Propellanes, small ring structures

But before we turn to this aspect of the structure of not only [l.l.l]propellane but certainly of other [m.n.ljpropellanes, let us consider how these and other small-ring [m.n.ljpropellanes are prepared, in more or less chronological order. 

From the time of van t Hoff (1) and Le Bel (2) the tetrahedral arrangement of substituents around a tetravalent carbon atom has been part of the foundation of organic stereochemistry. However, in the last 30 years, thanks to the rapid development of synthetic methods of organic chemistry as well as of experimental and theoretical methods of structure elucidation, many exciting saturated hydrocarbons with very unusual spatial structure have been synthesized. Cubane (1) was obtained as early as 1964 (3), triprismane (2) (4), a tetra-f-butyl derivative of tetrahedrane (3) (5), small-ring propellanes with structures involving inverted carbon atoms, 4-6 ([3.2.1], [4.1.1] and... 

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