Macrocyclic dimers

Figure 1.11 Covalent capture of peptide macrocycle dimer (Ghadiri).

The incorporation of a 2,6-pyridyl unit also prevents formation of the dimer-dimer catenane4, but gives the macrocyclic dimer 20 and tetramer 21 in 15 and 33% yield respectively (Figure 9) [22]. 

Stages involved in the reaction of 2,3-butanedione with propylenediamine have been monitored by NMR spectroscopy as well as by the isolation of products. The reduced 1,4-diazepine 194 was isolated, together with the macrocyclic dimeric product 196 and the tetrahydropyrimidine 195. NMR spectroscopic evidence was obtained for the first formed imine 193 and the tautomeric diazepine 197 [02H11]. 

The 2,8-bis(mercaptomethyl)-analogue of Troger s base 210 was obtained by reductive cleavage by dithiothreitol of the disulfide linkages of the macrocyclic dimeric Troger s base 208 and of the bis-(4-nitrophenylmethyl)disulfide moiety of 209 (Scheme 37) <1999AGE3713, 1999TL1289>. 

Hoye, T. R., Humpal, P. E., Moon, B. Total Synthesis of (-)-Cylindrocyclophane A via a Double Horner-Emmons Macrocyclic Dimerization Event. J. Am. Chem. Soc. 2000, 122, 4982-4983. 

We further assume that the phenyl rings of the TMA molecules are located in threefold hollow sites of Au(lll). The corresponding model is depicted in Fig. lOD (Table 1). We notice that the substrate-adsorbate interaction ( 7r-ring in threefold hollow sites) reduces the distance between the TMA centers of one centrosymmetric dimer by approximately 10%. The model predicts further the misalignment of the dimer axis by - 5° with respect to the [110] substrate direction, which results from the directional nature of hydrogen bonds in the alternating arrangement of centrosymmetric and macrocyclic dimers. 

The transition metal-catalyzed reductive carbonylation of o-substituted nitrobenzenes is a useful method for the synthesis of nitrogen heterocycles. Application of this methodology to the preparation of l,4-dihydro-2/f-3,l-benzoxazin-2-one derivatives and to the synthesis of the 3,1-benzox-azepin-2-one (42) has been reported <93JOM(451)157>. Reaction of 2-(2-nitrophenyl)ethanol (41) (100% conversion) with carbon monoxide in the presence of a palladium(Il) catalyst gave (42) in 60% yield, together with some of the macrocyclic dimer (43) ( nation (2)). It is suggested that a nitrene complex may not be involved with the palladium catalyst in view of the reaction path selectivity observed <93JOM(45i)l57>. 

Similarly, benzodithiane undergoes BFj-catalyzed addition of alkenes to afford analogous products (184 Rz = Mez, Etz, (CHz)3) in modest-to-excellent yield (Equation (60)) macrocyclic dimers represent the major products under some reaction conditions <92TL947>. 

Diara et al. carried out interesting applications of the cyclopentanone formation. Stereoselective synthesis of a-substituted cyclopentanone 54 with a quaternary carbon stereocenter was carried out by the reaction of the allenylcyclobutanol 52 with 4-iodoanisole (53) [9]. Intramolecular reactions of the stereoisomers 55 and 57 in the presence of silver salt in toluene afforded different products depending on their stereochemistry. The macrocyclic dimeric product 56 was obtained from... 

Trichloro(4-acetoxybutyl)tin, CH3COO(CH2)4SnCl3, forms a macrocyclic dimer by 0---Sn donation (2.463 A) [254] and co-hydroxyalkyltrichlorostannanes, HO(CH2) SnCl3 (n = 3-5) self-assemble into chains by 0-Sn donation (Sn-0 2.447 A) in the solid state, whereas in solution they degrade to monomers [255]. 

The bisdihydrofuran substrate 43 likewise led to the extended RRM product 44 in a preparatively useful yield (Scheme 2.17) [Hb]. However, it is currently not easy to predict the feasibility of such a domino process, because a compound similar to 43 lacking the two methyl groups and featuring a 2,5-cis substitution of the heterocycles failed to give the desired RRM product and only produced the corresponding macrocyclic dimer instead. 

Another approach to symmetrical sucrose macrocyclic dimers is presented in Scheme 18. 

Macrocyclic dimer coupling agent 1,4-a,a -Dibromo xylene 2450 119... 

Hence, it has been suggested that macrocyclic dimers 3 could be considered as the probable catalytic species, however they are thermodynamically disfavored compared to the square dimers (Scheme 2.18). 

Relative stability of macrocyclic dimers vs. square dimers, kcalfmol Af(ZPVE) AG(29ai5)... 

Scheme 2.18 Formation of macrocyclic dimers 3 and energies of the most stable conformers relative to the square dimers. (Reproduced with permission from Gridnev, I. D. et al., v4CS Catal., 2,2137-2149,2015.)...

Heterocyclophane 177e was also obtained on a platinum cylindrical electrode by the preparative electrochemical oxidation of podand 158e in a diaphragm (cellulose) glass electrolyzer. The electrosynthesis was carried out for 4 h. The mass spectrometric investigations of the mixture after the electrolysis showed the existence of two macrocyclic products 152e (m/z = 830), and the macrocyclic dimer (m/z = 1660). The preparative yield was 40 % (Mamedov et al. 2007). There was no starting compound in the solution. 

Tolmachev, A.I., Zaitsev, A.K., Koska, N., and Schuster, G.B., Counter-ion effects in cationic dyes photophysics and photochemistry of a macrocyclic dimer of dimethylindocarbocyanine, /. Photochem. Photobiol. A Ghent., 77, 237,1994. 

---