Abstract
The reactivity of various polyamines with diethyloxalate has been investigated. It appears that, in similar experimental conditions, primary diamines give predominantly (2+2) adducts while the use of secondary benzylated polyamines results in (1+1) condensation. Although the intermediate tetraamides formed in the first case are extremely poorly soluble and show very slow reactivity towards reducing agents, cyclam has been obtained by using ultrasounds during the reaction of the corresponding tetraoxomacrocycle with BH3/THF. The (1+1) cyclization reaction of diversely N-benzylated linear tetraamines, whose selective syntheses have been devised herein, gives access to various N-benzylated cyclens and cyclams. New macrocyclic ligands containing both amine and amide type nitrogen atoms have been formed as intermediates in these syntheses. Two compounds containing an aminal function exhibit an unexpected reactivity, leading to the formation of new bisaminal products whose structures have been established by X-ray diffraction.
Highlights
The chemistry of tetraazacycloalkanes, especially cyclen and cyclam, has undergone a considerable development in the last thirty years, owing to their coordination properties
The nature of the starting polyamine is a key parameter since [1+1] or [2+2] adducts can be preferably obtained depending on the presence or not of benzyl groups on the terminal nitrogen atoms
The reaction of ethylene diamine or 1,3-propanediamine with diethyloxalate gives tetraamides which appear to be quite reluctants towards reduction, cyclam can be obtained in 19 % overall yield, in only two steps, providing that ultrasounds are used during the reduction step
Summary
The chemistry of tetraazacycloalkanes, especially cyclen and cyclam, has undergone a considerable development in the last thirty years, owing to their coordination properties. Since the first syntheses of cyclen and cyclam in the early 70’s, there has been a still growing interest in the search of more convenient approaches for the preparation of these tetraazacycloalkanes and their derivatives. This interest is due to the usefulness of these macrocycles in many different fields including removal of metals from liquids,[2] purification of gases,[3] catalysis,[4] sensors and probes,[5] as well as medical applications.[6].
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