Tris amine, branched

Direct addition of ammonia to olefmic bonds would be an attractive method for amine synthesis, if it could be carried out smoothly. Like water, ammonia reacts with butadiene only under particular reaction conditions. Almost no reaction takes place with pure ammonia in organic solvents. The presence of water accelerates the reaction considerably. The reaction of aqueous ammonia (28%) with butadiene in MeCN in the presence orPd(OAc)i and PhjP at 80 C for 10 h gives tri-2,7-octadienylamine (47) as the main product, accompanied by a small amount of di-2,7-octadienylamine (46)[46,47], Isomeric branched... 

PAMAM dendrimers are synthesized in a multistep process. Starting from a multifunctional amine (for example ammonia, ethylenediamine, or tris(2-amino-ethyl)amine) repeated Michael addition of methylacrylate and reaction of the product with ethylenediamine leads to dendrimers of different generation numbers [1,9]. Two methylacrylate monomers are added to each bifunctional ethylenediamine generating a branch at each cycle. Unreacted ethylenediamine has to be completely removed at each step to prevent the initiation of additional dendrimers of lower generation number. Excess methylacrylate has also to be removed. Bridging between two branches of the same or of two different dendrimers by ethylenediamine can also be a problem, and has to be avoided by choosing appropriate reaction conditions. 

The branched tetradentate ligand tris(2-aminoethyl)amine (tren) forms rather stable metal complexes with most transition metal ions. It is a very hard and basic ligand and consequently its iron(II) complexes are all high-spin. Later we will discuss hexadentate derivatives of this ligand which form crossover complexes (see Sect. 3.2). 

Depending on the number of amine groups in the molecule, the amine can be a mono-, di-, tri-, or polyamine. Aliphatic amines can also be classified by their molecular structure as linear, branched, aliphatic, or containing aromatic groups. However, the most valuable method of classification is by functionality. 

Poly(ethylenimine) (PEI) has been examined extensively both in its classical, random branched topology [125] and in its linear form [126]. The various architectural and topological forms of PEI have been reviewed recently [127], Here we describe the first example of this polymer system as an ideal, hyper-branched molecular assembly. Synthesis of a tri-dendron poly(ethyleneimine) dendrimer derived from an ammonia core involved, first the selective alkylation of diethylenetriamine (DETA) with aziridine to produce a symmetrical core cell, namely tris-(-2-aminoethyl)amine. Subsequent exhaustive alkylations of the terminal amino moieties with activated aziridines [2, 127, 128], such as IV-tosyl- or N-mesylaziridine gave very good conversions to the first-generation protected... 

The authors studied the polymerization of formaldehyde with amines including tertiary amines at —78°C in various solvents (Table 1), and determined the conversion after 15 min reaction time. Tertiary amines are highly reactive initiators for formaldehyde polymerizations even at the level of 10 mole T per mole 1 of formaldehyde. The reactivity of the amine is related to its pXg value but also to the branching of the aliphatic side chains of the substituents on the nitrogen atom. Branched amines, especially when the branching is on the a-carbon atom as in the case of a tertiary butyl group, are less effective initiators than tertiary amines with n-alkyl chains. The pX a of the amine is not the essential feature for an efficient tertiary amine initiator, because pyridine was almost as effective as tri-n-butylamine but quinoline, with a similar pK g as pyridine, is almost inactive (Table 1). 

Since polyamines are industrially available compounds, we returned to our first successful cacade synthesis in 19781 where we produced dendritic oligoamines. It seemed attractive to pursue this synthesis with new preparative and analytical methods, which then were limited. As starting materials, we selected the commercially available tris(2-ami-noethyl)amine (TREN) due to its inherently branched structure. The synthesis was accomplished in a manner identical to that conducted 16 years ago, affording a 90% yield of the first-generation dendrimer 46 by reaction of TREN with acrylonitrile and catalytic amounts of acetic acid (Scheme 10). 

Phase-transfer agents are the most popular catalysts for the Halex reaction with alkaline fluorides. All types of transfer agents have been claimed tetraalkyl-ammonium halides (refs. 34, 48), Aliquat 336 (ref. 49), branched pyridinium halides (eventually supported on a polymer) (refs. 50 to 53), tetraalkylphosphonium chlorides (refs. 42, 54 - 57) or bromides (ref. 12), crown-ethers (refs. 58, 59) eventually associated with Ph4PBr (refs. 43, 60), tris-(dioxa-3,6-heptyl)amine (TDA-1) (ref. 61) or polyethyleneglycols (PEG) (ref. 62). 

As stated in Section 2.4, the condensation reaction may be the basis for the mechanism of stepwise polymerization. As long as the functionality equals 2 (di-acid and di-alcohol in polyester or di-amine in polyamide), only linear chains are obtained. However, once polyfunctionality prevails (appearance of tri-alcohol like glycerol, or tri-acid), reactive branches are formed that may interact and lead to a three-dimensional structure, called cross-linked (gelation). This is the basis for thermosetting polymers on one hand, or for stabilizing the elastomeric chain on the other hand (replacing vulcanization). 

Chemists have synthesized a variety of multivalent glycocomimetics with a broad range of different architectures. Relatively small branched molecules such as pentaerythri-tol or tris(hydroxymethyl)amine have been glycosylated to... 

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