Dimethyl Sulfide → 5-(Methylsulfanyl)-2,3-dihydro-1H-pyrrolizine-1-carbonitrile

A solution of 1.15 g N-chlorosuccinimide in 40 ml of dry dichloromethane was cooled, in an atmosphere of nitrogen, to -10° C. (bath temp.) and a solution of 1 ml dimethylsulfide in 10 ml of anhydrous dichloromethane was added dropwise with stirring over a 10 min. period. After a further 10 min. at this temperature, the bath temperature was lowered to -55° C. and a solution of 1.08 g of 1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carbonitrile (I) in 10 ml of dry dichloromethane was added with stirring over a 10 min. period. The cooling bath was then removed and when the internal temperature had reached ambient the solvent was removed in vacuo. The residual solid sulfonium salt (II) was suspended in toluene (100 ml) and heated at reflux temperature in a nitrogen atmosphere for 5 min. The solvent was decanted from an insoluble tar, 100 ml of toluene was added to the tar and the mixture was heated at reflux temperature for 20 min. The toluene solutions were combined and evaporated. The residue was taken up in ether, the ether solution was washed with water, dried over sodium sulfate and evaporated in vacuo to give an oil which was passed through a short column of silica gel with dichloromethane. The nearly colorless oil obtained on evaporation of the solvent (1.20 g) was sufficiently pure for use in the next reaction. For analysis a sample was purified by HPLC (lichrosorb column, 50 cm×3/8 in.) using hexane-ethyl acetate (85:15) as the eluting solvent at 1100 p.s.i.g. and a flow rate of 9.7 ml/min. The sulfide (III) had a retention time of 13.5 min. On evaporation of the solvent it crystallized and then it was recrystallized from ether-hexane. m.p.: 58°-58.5° C.