Theoretical and experimental insights into cycloaddition reactions

Abstract

In this article, a description has been given of theoretical and experimental investigations of the factors beyond frontier molecular orbital interactions which are important in influencing mechanisms, rates, and regioselectivities of cycloadditions and related reactions of unsaturated systems. Closed-shell repulsion, geometrical distortions, polarization, and secondary orbital interactions have all been shown to be influential. Electrostatic interactions and correlation effects have not been discussed, but will provide further refinements — or confusion, depending upon the reader's point of view! As Professor Huisgen recently commented, there are now a distressingly large number of “buttons to push”, to explain various phenomena91). This is, indeed, the case at the present time, primarily due to our limited knowledge about the magnitudes of these many effects. The cases discussed here constitute examples where the cited effects seem to prevail over others, but similar effects will be present to some extent in all reactions. Our current research efforts constitute attempts to understand more generally when these effects are significant, and to be able to understand and predict rates and products of organic reactions.