Topological diastereoisomers

With two more electrons, and rather more complicated structures, the Nazarov-like reactions of the carbamates 6.536 and 6.538 are conrotatory, with the torquoselectivity determined, as in the Favorskii reactions, by which side of the conjugated system the nucleofugal group departs from, clockwise as drawn for the carbamate 6.536 and anticlockwise for its diastereoisomer 6.538.964 The topological sense of the event in the left-hand ally lie system corresponds to an anti Sn2 reaction in both cases. 

To make a knot is a task easily accomplished by a child playing with a rope, or even by a careless adult with shoelaces. For a chemist playing with molecules this is an intrinsically difficult problem and so far only a few of these topologically interesting compounds have been synthesized. A strategy that finally led to success is based on the self-assembly of double-helical copper phenanthroline complexes. The helix represents the core structure from which the trefoil knot 30 in Fig. 15 is obtained in a final cyclization step. It is important to note that a trefoil knot is chiral. The resolution of the two enantiomers was recently accomplished by fractional crystallization of the diastereoisomers obtained with a chiral counterion. 

The studied diastereoisomers have been separated by adsorption TLC on silica gel plates activated 30 min at 120 C before use. The spotted plates were developed three times, for menthols with the binary mixture n-hexane-ethanol (85 +15, v/v) and for thujols with benzene. The experimental Rp and Rm values of investigated diastereoisomers and the numerical values of the proposed stereoisomeric topological indexes (/sn) and the modified version of the index Bsti are given by the author [43]. The data demonstrate close correlation between Rp and Rm values and the numerical values of the topological indexes. 

The calculated Rp ( 0.030 deviation) and Rm values for the diastereoisomers of menthol and thujol are in good agreement with the experimental data that attest the physicochemical significance of the topological indexes proposed by the author. Such indexes can be used for analytical identification of diastereoisomers separated by TLC. 

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