Synthesis and assembly of self-complementary calix[4]arenes.

Abstract

A calix [4]arene was designed to reversibly dimerize and form an egg-shaped enclosure. Adhesive interactions in the assembly were provided by four self-associating ureas, which form a cyclic array containing 16 hydrogen bonds. The synthesis was completed in four steps from theEvidence for dimerization of the calixarene tetraurea was provided by 'H NMR, mass spectrometry, and the observation of encapsulated molecules. The resulting cavity was of sufficient size to capture guests such as ethyl benzene andp-xylene.

Synthesis and capsule formation of upper rim substituted tetra-acrylamido calix[4]arenes

“…Amide substituted calix [n]arenes could display such an unusual hydrogen bonding motif by dimerisation, although in a cyclic form, by using the structural complementarity of their C=O and N-H moieties. Similar hydrogen bonding motifs have been described by the groups of Rebek 3-5 and Böhmer 6 using a self complementary non-covalent assembly via 16 hydrogen bonds of tetra-ureido calix [4]arenes. A related dimerisation between calix [6] substituted dipeptides has recently been described by de Mendoza et al 7 In this assembly 18 hydrogen bonds are formed between three sets of dipeptides linked to the calix [6]arene scaffold.…”

“…A related dimerisation between calix [6] substituted dipeptides has recently been described by de Mendoza et al 7 In this assembly 18 hydrogen bonds are formed between three sets of dipeptides linked to the calix [6]arene scaffold. It should be noted that both N-linked and C-linked peptide calix [4]arenes introduced by the Ungaro group 8,9 did not show dimerisation by self complementary assembly, possibly due to unfavourable stereoelectronic effects or lack of secondary interactions stabilising the assembly. Related resorcinarene molecular capsules have been reported by Atwood and coworkers.…”

“…10 Dimeric capsules formed by electrostatic interactions have been reported by the groups of Reinhardt and Schrader. 11, 12 In this contribution we like to describe in detail the synthesis and supramolecular chemistry of tetra-acrylamido calix [4]arenes. Part of this work has been reported as a short communication.…”

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Upper rim substituted tetraiodo calix [4]arenes are coupled to a variety of acrylamides using the palladium catalysed Heck reaction. Tetra-acrylamido upper rim substituted calix [4]arenes are obtained in good yields with exceptionally high stereoselectivity, to produce the all-trans isomers.

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“…Tetra-acrylamido upper rim substituted calix [4]arenes are obtained in good yields with exceptionally high stereoselectivity, to produce the all-trans isomers. Tetra-acrylamido calix[4]arenes derived from secondary acrylamides are shown to dimerise via eight hydrogen bonds to form dimeric capsules, which are able to include small organic molecules.…”