Sugar based diphosphites

Figure 2.46 Possibilities of variations in sugar-based diphosphites.

Prochiral unsaturated seven-membered ring acetals have been transformed with a Rh catalyst based on (R, )-BINAPHOS or sugar-based diphosphites into the 5-formyl compounds with good enantioselectivity (Scheme 4.95) [62, 64b]. Highest enantiomeric excess values were noted at moderate temperatures (40-45 C). The enantioenriched compounds can be further converted within four steps into 3-hydroxymethyl butyrolactone, an important chiral building block. 

Another successful family of ligands is the sugar-based furanoside ligands 4, 19-23 (Fig. 5) [21-23,43,50]. The modular construction of these ligands allows to fine tune (a) the different configurations of the carbohydrate backbone and (b) the steric and electronic properties of the diphosphite substituents. They show excellent enantioselectivity on both the S and R enantiomer of the product (up to 93%) and excellent regioselectivity (up to 98.8%) under mild conditions (Table 2). 

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