Transition-Metal- and Halogen-Free Oxidation of Benzylic sp3 C–H Bonds to Carbonyl Groups Using Potassium Persulfate

Abstract

Aryl carbonyl compounds including acetophenones, benzophenones, imides, and benzoic acids are prepared from benzyl substrates using potassium persulfate as oxidant with catalytic pyridine in acetonitrile under mild conditions. Neither transition metals nor halogens are involved in the reactions.

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

“…Benzylamines and derivatives thereof have been described in literature to be susceptible to oxidation by diverse reagents (tritylium ion [40], silver [38] and cerium salts [41], peroxides [42][43][44] and persulfates Scheme 2: Overview of published cyclization methodologies for the synthesis of fluorenones starting from functionalized biaryls. [45], nitroxyls [46], hypervalent iodine compounds [39,47], or tetrahalomethanes [48]) to give imines, iminium salts, aldehydes and other, in some cases dimeric products [49]. Here, oxidation of the benzylic amino moiety should lead either to iminium ions (or N-acyl iminium ions) 4a as strong electrophiles or to stabilized radicals 4b which could undergo cyclization to give the fluorenone backbone.…”

“…This prompted us to perform a systematic investigation of the potential of oxidative cyclizations of aminomethylated biaryls 2 and related compounds to fluorenones. Benzylamines and derivatives thereof have been described in literature to be susceptible to oxidation by diverse reagents (tritylium ion [ 40 ], silver [ 38 ] and cerium salts [ 41 ], peroxides [ 42 – 44 ] and persulfates [ 45 ], nitroxyls [ 46 ], hypervalent iodine compounds [ 39 , 47 ], or tetrahalomethanes [ 48 ]) to give imines, iminium salts, aldehydes and other, in some cases dimeric products [ 49 ]. Here, oxidation of the benzylic amino moiety should lead either to iminium ions (or N -acyl iminium ions) 4a as strong electrophiles or to stabilized radicals 4b which could undergo cyclization to give the fluorenone backbone.…”

An efficient and practical aerobic oxidation of benzylic methylenes by recyclable N-hydroxyimide

“…p -NO 2 , p -CN) on the ring, which are difficult to be synthesized through Friedel–Crafts acylation. A range of oxidants were used in methylene oxidations, 2 of which oxygen is the most “green” one.…”

Radical Propagation Facilitating Aerobic Oxidation of Substituted Aromatics Promoted by Tert‐Butyl Hydroperoxide

“…In order to reduce the induction period and facilitate the radical propagation, numerous metal (Au, Pd, Cu, Co et al) or metal free (g-C 3 N 4 , N-hydroxyphthalimide, carbon materials et al) based catalysts have been developed. [15,17,[20][21][22][23][24][25][26][27][28][29][30][31][32][33] However, these metal or metal-free catalysts are expensive, complexly prepared or harmful to the environment.…”

“…or metal free (g‐C 3 N 4 , N‐hydroxyphthalimide, carbon materials et al.) based catalysts have been developed [15,17,20–33] . However, these metal or metal‐free catalysts are expensive, complexly prepared or harmful to the environment.…”