Conformation calixarene-related compound

Three macrobicycles 40b (216), 40h (212), and 40k (211) were characterized by X-ray crystallography. Fig. 31 displays the structure of 40h. The compounds adopt a highly folded conformation, reminiscent of calixarenes (23) and related Schiff-base macrocycles (181). 

Calixarenes are [1 Jmetacyclophanes (1) that acquired their name because of the resemblance of the shape of one of the conformers of the smallest member of their family to a type of Greek vase called a calix crater (Figure 1.1). The name was initially chosen to apply specifically to the phenol-derived cyclic oligomers, but it has subsequently taken on a more generic aspect and is now applied to a wide variety of structurally related types of compounds. The calixarenes were first discussed in comprehensive fashion in 1989 in the first volume of Monographs in Supramolecular Chemistry, where the literature on the subject that had been published up to that time was covered in reasonably complete detail in 222 pages. Since 1989, however, there has been such a rapid expansion of the field that a somewhat less comprehensive coverage of topics is now necessary if this... 

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