CAr-O Rotamers in 3,3'-Disubstituted BINOL Esters.

Rotamers around the CAr-O bond were disclosed in 3,3'-disubstituted BINOL esters by NMR spectroscopy. A bulky R1 group increased the rotational barrier. The pivalate showed two rotamers at 2 °C, and broad signals were observed close to room temperature when R2 = Ph. The highest rotational barrier was recorded for the (tetracyanocyclopentadienyl)carboxylate, and C-O rotamers were present at room temperature. DFT calculations indicated the presence of repulsion between R1 and R2 during rotation of the CAr-O bond.