Effect of forced coplanarity of biphenyl rings on the ease of formation and stability of phenolic cations

Electrochemically Controlled Chemically Reversible Transformation of α-Tocopherol (Vitamin E) into Its Phenoxonium Cation

“…The cyclic voltammetric response observed for α-TOH in neutral organic media is similar to that seen for 2,6-di- tert -butyl-4-(4-dimethylaminophenyl)phenol, where it was shown that the reverse peak detected during CV experiments was due to reduction of the phenoxonium ion that formed rapidly following two-electron oxidation of the phenol . It has been noted that the presence of bulky electron donating substituents in the 4-position are critical for the stabilization of phenoxonium cations, ,,, with 2,6-di- tert -butyl-4-(4-dimethylaminophenyl)phenoxonium found to be sufficiently stable to be isolated as a solid salt . However, the bulkiness cannot be the only factor since 2,4,6-tri- tert -butylphenol does not readily lead to a stable phenoxonium ion following oxidation [Figure b (black line)].…”

Anodic oxidation of 1,2,3,4-tetrahydronaphthalene and isochroman analogs of 1-benzyl and 1-phenethyl isoquinoline alkaloids. Products and mechanism of the intramolecular cyclization

“…3,3',4,4'-Tetramethoxybenzalacetone (29) 19 (mp 124-125 °C, 70.8 g, 0.2 mol) was dissolved in ethanol (300 mL) and submitted to catalytic hydrogenation at 1 atm with Pd/C (10%, 5 g) as catalyst. When the theoretical amount of hydrogen had been consumed, the catalyst was filtered off and the filtrate was evaporated to yield pure 41:80.2 g (100%); mp 83-84 °C; NMR 6.77 (6 H, m, ArH), 3.90 (12 H, s, OCH3), 2.80 (8 H, m, CH2). l,5-Bis(3,4-dimethoxyphenyl)-3-pentanol (42).…”

“…Dienone 18a from 17a: mp 99-101 and 138-139 °C; NMR 6.87 (1 Hs, s), 6.65 (1 H4, s), 6.40 (1 Hb s), 6.30 (1HB, s), 3.92 (3 H, s, OCH3), 3.88 (3 H, s, OCH3), 3.81 (3 H, s, OCH3), 3.10 (3 H, m, H9 and H10), 2.00 (2 H, m, His), 1.57 (4 H, m, Hn and H12); IR v 2940, 2850,1666, 1640,1620,1520,1470 cm-1.…”

“…Found: 326.1521. Dienone 19a from 17a: mp 168-171 °C; NMR 6.98 (1 Hg, s), 6.68 (1 H4, s), 6.45 (1 Hb s), 5.98 (1 HB, s), 3.93 (6 H, s, OCH3), 3.73 (3 H, s, OCH3), 2.67 (4 H, m, Hi0 and Hi3), 1.73 (5 H, m, H9, Hlb and Hi2); IR v 3090, 2985, 2840,1665,1640,1595,1520,1460 cm"1.…”

“…Dienone 20a from 17a: mp 166-167 °C; NMR 6.86 (1 HB, s), 6.42 (1 H4, s), 6.27 (1 Hb s), 5.80 (1 H8, s), 3.92 (3 H, s, OCH3), 3.78 (3 H, s, OCH3), 3.60 (3 H, s, OCH3), 2.48 (3 H, m, H9 and H10), 1.78 (2 H, m, Hi3), 1.20 (4 H, m, Hn and Hi2).…”