Synthesis of chiral 1′-substituted oxazolinylferrocenes as chiral ligands for Pd-catalyzed allylic substitution reactions

Abstract

Chiral 1-oxazolinyl-1′-(diphenylphosphino)ferrocenes 4 and 1-oxazolinyl-1′-(phenylthio)ferrocenes 5 were prepared from 1,1′-dibromoferrocene through 1-oxazolinyl-1′-bromoferrocenes 3. The compounds 4 and 5 were employed as chiral ligands in Pd-catalyzed asymmetric allylic substitution reactions. High enantioselectivities (82–99% ee) and high yields (96–99%) were observed in the substitution reactions of 1,3-diphenylprop-2-enyl acetate and dimethyl malonate with the catalysts generated from [(π-allyl)PdCl] 2 and 4, while the use of 5 led to inferior results (20–75% ee and 25–28% yields). 1H-, 13C-, and 31P-NMR data are analyzed for the complexes obtained from the reactions of [(η 3-allyl)PdCl] 2 and [(η 3-1,3-diphenylallyl)PdCl] 2 with 4a and 4b.