Calix pyrrole structure

Figure 1 shows the general structure of calixpyrroles. The basic ring structure resembles that of porphyrin. In the past, four pyrrole rings linked by methylene groups to form colourless macrocycles (that feature in the biosynthetic pathways to pyrrole pigments) were referred to as porphyrinogens [22], The term calix[4]pyrrole was later ascribed to these macrocycles and their synthetic derivatives because of their relation to calix[4]arenes [23],... 

Structurally somewhat related to recorcin[4]arene derivatives 30a-c is the calix [4]pyrrole derivative 31 described by the Ballester group [74]. 

As with the multi-species components, it is not necessary for hydrogen bonding to be used in order to form dimeric capsules. This is highlighted by the recent synthesis of a molecule which assembles into dimers that are held together by n-interactions [137]. The meso-hexaphenyl calix[6]pyrrole 59 assembles into a dimeric capsule via the interactions between six phenyl groups arranged in a central belt around the capsule. The capsule is capable of holding two molecules of chloroform simultaneously, as seen in the solid state structure (Fig. 51). Similar phenyl interactions have been observed in ap-phenylcalix[5]arene which has been shown to dimerise and include C60 within its cavity (Fig. 52) [138]. 

Cafeo, G., Kohnke, F. H., La Torre, G. L., White, A. J. P., Williams, D. J. From large furan-based calixarenes to calixpyrroles and calix[n]furan[m]pyrroles syntheses and structures. Angew. Chem., Int. Ed. Engl. 2000, 39, 1496-1498. 

In BF3 Et20-catalysed (3-I-1) condensations of 38 (Y = NH, R = H) and 38 (Y = O, R = H) with 2,5-Z)A(hydroxymethyl)pyrrole, unsubstituted calix[4]pyrrole (2) and calix[I]furan[3]pyrrole (37), respectively, were isolated for the first time (2001T2103). The appearance of only two singlets for four methylene bridges in the NMR spectrum of 37 suggests its conformational inversion in solution. However, its X-ray structure reveals 1,2-alternate conformation in the solid state. 

The bipyrrole based hybrid calix[2]bipyrrole[2]furan 48 (Z = O), obtained by BF3 Et20 catalysed reaction of 22 (R = Me) with 47 (Z = O) selectively recognizes benzoate ion. In its X-ray structure (Figure 4) two pyrrole rings in each bipyrrole unit are oriented in opposite directions (2003JA13646). 

Anzenbacher, P. Jursikova, K. Lynch. V.M. Gale. P.A. Sessler. J.L. Calix[4]pyrroles containing deep cavities and fixed walls. Synthesis structural studies, and anion binding properties of the isomeric products derived from the condensation of p-hydroxyacetophenone and pyrrole. J. Am. Chern. Soc. 1999, 121. 11020. 

Figure 12. X-ray crystal structure of /i-oclabromo-rneso-octamethyl-calix[4]pyrrole compound 10. The molecule adopts a chair-like flattened 1,2-alternate conformation in the solid state. Crystal structure originally published in Gale, P. A. Sessler, J. L. Allen, W. E. Tvermoes, N. A. Lynch, V. Chem, Commun. 1997, 665, Diagram produced using data from the Cambridge Crystallographic Database.

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