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.
García
José I
JI
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
Jiménez-Osés
Gonzalo
G
López-Sánchez
Beatriz
B
Mayoral
José A
JA
Vélez
Andrea
A