A THF solution of LDA (1.92 M, 31.5 mL) was slowly added dropwise to a stirred solution of tetrahydro-4H-pyran-4-one (5.5 g) in THF (30 mL) at -70 °C under argon protection. The reaction mixture was continued to be stirred at -70 °C for 30 min. Subsequently, a THF (30 mL) solution of N-phenylbis(trifluoromethanesulfonyl)imide (21.6 g) was added. The reaction system was slowly warmed to room temperature and stirred for 18 hours. Upon completion of the reaction, the solvent was removed by evaporation and the crude product was purified by medium pressure liquid chromatography (MPLC) on alumina (ICN, N32-63) with 5% ethyl acetate/isohexane solvent mixture as eluent. After collection of the target fractions, they were further purified by Kugelrohr distillation (100 °C/10 mmHg). For complete removal of residual trifluoromethanesulfonamide reagent, a second MPLC purification was performed (silica gel, eluent as above), followed by another Kugelrohr distillation to afford 3,6-dihydro-2H-pyran-4-trifluoromethanesulfonate as a colorless oil in a 40% yield (5.1 g), stored at -20 °C. The product was characterized by NMR (300 MHz, CDCl3): δ 2.24 (m, 2H), 3.90 (m, 2H), 4.25 (m, 2H), 5.82 (m, 1H).
