2-Aminopyridine 2-Aminopyrimidine

A -Aryl- and 7V-imidoylsulfimides from 2-aminopyridine, 2-aminopyrimidine, A-phenyl-benzamide, and 2-aminobenzoxazole reacted with 2,3-diphenylcyclopropenone to give pyrimi-din-4-ones 22-25, respectively, by intramolecular interception of the ketene intermediate." ... 

Substituted imidazo[l,2-typical example of this versatile reaction, (40) reacted with 2-aminopyridine (39) to give the imidazopyridine (43) in 86% yield via intermediates (41) and (42) (Scheme 12). 

Aminocoumaiins Aminoindazoles Aminopurines Aminopyridines Aminopyrimidines Aminouracils Aminopyrazines Aminopytidazines Aminoquinazolines Amino-1,2,4-triazines Amino-1,2,4-triazoles Aminopteridines Aminobenzimidazole Aminopyrimidopyrimidines Aminobenzotriazines Cytosines... 

Thiophenealdehyde has been used in the reductive alkylation of 2-aminopyridine and 2-aminopyrimidine. 2-Arylamino-4- (2-thienyl )thiazoles have been prepared by the reaction of 2-acetylthio-phene with A-arylthioureas in the presence of iodine, ... 

The diazotization of amino derivatives of six-membered heteroaromatic ring systems, particularly that of aminopyridines and aminopyridine oxides, was studied in detail by Kalatzis and coworkers. Diazotization of 3-aminopyridine and its derivatives is similar to that of aromatic amines because of the formation of rather stable diazonium ions. 2- and 4-aminopyridines were considered to resist diazotization or to form mainly the corresponding hydroxy compounds. However, Kalatzis (1967 a) showed that true diazotization of these compounds proceeds in a similar way to that of the aromatic amines in 0,5-4.0 m hydrochloric, sulfuric, or perchloric acid, by mixing the solutions with aqueous sodium nitrite at 0 °C. However, the rapidly formed diazonium ion is hydrolyzed very easily within a few minutes (hydroxy-de-diazonia-tion). The diazonium ion must be used immediately after formation, e. g., for a diazo coupling reaction, or must be stabilized as the diazoate by prompt neutralization (after 45 s) to pH 10-11 with sodium hydroxide-borax buffer. All isomeric aminopyridine-1-oxides can be diazotized in the usual way (Kalatzis and Mastrokalos, 1977). The diazotization of 5-aminopyrimidines results in a complex ring opening and conversion into other heterocyclic systems (see Nemeryuk et al., 1985). 

Aldehydes and the corresponding 2-aminopyridine, pyrazine, or pyrimidine are admixed in presence of a catalytic amount of clay (50 mg) to generate iminium intermediate. Isocyanides are subsequently added to the same container and the reactants are further exposed to MW to afford the corresponding imidazo[l,2-a]pyridines, imi-dazo[l,2-a]pyrazines and imidazo[l,2-a]pyrimidines (Scheme 6.48). The process is general for all the three components, e. g. aldehydes (aliphatic, aromatic and vinylic), isocyanides (aliphatic, aromatic and cyclic) and amines (2-aminopyridine, 2-amino-pyrazine and 2-aminopyrimidine). A library of imidazo[l,2-a]pyridines, imidazo[l,2-ajpyrazines and imidazo[l,2-a]pyrimidines can be readily obtained by varying the three components [151]. 

Compound 642, obtained by condensation of glyoxal with benzotriazole and morpholine undergoes interesting [2+3] cyclocondensation with 2-aminopyridine to give imidazo[l,2- ]pyridine 643 (Equation 15) <2003JOC4935>. Similar derivatives of piperidine and pyrrolidine are also described. 2-Amino- and 6-aminopyrimidines react similarly to give imidazo[l,2- ]- and imidazoll - pyrimidines, respectively. 

Anilines, bis(2-amino-4-chlorophenyl)disulfide, naphthylamine, 2- and 3-aminopyridines, 2-aminopyrimidines, 2-, 3-, 5-, 6-, 7-, and 8-aminoquino-lines, 6-aminocoumarin, and 2-aminopyrazine were reacted in the absence or presence of a solvent (ethanol, toluene) with ethyl orthoformate and isopropylidene or 4-heptylidene malonates to give alkylidene (het)aryl-aminomethylenemalonates (442, R = R2 = Me, Pr) in 32-100% yields [69BRP1147759 75USP3907798 88JAP(K)239269]. p-Toluenesulfonic acid monohydrate was sometimes applied as catayst. 

The use of vinylphosphonium salts in heterocyclic synthesis continues to be exploited. The kinetically controlled reactions of the / -acylvinylphosphonium salts (143) with 2-aminopyridine lead to the salts (144) similar reactions occur with 2-aminopyrimidine and cytosine. Under conditions where thermodynamic control prevails, the salts (145) are formed predominantly, resulting from a Dimroth rearrangement of (144).136... 

Aminopyrimidines have been studied by Albert et al. (1948), and, by relying on the pAj-values at 20° of aminopyridines, there is no doubt that the 4-amino-derivative is protonated on the ring nitrogen N-1 (pAj = 5 69, as compared with pA = 1-23 for unsubstituted pyrimidine). The 2-amino-derivative is a weaker base (pAg = 3 45) and the 5-amino-derivative is weaker still (p/Cg = 2-60). An interesting ultraviolet spectral correlation has recently been pointed out (Albert and Taguchi, 1973) between compounds containing the 2-aminopyrimidinium and 2-pyrimidone structures ([59] and [60]). 

Cyclic amidines (213) react with chlorocarbonylsulfenyl chloride to give bicyclic 1,2,4-thia-diazoles. The product isolated from this reaction depends on the mode of addition. When (213) is added to chlorocarbonylsulfenyl chloride, 3-oxo derivatives (214) are isolated via the postulated intermediate (215). Addition of chlorocarbonylsulfenyl chloride to (213) leads to 5-oxo derivatives (216), via the proposed bis(intermediate) (217) (Scheme 47) <84CHEC-I(6)463). Cyclic amidines (213) have also been treated with 1-chloro-l-phenyliminomethanesulfenyl chloride (210) to afford 2>H-1,2,4-thiadiazoles (218). The other possible product from this reaction, the 2/7-isomer (219) has been shown to be unstable, rearranging to a benzothiazole. Heterocycles (213) which have been used in this transformation include 2-aminopyridine, 3-aminopyridazine, 2-aminobenzothiazole, 2-aminopyrimidine and 2-aminothiazole (Equation (33)) <86S1027>. 

Aminopyrimidines react with DMAD in the presence of a catalytic amount of a strong acid to give pyrrolo[3,4-f]pyridines in a cycloaddition reaction (Equation 66) <2001SL57>. In the absence of the acid catalyst, aminopyridines are produced in the reaction. 

Nucleophilic reagents can also react with 2- and 4-aminopyridines at the carbon atom which carries the amino group in a replacement reaction (e.g. 738 — 739) similar to, but far less facile than, that undergone by chloro and alkoxy compounds, etc. In this way aminopyrimidines can be converted into pyrimidinones by direct acidic or alkaline hydrolysis under rather vigorous conditions. 

Aminopyrazines, like aminopyridines and aminopyrimidines, form p-aminobenzenesulfonyl derivatives, and one of these, 2-sulfanilamido-3-methoxypyrazine (11), is clinically used as an antibacterial agent.320 Bromination of compound 11 in methanol gives a product (114)321,322 which was originally incorrectly formulated as a hydrate.323 The correct structure follows from spectroscopic evidence and alkaline... 

Similar reactions have been carried out with amidines (67NEP6610627). Thus tri-chloroacetamidine (309) reacts with chlorothioformate esters to produce thioacyl products (310) which are readily oxidized to 5-alkoxy-3-trichloromethyl-l,2,4-thiadiazoles (311). The yields in both steps are about 80% (Scheme 111). The bromine oxidation of N-thiocarbamyl derivatives (312) of cyclic amidines (2-aminopyridine, 2-aminothiazole, 2-aminopyrimidine) yields thiadiazolium salts (313) (71JPR1148). In the 2-aminopyridine series, products of type (230 Scheme 81) are obtained in 20-73% yield when R is an ethoxycar-bonyl group (750PP55). 

In a series of publications (75JOC2600, 70JOC1965, 73JOC3087), Potts and coworkers have reported that cyclic amidines (290) readily condense with trichloromethylsulfenyl chloride (329) to yield the sulfenamides (330 Scheme 119). Treatment of the latter compounds with aromatic amines in the presence of triethylamine results in cyclization, possibly via an intermediate such as (331), to produce bicyclic products of type (332). Heterocycles (290) which have been used successfully in this reaction include 2-amino-l,3,4-thiadiazoles, 3-aminopyridazines, 2-aminopyrimidines, 2-aminopyrazines, 2-aminopyridines, 3-aminoisoxazoles and 5-amino-1,2,4-thiadiazoles. The sulfenamide derivative (330) of 2-aminopyridine also was found to react with sodium sulfide and with diethyl malonate to produce (333) and (334) respectively. Attempts to hydrolyze (332) to (295) under acidic conditions failed. 

Solid-supported a-bromoketone 148 was condensed with various 2-aminopyridines or 2-aminopyrimidine derivatives to give imidazo[l,2-a]pyridines or imidazo[l,2-fl]pyriniidine derivatives 149 after cleavage with acid <03TL6265>. An abnormal aza-Wittig reaction on solid-phase parallel synthesis of 3-aryl-2,4-dioxo-l,3,5-triazino[l,2-a]benzimidazoles was observed <03TL3705>. New spiroimidazolidinone derivatives 151 were prepared Irom SynPhase lanterns from dipeptides anchored on the solid-supports 150 <03JCO356>. 

We are investigating a series of reactions of aminopyridines and aminopyrimidines and main group compounds. These heterocycles can form adducts with both kinds of nitrogen atoms pyridinic or anilinic. Bonding of several aminopyridines to heteroatoms such as boron, silicon, or phosphorus gives polyfunctional molecules rich in lone pairs and therefore candidates to be used as ligands. 

Now, we are actively investigating the adducts of several aminopyridines and aminopyrimidines in order to know the reactivity of the different isomers and how the substitution of the NH by a heteroatom affects the coordinating behaviour. We are also interested in collecting multinuclear NMR data of these systems that could be used to study more complex molecules. 

Multicomponent reactions have been described for several syntheses of imidazoles. Highly efficient methods for the syntheses of spiroimidazolinones via microwave-assisted three-component one-pot sequential reactions or one-pot domino reactions have been described <06JOC3137>. Multicomponent reactions between 2-aminopyrimidine, aldehydes and isonitriles afforded imidazo[l,2-a]pyrimidines <06TL947>. Two novel one-step microwave mediated syntheses of arrays of 3-iminoaryl-imidazo[l,2-a]pyridines and imidazo[l,2-a]pyridyn-3-ylamino-2-acetonitriles were synthesized by multicomponent reactions under microwave condition in methanol by simply mixing a-aminopyridines, aldehydes, and trimethylsilylcyanide catalyzed by polymer-bound scandium triflate <06TL2989>. 3-Aminoimidazo[l,2-a]pyridines have been synthesized via the multicomponent reaction of aldehydes, isocyanides and 2-aminopyridines in the presence of the ionic liquid l-butyl-3-methylimidazolium bromide [bmim]Br<06TL3031>. 

The two C-nucleosides derived from 2-aminopyridine (144) and 2-aminopyrimidine (145) have been used to enhance base triplets involving C-G and G-C base pairs. 2-Aminopyridine, which has a pXa of 6.8, was shown to recognise the dG-dC base pair better than dC-dG, whilst 2-aminopyrimidine, with a pXa of 3.3, forms more stable triplets with dC-dG. 

Pyrimidines (see Sections I, II, and V,D). In the previous review, a number of incorrect deductions were made from preparative work about the effect of an amino substituent on reactivity. The positional order 5 > 2 > 4 was arrived at for the activating effect of this group. Consideration of kinetic results for 2-, 3-, and 4-aminopyridines shows that the order of the activating effect of an amino group is para > meta > ortho and the reactivity order for aminopyrimidines is therefore predicted to be 4 (with reaction occurring at N-1) > 5 > 2. Furthermore, kinetic data (Table II) show an amino substituent to be more activating than a methyl or chloro group in the same position, in contrast to predictions made from preparative work. 

Treatment of polymer-bound 5-(2-bromoacetyl)pyrroles with 2-aminopyridines or 2-aminopyrimidines resulted in the formation of imidazo[l,2-a]pyridylpyrroles or imida-zo[l,2-a]pyrimidylpyrroles respectively. Optimal reaction conditions for this heterocyclization were 7 h at 60 °C in DMF/EtOH (1 1) (Fig. 6.17). 

Two moles of a 2-aminopyridine react with di-iodomethane to give a tricyclic quaternary salt. Electron-withdrawing substituents in the pyridine ring inhibit the reaction of several aminopyrimidines, aminopyrazine, aminoimidazoles and aminopyrazoles, only 4-aminopyrimidine reacted [3089]. 

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