Oxygen Atom Transfer in the Oxidation of Dimethyl Sulfoxide by Oxoammonium Cations

Abstract

Cyclic oxoammonium salts and DMSO are known as important reagents for their diverse and unique reactivity. In the present work, we have studied the reaction of six-and fivemembered oxoammonium salts with DMSO. The reaction includes ∼100% selective transfer of the O atom from the >N + O group to the S atom of DMSO and structural rearrangement of the remaining cationic framework, leading to the formation of hydrolytically unstable iminium salts. The logarithms of the bimolecular rate constants k of the reaction correlated linearly with the reduction potentials E >N + O/>NO • , a relationship known for other electrophile−nucleophile combinations. The kinetic data and results of the DFT calculations allow for the suggestion that the studied process proceeds via the prereactive charge-transfer complex >N + O•••S (O)Me 2 and its direct concerted rearrangement to the iminium salts. An alternative mechanism that includes intermediate steps with discrete nitrenium cations can be ruled out on the basis of product analysis and DFT computations. The obtained results allow a deeper understanding of the redox chemistry of a pair of nitroxide radicals-oxoammonium cations.

Chemoselective Oxidation of Thiols with Oxoammonium Cations

“…1 H NMR (400 MHz, CD 3 CN): δ 6.32 (bs, 1H exchanges) 4.55–4.44 (m, 1H), 4.29–4.24 (m, 1H), 3.76 (dd, J = 13.6, 8.4 Hz, 1H), 2.56 (s, 3H), 2.36 (s, 3H), 2.37–2.35 (m, 1H), 2.16 (dd, J = 13.3, 10.1 Hz, 1H), 1.90 (s, 3H), 1.69 (s, 3H), 1.58 (s, 3H); 13 C­{ 1 H} NMR (101 MHz, DMSO- d 6 ): δ 187.7, 169.7, 71.2, 59.8, 46.4, 44.5, 27.9, 26.8, 25.4, 25.0, 22.4. Note: the spectral data is consistent with that reported for the perchlorate salt that can be found in ref .…”

“…Sulfenic acids such as 67 are effective electrophiles and will react with a second equivalent of the nucleophilic thiophenol 23 or thiolate 23a as shown in Scheme with loss of water or hydroxide to afford the desired disulfide product 24 . ,,, Disulfide formation via sulfenic acids is particularly facile, and the lifetime of sulfenic acid intermediates in biological systems is often dependent on their proximity to adjacent thiols, which rapidly form disulfide linkages by loss of water . A second minor avenue for consumption of 67 can occur through self-condensation with loss of water or hydroxide to afford thiosulfinate 70 (Scheme , path I). ,,, In a process similar to the reaction of oxoammonium cations with DMSO, 70 in the presence of a second equivalent of 1 should afford 71 , leading to the production of iminium salt 56 and thiosulfonate 25 (Scheme , path I). Experimentally, 56 is observed in small amounts (<10% of the mixture) in the crude 1 H and 13 C NMR spectra of reactions run in MeCN solvent.…”

“…1 H NMR (400 MHz, D 2 O): δ 4.59–4.50 (m, 1H), 4.44 (dd, J = 14.0, 7.6 Hz, 1H), 3.86 (dd, J = 12.8, 9.0 Hz, 1H), 2.66 (s, 3H), 2.44 (s, 3H), 2.5–2.35 (m, 1H), 2.22 (m, J = 12.6, 10.0 Hz, 1H), 2.00 (s, 3H), 1.73 (s, 3H), 1.62 (s, 3H); HRMS (ESI-ICR) m/z calcd for C 11 H 21 N 2 O [M–BF 4 ] + : 197.1648, found: 197.1648. Note: the spectral data is consistent with that reported for the perchlorate salt that can be found in ref .…”

The Utility of Oxoammonium Species in Organic Synthesis: Beyond Alcohol Oxidation

“…In 2021, Sen' et al reported an oxygen atom transfer reaction from oxoammonium species to dimethyl sulfoxide (Scheme 32c). 199 Scheme 32. Oxidative transformation of organosulfur compounds using oxoammonium species 3-7-2.…”

Reactions of sulfoxides with reactive oxygen species to reveal the radical chemistry of pollution-derived particulate matter

“…The structural similarities of the lactam derivatives 6 and 7 with 9 relating to methyl group migration prompted further investigation. We found that treatment of 9 with peroxyl radicals (ROO ) produced appreciable amounts of products 6 and 7 by LC-MS. Based on recent seminal work from Luzhkov, 18 we propose the following mechanism for the formation of iminium ion 9 (Scheme 2). Oxidation of nitroxide 1 to oxoammonium ion 8 promotes an oxygen atom transfer reaction with DMSO causing N-O bond cleavage and methyl migration to iminium ion 9.…”