A novel dihydroazepine‐bridged BIPHEP phosphoramidite ligand with an amino acid moiety in the backbone was synthesized and evaluated in the Rh‐catalyzed asymmetric hydrogenation. The scorpion tail‐like amino acid backbone is capable of hydrogen bond formation and able to shift the rotamer composition of the biphenyl axis with the two scissor‐like arms. Pivaloyl‐l‐valine was studied as chiral selector unit and compared with pivaloylglycine as the achiral reference substance. The enantiomerization barrier of the pivaloylglycine‐modified biphenylamide was determined to be ΔG≠=110 kJ/mol. In the case of pivaloyl‐l‐valine, the (Sax) isomer is thermodynamically favored. Due to the relatively high barrier, the ligand is atropisomeric at room temperature and allows the preparative separation of the stereoisomers. The obtained phosphoramidite ligands were separated by chiral HPLC. For the first eluting rotamer, Rh complex ([Rh(cod)(L)2]BF4) was generated in situ and examined in the enantioselective hydrogenation of 2‐acetamidoacrylate and methyl 2‐acetamido‐3‐phenylacrylate, achieving enantiomeric excesses of up to 94 %.

Chiral compounds with a 1,2‐diamine structure motif and their derivatives are of great interest in organic chemistry and are broadly used in asymmetric transformations, as chiral auxiliaries, (co)ligands, and ligand core structure. Here, we present a straightforward, diastereoselective synthesis for a diamide‐bridged biaryl ligand. The ring closing reaction of the racemic atropos biphenyl 6,6′‐dimethoxy‐[1,1′‐biphenyl]‐2,2′‐dicarboxylic acid with (R,R)‐diaminocyclohexane yields the diasteromerically and enantiomerically pure cyclic (Sax,R,R)‐BIPOL, which can be used as a versatile chiral ligand. By NMR spectroscopy, we observed the formation of intermolecular aggregates of the diamide‐bridged BIPOL with anhydrous DMSO‐d6. DFT calculations at the B3LYP/6‐31G* level of theory corroborate the high interconversion barrier for the biaryl axis of ΔGǂ = 148.7 kJ mol−1 and the favoured formation of (Sax,R,R)‐BIPOL as single stereoisomer.