Cage-Shaped Molecules with High Symmetries

Abstract

Chiral and achiral hydrocarbons of high symmetry have attracted continuous attention of synthetic and physical organic chemists because of their potential interesting properties.^[1]–[5] Two strategies have been applied to the derivation of new compounds of given symmetries. The first is a vertex strategy in which substituents are placed on vertices of a parent skeleton.^{[6, 7]}The second (edge strategy) consists of the insertion of methylene or other units into the edges (bonds) of a parent skeleton. In particular, the latter is versatile methodology used to guide synthetical studies concerning cage-shaped compounds of high symmetry. Thus, there have appeared many papers that reported successful syntheses of such compounds. For example, a selected list of achiral hydrocarbons reported contains prismane of D _3h symmetry,^[8] iceane (tetracyclo[5.3.1.1^2,6.0^4,9]dodecane) of D _3h symmetry,^[9]–[11],([2₆](1,2:3,4:5,6-tris(bicyclo[2.2.2]octa-2-eno)benzene of D _3h symmetry,^[12] superphane ([2₆](l,2,3,4,5,6)cyclophane) of D _6h symmetry,^[13] pentaprismane of D _5h symmetry,^[14] a tetrahedrane of T _d symmetry,^[15] cubane of O _h symmetry,^[16] and dodecahedrane of I _h symmetry.^[17] Chiral hydrocarbons of high symmetry have also been investigated synthetically and physicochemically, e.g., twistane of D ₂ symmetry^{[18, 19]} and D ₃-trishomocubane of D ₃ symmetry.^[20]–[22] Although several theoretical studies have discussed the two methodologies,^{[23, 24]} there have emerged no comprehensive studies concerning the following problem: what symmetries are realized and how many isomers are allowed on the basis of a skeleton of a given symmetry.

Reprinted with permission from S. Fujita, Tetrahedron, 46, 365–382 (1990). ©(1990) Pergamon Press PLC. See also S. Fujita, Bull, Chem. Soc. Jpn., 62, 3771–3778 (1989).