Ring-closure reactions trimethylene

A classical topic for illustration of the above principles is the analysis of the behaviour of the system trimethylene cyclopropane methylene + ethylene (11). Ring closure of trimethylene is a simple example of an electrocyclic reaction (8a) ... 

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. 

Figure 6.16 The ring-closure reaction of 1,2-dimethyltrimethylene. Contour diagrams of the surface and the SOC surface (a) of trimethylene and (b) of its 1,2-dimethyl derivative. Triplet-singlet intersection SgT = 0 is indicated by heavy lines.

Figure 7. Triplet PE (top) and SOC surfaces (bottom) for the ring-closure reaction of trimethylene (left) and 1,2-dimethyltrimethylene (right), as a function of the CCC valence angle y and the conrotatory motion (a = P) of the radical centers. SOC values vary between 0 cm in the middle of the diagram and 7.5 cm at the upper right and left corners. T -Sq intersection = 0 is indicated by heavy lines.

On orbital symmetry grounds, the addition of ethylene to ethylene with ring closure (cycloaddition) should be thermally forbidden. If one compares this reaction with the reaction of trimethylene with approaching ethylene and butadiene (Fig.4), it is readily seen that, the A level being below the S level in trimethylene, the behaviour with respect to cycloaddition to olefins is reversed, that is, trimethylene is essentially an anti-ethylene structure. This principle can be generalized for instance (16) ... 

The stable products of the reaction are the cyclopropanes and isomeric olefins. The decomposition of cis- and tra j-3,5-dimethyl-1-pyrazolines are of special interest in that they exhibit a stereochemical reversal in the dimethyl cyclopropane product. The cw-pyrazoline forms predominantly trans, and the franj-pyrazoline predominantly cw-dimethyl cyclopropane. This is a consequence of the orbital symmetry of the intermediate trimethylene species which requires a conrotatory motion as the preferred mode of ring closure, and as such lends experimental support to the validity of Hoffman s mo calculations. 

Reaction of ethylene dibromide or trimethylene dibromide with an insufficiency of sodiomalonic ester can lead to ring closure to cyclopropane384 or cyclobutane derivatives,385 respectively (reaction b). 

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