Quantum Chemical Characterization of Factors Affecting the Neutral and Radical-Cation Newman–Kwart Reactions

Abstract

Details of the electronic and geometric structures of stationary points along the reaction coordinate of the Newman Kwart rearrangement, which transforms an O-arylthiocarbamate to an S-arylcarbamothioate, are examined using quantum chemical methods for a large number of compounds considering both the thermal reactions of uncharged substrates as well as the corresponding reactions of radical cation substrates generated under photoredox conditions. The uncharged mechanism, which has intrinsically high 298 K free energies of activation (in excess of 30 kcal.mol-1), has the character of nucleophilic aromatic substitution and is thus accelerated by electron-withdrawing substituents on the aromatic ring. The radical cationic mechanism, by contrast, has 298 K free energies of activation that are typically below 20 kcal.mol-1, and is accelerated by electron donating substituents on the aromatic ring, which stabilize the hole character that is transferred to this fragment from the thiocarbamate fragment as the reaction proceeds. Opportunities to further accelerate the radical cation reaction are revealed by computational assessment of alternative amino groups for the thiocarbamate functionality. File list (5) download file view on ChemRxiv QCC_NK_181208.pdf (0.90 MiB) download file view on ChemRxiv QCC_NK_181208.docx (1.88 MiB) download file view on ChemRxiv QCC_NK_SI_181208.docx (192.73 KiB) download file view on ChemRxiv QCC_NK_SI_181208.pdf (412.48 KiB) download file view on ChemRxiv Geometries.xyz (479.10 KiB)

Concerted Nucleophilic Aromatic Substitution Reactions

“…More recently, a radical cation version of the Newman–Kwart rearrangement has been discovered that proceeds under mild conditions and that has quite a different response to substituents than in the thermal rearrangement. Cramer has reported recent studies that provide further computational characterisation of the thermal Newman–Kwart rearrangement as well as its radical cation counterpart; the radical cation variant is also viewed as being a concerted substitution reaction …”

“…On ar elated theme,S anford et al reported am ild deoxyfluorination of phenols 97 via aryl fluorosulfonate intermediates 98. [57] This transformation was found to be compatible with ortho-, meta-, or para-electron-withdrawing groups,a nd could also be applied to electron-neutral and moderately electron-rich substrates to provide fluorinated products [100][101][102][103][104][105][106][107][108][109][110][111].…”

“…Cramer has reported recent studies that provide further computational characterisation of the thermal Newman-Kwart rearrangement as well as its radical cation counterpart;the radical cation variant is also viewed as being aconcerted substitution reaction. [101][102][103]…”

“…Cramer has reported recent studies that provide further computational characterisation of the thermal Newman-Kwart rearrangement as well as its radical cation counterpart;the radical cation variant is also viewed as being aconcerted substitution reaction. [101][102][103] 9. Sulfur Nucleophiles Sulfur nucleophiles have also featured prominently in the recent literature.T obisu, Chatani, et al have just reported [104] an unusual outcome to reaction of 2,2'-bis(methythio)-1,1'biaryls 290 (Scheme 40) with catalytic amounts of methanethiolate salts in dimethylformamide (DMF) as solvent.…”

Konzertierte nukleophile aromatische Substitutionen

“…Ausd en Ergebnissen wurde geschlossen, dass auch die radikal-kationische Version eine konzertierte Substitutionsreaktion darstellt. [101][102][103]…”