2.6- Diaminopyridine, formation

Figure 10.8 Nanotube formation upon introducing a c/s-double bond in a diaminopyridine alkylamide and their corresponding alkyl chain packing in DAP-2. Reprinted with permission from [75] (2004) American Chemical Society.

Complementary triple hydrogen-bond formation involving transition metal complexes has been little studied. Mingos et al. [68] have investigated the cocrystallisation of platinum(II) complexes of the uracil derivative orotic acid (2,6-dioxo-l,2,3,6-tetrahydropyrimidine-4-carboxylic acid), which generally coordinates as the dianion, and 2,6-diaminopyridine (2,6-dap), in which complementary A-D-A---D-A-D triple hydrogen bonds are formed between the orotate... 

Diaminopyrimidine is reported to react with triphenylphosphite to give 1,3,2-diazaphos-pholo[l,5-. In both cases, however, the physical properties of the isolated materials are in accord with oligomers rather than with monomeric azaphospholes. 

Random polynorbomene-based terpolymer 5 (Fig. 5.8) functionalized with SCS palladated pincer complexes, dibenzo[24]crown-8 (DB24C8) rings, and 2,6-diaminopyridine units was synthesized by ROMP (South et al. 2006). The palladium complex serves as the anchoring unit for metal coordination, 2,6-diaminopyridine as the DAD hydrogen bonding moiety, and DB24C8 as the precursor for pseudorotaxane formation, which has been smdied extensively by Stoddart and his group... 

Figure 5.8 Three recognition motifs based on (a) hydrogen bonding interactions between 2,6-diaminopyridine and thymine, (b) metal coordination of suUur-carbon-sulfur (SCS) Pd pincer with pyridine, (c) pseudorotaxane formation between dibenzo[24]crovvn-8 (DB24C8) and dibenzylammonium ions, and (d) fuUy functionaUzed terpolymer 5.

Imidazo[4,5- ]pyridines 117 <2003BML2485>, 118 <2004BML3165>, 119 <2005BML2129>, and 120 <2003BML289> have been prepared from the corresponding diaminopyridine and the appropriate trialkyl ortho-formate or, in the case of 120, triethyl orthopropionate. However, in each case, the authors fail to report product yields. 

The reaction of 2,6-diaminopyridine with bromomalondialdehyde does not result in the formation of 18b, yielding instead 5-amino-2-formylimidazol l,2-a]pyridine.20... 

In a series of publications and patents,63 64 66"79 Wieniawski and coworkers reported the results of investigations of the reaction of sugar isothiocyanates with amines and various substituted hydrazides of heterocyclic acids. The reaction of isothiocyanate 2 with 2,6-diaminopyridine 81 was described,63 and the formation of dithioureide 82 as the sole product was observed. The... 

This was realized with derivatives of the complementary heterocyclic groups 2,6-diaminopyridine P and uracil U bearing long aliphatic chains [9.150]. Whereas the pure compounds did not show liquid crystalline behaviour, 1 1 mixtures gave a metastable mesophase of columnar hexagonal type. The existence of the latter was attributed to the formation of a mesomorphic supermolecule 173 via association of the complementary components. 

Often designated briefly as Hamilton receptor , this barbiturate receptor niche (Fig. 6.12) consists of an isophthaloyl spacer flanked by two acylated 2,6-diaminopyridine moieties. Macrocyclisation with a rigid diphenylmethane unit generates a non-collapsing host cavity suitable for selective complexation of barbiturate guest molecules via formation of six hydrogen bonds. 

Two of the reactions summarized in Tables VI and VII require some comment. The reaction of 3-hydroxypyridine with an excess of sodamide at 210° results in the elimination of the hydroxyl group and the formation of 2,6-diaminopyridine. Plazek288 attributed this to the reduction of the phenolic function by nascent hydrogen. More recently, however, this reaction has been interpreted as providing evidence for the intermediacy of a 2,3-pyridyne species in this reaction271 ... 

The relevance of thymine/2,6-diaminotriazine interactions has been exploited by a variety of authors to effect a reversible, yet stable association of catalysts, nanoparticles and other fimctional molecules onto polymeric molecules. Thus, Shen et al. [94,95] reported on the formation of catalyst-supported structures for ATRP-polymerization via hydrogenbonding systems (Fig. 19). The relevant Cu(I)-catalyst was affixed onto a poly(styrene) gel either via the thymine/2,6-diaminopyridine or the maleimide/2,6-diaminopyridine couple. The catalyst was able to mediate a living polymerization reaction of MMA in both cases, obviously acting in its dissociated form. The catalyst could be reused, retaining about half of its catalytic activity for further use. A strong solvent effect was observed, explainable by the dissociation of the catalyst from the support upon addition of strongly polar solvents. 

Pyridine rings containing electron-donating substituents are deactivated toward the Chichibabin reaction relative to pyridine. Pozharskii et al. have studied the amination of the three isomeric aminopyridines. Treatment of an aminopyridine results in evolution of ammonia and formation of the sodium salt of the heterocycle. The sodium salt of 2-aminopyridine (88) was readily aminated at 160-180°C, forming 2,6-diaminopyridine (65) in 70-80% yield. 

Pozharskii continued the investigation with dialkylaminopyridines (73CHE1119). Amination of 2-dimethylaminopyridine resulted in formation of 2,6-diaminopyridine (65). No significant amount of 2-amino-6-dimethyl-aminopyridine was found, suggesting that the dimethylamino moiety is displaced prior to amination. It is interesting to find that 4-dimethylaminopyri-dine was aminated to 2-amino-4-dimethylaminopyridine since it represents... 

On the subject of spontaneous generation of chirality, it is of interest to know that spontaneous formation of chiral aggregates from nonchiral monomers is known to occur, e.g. the assembly of tetra-alkyl benzimidocyanins 3 as monitored by CD (circular dichroism). Formation of chiral crystals from achiral monomers is also reported, e.g. by photodimerization in the solid state. " In a recent example, chiral crystals of acridine 4 and diphenylacetic acid 5 give excess of the (.S)-product 6 upon a photodecarboxylating condensation reaction. Symmetry breaking is also known to occur for supramolecular complexes of achiral components e.g. glu-tarimide 7 and the diaminopyridine 8, and, as will be discussed below, in monolayers at the air-water interface. ... 

N02 diazotate p-choroaniline with subsequent combination of the product with 2,6-diaminopyridine and action of ammine complexes of Cu(II). This results in the formation... 

The UV absorption spectrum of 2,6-diaminopyridine in ethanol/isooctane mixed solvent with variable temperature or ethanol concentration is consistent with the formation of the hydrogen-bonded complex of (/i)-6-amino-2( l//)-pyridinimine with two molecules of ethanol. The formation of the imino form may be restricted to the 2,6-diaminopyridine and its methyl derivatives, in which each amino group at the 2- and 6-positions has at least one hydrogen atom. Ab initio STO-3G calculations... 

The classical synthesis of IPs consisted in cyclization of o-DAP with carboxylic acids, their derivatives and precursors. This method was used to prepare the majority of IP derivatives with various substituents in the imidazole and pyridine rings. However, it should be mentioned that cyclization of o-diaminopyridines with carboxylic acids and their derivatives occurs less readily than that of o-phenylenedia-mines. Whereas the latter are cyclized into benzimidazoles when heated with carboxylic acid for a short time (51CRV397), boiling a 2,3-DAP and an acetic anhydride mixture for 2h affords only 2,3-diacetylaminopyridine, and fusion of this diamine with benzoic anhydride resulted only in the formation of 2,3-dibenzoyl-aminopyridine (64JOC3403). 

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