Cook Me and Call Me the Molecular Dice!

Key words

cubanes - hydrocarbons - strained structures

Significance

Cubane (9) is a highly strained hydrocarbon in which eight carbon atoms are arranged at the corners of a cube, adopting unusually 90° bonding angles. Before it was first synthesized in 1964 by Eaton and Cole, researchers believed that such cubic carbon-based molecule would be too unstable to exist. Initially, cubane was considered just a laboratory curiosity of interest only to academics, however, over time this remarkable hydrocarbon and derivatives have found applications in controlled energy storage, the explosives industry, pharmaceuticals, and polymer science.

Comment

The classic synthesis of cubane starts from 2-cyclopentenone and consists of fifteen discrete steps with an overall yield of about 5%. There are three key synthetic elements: (a) the highly endo-selective Diels–Alder reaction of 2-bromo­cyclopentadienone (1) generated in situ, producing the endo-dimer 2 (J. Am. Chem. Soc. 1964, 86, 962); (b) the [2+2] photocyclization of 3, obtaining 4; and (c) the double Favorskii ring contraction of the cage diones 4 and 7, producing 5 and 8, respectively. Nowadays, the chemistry of cubane is well developed and it can be easily obtained on a multi-gram scale (see Review below).

Review

K. F. Biegasiewicz, J. R. Griffiths, G. P. Savage, J. Tsanaktsidis, R. Priefer Chem. Rev. 2015, 115, 6719–6745.