2-Aminobenzaldehyde, macrocycle from

The anhydrotrimer of 2-aminobenzaldehyde, formed from the monomer on standing, or more quickly by the action of dilute acid,15 has proved to have structure 5a.13,16 The anhydro tetramer (5b)13,16 is obtained when the monomer is dissolved in 5 N hydrochloric acid and the precipitated red anhydro tetramer dihydrochloride,15 for which structure 6 has been proposed,13 is made basic with aqueous pyridine. At low concentrations (e.g., 10-5 M), equilibrium favors depolymerization to the monomer, but at higher concentrations (e.g., 10-2 M), 5a and 6 are formed in proportions depending on the strength of acid. The reaction mechanism for the formation of these oligomers has been discussed.13 The trimer (5a) and the tetramer (5b) consist of three tightly bound tetrahydroquinazoline rings and 6 has a macrocyclic structure. It is... 

A more preorganized ligand system is derived from the self-condensation of o-aminobenzaldehyde. The tridentate form of the hgand (25) (TRT) imparts considerable inertness toward substitution. For example, the salts of the [Ni(TRl)(H20)3] + ion can be resolved into optical isomers. A copper(ll) complex of the methyl-substituted tetradentate macrocycle Me4TAAB, in which bis-coordination occurs, displays a dynamic Jahn Teller distortion based on crystallographic evidence. ... 

The earliest example (1) of a synthetic macrocyclic ligand containing an imine linkage was derived from the mixed Schiff base-aldol condensation of acetone with nickel(II) ethylenediamine complexes. In 1964 Curry and Busch reported the iron(II)-templated condensation of 2,6-diacetylpyridine with triethylenetetramine to give iron(III) complexes of the macrocycle (4). This was followed by the observation that the selfcondensation of o-aminobenzaldehyde gave, in the presence of nickel(II) ions, complexes of the macrocyclic ligands (2,3). In all of these examples no macrocycle was obtained in the absence of a metal ion. 

The strategy of Scheme 2-24 for the synthesis of macrocyclic metal complexes by template condensation of monoaminodicarbonyl compounds with polyfunctional diamines is not limited to examples drawn from the chemistry of o-aminobenzaldehyde derivatives. In Section 3.1, in particular, various macrocyclic products built up by using 2,6-diformylpyridine and related compounds as ligsons are considered. 

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