Enantiomers entrapment

Brucine has been used to produce enantiomerically enriched compounds by selective reaction with or destruction of one of the enantiomers. The optical purity of the resulting compound is usually modest, although some exceptions have been described. For example, dibromo compound (9) was obtained [enriched in the (—)-enantiomer] by selective destruction of the (+)-enantiomer with brucine in chloroform. The resolution of ( )-2,3-dibromobutane may have also been a case of enantioselective destruction, although more recent reports suggest that it is more likely a case of enantioselective entrapment in the brucine crystals (eq 14). ... 

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. 

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