Mandelic acid homochiral

Equation B5.6 depicts the reaction of an achiral aldehyde with a homochiral boron enolate derived from (5)-mandelic acid. Again the geometry of the enolate controls the relative stereochemistry of C2 and C3 and so only the two erythro isomers are formed. In this case, however, the homochiral centre in the boron enolate results in approach to one face of the aldehyde being strongly preferred over approach to the other face and a product ratio of 2R,3S 2S,3R = 28 1 is observed. 

CavaUuzzi MM, Bruno C, Lentini G, Lovece A, Catalano A, Carocci A, Franchini C. One-step synthesis of homochiral O-aryl and 0-heteroaryl mandelic acids and their use as efficient IH NMR chiral solvating agents. Tetrahedron Asymm. 2009 20 1984-1991. 

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