Chemo- and regioselective oxygenation of C(sp3)–H bonds in aliphatic alcohols using a covalently bound directing activator and atmospheric oxygen

Ozawa, Jun; Tashiro, Masayuki; Ni, Jizhi; Oisaki, Kounosuke; Kanai, Motomu

doi:10.1039/c5sc04476f

Cited by 41 publications

(24 citation statements)

References 54 publications

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“…34) Although the best precatalyst performance still remains inferior to that of 1 itself, these investigations provide fundamental information on the design of novel N-oxyl radical catalysts and effective radical directing activators. 16) Further studies on the functionalization of these compounds that may eventually lead to more active and selective catalysts are ongoing in our laboratory and results will be reported elsewhere in due course.…”

Section: Resultsmentioning

confidence: 97%

“…As expected, protection of the Nhydroxy moiety in 29 as a PMBether, followed by nucleophilic trifluoromethylation successfully furnished alcohol 31. However, our general protocol (Chart 1), consisting of chlorination (Et 3 N-MsCl) followed by silver-mediated S N 1 substitution, 16) did not afford 32 or 33 from 30, most likely on account of the low reactivity of the chlorinated intermediate towards the silver salt. As an alternative, we chose to carry out a onepot mesylation-substitution reaction.…”

Section: This Article Is Dedicated To Professor Satoshi ōMura In Celementioning

confidence: 89%

“…16) Simultaneous modifications of the aromatic substituents (R 1 -R 4 ) should further improve these properties (Fig. 2).…”

Section: This Article Is Dedicated To Professor Satoshi ōMura In Celementioning

confidence: 99%

“…Initially, 1 was converted into intermediate 2 in three steps, following our previously reported procedure. 16) Then, the chloro group of 2 was substituted with methoxy, 2,2,2-trifluoroethoxy, or acetophenone moieties under silver-mediated S N 1 conditions, using the corresponding alcohols or a silyl enol ether (7). The ensuing removal of the protecting benzyl group under hydrogenolysis conditions afforded N-hydroxy precatalysts 5, 6, and 9.…”

Section: This Article Is Dedicated To Professor Satoshi ōMura In Celementioning

confidence: 99%

“…20) As the removal of the benzyl group was unsuccessful in this case, the p-methoxybenzyl (PMB) group was selected as a protecting group for the N-hydroxy moiety (Chart 3). The PMB group could be removed successfully in the last step under trifluoroacetic acid (TFA)/C 6 Me 5 H conditions 16,21) to afford 28.…”

Section: This Article Is Dedicated To Professor Satoshi ōMura In Celementioning

confidence: 99%

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Enhanced Structural Variety of Nonplanar N-Oxyl Radical Catalysts and Their Application to the Aerobic Oxidation of Benzylic C–H Bonds

Kadoh

Oisaki

Kanai

2016

CHEMICAL & PHARMACEUTICAL BULLETIN

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The design and synthesis of structurally variable, nonplanar N-oxyl radical catalysts and their application to the aerobic oxidation, etherification, and acetoamidation of benzylic C-H bonds are described. The catalytic oxidation of C-H bonds represents a powerful tool to synthesize oxygenated functional molecules from simple hydrocarbons in a straightforward way. Electron-deficient N-oxyl radical catalysts, such as phthalimidoyl N-oxyl (PINO) radical, generated from N-hydroxyphthalimide (1), have attracted much attention because of their applications in the oxidation of C-H bonds with high bond dissociation energy (BDE). However, a few sites in 1 are available for structural modifications and improvements of the catalytic performance. By replacing one carbonyl group in 1 with a trifluoromethyl (CF 3 )-substituted sp 3 -carbon, we generated an additional tunable site and a nonplanar backbone, while retaining the desirable electronwithdrawing properties and increasing the lipophilicity with respect to 1. We synthesized a variety of Nhydroxy pre catalysts containing such a CF 3 moiety, and investigated their utility in the aerobic oxidation of benzylic C-H bonds. Precatalysts with electron-withdrawing substituents, such as trifluoroethoxy and the acetophenone moieties, afforded higher yields than a corresponding methoxy-substituted analogue. The introduction of substituents at the aromatic ring was also effective, as evident from the performance of 7-CF 3 and 4,5,6,7-tetrafluoro precatalysts. Especially the combination of trifluoroethoxy-and 4,5,6,7-tetrafluoro substitution afforded a superior performance. These catalyst systems exhibited high functional group tolerance during the aerobic oxidation of C-H bonds, and benzylic etherification and Ritter-type reactions could be carried out at room temperature when a selected precatalyst and N-bromosuccinimide (NBS) were used.

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Section: Resultsmentioning

confidence: 97%

Section: This Article Is Dedicated To Professor Satoshi ōMura In Celementioning

confidence: 89%

“…16) Simultaneous modifications of the aromatic substituents (R 1 -R 4 ) should further improve these properties (Fig. 2).…”

Section: This Article Is Dedicated To Professor Satoshi ōMura In Celementioning

confidence: 99%

Section: This Article Is Dedicated To Professor Satoshi ōMura In Celementioning

confidence: 99%

Section: This Article Is Dedicated To Professor Satoshi ōMura In Celementioning

confidence: 99%

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Enhanced Structural Variety of Nonplanar N-Oxyl Radical Catalysts and Their Application to the Aerobic Oxidation of Benzylic C–H Bonds

Kadoh

Oisaki

Kanai

2016

CHEMICAL & PHARMACEUTICAL BULLETIN

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Green Oxidative

Lan

Wang

et al. 2019

Green Oxidation in Organic Synthesis

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Organic Molecular Catalysts in Radical Chemistry: Challenges Toward Selective Transformations

Uraguchi

Ohmatsu

Ooi

2019

Molecular Technology

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Chemo- and regioselective oxygenation of C(sp³)–H bonds in aliphatic alcohols using a covalently bound directing activator and atmospheric oxygen

Abstract: Aerobic, site-selective C(sp3)–H oxygenation using a novel N-oxyl radical directing activator (chemically reactive directing group) is described.

Cited by 41 publications

References 54 publications

Enhanced Structural Variety of Nonplanar <i>N</i>-Oxyl Radical Catalysts and Their Application to the Aerobic Oxidation of Benzylic C–H Bonds

Enhanced Structural Variety of Nonplanar <i>N</i>-Oxyl Radical Catalysts and Their Application to the Aerobic Oxidation of Benzylic C–H Bonds

Green Oxidative

Organic Molecular Catalysts in Radical Chemistry: Challenges Toward Selective Transformations

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