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1,3,5 trinitrocubane and 1,3,5,7 tetranitrocubane(TNC) |
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As we mention early, addition of nitro groups cannot be done through direct transmetalation. Thus, we need found some indirect route. This is done by introducing a substituent on each of 3 ortho carbons and remove the ortho-activating group in the end. |
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By adding a electron-withdrawing group such as a cyano group will help the case here. This choice of original substituent is important here and when cyano group is chosen, it activates the cubane nucleus without affecting the ortho directing by the diamide (for details please refer to electron-withdrawing group-cyanite). When the dicyano amide was treated with TMPMgBr in THF and quenched with CO2. The ortho (to amide) carboxylic acid was the only product. Even when the much activated tricyanoamide is treated with TMPMgBr and CO2 ,again, the ortho position ( to amide) carboxylic acid was formed.
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| The removal of the carboxamido group is done through a smart yet tedious process. The cyano group is converted to acid group first. Then, it is reduced to alcohol by lithium aluminium hydride. At same time, the carboxamido is reduced to aminotetrol. The alcohols are protected as acetates and amino tetrol is converted to carboxylic acid. The carboxylic is then removed through Barton Decarboxylatio. A detail mechanism is provided below. | |||||||||||||||||||||||||||
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| The cubane-1,3,5,7-teracarboxylic acid is converted to TNC on the mechanism as follow: | |||||||||||||||||||||||||||
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| The whole process is very clever, but it is very long. Thus, in 1997, a improved synthesis method for TNC was proposed by making use of the photochemsitry. | |||||||||||||||||||||||||||
