Molecular pyramids - from tetrahedranes to [6]pyramidanes.

The study of 3D architectures at a molecular scale has fascinated chemists for generations. This includes molecular pyramids with all-carbon frameworks, such as trigonal, tetragonal and pentagonal pyramidal geometries. A small number of substituted tetrahedranes and all-carbon [4]-[5]pyramidanes have been experimentally generated and studied. Although the hypothetical unsubstituted parent [3]-[6]pyramidanes have only been explored computationally, the formal replacement of carbon vertices with isolobal main group element fragments has provided a number of examples of stable hetero[m]pyramidanes, which have been isolated and amply characterized. In this Review, we highlight the synthesis and chemical properties of [3]-[6]pyramidanes and summarize the progress in the development of chemistry of pyramid-shaped molecules.