‘Chiral Fluoride’ Separates Alcohols

Thanks to the unusual combination of a crown ether moiety and a chiral organocatalyst, chemists in South Korea have developed a simple method for separating enantiomers of silyl-protected secondary alcohols (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201004777). In the presence of potassium fluoride, the mix-and-match molecule created by Choong Eui Song and colleagues at Sungkyunkwan University generates a “chiral fluoride” species that can selectively desilylate one enantiomer in a racemic mixture of silylated secondary alcohols. During the process of designing the catalyst, Song’s team discovered it was necessary to incorporate halogens at the 3 and 3ʹ positions of the BINOL (1,1ʹ-bi-2-naphthol) organocatalyst. An X-ray crystal structure of the catalyst-KF complex reveals that the Lewis basic halogen atoms interact strongly with the potassium ion. “This study can open up a new avenue of research for chiral-fluoride-catalyzed asymmetric reactions, which have vast synthetic potential but remain a relatively undeveloped field,” the researchers note.