Nickel Catalysis Enables Hetero [2+2+1] Cycloaddition Between Yne‐Isothiocyanates and Isonitriles with Low Catalyst Loading

Nickel(II) can be used to catalyze the hetero [2+2+1] cycloaddition of 2-alkynylaryl iso-thiocyanates and isonitriles in 2-methyltetrahydrofuran (2-MeTHF) to give a wide array of thieno[2,3-b]indoles in excellent yields. The reaction is featured by employing as little as 0.3 mol% nickel(II) acetylacetonate [Ni(acac) 2] under air conditions in the absence of any additives (additional reducing agents and external ligands). This is the first successful example to apply nickel(II) directly in hetero [2+2+1] cycloadditions.