Water → 3-Chloro-8-trifluoromethanesulfonyloxy-naphthalene-2-carboxylic acid ethyl ester

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Reaction Steps

Trifluoromethanesulfonic anhydride (2.46 g, 8.73 mmol, 1.2 equiv) was added at −20° C. under an atmosphere of argon to a solution of 3-chloro-8-hydroxy-naphthalene-2-carboxylic acid ethyl ester (1.82 g, 7.28 mmol) in pyridine (55 ml). After 1 hour at 0° C., an additional portion of trifluoromethanesulfonic anhydride (2.46 g, 8.73 mmol, 1.2 equiv) was added, and stirring was continued at 0° C. for another 1.5 hours. Cold water (4° C., 100 ml) was carefully added, and the reaction mixture was extracted with EtOAc (1 liter in total). The combined organic layers were washed with concentrated aqueous NH4Cl solution and brine, dried over Na2SO4, filtered and concentrated in vacuo. Purification via flash chromatography (slow gradient of hexane/EtOAc 100:0 to 90:10) afforded the title compound (2.45 g, 88%, inseparable 1:1.3 mixture of regioisomers A:B) as an oil. 1H NMR (400 MHz, CDCl3): δ=8.56 (s, 1H isomer B), 8.40 (s, 1H isomer A), 8.12 (s, 1H isomer A), 8.01 (s, 1H isomer B), 7.93-7.91 (m, 1H isomer A), 7.81 (d, J=8.6 Hz, 1H isomer B), 7.62-7.51 (m, 2H isomer A+2H isomer B), 4.47 (q, J=7.1 Hz, 2H isomer A+2H isomer B), 1.45 (t, J=7.1 Hz, 3H isomer A+3H isomer B). 19F NMR (377 MHz, CDCl3): δ=−73.02. MS (ES+): 383 (M+H)+.

Provenance & Evidence