a,b
a Reaction conditions: Carbon rod anode (Ø = 6 mm), carbon rod cathode (Ø = 6 mm), constant current = 10 mA, undivided cell, 1 (0.5 mmol), 2 (0.8 mmol), S (0.6 mmol), TBAI (0.5 mmol), MeCN (4 mL), H2O (2 mL), room temperature, N2, 12 h. b Isolated yield.
As mentioned above, many examples of the synthesis of thiosulfonates and selenosulfonates are presented in the literature, but the methods to synthesize sulfonotelluroates remains a challenge. Our proposed electrocatalytic three-component reaction could be extended to the synthesis of sulfonotelluroates using elemental tellurium as the tellurium source (Scheme 6). Under the modified conditions,[12] sulfonotelluroate 5aa was obtained in 76% yield by the reaction of indole 1a , sodiump -toluenesulfinate 2a , and elemental tellurium. Moreover, the electronic characteristics and positional variations of substituents on the phenyl ring of indoles have no effect on the product yield. Further, an array of structurally diverse indoles can successfully participate in this cascade cross-coupling. Further, various functional groups such as Me, OMe, and NO2 can be well-suited for this transformation (5ab5af ). Interestingly, benzothiophen also gave the corresponding product (5ag ) in 47% yield, and N-ethyl-indole gave the desired product (5ah ) in 62% yield. Further, in this method, cyclopropyl or 4-chlorophenyl-substituted sodium sulfinates could be used as coupling partners, resulting in the efficient for-mation of corresponding sulfonotelluroates (5ai and 5aj ).
Scheme 6 Synthesis of sulfonotelluroates