1-Phosphino-2-sulfenylferrocenes as planar chiral ligands in enantioselective palladium-catalyzed allylic substitutions.
The synthesis of a wide structural variety of enantiopure 1-phosphino-2-sulfenylferrocene ligands 1 possessing exclusively planar chirality is described. In the case of the readily available tert-butylsulfenyl derivatives very high enantioselectivities were obtained in the palladium-catalyzed allylic substitution of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate (ee's up to 97%) and nitrogen nucleophiles (ee's up to 99.5%). Palladium complexes of these ferrocenes were characterized by NMR and X-ray diffraction, revealing the P,S-bidentate character of the ligands 1 and the formation of a single epimer on the stereogenic sulfur atom resulting from the complexation with palladium. A model justifying the observed asymmetric induction exerted by this novel family of chiral ferrocenes, supported by solution NMR studies on a palladium allylic complex, is discussed.
García Mancheño
Olga
O
Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco 28049 Madrid, Spain.
Priego
Julián
J
Cabrera
Silvia
S
Gómez Arrayás
Ramón
R
Llamas
Tomás
T
Carretero
Juan Carlos
JC