclization to 4-hydroxyquinolines177 by action of hot sulphuric acid or hydrochloric acid in a Conrad-Limpach synthesis. 

The first stage involves reduction of the nitro group to an amine, condensation with the ketone give an imine, and then the interesting step, reduction of the imine to the secondary amine. Tr. imine binds to the catalyst on the side away from the butyl group - the only group not in the plane The product is shown as one enantiomer but it is, of course, racemic if the starting material s racemic. 

The azomethine ylide must be formed from the amino acid and acetone. Briefly, the amine condenses with acetone to give an iminium ion. Decarboxylation produces the 1,3-dipole, which can undergo [3 + 2] cycloaddition to C60 to give the observed product. By now you should be able to draw a mechanism for formation of the iminium ion. 

FIGURE 5.3 Initial primary amines condensed with 2-(2-bromoethyl)benzaldehyde (11) to form iminium salts. 

V-Alkyl-substituted guanidin-2-amines condense with 1,2-dicarbonyl compounds to give A -alkyl-l,2,4-triazin-3-amines 7 and 8.115 6-Substituted 1,2,4-triazin-3-amines 7 can also be prepared by reaction of 2-(hydroxyimino)-l-phenylethan-l-onen5 or dibromo ketones with guanidin-2-amine.141 24 2... 

If hydroformylation is carried out in the presence of primary or secondary amines, condensation with the initially formed aldehyde and subsequent hydrogenation of the resulting imine or enamine can occur under suitable conditions. The overall reaction sequence is referred to as hydroaminomethylation. The intramo-... 

Tetrahydroquinolines. These amines condense with acetaldehyde to foim 4-benzotriazolyl-l,2,3,4-tetrahydroquinolines. The benzotriazole group can be replaced with nucleophiles. 

For ketoester the substrate, the hydrazone forms exclusively between the hydrazine and with more active ketone. The corresponding hydrazone-ester then cyclizes to produce the pyazolone. Mechanistically, the more basic and less substituted hydrazine amine condenses with the ketone. The resultant hydrazine-ester then cyclizes to the pyrazolol, which could also tautomerize to the corresponding pyrazolone. 

In the first stage (Equation 9), the amine condenses with chlorosulfonic acid to give the pyridinium sulfamate 27, which subsequently reacts with the carboxylic acid to yield the corresponding acid amide 28 (Equation 10). In this reaction, the yields of the amides are generally high, but the best yields were obtained with aliphatic acids. ... 

Both primary and secondary amines condense with formaldehyde and phthalimide to give solid products having sharp melting-points. The derivatives from primary aromatic amines are N-... 

In the absence of (reactive) nucleophiles, H CHO can undergo polycondensations with amines. Condensation with ammonia forms hexa[ C]methylenetetramine (181),... 

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