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Transformation, asymmetric preferential crystallization

However, cases known as second-order asymmetric transformation, which involve preferential crystallization of one diastereomer from an equilibrating mixture, can be excluded. [Pg.49]

Figure 14. Mutarotation of an iminazoline (a) removal from the system by crystallization (b) asymmetric transformation, but no preferential crystallization (c) racemization and (d) no epimerization... Figure 14. Mutarotation of an iminazoline (a) removal from the system by crystallization (b) asymmetric transformation, but no preferential crystallization (c) racemization and (d) no epimerization...
In Figure 14(b), the combination of proline and 2-aminomethyl pyrrolidine, the asymmetric transformation was observed but no preferential crystallization occurred. In Figure 14(c) only racemization was observed. Moreover, in Figure 14(d), non-coplanarity of the iminazoline and a-branched carbon prevented the double-bond shift and epimerization did not occur. [Pg.66]

It is noteworthy that the higher-melting R, R diastereomer of 75 crystallizes preferentially in a typical second-order asymmetric transformation - from an equilibrium mixture of the two diastereomers in methanol containing hydrochloric acid and sodium iodide, thereby provding a simple method of converting almost all of the original mixture of 75 into the more desirable R, R diastereomer ... [Pg.112]

If Eisenlolir and Meier are correct, the re.sult mast be cla.s.sed not as an asymmetric synthesis but as a second-order asymmetric transformation. The diastereoisomerides of II have no real existence in solution but as soon as crystallization sets in, the less soluble would be expected to separate out preferentially. There is, however, a complicating factor here which still makes it uncertain how this synthesis should be classified. Diastereoisomerides should differ significantly in all their phy.sical properties, and it is difficult to accept Eisenlohr and Meier s assertion that the diastereoiso-meric forms of II eliminate carbon dioxide at the same rate. It seems likely that the final optical activity is the resultant of two factors—a more or less one-sided asymmetric transformation, followed by optically selective breakdown of diastereoisomerides. [Pg.100]


See other pages where Transformation, asymmetric preferential crystallization is mentioned: [Pg.381]    [Pg.791]    [Pg.180]    [Pg.110]    [Pg.86]    [Pg.2]    [Pg.323]   


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Crystallization transformation

Preferential crystallization

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