Chemoselective synthesis of δ-lactones via benzyl radical cyclization utilizing K2S2O8–CuCl2

Mechanistic analysis of a copper-catalyzed C–H oxidative cyclization of carboxylic acids

“… 6 These findings coupled with other substrate selectivity data and the absence of detectable products of decarboxylation have led us to speculate that a sulfate radical anion functions as the active oxidant in this reaction. Our conclusion differs from prior literature reports 7 – 11 for related processes, all of which have suggested that intramolecular C–H abstraction by a carboxylate radical initiates the cyclization event. In this study, we have leveraged the power of mass spectrometry to obtain evidence in support of our earlier proposal as well as additional mechanistic insights that reveal the complex nature of this process.…”

“…Reported studies of C–H oxidative lactonization reactions have posited reaction mechanisms that occur by way of carboxylate radical generation and subsequent 1,6-H-atom abstraction. 7 – 10 In order to query if such a carboxylate radical is responsible for formation of 4 and 5 , Barton ester 7 was prepared 33 , 34 and heated for 2 h in BrCCl 3 ( Scheme 3a ). Substrates of this type can fragment under thermal conditions to give transient radical species.…”

Free Radical Triggered Convenient Synthesis of Bis(indolyl)methane with Potassium Peroxodisulfate as Catalyst

“…It is believed that the current reaction proceed via a free radical path in presence of potassium peroxodisulfate, which is known as free radical initiator. [27,29] To prove the possible involvement of free radical path, 2 equivalent (1 mmol) of TEMPO (2, 2, 6, 6-tetramethylpiperidine-N-oxyl) was used as the radical-trapping agent under the standard reaction conditions and we observed that there was suppression of the formation of our desired product. This indicates that the reaction proceeds through the radical mechanism.…”

Peroxydisulfate‐Mediated Transition‐Metal‐Free Oxidative C(sp3)−H Bond Lactonization

“…For instance, Nikishin et al . and Mahmoodi et al . reported the copper‐mediated transformation of linear alkanoic acids to lactones using peroxydisulfate.…”