New chiral ligands derived from mandelic acid: Synthesis and application in the asymmetric phenyl transfer reaction to an aromatic aldehyde

Starting from inexpensive enantiopure (R)- and (S)-mandelic acid, a range of alpha-hydroxy-2-oxazolines has been prepared. The synthesis involves the condensation of the acid chloride with a vicinal amino alcohol, followed by intramolecular cyclization to form the oxazoline ring. The resulting compounds have been used as ligands in the asymmetric phenyl transfer reaction to 4-chlorobenzaldehyde, employing a mixture of triphenylborane and diethylzinc as the phenyl source. Good yields (up to 76%) and moderate enantioselectivities (up to 35%) have been achieved.