2.2.2-Propellane

Synthesis

[2.2.2]Propellane 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 [2.2.2]propellane skeleton.]]

The synthesis begins with photochemical [2+2]cycloaddition 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 [2.2.2]propellane 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.

References

References

1. "Houben-Weyl Methods of Organic Chemistry Vol. E 17e, 4th Edition Supplement (E-Book PDF) - Thieme.de - Thieme Webshop - Armin de Meijere, Holger Butenschön, Hak-Fun Chow, Lutz Fitjer, Günter Haufe".
2. (1973). "[2.2.2]Propellane system". [[J. Am. Chem. Soc.]].