4,4-Azobis(4-cyanovaleric acid) → 4-Cyano-4-[(phenylcarbonothioyl)thio]pentanoic Acid

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The synthesis scheme for (thiophen-3-yl)ethyl-4-cyano-4-(phenylcarbonothioylthio)pentanoate is shown in FIG. 15 and is performed as follows. First, the intermediary molecule, 4-Cyano-4-((thiobenzoyl)sulfanyl)pentanoic acid is synthesized by dissolving 4,4′-Azobis(4-cyanovaleric acid) (4.19 g, 0.0149 mol) and bis(thiobenzoyl)disulfide (3.07 g, 0.01 mol) in ethyl acetate (200 mL) in a 500 mL round-bottom flask equipped with a condenser. The mixture is degassed by bubbling with nitrogen and heated to reflux for 20 hours under nitrogen. The reaction is allowed to cool to room temperature, and the solvent is removed in vacuum. The crude product is purified by column chromatography (silica gel) using ethyl acetate:hexanes 2:3 as the eluent. After removal of solvent, the red fraction gives 4-cyano-4-((thiobenzoyl)sulfanyl)-pentanoic acid as a red oil. The product is solidified upon sitting at −20° C. 1H NMR (CDCl3) δ (ppm): 1.93 (s, 3H, CH3); 2.38-2.80 (m, 4H, CH2CH2); 7.42 (m, 2H, m-ArH); 7.56 (t, 1H, J=8 Hz p-ArH); 7.91 (d, 2H, J=7.3 Hz, o-ArH). 13C NMR (CDCl3) δ (ppm): 24.1, 29.5, 32.9, 45.6, 118.4, 126.7, 128.6, 133.1, 144.4, 177.3, 222.1.

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