A. 1-Pyrrolidinocyclohexene.⁴ A solution of 29.4 g. (0.300 mole) of cyclohexanone and 28.4 g. (0.394 mole) of pyrrolidine in 150 ml. of benzene is placed in a 500-ml., one-necked flask attached to a Dean-Stark trap. The solution is refluxed under a nitrogen atmosphere until the separation of water ceases (Note 1). The excess pyrrolidine and benzene are removed from the reaction mixture on a rotary evaporator. The resulting residue is stored under refrigeration and distilled just before use in the next step, yielding 44.6 g. (98%) of 1-pyrrolidinocyclohexene, b.p. 76–77° (0.5 mm.), 105–106° (13 mm.).

B. 2,2-(Trimethylenedithio)cyclohexanone. A solution of 3.02 g. (0.0200 mole) of freshly distilled 1-pyrrolidinocyclohexene, 8.32 g. (0.0200 mole) of trimethylene dithiotosylate⁴ (Note 2), and 5 ml. of triethylamine (Note 3) in 40 ml. of anhydrous acetonitrile (Note 4), is refluxed for 12 hours in a 100-ml., round-bottom flask under a nitrogen atmosphere. The solvent is removed with a rotary evaporator, and the residue is treated with 100 ml. of 0.1 N hydrochloric acid for 30 minutes at 50° (Note 5). The mixture is cooled to ambient temperature and extracted with three 50-ml. portions of diethyl ether. The combined ether extracts are washed with 10% aqueous potassium hydrogen carbonate solution (Note 6), until the aqueous layer remains basic to litmus, and with saturated sodium chloride solution. The ethereal solution is dried over anhydrous sodium sulfate, filtered, and concentrated on a rotary evaporator. The resulting oily residue is diluted with 1 ml. of benzene then with 3 ml. of cyclohexane. The solution is poured into a chromatographic column (13 × 2.5 cm.), prepared with 50 g. of alumina (Note 7) and 3:1 cyclohexane–benzene. With this solvent system, the desired product moves with the solvent front; the first 250 ml. of eluent contains 95% of the total product. Elution with an additional 175 ml. of solvent removes the remainder. The combined fractions are evaporated, and the pale-yellow, oily residue crystallizes readily on standing. Recrystallization of this material from pentane gives 1.82 g. (45% yield) of white, crystalline 2,2-(trimethylenedithio)cyclohexanone, m.p. 52–55° (Note 8).