Potassium tert-Butoxide Mediated Arylation of 2-Substituted Malononitriles Using Diaryliodonium Salts

Abstract

Direct arylation of 2-substituted malononitriles using diaryliodonium salts without involving transition-metal catalysts was developed. By using potassium tert-butoxide as a promoter, the desired 2-substituated α-arylmalononitriles derivatives were synthesized in good to excellent yields of 55–96%. This synthetic method provided an efficient way to prepare a variety of 2-substituted arylmalononitriles which were useful in agrochemicals.

Key words

arylation - diaryliodonium salts - metal-free - arylmalononitriles - agrochemicals

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• 11 General Procedure for the Synthesis of 3 and 4 An oven-dried Schlenk tube was charged with 2-substituted malononitriles (0.5 mmol, 1 equiv), the tube was evacuated and charged with nitrogen, then 2 mL anhydrous DCM and t-BuOK (61.7 mg, 0.55 mmol, 1.1 equiv) were added, and the mixture was stirred at 0 °C for 5 min. The solution of diaryliodonium salts (0.55 mmol, 1.1 equiv) in 2 mL anhydrous DCM was added through a syringe subsequently for 5 min. The reaction was stirred for another 1 h, and the reaction temperature was elevated to r.t. The reaction mixture was quenched with 20 mL water, then the mixture was extracted with EtOAc (3 × 10 mL). The combined extracts were washed with brine, dried over Na₂SO₄, and filtered. After the solvent was removed under vacuum, and the residue was purified by flash chromatography to give the desired product. Analytical data for representative sample 3a is provided below. 2-Ethyl-2-phenylmalononitrile (3a) 81.7 mg (96% yield), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.58–7.53 (m, 2 H), 7.52–7.45 (m, 3 H), 2.29 (q, J = 7.4 Hz, 2 H), 1.23 (t, J = 7.4 Hz, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 132.0, 129.9, 129.7, 125.8, 115.0, 43.2, 36.6, 10.0. HRMS (EI): m/z calcd for C₁₁H₁₀N₂ [M]⁺: 170.0844; found: 170.0843.