Cyclopropanes as well as carbon-carbon triple bonds are systems being high in energy. Therefore, both moieties are ideally suited for a cascade of consecutive reactions (domino reactions).
In a first part, domino reactions based on ring-enlargement reactions of donor-acceptor-substituted cyclopropanes are discussed. Aldehyde, ketimines and thioketones are utilized as acceptors whereas ether moieties serve as donor. A rearrangement leads to the respective five-membered rings which tend to eliminate water. As a result, aromatic systems are formed. Depending on the substrate domino cascades are initiated which are able to transform the biscyclopropane derivative 1 in one step into the corresponding quaterpyrrol 2. In a second part, Pd-catalyzed domino reactions starting with triple bonds attached to carbohydrate derivatives 4 are reported to construct a variety of chroman- and isochroman-type structures such as 5. Such domino sequences are also employed to a variety of other processes leading to complex scaffolds in a facile and efficient fashion.