3-Bromo-2-chloropropene (1.4 mL, 13 mmol, 1.1 eq.) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU; 1.8 mL, 12 mmol, 1.0 eq.) were sequentially added to dichloromethane. A solution of 2-hydroxyisoindoline-1,3-dione (N-hydroxyphthalimide; 2.0 g, 12 mmol, 1.0 eq.) in NN-dimethylformamide (DMF; 30 mL) was stirred at 23 0 C. The resulting solution was changed from yellow to dark red to colorless in about 5 min, and it was stirred at 230 C for 18 h. The reaction mixture was diluted with 1 M aqueous hydrochloric acid (HCl; 300 mL). The white precipitate obtained was vacuum filtered and washed with water to give a white powder (2.3 g) which was dissolved in CH2Cl2 (53 mL). Hydrazine hydrate (570μL, 12 mmol, 1.1 eq.) was added and the white suspension obtained was stirred at 230 C for 18 h. The reaction mixture was vacuum filtered. The filtrate was diluted with 0.1 M NaOH aqueous solution (200 mL) and extracted with CH2Cl2 (3× 50 mL). The combined organic layers were dried over Na2SO4, gravity filtered, and concentrated by rotary evaporation to afford white semi-solid trans-3-chloro-2-propenylhydroxylamine.
