A. 1-[(Z)-4-Chloro-2-butenyl]-1-azonia-3,5,7-triazatricyclo[3.3.1.1^3,7]decane chloride (2). A 1-L, single-necked, round-bottomed flask is charged with 34.4 g (246 mmol) of hexamethylenetetramine and 500 mL of chloroform (CHCl₃) (Note 1). cis-1,4-Dichlorobut-2-ene (30.2 g, 242 mmol) is added, the flask is fitted with a reflux condenser (Note 2), and the mixture is heated to reflux with a heating mantle. After 4 hr, the mixture is cooled to room temperature, and filtered through a sintered glass funnel (10–20 μ porosity). The resulting white solid, quaternary salt 2, is washed with two 100-mL portions of CHCl₃, and the filtrate is heated to reflux for an additional 18 hr, cooled, and filtered. The resulting light brown solid 2 is washed twice with 50-mL portions of CHCl₃. The combined solids are dried in a desiccator under reduced pressure (1 mm) to afford 58.6 g (91%) of 2 (Note 3).

B. (Z)-4-Chloro-2-butenylammonium chloride (3). A 1-L, single-necked, round-bottomed flask, equipped for magnetic stirring, is charged with 400 mL of 95% ethanol (EtOH) and 70 mL of concd hydrochloric acid (HCl) is slowly added (slightly exothermic reaction). To the still warm solution is added solid 2 (58.5 g, 221 mmol) in one portion. The reaction initially becomes homogeneous and slightly orange colored, then after 45 min a precipitate begins to form. The reaction mixture is allowed to stir at room temperature for 18 hr, cooled to 0°C, and the precipitate (NH₄Cl) is collected by filtration using a 10–20 μ porosity sintered glass funnel. The collected solid is washed on the funnel twice with 100 mL of cold 95% EtOH. The filtrate is concentrated by rotary evaporation, and the remaining semisolid is taken up in 40 mL of cold 95% EtOH. The resulting precipitate (NH₄Cl) is again collected on the filter and washed with cold 95% EtOH (2 × 20 mL). This procedure (rotary evaporation, solution in 95% EtOH, cooling, filtration) is repeated once more.

The solid remaining upon concentration of the filtrate from the final filtration is dissolved in 80 mL of warm ethyl acetate (EtOAc). Upon cooling, the product crystallizes. Hexane is added (30 mL) and the crystals are collected on a 10–20 μ porosity sintered-glass funnel. The solid is washed with 60 mL of hexane. The filtrate is concentrated by rotary evaporation to give an additional amount of solid that is recrystallized from a minimum amount of EtOAc and hexane as before. The combined solids are dried in a desiccator under reduced pressure (1 mm) for 2 hr to give 28.1–30.4 g (90–96%) of 3 as a light yellow crystalline solid (Note 4).

C. 3-Pyrroline (4). A 200-mL round-bottomed flask, equipped with a reflux condenser, is charged with 66.4 g (437 mmol) of 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU) which is cooled to 0°C in an ice bath while 3 (30.3 g, 213 mmol) is added in portions through the top of the condenser. Toward the end of the addition, the resulting slurry becomes orange, gas is evolved, and mixture begins to reflux (the reaction is exothermic). Any remaining salt 3 is added, and, when boiling subsides, a short-path distillation head wrapped in glass wool is put in place (Note 5). A 50-mL receiving flask is totally immersed in a −78°C bath (dry ice-isopropyl alcohol). The orange solid mixture is heated using a heating mantle during which time the solid liquifies and 3-pyrroline (4) distills at 85–92°C at atmospheric pressure. ( CAUTION: some foaming occurs initially, but subsides during the reaction). Heating is continued until no more 3-pyrroline distills, affording 11.05 g (75%) of 3-pyrroline as a clear oil (Note 6), (Note 7).