Selective enclathration

The gas-solid addition of HCl or HBr to simple alkylated oxiranes requires their inclusion. (-)-(M)-Tri-o-thymotide (150) (P3i21) selectively enclathrates the oxiranes 151 or 153 with 13-14% ee for (-i-)-(3P)-151 or 51-5Wo ee for (-1-)-(2P,3P)-153. Isolated molecules in the chiral cages of 150 react stereoselectively with HCl or HBr gas to give the products 152 and 154, respectively, in almost stereopure form according to the optical rotations after quantitative reaction under the influence of the chiral environment [78] (Scheme 17). The host lattice is preserved during the reactions, but destroyed during liberation of the product molecules. 

This order shows that the size of the guest molecules seems to be important for selective enclathration of CA, although the order is not in proportion to the molecular size. 

This order indicates that the aG-type host framework is more favorable than the other two trans-types ((TP or aT), and the 1 1 aG type is more favorable than 2 1 aG. In addition, this order agrees with the fact that less-selective enclathrations (entry 1, 12 and 21) were observed when they construct the same host frameworks at the same host-guest ratios in a single-component system. For example, both benzene and toluene can be included in the same 1 1 aG type. In the same way, less-selective enclathrations were also observed in the cases of ethylbenzene vs. n-propylbenzene (1 1 (3P) and n-amylbenzene vs. n-hexylbenzene (2 1 aG). 

Selective Enclathration Using Other Bile Acids... 

This selectivity is completely different from that in the case of CA as host. The difference between the two hosts is ascribed to the different shapes of their cavities. Figure 14 shows typical cross-sections of host cavities with arrays of o-xylene, where the guest molecules are arrayed in cavities that do not possess grooves. In the case of CA, the grooves play an important role in selective enclathration, while the DCA cavity has no grooves. This means that the mechanism of separation differs between the CA and the DCA hosts. 

NOE experiment as well as by a molecular dynamic simulation. The selective enclathration of the cz5-isomer was observed when cis-trans mixtures of either 5 or 6 in hexane were stirred with a D2O solution of 3. The NMR spectra confirm... 

H and C NMR lineshapes for selected enclathrated guest molecules, as well as reference lineshapes for the pure solid materials are shown in Figs. 3 and 4. The lineshapes for guest molecules in the... 

The selectivities for the guest compounds by enclathration seem to be dependent on the four types. The order of preference is given below ... 

Competition experiments by enclathration can be employed to separate isomers with similar boiling points, and if we consider the selectivity diagram of the two-component systeins A-B with = 3, discussed earlier, we can employ a McCabe-Thiele-type plot to show that by starting with an initial mixture of Xa = 0.1, we can achieve an enrichment Xa = 0.93 in three successive crystallization steps (Fig. 7). 

Beketov, K. Weber, E. Seidel. J. Kohnke, K. Makhka-mov, K. Ibragimov, B. Temperature controlled selectivity of isomeric guest inclusion Enclathration and release of xylenes by l,l -binapthyl-2,2 -dicau boxylic acid. Chem. Commun. 1999. 91 -92. 

We have investigated the mechanism of enantiomeric enrichment by enclathration by studying TADDOL type hosts (derivatives of Q ,Q ,Q , Q -tetraaryl-l,3-dioxolane-4,5-dimethanol) which enclathrated 2-butylamine mixtures of varying enantiomeric composition. In particular, the host (/J,.R)-(—)-tran5 -4,5-bis-(hydroxydiphenylmethyl)-2,2-dimethyl-1,3-dioxolane entraps different proportions of both enantiomers of 2-butylamine, depending on the initial composition of the mother liquor. The system is subtle, in that the compounds crystallize in PI with Z = 2 and the two independent host molecules behave differently. The selectivity curves of molecules 1 and 2, and the overall selectivity are shown in Figure 8. 

Analysis of the variation in the torsion angles which control the conformation of the phenyl rings of the host and the concomitant volume of the space available for the enclathrated 2-butylamine guests shows that enhanced enantiomeric selectivity arises from smaller guest volumes. 

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