Benzothiazolium salts as reagents for the deoxygenative perfluoroalkylthiolation of alcohols

Abstract

A series of 2-(perfluoroalkylthio)benzothiazolium (BT-SRF) salts have been synthesized that serve as convenient sources of hitherto underexplored perfluoroalkylthiolate anions. An investigation of their reactivity in a deoxygenative nucleophilic substitution reaction led to the development of an unprecedented process that provides pentafluoroethyl and heptafluoropropyl thioethers directly from readily available alcohols.

Recent trends in dehydroxylative trifluoro-methylation, -methoxylation, -methylthiolation, and -methylselenylation of alcohols

“…As for the mechanism, the authors speculated that the reaction most likely proceeds through the formation of key electrophilic 2-alkoxybenzothiazolium species A via nucleophilic attack of the alcohol 30 in the presence of NEt( i Pr) 2 at the C2-position of the BT-SCF 3 reagent 29 and subsequent nucleophilic substitution reaction with in situ generated -SCF 3 anion (Scheme 18). Guided by the same principle, a similar dehydroxylative functionalization strategy was applied by the same research group towards the synthesis of various peruoroalkyl thioethers 32 and thioesters. 33 In a recent report, Wu, Xiao, and colleagues accomplished the direct conversion of alcohols 32 into the corresponding triuoromethyl thioethers 33 using AgSCF 3 as a source of F 3 CS group and the Ph 3 P/ICH 2 CH 2 I/n-Bu 4 NI combination as an activation system in a 2 : 1 mixture of DMF and MeCN.…”

“…As for the mechanism, the authors speculated that the reaction most likely proceeds through the formation of key electrophilic 2-alkoxybenzothiazolium species A via nucleophilic attack of the alcohol 30 in the presence of NEt( i Pr) 2 at the C2-position of the BT-SCF 3 reagent 29 and subsequent nucleophilic substitution reaction with in situ generated –SCF 3 anion ( Scheme 18 ). Guided by the same principle, a similar dehydroxylative functionalization strategy was applied by the same research group towards the synthesis of various perfluoroalkyl thioethers 32 and thioesters. 33 …”

Electrophilic Reagents for the Direct Incorporation of Uncommon SCF2CF2H and SCF2CF3 Motifs

“…However, the electrophilic reactivity shown is limited to the modification of two examples of activated aromatics (phenol and 1,3-dimethoxybenzene), ethynyl lithium, and Grignard nucleophiles . On the other hand, although mechanistically different to the prototypical N -electrophilic reagents, the in situ-generated – SC 2 F 5 anion from either sulfenamide reagents by Billard or from benzothiazolium reagents by Hopkinson enabled the formal incorporation of the SCF 2 CF 3 motif via nucleophilic substitution of halides, tosylates/mesylates, or alcohols, respectively. Concerning the other potentially valuable SCF 2 CF 2 H fragment, and although recent efforts have been undertaken toward the development of tetrafluoroethylation protocols, , direct transfer of tetrafluoroethylthioether units still remains uncharted …”

Shelf-stable electrophilic reagents for the direct incorporation of SCF2CF2H and SCF2CF3 motifs

“…However, the electrophilic reactivity shown is limited to the modification of two examples of activated aromatics (phenol and 1,3-dimethoxybenzene), ethynyl lithium, and Grignard nucleophiles. 18 On the other hand, although mechanistically different to the prototypical N-electrophilic reagents, the in situ generated -SC2F5 anion from either sulfenamide reagents by Billard 19 or from benzothiazolium reagents by Hopkinson 20 enabled the formal incorporation of the SCF2CF3 motif via nucleophilic substitution of halides, tosylates/mesylates, or alcohols, respectively. Concerning the other potentially valuable SCF2CF2H fragment, and although recent efforts have been undertaken towards the development of tetrafluoroethylation protocols, 21,22 direct transfer of tetrafluoroethylthioether units still remains uncharted.…”