New synthesis of 3-aroylcyclopropane-1,1,2,2-tetracarbonitriles

Abstract

Many 1,1,2,2-tetracyanocyclopropanes were successfully prepared by Wideqvist reaction. The process consists in treating carbonyl compounds with monobromomalonodinitrile in ethanol or water at room temperature for 0.5–12 h in the presence of potassium iodide as reductant [1, 2]. We developed a new synthesis method for 3-aroylcyclopropane-1,1,2,2-tetracarbonitriles IIa–IIc based on Wideqvist reaction but without potassium iodide. The latter was excluded from the reaction to avoid side processes since the cyclopropanes containing five and six electron-withdrawing substituents were known to actively react with iodides [3–6]. Our synthesis of 3-aroylcyclopropane-1,1,2,2tetracarbonitriles involves a treatment of substituted phenylglyoxal monohydrates in 2-propanol solution with an excess of monobromomalonodinitrile which simultaneously acts as a reductant converting into dibromomalonodinitrile. We assume the following reaction scheme: The formed dicyanomethylene derivatives of phenylglyoxal A react with the second monobromomalonodinitrile molecule leading to compounds IIa–IIc. Compounds analogous to cyclopropanes IIa–IIc were formerly obtained by the reaction of ω-chlorinated acetophenones with tetracyanoethylene in dioxane medium [7]. Hence the method we developed is a new procedure for preparation of 3-aroylcyclopropane1,1,2,2-tetracarbonitriles. The structure of synthesized cyclopropanes IIa–IIc was confirmed by IR, 1H NMR, and mass spectra. 3-Benzoylcyclopropane-1,1,2,2-tetracarbonitrile (IIa). To a solution of 1.52 g (0.01 mol) of phenylglyoxal monohydrate (Ia) in 20 ml of 2-propanol was added at stirring in one portion 4.35 g (0.03 mol) of monobromomalonodinitrile. The mixture was stirred for 15 min, the separated precipitate was filtered off and washed in succession with small portions of 2-propanol and water. Yield 1.96 g (80%), mp 211–212°C (decomp.). IR spectrum ν, cm–1: 1692.31 (C=O), 2264.03 (C≡N), 3033.24 (CH). 1H NMR spectrum (DMSO-d6), δ, ppm: 8.25 d, 7.8 t, 7.6 t (5H, C6H5), 5.65 s (1H, CH of cyclopropane). Mass spectrum, m/z (Irel, %): 246 (15) [M]+, 105 (100) [M – 141]+, 77 (60), 51 (40), 38 (10). Compounds IIb and IIc were prepared similarly. Ar