Development of Rigid Tricyclic Ligands and their Application to Asymmetric Catalysis

点击翻译按钮获取中文摘要

Design and development of chiral ligands for the transition-metal catalyzed reactions are most facinating and challenging task. As part of our research on development of new monodentate chiral phosphines, we succeeded in development of a new class of chiral ligands, P-chirogenic diaminophosphine oxides, and their application to Pd-catalyzed asymmetric construction of quarternary carbons.The P-chirogenic diaminophosphine oxides were prepared from aspartic acid anhydride via the corresponding dianilide, the triamine, and the corresponding triaminophosphine. The absolute structure of the diaminophosphine oxide was unequivocally determined by X-ray crystal structure analysis.With an optically pure P-chirogenic diaminophosphine oxide in hand, we attempted to use this molecule as a chiral phosphorus ligand, which expected to generate by tautomerization from the diaminophosphine oxide (V) to the diaminohydroxyphosphine (III). Catalytic enantioselective synthesis of a quaternary carbon center is a challenging task in organic synthesis. We first examined asymmetric allylie substitution of cinnamyl acetate with ethyl 2-oxo cyclohexane carboxylate. With the use of (allylPdCl)_2 and the diaminophosphine oxide, the reaction smoothly proceeded in the presence of N,O-bis(trimethylsilyl)acetamide (BSA) and Zn(OAc)_2 to afford the product in 92% ee and quantitative yield. BSA was found to be excellent inducer of tautomerism from the pentavalent phosphorus compound to the trivalent phosphorus ligand.Further investigation on optimization of ligand structure are in progress.