Cyclopropylmagnesium bromide (0.5 M in THF, 25 mL, 12.5 mmol) was added dropwise to a stirred solution of trimethylborate (1.69 g, 1.81 mL, 16.25 mmol) in tetrahydrofuran (7 mL) under nitrogen protection at -78°C. A white precipitate was observed during the reaction. A white precipitate was observed to form during the reaction. after 1 h, the reaction system was slowly warmed to room temperature and stirring was continued overnight. Upon completion of the reaction, the reaction was quenched with 2.0 N aqueous hydrochloric acid (20 mL) and the mixture was stirred for 1 hr. Subsequently, the reaction mixture was extracted with dichloromethane (15 mL) and the aqueous phase was back-extracted with deionized water (2 x 15 mL). All aqueous phases were combined and extracted with methyl tert-butyl ether (4 x 40 mL). The organic phases were combined, dried with anhydrous magnesium sulfate and concentrated under reduced pressure to give a white solid product. Two recrystallizations were carried out via a solvent mixture of dichloromethane and hexane, resulting in 252-297 mg of white solid product in 27% yield. The product was characterized by NMR hydrogen spectroscopy (250 MHz, CDCl3): δ 0.56-0.50 (2H, m, CH2), 0.42-0.40 (2H, m, CH2), -0.08 to -0.20 (1H, m, CH).
