Amines boronate assemblies

Severin and coworkers reported (146) the reaction of tris(2-aminoethyl)amine and 4-formylphenylboronic acid with penta-erythritol to give, via multicomponent assembly, the boronic acid based macrobicyclic cage 35 (Fig. 25). The cage has the form of an ellipsoid with a diameter of 20.5 A and binds two Cud) ions in a fashion similar to the smaller tren-based cryptands. The reversible formation of boronic esters has also been employed to build other hollow structures such as nanotubes (147) and porous covalent organic frameworks (148,149). 

Jamison has reported the unprecedented nickel-catalyzed assembly of allylic amines 156 from three simple starting materials alkynes, imines, and trialkylbor-anes or boronic acids. The participation of boronic acids in this methodology greatly enhances its synthetic potential, owing to their greater availability (Scheme 8.68) [145]. An asymmetric version of the reaction has also been developed but gave only moderate enantiomeric excesses (33 to 42%). 

It was found that the presence of an amino or aldehyde groups in the meta-position of the arylboronic acid did not interfere in the macrocyclization reaction. This allowed the effective assembly of functionalized boronic acids, dihydroxypyridine ligands, and amines or aldehydes, respectively, in a multicomponent procedure affording pen-tameric boronic acid macrocycles (Scheme 4.7) and tetramer derivatives (Scheme 4.8). 

Boronic Acid-Chiral Amine Assemblies for NMR Determination of the e.e. Values of Chiral Diols... 

It is challenging to determine the e.e. value of simple chiral hydrox-ylamines because there is only one binding site. However, based on the B-N interaction, the e.e. value of simple amines can also be determined by using H NMR analysis based on the three-component assembly of 2-formylphenylboronic acid, racemic BINOL and the chiral hydroxyl-amines to afford a mixture of diastereomeric nitrono-boronate esters whose ratio is an accurate reflection of the enantiopurity of the parent hydroxylamine (Scheme 6.3). ... 

Incorporation of this coordinative amine ligand within the cycle structure is an alternative approach for generating stable macrocycles. In this regard, alkyl bridged bis(2-hydroxyphenylmethyl) amines have been reacted with 4,4 -biphenyldiboronic acid (Fig. 19a). Esterification proceeds with concomitant coordination of the amine to the resulting ester. The paraquat dication is complexed by this assembly in a 1 1 manner (Fig. 19b) through ionic interactions (anionic boronate with pyridyl cation), attractive n-n interactions (between biphenyl components) and C —H —O hydrogen bonds (paraquat... 

FIGURE 19. (a) Acyclic boronate diesters form macrocyclic assemblies with coordinate amines for added stability, (b) These macrocyles bind paraquat in a 1 1 manner. 

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