Ring-closure reactions tetramethylene

Many polyamines are now available from Aldrich, Fluka, Phaltz and Bauer, Sigma, and TCI chemical companies. The available compounds include tri-and tetraamines with a mix of ethylene, trimethylene, and tetramethylene units between the nitrogen atoms. Of particular interest are tetraamines where the two internal amines are tertiary and the terminal amines are secondary. These compounds can be used in the ring closure reaction to form the peraza-crowns. 

Fig. The diradical reaction shown shcmaticallyin an energy diagram. After elimination of carbon ntortoxidefrom the parent cyclopentanonephtochemicaUy the tetramethylene diradical is created this can undergo ring closure to yield cyclobutane or can produce two ethylenes.

This reaction, like dicarbene recombination, also has its analog in coordination chemistry, that is, reductive elimination of tetramethylene and pentamethylene ligands from platinum complexes yields cyclobutane and cyclopentane, respectively (777). According to this direct ring closure mechanism, the observed selectivity for dehydrocyclization of n-alkanes on metals (nonformation of quaternary-secondary and tertiary-secondary C-C bonds in reactions of type A and B) should be interpreted in terms of simple steric effects. However, although, in the case of platinum, the concepts of steric hindrance could account for the change of selectivity that occurs with decreasing metal particle size (i.e., cyclization of n-hexane takes place on... 

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