Developing Chiral Dibenzazepine-Based S(O)-Alkene Hybrid Ligands for Rh(I) Complexation: Catalysts for the Base-Free Hayashi–Miyaura Reaction

• Published in: Organometallics Vol. 37; no. 21; pp. 3983 - 3992
• Main Authors: Chelouan, Ahmed, Bao, Siyuan, Frieß, Sibylle, Herrera, Alberto, Heinemann, Frank W, Escalona, Ana, Grasruck, Alexander, Dorta, Romano
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12-11-2018
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.8b00591

A stereodivergent synthesis using inexpensive reagents, i.e., dibenzazepine and glucose-derived t-Bu-sulfinate diastereomers (R S)-6 or (S S)-6, affords respective S­(O)-alkene hybrid ligands (S)-7 and (R)-7 on gram scales and in excellent optical purity (ee > 99%). Phenyl substitution of the dibenzoazepine backbone generates planar chirality to give epimerization-resistant (pS,R S)-10 diastereoisomer in high isomeric purity. Furthermore, the crystal structure of widely used sulfinate (R S)-6 is disclosed for the first time since its discovery a quarter of a century ago. Ligands 7 and 10 coordinate Rh­(I) in a bidentate fashion through the S atoms and the alkene functions as evidenced by the crystal structures of complexes (R)-11 and (S N,S S)-12. (R)-11 catalyzes the conjugate addition of arylboronic acids to enones with enantioselectivities of up to 77% ee. The reaction proceeds smoothly also under base-free conditions at 40 °C. The planar chirality in ligand (pS,R S)-10 is shown to override and invert the sense of chiral induction predicted by the configuration of the sulfur donor atom.