Synthesis and Stereochemical Properties of “Extended” Biphenols Bridged by ortho‐, meta‐, and para‐Phenylene Spacers

Abstract

AbstractA series of isomeric biphenols based on para‐ (1), meta‐ (2), and ortho‐ (3) terphenyl backbones was synthesized. Suzuki cross‐coupling methodology was employed for the construction of the terphenyl backbone of their methyl‐protected precursors (respectively 8, 13, and 16). Using K2CO3 as the base, the best reaction conditions involved DMF at 100 °C as solvent. Anhydrous conditions greatly improved the yields of the sterically crowded systems (particularly 16). ortho‐Terphenyls 3 and 16 exist as mixtures of syn/anti atropisomers in solution. Compound 16 crystallizes in the anti‐in form. DFT calculations at the B3LYP/6‐311+G(d,p) level indicate that for both compounds the anti‐in form is more stable than the syn form by 6.07 and 2.07 kJ mol–1 for 16 and 3, respectively. These ΔΔG0 values are higher by the same factor (of two) than those obtained in solution at 240 K (3.17 and 0.93 kJ mol–1). The atropisomeric properties of 16 and 3 are finally discussed in the context of ortho‐terphenyls in the literature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)