Isomannide and isosorbide as new chiral auxiliaries for the stereoselective synthesis of tertiary α-hydroxy acids

Isomannide and isosorbide are selectively protected to provide new chiral auxiliaries suitable for the preparation of enantiopure tertiary α-hydroxy acids. Diastereoselective additions of organozinc reagents on the derived phenylglyoxylates afford the desired α-hydroxy acids with 60–99% ee after saponification. Both absolute configurations of the α-hydroxy acids can be accessed, by adapted choice of either the starting diol or the protecting group.