IBS-Catalyzed Regioselective Oxidation of Phenols to 1,2-Quinones with Oxone®

Abstract

We have developed the first example of hypervalent iodine(V)-catalyzed regioselective oxidation of phenols to o-quinones. Various phenols could be oxidized to the corresponding o-quinones in good to excellent yields using catalytic amounts of sodium salts of 2-iodobenzenesulfonic acids (pre-IBSes) and stoichiometric amounts of Oxone® as a co-oxidant under mild conditions. The reaction rate of IBS-catalyzed oxidation under nonaqueous conditions was further accelerated in the presence of an inorganic base such as potassium carbonate (K2CO3), a phase transfer catalyst such as tetrabutylammonium hydrogen sulfate (nBu4NHSO4), and a dehydrating agent such as anhydrous sodium sulfate (Na2SO4).

4,5‐Dimethyl‐2‐Iodoxybenzenesulfonic Acid Catalyzed Site‐Selective Oxidation of 2‐Substituted Phenols to 1,2‐Quinols

“…[6,7] In general, iodine(III) and iodine(V) reagents have been used for para-a nd ortho-selective oxidations, respectively (Scheme 1a). [6] Recently,i ns itu generated organoiodine(III)-and organoidodine(V)-catalyzed [8] regioselective oxidation to 1,4-benzoquinols, [9] 1,4-benzoquinones, [9] and 1,2-benzoquinones [10] has also been developed. However,t he catalytic site-selective hydroxylative dearomatization of 2-substituted phenols to 1,2-benzoquinols has not yet been reported.…”

“…Indeed, the reaction rate at 20 8 8Cw as accelerated by 1.5-to 3-fold with the use of precatalysts substituted with electron-donating groups [15a] (10 b-d; entries 5-7). Although the highest reactivity was observed with 5-MeO-pre-IBS (10 d), it was unstable under these reaction conditions.Additionally,the oxidation rate could be further accelerated with the use of buffered Oxone, [10] which was prepared by premixing of Oxone and potassium carbonate (0.5 equiv) in DMC at room temperature,a nd 8a was obtained in 82 %yield after ashorter reaction time (entry 8). As expected, almost no reaction proceeded with the use of the 10 e (entry 9).…”

Hypervalent Iodine‐Catalyzed Oxidative Functionalizations Including Stereoselective Reactions

“…Recently, Ishihara and co‐workers43 demonstrated the first example of hypervalent iodine(V)‐catalyzed regioselective oxidation of phenols 68 to o ‐quinones 70 . Various phenols including naphthols and phenanthrols were oxidized to the corresponding o ‐quinones in good to excellent yields using sodium 2‐iodobenzenesulfonic acid 69 as precatalyst, tetra‐ n ‐butylammonium hydrogen sulfate ( n Bu 4 NHSO 4 ) as phase‐transfer catalyst, and oxone as an oxidant under mild reaction conditions (Scheme ).…”

Synthesis and antioxidant activity of DOPA peptidomimetics by a novel IBX mediated aromatic oxidative functionalization

“…two OMe moieties at 3.74 and 4.11, and the Gly CH 2 group at 3.93 ppm) conrmed the mono-substitution pattern. 38 On the basis of these data, the reaction was extended to a-amino acids 3-9 to obtain the corresponding L-DOPA peptidomimetics N-Boc-Ala-N-Boc-DOPA-OMe (12), N-Boc-Val-N-Boc-DOPA-OMe (13), N-Boc-Leu-N-Boc-DOPA-OMe (14), N-Boc-Phe-OMe (1) with N-protected a-amino acids.…”