Facile and Selective Cross‐Coupling of Phenols Using Selenium Dioxide

Abstract

Nonsymmetric biphenols are important structural motifs in organic chemistry. Therefore, an easy and versatile protocol for oxidative cross‐coupling is essential to generate these so‐called “privileged ligands”. We developed an efficient and selective oxidative pathway to synthesize 2,2′‐biphenols as well as 2,4′‐ and 4,4′‐biphenols. The use of selenium dioxide, a stable, powerful, and commercially available oxidizer, in 1,1,1,3,3,3‐hexafluoroisopropanol allowed the oxidative coupling of alkyl‐, alkoxy‐, and halogen‐substituted phenols.

Bio-inspired oxidative phenolic coupling: Total synthesis of the diarylether heptanoid (±)-pterocarine

“…Cinnamic acid derivative 11 is a known 9 commercially available molecule that was converted to the corresponding phosphonate (12) following standard conditions. 10 Horner-Wadsworth-Emmons reaction with aldehyde 13 gave dienone 14 in high yield.…”

Catalytic Aerobic Phenol Homo‐ and Cross‐Coupling Reactions with Copper Complexes Bearing Redox‐Active Guanidine Ligands

“…This resultc an be explained by ac ompetitive inhibition of the catalystd ue to the coordination of HFIP to the catalyst. [20,30,31] Subsequently,w et ested the redox-activel igand 1 2 + + ,w hich was also used for phenol coupling [60] in aP CET reaction. In addition to the higher costs of HFIP,t he dramatic decrease in the reactionr ate led us explore an ovel concept that is not restricted to the use of this solvent.…”

“…The observed decreasei nt he reaction rate seems to be ag eneral problem of HFIP as indicated by the required high catalyst loadings and temperatures, as well as long reaction times in the cross-coupling reaction of phenols in previous works (see Scheme 2). [20,30,31] Subsequently,w et ested the redox-activel igand 1 2 + + ,w hich was also used for phenol coupling [60] in aP CET reaction. A quantitative reactiono f1 2 + + with both phenolsl ed to av alue of 53 %f or the cross-couplings electivity in CH 2 Cl 2 solution (Table 3, entry 6), close to the cross-coupling selectivity of 58 % for the benchmark catalyst( Ta ble 3, entry 1).…”

“…Spontane-ous radical-radical coupling of two phenoxyl radicals leads to the undesirable homo-coupling product AÀA (Scheme 1). [30] The best resultsw ere obtained when phenol A was added in af ivefold excess and HFIP was used as the solvent. Waldvogel et al presented another concept in electrochemical cross-coupling of phenols anda nilines, providing high chemoselectivities by shifting the oxidation potential of the phenols depending on the substitution pattern in a specific range by adding water or methanol to the electrolyte.…”

“…used stoichiometrica mountso f SeO 2 as the oxidantt oa chieve the cross-coupling products in high yields. [30] The best resultsw ere obtained when phenol A was added in af ivefold excess and HFIP was used as the solvent. More recently,P appo et al reporteda ni ron catalystw ith at etraphenylporphyrin ligand (TPP) for the selective oxidative cross-coupling reaction of phenols.…”