Resorcinarene

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General structure of resorcinarenes, R is an organic residue that can be varied over a wide range .

Resorcinarene (also Calix [4] resorcinarene) are macrocyclic compounds that are derived from resorcinol (1,3-dihydroxybenzene). The resorcinol units are connected to one another via two methylene bridges, so that a cyclic oligomer is formed from four aromatic resorcinol units. They are closely related to calixarenes , pillararenes and pyrogalloarenes and are structurally reminiscent of cyclodextrins . With Adolf von Baeyer and Donald J. Cram , two Nobel Prize winners a . a. with the chemistry of resorcinarenes.

synthesis

Resorcinarenes are usually prepared by condensation of an aldehyde with resorcinol with Brønstedt acid catalysis in a suitable solvent or solvent mixture under reflux . The product can be obtained in pure form and often in high yield by recrystallization or chromatography .

In a reversible Friedel-Crafts -like aromatic substitution , the aldehyde activated by the acid attacks the resorcinol in the ortho and para positions. The resulting alcohol can attack another molecule of resorcinol under acid catalysis, releasing water. In this reaction, no plastic is formed , as in the closely related synthesis of phenoplasts , since the reaction is reversible (Retro-Friedel-Crafts), is carried out under thermodynamic control and since the resorcinarenes formed is the thermodynamically more stable product.

As an alternative to the drastic reaction conditions mentioned above, resorcinarenes can also be prepared under solvent-free conditions or alternatively by Lewis acid-catalyzed protocols starting either from resorcinol / aldehydes or from benzyl alcohols or from cinnamic acid esters .

structure

Resorcinarenes each consist of four resorcinol molecules (1,3-dihydroxybenzene), which are linked by methylene bridges in the 4- and 6-position. Depending on the aldehyde used in the synthesis, the methylene bridges can each carry an aliphatic or aromatic radical which can have additional functionalities . The configuration of the stereocenters on the methylene bridges is (mostly) uniform.

Resorcinarenes can exist in different conformations , of which the vase-shaped is the most noticed, since it can be viewed as a hemisphere with its concave surface. This conformation, also known as bowl or crown-shaped, has an upper edge stabilized by hydrogen bonds and a lower edge. The upper edge is decorated with a total of eight hydroxyl groups , which can be covalently bridged in order to force or stabilize the vase conformation. Alternatively, the hydroxyl groups can also be functionalized to build cavitands or carcerands, which are characterized by a relatively large internal volume in which guest molecules can be incorporated.

Chemically closely related macrocycles are from the phenol derivative (hydroxybenzene) calixarenes and Pillararene , and the pyrogallol derivative (1,2,3-trihydroxybenzene) Pyrogalloarene .

history

Already Adolf von Baeyer was aldehydes with resorcinol react, the resulting resinous product, however, could not be characterized with the help of that analysis. Since then, other researchers have isolated crystalline products in similar reactions, but have found it difficult to characterize them. Half a century after Baeyer, Niederl and Vogel proposed the tetrameric cyclic structure for these products, which was only finally confirmed almost 50 years later ( see below ). Building on the preliminary work of Erdtman and colleagues, Högberg synthesized resorcinarenes and demonstrated their structure by NMR spectroscopy . Last doubts about the tetrameric structure of the resorcinarenes could later be dispelled by X-ray structure analysis. As one of the first to recognize u. a. Aoyama and colleagues investigate the potential of resorcinols for host-guest systems. It is now known that the unmodified concave resorcinarenes assemble under certain conditions to form hexameric capsules, in the interior of which catalytic reactions are again possible under certain conditions. Resorcinarenes are particularly popular as the basis of synthetic receptors ( see below ).

use

In supramolecular chemistry, resorcinarenes are used as the basis for building molecular containers (synthetic receptors) such as cavitands or carcerands, which can store guest molecules in their interior. But they are also used as filling material for chromatography columns .

Individual evidence

  1. ↑ a b A. G. Sverker Högberg: Cyclooligomeric phenol-aldehyde condensation products. 2. Stereoselective synthesis and DNMR study of two 1,8,15,22-tetraphenyl [14] metacyclophane-3,5,10,12,17,19,24,26-octols . In: Journal of the American Chemical Society . tape 102 , no. 19 , 1980, pp. 6046-6050 , doi : 10.1021 / ja00539a012 .
  2. ↑ Luigi Abis, Enrico Dalcanale, Annick Du Vosel, Silvia Spera: Structurally new macrocycles from the resorcinol-aldehyde condensation. Configurational and conformational analyzes by means of dynamic NMR, NOE, and T1 experiments . In: Journal of Organic Chemistry . tape 53 , no. 23 , 1988, pp. 5475-5479 , doi : 10.1021 / jo00258a015 .
  3. ↑ Brett A. Roberts, Gareth WV Cave, Colin L. Raston, Janet L. Scott: Solvent-free synthesis of calix [4] resorcinarenes . In: Green Chemistry . tape 3 , no. 6 , 2001, p. 280-284 , doi : 10.1039 / B104430N .
  4. ↑ Jochen Antesberger, Gareth WV Cave, Matthew C. Ferrarelli, Michael W. Heaven, Colin L. Raston, Jerry L. Atwood: Solvent-free, direct synthesis of supramolecular nano-capsules . In: Chemical Communications . No. 7 , 2005, p. 892-894 , doi : 10.1039 / B412251H .
  5. ↑ Bruno Botta, Maria C. Di Giovanni, Giuliano Delle Monache, Maria C. de Rosa, Eszter Gacs-Baitz, Maurizio Botta, Federico Corelli, Andrea Tafi, Antonello Santini: A Novel Route to Calix [4] arenes. 2. Solution- and Solid-State Structural Analyzes and Molecular Modeling Studies . In: Journal of Organic Chemistry . tape 59 , no. 6 , 1994, pp. 1532-1541 , doi : 10.1021 / jo00085a047 .
  6. ^ Donald J. Cram: Cavitands: Organic Hosts With Enforced Cavities . In: Science . tape 219 , no. 4589 , 1983, pp. 1177–1183 , doi : 10.1126 / science.219.4589.1177 .
  7. ↑ Adolf Baeyer,: About the compounds of aldehydes with phenols . In: Reports of the German Chemical Society . tape 5 , no. 1 , 1872, p. 280-282 , doi : 10.1002 / cber.18720050186 .
  8. ↑ Adolf Baeyer,: About the compounds of aldehydes with phenols and aromatic hydrocarbons . In: Reports of the German Chemical Society . tape 5 , no. 2 , 1872, p. 1094–1100 , doi : 10.1002 / cber.187200502157 .
  9. ^ Joseph B. Niederl, Heinz J. Vogel: Aldehyde — Resorcinol Condensations . In: Journal of the American Chemical Society . tape 62 , no. 9 , 1940, p. 2512-2514 , doi : 10.1021 / ja01866a067 .
  10. ↑ H. Erdtman, F. Haglid, R. Ryhage: Macrocyclic Condensation Products of Veratrole and Resorcinol . In: Acta Chemica Scandinavica . tape 18 , no. 5 , 1964, pp. 1249-1254 , doi : 10.3891 / acta.chem.scand.18-1249 .
  11. ↑ AG Sverker Högberg: Two stereoisomeric macrocyclic resorcinol-acetaldehyde condensation products . In: Journal of Organic Chemistry . tape 45 , no. 22 , 1980, pp. 4498-4500 , doi : 10.1021 / jo01310a046 .
  12. ↑ Donald J. Cram, Kent D. Stewart, Israel Goldberg, Kenneth N. Trueblood: Complementary solutes enter nonpolar preorganized cavities in lipophilic products . In: Journal of the American Chemical Society . tape 107 , no. 8 , 1985, pp. 2574-2575 , doi : 10.1021 / ja00294a075 .
  13. ↑ Yasuhiro Aoyama, Yasutaka Tanaka, Hiroo Toi, Hisanobu Ogoshi: Polar host-guest interaction. Binding of nonionic polar compounds with a resorcinol-aldehyde cyclooligomer as a lipophilic polar host . In: Journal of the American Chemical Society . tape 110 , no. 2 , 1988, doi : 10.1021 / ja00210a073 .
  14. ↑ Alexander Shivanyuk, Julius Rebek Jr .: Reversible encapsulation by self-assembling resorcinarene subunits . In: Proceedings of the National Academy of Sciences of the USA . tape 98 , no. 14 , 2001, p. 7662-7665 , doi : 10.1073 / pnas.141226898 .
  15. ↑ Jerry L. Atwood, Leonard J. Barbour, Agoston Jerga: Organization of the interior of molecular capsules by hydrogen bonding . In: Proceedings of the National Academy of Sciences of the USA . tape 99 , no. 8 , 2002, p. 4837-4841 , doi : 10.1073 / pnas.082659799 .
  16. ↑ Alessandra Cavarzan, Alessandro Scarso, Paolo Sgarbossa, Giorgio Strukul, Joost N. Reek, H .: Supramolecular Control on Chemo- and Regioselectivity via Encapsulation of (NHC) -Au Catalyst within a Hexameric Self-Assembled Host . In: Journal of the American Chemical Society . tape 133 , no. 9 , 2011, p. 2848–2851 , doi : 10.1021 / ja111106x .
  17. ^ Julius Rebek Jr .: Molecular Behavior in Small Spaces . In: Accounts of Chemical Research . tape 42 , no. 10 , 2009, p. 1660-1668 , doi : 10.1021 / ar9001203 .
  18. ↑ Donald J. Cram: Molecular container compounds . In: Nature . tape 356 , no. 6364 , 1992, pp. 29-36 , doi : 10.1038 / 356029a0 .
  19. ^ Donald J. Cram: The Design of Molecular Hosts, Guests, and Their Complexes . In: Nature . tape 240 , no. 4853 , 1988, pp. 760-767 , doi : 10.1126 / science.3283937 .