Metal-free thermal organocatalytic pinacol coupling of arylaldehydes using an isonicotinate catalyst with bis(pinacolato)diboron

The metal-free thermal organocatalytic pinacol coupling of arylaldehydes has been developed. The intermolecular coupling of arylaldehydes catalyzed by t-butyl isonicotinate with bis(pinacolato)diboron as the co-reducing agent afforded 1,2-diphenylethane-1,2-diols. This reaction was also applicable to the intramolecular coupling of 1,1′-biphenyl-2,2′-dicarbaldehydes to afford 9,10-dihydrophenanthrene-9,10-diols. Various functional groups were tolerated under this coupling condition.