2.2.2-Propellane
Introduction '''2.2.2Propellane''', formally '''tricyclo2.2.2.01,4octane''' is an organic compound, a member of the propellane family. It is a hydrocarbon with formula C8H12, or C2(C2H4)3.Its molecule has three rings with four carbon atoms each, sharing one C–C bond.This compound is unstable (although not as much as 1.1.1-Propellane|1.1.1propellane; however it is less persistent than 1.1.1propellane). The bond angles on the shared carbons are considerably strained: three of them are close to 90°, the other three to 120°. The strain energy is estimated to be 93 kcal/mol (390 kJ/mol).
Synthesis 2.2.2Propellane was first synthesized in 1973 by the group of Philip Eaton (who had earlier obtained cubane), according to the following scheme::File:222propellaneSynthesis.png|thumb|none|400px|Synthesis of the 2.2.2propellane skeleton.The synthesis begins with photochemical 2+2cycloaddition of ethene on the cyclohexene derivative '''1''' to produce the bicyclic compound '''2''', followed by elimination reaction with potassium ''t''-butoxide of acetic acid to cyclobutene '''3''', followed by another cycloaddition with ethylene to '''4'''. This compound is converted to the diazo ketone '''5''' by deprotonation (using acetic acid and sodium methoxide) and reaction with tosyl azide. The ketone then undergoes Wolff rearrangement to ketene '''6'''. Ozonolysis forms the ketone '''7''', another  diazotation yields the diazo ketone '''8''', which undergoes Wolff rearrangement again to the ketene '''9'''. Reaction with dimethylamine affords the 2.2.2propellane backbone with a dimethylamide substituent '''10'''.The final product '''10''' was found to spontaneously isomerize in solution to the monocyclic  amide '''11''', with a half-life of 28 minutes at room temperature.
Derivatives A highly fluorinated 2.2.0propellane was also synthesized by the group of David Lemal.
See also * 1.1.1-Propellane|1.1.1Propellane
References