Desymmetrizations meso-diamines

Scheme 41.55 Seidel s dual catalysis-based desymmetrization of meso-diamines.

Scheme 43.4 Catalytic enantioselective desymmetrization of meso-diamines by merging nucleophilic and HB catalysis.

As summarized in Scheme 13.22, Oriyama et al. applied the chiral diamine 44 -albeit in equimolar amounts (relative to the diol) - to the desymmetrization of several meso-diols [37a]. In three instances the mono-benzoylated products were obtained with >90% ee and in satisfactory chemical yields [37a]. 

Selectivity in enantiotopos-differentiating acylation and phosphorylation of meso-diols can rival that of enzymes. The organocatalysts employed include chiral phosphines, chiral diamines, chiral DMAP derivatives and peptides identified from combinatorial libraries. The highest selectivity in meso diol desymmetrization has been achieved with a planar-chiral Fu catalyst. It seems the substrate scope of this process is not yet broadly explored. Because of their sequential variability it is to be... 

The catalytic efficiency of the diamines, 24 and 25, derived from the truncated cinchona alkaloids, quincorine and quincoridine, respectively, for the desymmetrization of meso- 1,4-diols was also investigated by Kiindig and coworkers [31a, b[. Both pseudoenantiomers 24 and 25 efficiently catalyzed the desymmetrization of the meso-complex 26 with benzoyl chloride, giving the enantiopure monobenzoylated Cr (CO)3 complexes, 27 and ent-27, respectively, with up to 99% ee (Scheme 11.17). This process will provide easy access to new planar chiral complexes. 

Finally, reaction E in Fig. 4 illustrates a stereoselective synthesis that proceeds by differentiation of two enantiotopically related groups of a meso compound. Here, one hydroxyl group of d.s-1,2-cyclohexanediol is preferentially benzoylated in the presence of one molar equivalent of an enantiomerically pure diamine [26]. These desymmetrization reactions (that have many biological versions) are also called meso-tricks , and are currently receiving a great deal of attention for the preparation of new chiral building blocks [27]. 

A simple nucleophilic catalyst such as 4-(dimethylamino)pyridine (DMAP, 23) has been found to be the ideal catalyst in the kinetic resolution of amines when it was used in combination with a chiral hydrogen-bonding (HB) catalyst [13]. The combined catalyst system formed from DMAP and HB catalyst exhibited excellent enanhoselective induction in the kinetic resoluhon of benzylic [13a], propargyHc [13b], and aUylic amines [13c] as well as in the desymmetrization of meso-1,2-diamines (Scheme 43.4) [13d]. 

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