Abnormal Structures vs. Classical Theory

A student who starts taking classes in organic chemistry is very likely to get the impression that its theory rests on a set of postulates as unshakable as those of Euclidean geometry. By the end of the first semester one is supposed to learn that four substituents around an sp carbon atom are positioned at the corners of a tetrahedron with an angle of 109.5° between the orbitals, while planar and 

1 Distortions of sp Carbon Configuration. Flattened and Pyramidalized sp Carbon 

The impetus to prepare a novel type of carbon framework, like that present in the structures 138a or 139, prompted intensive studies to elaborate new synthetic protocols. Examples illustrative of the strategy were shown earlier e.g. Sections 2.19.2 and 3.2.6), but the existing data are too scarce to discuss the specifics of the chemical reactivity of fenestranes arising from the planarization effects. 

It is also relevant to add that while the experimental studies in this area have actually originated from rather abstract considerations advanced by organic chemists, the fenestrane-like design had been employed in Nature for a long while in the creation of the framework of several natural compounds (such as laurenene 146). What their functions are and how (or if) the functions are related to the specificity of their structure are still questions to be answered. It is also worth noting that synthesis of 146 was achieved rather easily (see refs, in 22b) by employing the methods elaborated in the course of studies aimed at the preparation of the fenestrane framework. 

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