Torands

This chapter illustrates torand synthesis with the preparation of unsubstituted torand 1 by the route developed for synthesis of tributyltorand 2.1,6,7 The synthesis of 1 is two steps shorter than that of 2 because commercially available 1,2,3,4,5,6,7,8-octahydroacridine, 5, replaces the 9-butyl derivative, which is prepared in two steps.11,12 Many of the intermediates could also be 

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Inclusions of Other Grown Analogues. A variety of crown analogues and hybrid modifications (24—28) with other topological features (lariat ethers (31,32), octopus molecules (33), spherands (eg, (12) (34), torands (35)) including chiral derivatives (36) have been prepared and demonstrated to show particular inclusion properties such as chiroselective inclusion (Fig. 4) (37) or formation of extremely stable complexes (K ">(LR) for (12)... 

Numerous modifications of calixarenes, spherands and similar systems have been synthesized 241 [40], 242 [41], calixspherands like 243 [42] and torands like 244 [43] to name but a few pertaining interesting ligands. 

AC and AEC complexation is also effected efficiently by other macrocyclic ligands such as the spherands 13, cryptospherands 14 [2.9, 2.10], calixarenes [2.38, A.6, A.23], torands [2.39], etc., some of them, for instance the spherands displaying particularly high stabilities. A special case is represented by the endohedral complexes of fullerenes in which the cation (Sr2, Ba2+, lanthanides) is locked inside the closed carbon framework [2.40],... 

Numerous macrocyclic and macropolycyclic ligands featuring subheterocyclic rings such as pyridine, furan or thiophene have been investigated [2.70] among which one may, for instance, cite the cyclic hexapyridine torands (see 19) [2.39] and the cryptands containing pyridine, 2,2 -bipyridine (bipy), 9,10-phenanthroline (phen) etc. units [2.56,2.57,2.71-2.73]. The [Na+ c tris-bipy] cryptate 20 [2.71] and especially lanthanide complexes of the same class have been extensively studied [2.74, 2.75] (see also Sect. 8.2). 

Bell TW et al (1992) A supramolecular assembly of two torands, two lithium ions and three water molecules. Angew Chem Int Ed Engl 31 348-350... 

In Scheme 6.1, outlining the synthesis of torand 1, each of the numbered arrows corresponds to one of the eleven protocols. This approach to 1 sequentially combines three octahydroacridine subunits, whereas the previously... 

Octahydroacridine units must be oxidatively functionalized at carbon atoms 4 and 5 in order to build up the fused-ring backbone of torand 1. The key pyridine-forming reactions (steps 6 and 11 in Scheme 6.1) both involve the condensation of a ketone with an a,p-unsaturated ketone. Unsymmetrically functionalized octahydroacridine derivatives are required so that each unit can be fused to a new pyridine ring first at one end and then at the other. The benzylidene groups serve as latent carbonyl groups that can be unmasked by ozonolysis. Step 2 introduces both a C-O bond at C4 and a benzylidene group at C5 in a convenient, one-pot reaction sequence. Scheme 6.3 shows the intermediates involved in this sequence converting 6 to 7. 

In steps 5 and 6 of Scheme 6.1 the torand backbone is built up from two molecules of ketone 9 via Mannich salt 10. Together these reactions constitute the most efficient method known so far for the synthesis of fused pyridines from cyclic ketones. The key intermediates involved in the transformation of 9 to 11 are shown in Scheme 6.7. In Protocol 5, ketone 9 reacts with /V,/V-dimethyl(methylene)ammonium chloride in acetonitrile.21 The HC1 salt of the resulting Mannich compound 10 precipitates from this solvent and the relatively pure product is isolated from the reaction mixture by filtration. 

Diketone 12 must be condensed with a third, doubly functionalized octahydroacridine unit in the last step of the torand synthesis (cf Scheme 6.1). The following protocols (8-10) describe the three-step synthesis of torand precursor 15 from octahydroacridine 5. The reagents involved in these three steps are shown in Scheme 6.11. According to Protocol 8, octahydroacridine is condensed with benzaldehyde in the presence of acetic anhydride,24 as in the second stage of Protocol 2 (cf Scheme 6.3). The crystalline product 13 precipitates from the reaction mixture in high yield and purity. Ozonolysis of 13 (Protocol 9) is conducted by the method described in Protocol 7 for conversion of 11 to diketone 12 (cf. Scheme 6.10) and the same precautions apply. The product diketone 1425 requires no further purification after removal of benzaldehyde by trituration with diethyl ether. The third octahydroacridine unit is then readied for torand cyclization in Protocol 10 by condensing diketone 14 with Bredereck s reagent, r-butoxybis(dimethylamino)methane,26 which is commercially available. The bis[p-(dimethylamino)]enone product 15 is easily purified by precipitation from ether/dichloromethane. 

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