Racemic enantioconvergent hydrolysis

In order to circumvent the disadvantages of kinetic resolution, several protocols were developed towards the enantioconvergent hydrolysis of epoxides, which lead to a single enantiomeric vicinal diol as the sole product from the racemate. 

Scheme 4.49 Enantioconvergent hydrolysis of racemic sulfate esters using a sulfatase.

An enantioconvergent transformation leads to a single enantiomeric product from a racemate [51]. Each enantiomer is transformed via independent pathways by the same catalyst or by two different catalysts (Figure 6.6). For example, the hydrolysis of epoxides may proceed with high regio- and stereoselectivity vdth inversion or retention of configuration. Several enantioconvergent transformations of epoxides are reported in the last section of this chapter. 

The full transformation of a racemic mixture into a chiral product is possible by the combination of formation of a chiral product and a fast racemization of the residual substrate. Dynamic KR is detailed in Chapter 5. There is another strategy for transforming the two enantiomers of a racemic substrate into the same enantiomer of the product (enantioconvergent reactions). Two different types of reactions must concern the two enantiomers. For example, hydrolysis of rac-l-phenyloxirane fuUy converted it into (R)-l-phenyl-l,2-dihydroxyethane in the presence of a biocatalyst [87,88]. The regioselectivity of the reaction is not the same for both enantiomers moreover, hydrolysis at the asymmetric centre occurs with inversion (Scheme 2.8). 

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