Copper(I) 2-Thiophenecarboxylate

Preparation of Iodomesitylene Dicarboxylates: Iodomesitylene diacetate (10 mmol), cyclohexyl carboxylic acid (20.5 mmol), and toluene (200 mL) are placed in flask. The solvent is removed by a rotary evaporator at 55 °C. This step is repeated with toluene (100 mL) as needed. The residue is concentrated in vacuo, to provide iodomesitylene dicarboxylates that can be directly used in the decarboxylative sp³ C–N coupling reactions without further purification. sp³ C–N Coupling Reaction: Ir(F-Meppy)₂(dtbbpy)PF₆ (4.9 mg, 5.0 µmol), copper(I) 2-Thiophenecarboxylate (19 mg, 0.10 mmol), bathophenanthroline (50 mg, 0.15 mmol), 2-tert-butyl-1,1,3,3-tetramethylguanidine (0.21 mL, 171 mg, 1.0 mmol), 3-chloro-1H-indazole (76 mg, 0.50 mmol), iodomesitylene dicyclohexanecarboxylate (500 mg, 1.0 mmol), and 1,4-dioxane(12 mL) is placed in vial. The solution is sonicated until it becomes homogeneous and is then degassed with nitrogen. The reaction is stirred and irradiated using two 34-W blue LED lamps for 1 h. After the reaction has completed, the reaction mixture is diluted with water and EtOAc. The aqueous layer is extracted with EtOAc. The combined organic layers are washed with brine, dried over Na₂SO₄, filtered and concentrated in vacuo. The residue is purified by flash chromatography (30:1 hexane/EtOAc) on silica gel to afford the title compound (99 mg, 84% yield, >20:1 r.r.) as a colorless oil.

Typical Procedure:
Alkyne (0.2 mmol), TsN₃ (1.0 eq.), alkenyl alkyl ether (3.0 eq.), CuTC (10.0 mol%), Rh₂(OAc)₄ (1.0 mol%), and DCE (0.2 M) are added to an oven-dried test tube under nitrogen atmosphere. The reaction mixture is stirred at ambient temperature for 3 h and then, heated at 80 °C for 4–13 h. After the reaction mixture is filtered through short path of celite with CH₂Cl₂, the filtrate is concentrated under reduced pressure. The residue is purified by silica gel column chromatography (ethyl acetate–hexane) to give pyrrole derivatives (Y. 65–81%).