Acid-Catalyzed Versus Thermally Induced C1-C1′ Bond Cleavage in 1,1′-Bi-2-naphthol: An Experimental and Theoretical Study

Experiments show that 1,1′-bi-2-naphthol (BINOL) undergoes facile C1-C1′ bond cleavage under action of triflic acid at temperatures above 0 °C to give mainly 2-naphthol along with oligomeric material. CASSCF and MRMP//CASSCF computations have demonstrated unambiguously that this unusual mode of scission of the biaryl bond can occur in the C1,C1′-diprotonated form of BINOL via a mechanism involving homolytic cleavage prompted by the intramolecular electrostatic repulsion. These findings also provide insights into the mechanism of a comparatively easy thermal cleavage of BINOL, implying the intermediacy of its neutral diketo form.