Stereoselectivity induced by support confinement effects. Aza-pyridinoxazolines: A new family of C(1)-symmetric ligands for copper-catalyzed enantioselective cyclopropanation reactions.
Aza-pyridinoxazoline ligands, a new class of C(1)-symmetric ligands, are described and tested in the heterogeneous enantioselective catalysis of a cyclopropanation reaction, with the aim of improving surface confinement effects by the clay support on the reaction stereoselectivity. In the case of trans/cis diastereoselectivity, these surface effects lead to a systematic reversal of selectivity, cis-cyclopropanes being favored. Regarding the enantioselectivities, support confinement has a positive effect in the case of major cis-cyclopropane products, leading to moderate enantioselectivity values (60% ee). A theoretical (DFT) mechanistic study is carried out to explain the origin of the enantioselectivity in the homogeneous phase at a molecular level, and to get insights on the geometries of the key intermediates and transition structures.
Departamento de Química Orgánica, Instituto de Ciencia de Materiales de Aragón and Instituto Universitario de Catálisis Homogénea, Facultad de Ciencias, Universidad de Zaragoza-CSIC, E-50009, Zaragoza, Spain. jig@unizar.es
José I
JI
García
Gonzalo
G
Jiménez-Osés
Beatriz
B
López-Sánchez
José A
JA
Mayoral
Andrea
A
Vélez