Pyramidanes: newcomers to the anti-van't Hoff-Le Bel family.

In this feature article, an overview of the chemistry of pyramidanes, as a novel class of main group element clusters, is given. A general introduction sets the scene, briefly presenting the non-classical pyramidal geometry of tetracoordinate carbon, as opposed to the classical tetrahedral configuration. Pyramidanes, as the simplest organic compounds possessing a pyramidal carbon atom, are then discussed from both computational and experimental viewpoints, to show the theoretical predictions on the stability and thus the feasibility of pyramidanes has finally culminated in the isolation of the first stable representatives of the pyramidane family featuring heavy main group elements at the apex of the square pyramid. Synthetic strategies towards pyramidanes, as well as their peculiar structural features, non-classical bonding situations, and specific reactivity, are presented and discussed in this review.