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Cubane<\/b>\u00a0(C8<\/sub>H8<\/sub>) is a synthetic\u00a0hydrocarbon<\/a>\u00a0molecule<\/a>\u00a0that consists of eight\u00a0carbon<\/a>\u00a0atoms<\/a>\u00a0arranged at the corners of a\u00a0cube<\/a>, with one\u00a0hydrogen<\/a>\u00a0atom attached to each carbon atom. A solid\u00a0crystalline<\/a>\u00a0substance, cubane is one of the\u00a0Platonic hydrocarbons<\/a>. It was first synthesized in 1964 by\u00a0Philip Eaton<\/a>, a professor of chemistry at the\u00a0University of Chicago<\/a>.[2]<\/a><\/sup>\u00a0Before Eaton and Cole’s work, researchers believed that cubic carbon-based molecules could not exist, because the unusually sharp 90-degree bonding angle of the carbon atoms was expected to be too highly\u00a0strained<\/a>, and hence unstable. Once formed, cubane is quite kinetically stable, due to a lack of readily available decomposition paths.<\/p>\n The other\u00a0Platonic hydrocarbons<\/a>\u00a0are\u00a0dodecahedrane<\/a>\u00a0and\u00a0tetrahedrane<\/a>.<\/p>\n Cubane and its derivative compounds have many important properties. The 90-degree bonding angle of the carbon atoms in cubane means that the bonds are highly strained. Therefore, cubane compounds are highly reactive, which in principle may make them useful as high-density, high-energyfuels<\/a>\u00a0and\u00a0explosives<\/a>\u00a0(for example,\u00a0octanitrocubane<\/a>\u00a0and\u00a0heptanitrocubane<\/a>).<\/p>\n Cubane also has the highest density of any hydrocarbon, further contributing to its ability to store large amounts of energy, which would reduce the size and weight of fuel tanks in aircraft and especially rocket boosters. Researchers are looking into using cubane and similar cubic molecules inmedicine<\/a>\u00a0and\u00a0nanotechnology<\/a>.<\/p>\n <\/p>\n The original 1964 cubane\u00a0organic synthesis<\/a>\u00a0is a classic and starts from\u00a02-cyclopentenone<\/i>\u00a0(compound\u00a01.1<\/b>\u00a0in\u00a0scheme 1<\/i>):[2]<\/a><\/sup>[3]<\/a><\/sup><\/p>\n Reaction with\u00a0N<\/i>-bromosuccinimide<\/a>\u00a0in\u00a0carbon tetrachloride<\/a>\u00a0places an\u00a0allylic<\/a>\u00a0bromine atom in\u00a01.2<\/b>\u00a0and further\u00a0bromination<\/a>\u00a0with\u00a0bromine<\/a>\u00a0in\u00a0pentane<\/a>\u00a0–methylene chloride<\/a>\u00a0gives the tribromide\u00a01.3<\/b>. Two equivalents of\u00a0hydrogen bromide<\/a>\u00a0are\u00a0eliminated<\/a>\u00a0from this compound with\u00a0diethylamine<\/a>\u00a0in\u00a0diethyl ether<\/a>\u00a0to\u00a0bromocyclopentadienone<\/i>\u00a01.4<\/b><\/p>\n In the second part (scheme 2<\/i>), the spontaneous\u00a0Diels-Alder dimerization<\/a>\u00a0of\u00a02.1<\/b>\u00a0to\u00a02.2<\/b>\u00a0is analogous to the dimerization of\u00a0cyclopentadiene<\/a>\u00a0to\u00a0dicyclopentadiene<\/a>. For the next steps to succeed, only the\u00a0endo isomer<\/a>\u00a0should form; this happens because the bromine atoms, on their approach, take up positions as far away from each other, and from the carbonyl group, as possible. In this way the like-dipole interactions are minimized in the\u00a0transition state<\/a>\u00a0for this reaction step. Both\u00a0carbonyl<\/a>\u00a0groups are\u00a0protected<\/a>\u00a0as\u00a0acetals<\/a>\u00a0with\u00a0ethylene glycol<\/a>\u00a0and\u00a0p<\/i>-toluenesulfonic acid<\/a>\u00a0inbenzene<\/a>; one acetal is then selectively deprotected with aqueous\u00a0hydrochloric acid<\/a>\u00a0to\u00a02.3<\/b><\/p>\n In the next step, the endo isomer\u00a02.3<\/b>\u00a0(with both\u00a0alkene<\/a>\u00a0groups in close proximity) forms the cage-like isomer\u00a02.4<\/b>\u00a0in a\u00a0photochemical<\/a>\u00a0[2+2]\u00a0cycloaddition<\/a>. The\u00a0bromoketone<\/a>\u00a0group is converted to ring-contracted\u00a0carboxylic acid<\/a>\u00a02.5<\/b>\u00a0in a\u00a0Favorskii rearrangement<\/a>\u00a0with\u00a0potassium hydroxide<\/a>. Next, the thermal\u00a0decarboxylation<\/a>\u00a0takes place through the\u00a0acid chloride<\/a>\u00a0(with\u00a0thionyl chloride<\/a>) and thetert-butyl<\/a>\u00a0perester<\/a>\u00a02.6<\/b>\u00a0(with\u00a0t-butyl hydroperoxide<\/a>\u00a0and\u00a0pyridine<\/a>) to\u00a02.7<\/b>; afterward, the acetal is once more removed in\u00a02.8<\/b>. A second Favorskii rearrangement gives\u00a02.9<\/b>, and finally another decarboxylation gives\u00a02.10<\/b>\u00a0and\u00a02.11<\/b>.<\/p>\n The cube motif occurs outside of the area of organic chemistry. Prevalent non-organic cubes are the [Fe4<\/sub>-S4<\/sub>] clusters found pervasively\u00a0iron-sulfur proteins<\/a>. Such species contain sulfur and Fe at alternating corners. Alternatively such inorganic cube clusters can often be viewed as interpenetrated S4<\/sub>\u00a0and Fe4<\/sub>\u00a0tetrahedra. Many organometallic compounds adopt cube structures, examples being (Cp<\/a>Fe)4<\/sub>(CO)4<\/sub>, (Cp*<\/a>Ru)4<\/sub>Cl4<\/sub>, (Ph3<\/sub>P<\/a>Ag)4<\/sub>I4<\/sub>, and\u00a0(CH3<\/sub>Li)4<\/sub><\/a>.<\/p>\n <\/p>\n <\/p>\n It was mentioned previously that cubane was first prepared in 1964 by Dr. Philip E. Eaton. He was partnered by Thomas W. Cole and together they successfully completed the first synthesis, shown schematically below:<\/p>\n <\/a><\/a><\/a><\/a><\/p>\n <\/a><\/p>\n <\/a><\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n This, however, was soon simplified by N.B.Chapman who condensed the process to give cubane-1,4-dicarboxylic acid in five steps and so cubane in six:<\/p>\n <\/p>\n n 1966 J C Barborak\u00a0et al<\/em>\u00a0discovered yet another new synthesis of cubane. It was slightly unconventional in the fact that it utilised cyclobutadiene as a key substance to the process. Before this,cyclobutadiene was usually unavailable for the purposes of organic chemistry due to it’s instability. The shorter synthesis is shown below:<\/p>\n <\/a><\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n<\/div>\n Since the synthesis of the cubane-1,4-dicarboxylic acid has become shorter and easier, a new decarboxylation method has also devised to give increased yields of the final cubane product. This has allowed the scale of production reach multikilogram batches in places (Fluorochem in California and EniChem Synthesis in Milan) eventhough cubane and its derivatives remain expensive to purchase.<\/p>\n Cuneane<\/a>\u00a0may be produced from cubane by a\u00a0metal-ion-catalyzed \u03c3-bond rearrangement<\/a>.[4]<\/a><\/sup>[5]<\/a><\/sup><\/p>\nSynthesis<\/h2>\n
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