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 (3ac —3ae ) 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
(3ag —3ai ). 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 (3ao —3aq ) 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