Thiophene macrocycles

Bauerle and co-workers have synthesized a macrocycle consisting of 8 thiophenes in conjugation by an oxidatively induced elimination of platinum complexes <03CC948>. The platinum complexes 55 were obtained by reaction of terthiophene with terminal acetylenic groups with cw-Pt(dppp)Cl2 in the presence of Cul and EtsN. C-C bond formation was effected by oxidatively induced elimination using iodine and the diacetylene bridged thiophene macrocycle 56 was converted to an all thiophene macrocycle 57 by reacting with sodium sulfide. 

The formation of cyclic tetramers was extended to various chlorosilanes. The reaction of MePhSiCl2 and Me(CH2=CH)SiCl2 gave a one-step synthesis of die thiophene macrocycles 20, 21 in reasonable yields. However, the synthesis appeared limited to compounds containing four thiophene units, since the reaction of aryl or ethynyl chlorosilanes gave only very low yields of the macrocycles 22, 23. 

The use of macrocyclic compounds of the thiophene series for the preparation of macrocyclic alicyclie ketones has been mentioned earlier. " A new synthesis of exaltone has been carried out using (136) as the starting material. ... 

Since analogous macrocyclic arrays with pyrrole rings have been termed calix[ ]pyrroles (cf. Gale PA, Sessler JL, Krai V, Lynch V (1996) J Am Chem Soc 118 5140) it would be appropriate to rename these thiophene-crowns as calix[n] thiophenes... 

Silver(I) complexes with macrocyclic nitrogen ligands are also very numerous. Mono- or homodi-nuclear silver-containing molecular clefts can be synthesized from the cyclocondensation of functionalized alkanediamines or triamines with 2,6-diacetylpyridine, pyridine-2,6-dicarbalde-hyde, thiophene-2,5-dicarbaldehyde, furan-2,5-dicarbaldehyde, or pyrrole-2,5-dicarbaldehyde in the presence of silver(I).486 97 The clefts are derived from bibracchial tetraimine Schiff base macrocycles and have been used, via transmetallation reactions, to complex other metal centers. The incorporation of a range of functionalized triamines has provided the conformational flexibility to vary the homodinuclear intermetallic separation from ca. 3 A to an excess of 6 A, and also to incorporate anions as intermetallic spacers. Some examples of the silver(I) complexes obtained are shown in Figure 5. 

Since its introduction by Allred and Liebsekind in 1996 [114], copper thiophene-2-carboxylate (CuTC) has emerged as a mild and useful reagent for mediating the cross-coupling of organostannanes with vinyl iodides at room temperature. CuTC is especially effective for substrates that are not stable at high temperature. In Paterson s total synthesis of elaiolide, he enlisted a CuTC-promoted Stille cyclodimerization of vinyl iodide 131 to afford the 16-membered macrocycle 132 under very mild conditions [115]. 

To hnish this section and chapter we will briefly discuss the synthetic routes pursued in order to obtain cyclothiophenes, fully a-conjugated macrocyclic oligothiophenes, i.e., joining boths ends of linear a-thiophenes (Kromer et al., 2000). One advantage of these macromolecules is that the mean diameter of the cavity can be tuned by selecting the initial building blocks. In Section 4.2 we will explore how such molecules, in particular cyclotrimeric terthiophenediacetylene, self-assemble on a surface. 

The synthesis of furan-(thiophene-, benzo[b]thiophene-)bridged macrocycles of 4,4 -bipyri-dine was reported <99T4709>. 

Newkome et al.294 have reviewed the preparation of synthetic macrocyclic compounds possessing heterocyclic subunits, more specifically, pyridine, furan, and thiophene. 

Alkanes and cycloalkanes. Obviously a variety of acyclic and cyclic hydrocarbon structures can be synthesized from the appropriate alkyl- or aryl-thiophenes (Scheme 46). The reaction is especially useful for the construction of macrocycles (Scheme 47). One of the most interesting applications of this reaction is in the synthesis of the chiral hydrocarbon butylethylmethylpropylmethane (210) (80JOC2754). The chiral acid (209) was the precursor, in which the thiophene was the potential n-butyl group. Raney nickel desulfurization, followed by standard manipulations to convert the acetic acid unit into an ethyl group, gave the hydrocarbon (210) (Scheme 48) this had [a]578 = -0.198°. It was established that... 

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). 

Polyrotaxanes have been prepared by threading multiple a-cyclodextrin units onto a bulky benzimidazole-based linear chain polymer with an aliphatic spacer where the cyclodextrin resides. The rotaxane forms as the cyclodextrin-bound precursor amine is polymerised. Compared to the polymer in the absence of the cyclodextrins, the glass transition temperature is raised by some 20 °C even though only ca. 16 % of the aliphatic spacers in the polymer are rotaxanated.28 A novel approach to polyrotaxanes involved the use of a metal ion such as Zn2+ to thread a phenanthroline-based macrocycle onto a thiophene-based complementary monomer. The resulting pseudorotaxane can then be electropolymerised and the Zn2+ ions removed to give a polyrotaxane, Scheme 14.5. The redox and conductivity properties of the polymer are very much dependent on whether a metal ion is bound or not.29... 

Konig et al. [95AG(E)661] have prepared a related series of Si-bridged macrocycles, including the first silacalix[4]arene, from the deprotonation of furan, thiophene, N-methylpyrrole or tert-butylanisole, followed by addition of dimethyldichlorosilane. 

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