a Reaction conditions: Carbon rod anode (Ø = 6 mm), carbon rod cathode (Ø = 6 mm), constant current = 10 mA, undivided cell, 1a (0.5 mmol), 2a (0.8 mmol), Se (0.6 mmol), TBAI (0.5 mmol), MeCN (4 mL), H2O (2 mL), room temperature, N2, 12 h, n.d. = not detected.b Isolated yield.
After the optimal reaction conditions were identified, the scope of indoles was investigated. An array of structurally diverse indoles participated in this transformation. Indoles with electron-donating groups at the phenyl ring, including 5-methoxy (3ab ), 3-, 6-, and 7-methyl-substituted indoles, proceeded smoothly to give selenosulfonates (3ac3ae ) with good to high yields (62%—86%). Notably, 6-benzyloxy substituted indole was successfully applied in the reaction (3af ). Moreover, indoles bearing electron-withdrawing groups on the phenyl ring gave good product yields (3ag3ai ). Further, the 3-methyl-substituted indole reacted to give product (3aj ) in 60% yield. Interestingly, N-methyl-indole (3ak ), dihydroquinoline (3al ), and N-phenyl-indole (3am ) were viable substrates. Moreover, benzothiophene was well-tolerated in this transformation (3an ), indicating the wide range of applicability of the method. In addition, the electrochemical protocols accommodated indole precursors with motifs, such as gemfibrozil, ibuprofen, and dicamba, giving the corresponding selenosulfonates (3ao3aq ) in good yields. These results highlight the potential practical applications of this method for the late-stage modification of pharmaceutical-related molecules.
Scheme 3 Scope of indolesa,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), 2a (0.8 mmol), Se (0.6 mmol), TBAI (0.5 mmol), MeCN (4 mL), H2O (2 mL), room temperature, N2, 12 h. b Isolated yield.
Next, we examined the generality of this electrocatalytic three-component reaction with respect to a range of sulfinic acid sodium salts 2 (Scheme 4). Halogen functionalities, F and Cl, remain intact after reaction (3ba and 3bc ), thereby offering easy handles for controlled installation of other peripheral functional groups at the halogenated positions. The application of benzenesulfinic acid sodium salt gave the desired products in 87% yield (3bd ). Notably, sulfinic acid sodium salts bearing fused rings and heteroaryl moieties were also employed in this reaction and gave products (3be and 3bf ) with satisfactory yields. Notably, the alkyl-substituted sulfinic acid sodium salt was well incorporated and the corresponding product (3bg ) was obtained in 63% yield.
Scheme 4 Scope of sulfinic acid sodium salts