Q1. What are the contributions in this paper?
To diphenylglycoluril ( 2 ), four aliphatic chains were attached, each with a vanillyl alcohol group at the end this paper.
A cage compound derived from cyclotriveratrylene and diphenylglycoluril sub-units
02 Sep 2010-Recueil des Travaux Chimiques des Pays-Bas (Elsevier Science bv)-Vol. 108, Iss: 6, pp 215-218
TL;DR: To diphenylglycoluril (2), four aliphatic chains were attached, each with a vanillyl alcohol group at the end as discussed by the authors, and three of them cyclized to form a cyclotriveratrylene unit.
Abstract: To diphenylglycoluril (2), four aliphatic chains were attached, each with a vanillyl alcohol group at the end. In an acid-catalyzed reaction, three of the vanillyl alcohol groups cyclize to form a cyclotriveratrylene unit. The resulting compound (3) has a well-defined cavity and a free, func- tionalized arm. Cyclization of four vanillyl alcohol groups (5) does not occur, probably for steric reasons.
Summary (1 min read)
Introduction
- Organic molecules containing an intramolecular cavity, as well as a nearby catalytic centre, are currently receiving a great deal of attention as synthetic equivalents of enzymes (so called synzymes)1.
- In a later stage, these groups can be converted into catalytic functions (Fig. 2,A ).
- The presence of these isomers can be seen in the l3C N M R spectrum which shows more than one signal for each carbon atom of 3.
- The authors found that the ratio 3/4 depends on the reaction conditions used.
- CPK models suggest that a "sofa" form of the cyclotetraveratrylene sub-unit in 5 is not possible for steric reasons.
General
- Unless otherwise indicated, commercial materials were used as received.
- Diethyl ether, toluene and hexane were distilled from sodium ketyl, while CHC13 was distilled from CaCl2.
- FAB mass spectra were recorded on a VG ZAB 2F spectrometer (matrix: 3-nitrobenzyl alcohol).
- Ele mental analyses were carried out by the Elemental Analytical Section of the Institute for Applied Chemistry TNO, Zeist, The Netherlands.
4-(6-B rom ohexyloxy)-3-m ethoxybenzaldehyde (1)
- The crude product was crystallized from ether.
- During this addition, the temperature rose to approximately 30°C.
- The resulting mixture was stirred for 1 h, brought to pH 6 with concentrated hydrochloric acid and evaporated under reduced pressure.
- The residue was first purified by gel-permeation chromatography (Sephadex LH-20, eluent CHC13).
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TL;DR: Determination of the activation parameters provides evidence for a concerted, rather than a stepwise, interconversion mechanism with entropies of -243 and -272 J mol (-1) K(-1) for (P)-(S,S,Lambda)-3 and (M-S, S-S)-4, respectively.
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References
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TL;DR: In this article, a four-armed tetra-l-imidazolyl ligand (Lig) equipped with the concavc framework of diphenyl glycoluril (tetrahydro-3a,6a-diphenylimidazo[4,5-<7] imidazole-2,5(l//,3/f)-dione) has been designed to construct a host that contains a potentially catalytically active metal center in or close to a cavity.
Abstract: A four-armed tetra-l-imidazolyl ligand (Lig) equipped with the concavc framework of diphenylglycoluril (tetrahydro-3a,6a-diphenylimidazo[4,5-<7] imidazole-2,5(l//,3//)-dione) has been designed to construct a host that contains a potentially catalytically active metal center in or close to a cavity. Reaction of Lig (arm = C H 2(OCH2C H 2)2Im) with Pd(CH3C N )2Cl2 results in the formation of a complex with the general formula [Pd(Lig)]Cl2. This complex has a cage structure that is unstable and collapses. The collapsed structure has either a left or a right twisted conformation. These conformations intcrconvert rapidly, the activation free energy of the process being 30 ± 2 kJ-mol“1. Ligands without oxygen atoms or only one oxygen atom per arm react with Pd(CH3C N )2Cl2 to afford cage complexes with the molecular formula [Pd(Lig)Cl]Cl. The cages of these complexes do not collapse. The imidazolyl groups and the chloride ions are involved in a scrambling process in such a way that at any moment the Pd2+ ion is surrounded by three imidazolyl groups and one chloride ion. Data are presented suggesting that intramolecular H bonding is a driving force for cage collapse. When catalytic systems are designed, it is particularly intriguing to mimic nature. In this respect, we are interested in synthesizing systems to imitate the behavior of metalloenzymes, u-hich are involved in substrate activation processes.1 Simplification of the very special three-dimensional structure of a metalloenzyme show's a cavity-containing molecule with binding sites (B) and one or more metal centers (M) in or close to the cavity. The metallo enzyme acts as a metallohost,2 and because of the special structure of the cavity, it is quite selective in binding a substrate (S); see Figure 1. In 1970 Breslow and Overman were the first to report a man-made system based on this MSB concept.3 They combined a naturally occurring cv-cyclodextrine with a nickel(II) ion and obtained a metallohost that shows metalloenzyme features. Tabushi’s team reported a carbonic anhydrase model in w'hich they also used this cyclodextrine as a host molecule.4 At this moment examples of fully synthetic metallohosts are scarce.5. Study of metallohosts shows that the organic part is a polydentate macroligand that must be able to furnish substrate-binding sites and the framework for a cavity. In this paper we report the design and synthesis of a new family of ligands having these properties. Several Pd(II) cage compounds based on the new macroligands have been prepared, and features of their solution dynamic behavior are described.6 Results and Discussion Strategy. Cram realized that in the design of cavity-containing molecules it is preferable to start from a concave building block.7 Our design for a ligand, w'hich has to supply the framework for a cavity-containing molecule, starts from such a block, viz. glycoluril (tetrahydroimidazo[4,5-d]imidazole-2,5(lZ/,3/f)-dione ( la ) ; Chart I) that has its convex side sterically shielded by two phenyl groups ( le ) .8 To the ureylene nitrogen atoms can then be attached four chains as spacer units (A), which are furnished with potential substrate-binding sites and terminated with metal-binding groups (L). In this w'ay w'hat may be called a heter otopic tetrapodal ligand or simply a tetrapodand is formed.9 Coordination of the four ligating groups to a metal center M results in the creation of a metallocage (Figure 2). Thus, in this design the metal center has a dual function. First, it acts as a template facilitating the formation of the desired cavity. Second, it is a potentially reactive site, e.g. a catalytic center. We have chosen ethylene glycol ether chains, which are known to possess binding properties,9 as spacer units and imidazolyl groups, which are excellent ligands to a variety of metal ions, as the metal-binding groups. For comparative purposes, tetrapodands containing either 2-oxaalkyl chains or H-hexyl chains as spacer units have also been prepared. f Present address: Department of Organic Chemistry, University of Nymegen, 6525 ED Nymegen, The Netherlands. Scheme 1
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TL;DR: In this article, the preparation characterization of cyclotetraveratrylene (6) was described and the conformational mobility associated with the cyclododecatetraene ring of 6 was studied by variable temperature proton magnetic resonance spectroscopy over the temperature range 229-319K Activation parameters for the interconversion of 6A were obtained: F≠(T) 12sd8-13·7 (± 0·3) kcal and S≠ ca - 11 (± 2) eu.
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TL;DR: The similar reaction of Va with various acids in organic solvents was found to afford both III and cyclotetraveratrylene (IV) in moderate yield.
Abstract: Acid treatment (60% HClO4) of veratrylamine N-tosylates (Va-d) as well as condensation of veratrole and formalin or of veratrylalcohol in the presence of strong acids was proved to give cyclotriveratrylene (III) mainly. On the other hand, the similar reaction of Va with various acids in organic solvents was found to afford both III and cyclotetraveratrylene (IV) in moderate yield.
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TL;DR: In this article, the synthesis of tetraimidazolyl ligand was described and the coordination of a metal center to a metallocryptand was shown to yield a metallope.
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