Recent Developments in the [5+2] Cycloaddition

The rapid generation of molecular complexity in a relatively easy manner has made the [5 + 2] cycloaddition approach a highly useful tool in the synthesis of a wide number of complex natural products and important biologically active products containing seven-membered rings. Besides the common and highly efficient [5 + 2] cycloadditions of oxidopyrylium and oxidopyridinium ions with pi-systems which offer an easy access to a wide range of novel heterocyclic seven-membered ring molecules with a oxygen or nitrogen bridge, and the less employed [5 + 2] photocycloadditions, the metal-catalyzed [5 + 2] cycloadditions have attracted a lot of attention and have become one of the most popular ways of constructing seven-membered ring products. All these cycloadducts can be synthetically manipulated easily toward a number of interesting molecular structures with high potential applications.