Stereoselective benzilic acid rearrangements: new advances on an old story

The benzilic acid rearrangement (BAR) is the oldest rearrangement on record. It is a powerful synthetic tool for accessing significant biologically active molecules. The reaction is both catalytic (generally Lewis acid) and stereoselective, recently the first catalytic asymmetric version was reported with astonshing results (ees of up to 97%) to give chiral tartronic esters. In this unique highlight, we look at the progress made over the last 10 years on the stereoseletive aspects of this synthetic transformation, showing interesting examples of this rearrangment in both acyclic and cyclic systems (like for instance its importance in the stereoselective synthesis of syn and anti -hydroxy-iso-evoninic acids, α-hydroxy-α-perfluoroalkyl esters, a selective nonsteroidal mineralocorticoid receptor antagonist, Geldanamycin type polyketides and (−)-isatisine A, etc. ) and the differnces in stereoselectivity encountered which culminated recently in the conquest of the first catalytic asymmetric example on record. The benzilic acid rearrangement (BAR) is a powerful method introducing key structural elements in many targets. In this article we discuss important recent stereoselective BARs that include the first enantioselective catalytic example.