CAr–O Rotamers in 3,3′-Disubstituted BINOL Esters

Rotamers around the C-Ar-O bond were disclosed in 3,3'-disubstituted BINOL esters by NMR spectroscopy. A bulky R-1 group increased the rotational barrier. The pivalate showed two rotamers at 2 degrees C, and broad signals were observed close to room temperature when R-2 = 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 R-1 and R-2 during rotation of the C-Ar-O bond.