Trisodium citrate → 4-[2-(pyrrolidin-N-yl)ethoxy]-6-methoxy-3,4-dihydronaphthalene

Participants

Reaction Steps

A solution of 3.09 g (17.5 mmol) 6-methoxy-1-tetralone in 3 mL of THF was cooled to −10° C. and sequentially treated with 5.17 g (19.3 mmol) diphenyl chlorophosphate and 18.3 mL (19.3 mmol) 1.05 M 2-mesitylmagnesium bromide in THF. The temperature during addition of this Grignard reagent was kept below 10° C. (The initially resulting slurry became homogeneous after ca one-fourth of the Grignard had been added). The resulting solution of 6-methoxy-3,4-dihydronaphth-1-yl diphenyl phosphate was then warmed to room temperature and 0.074 g (0.105 mmol; 0.6 mol%) dichlorobis(triphenylphosphine)palladium was added as a solid. The mixture was then heated to reflux, and a solution of 19.3 mmol 4-(2-pyrrolidin-N-yl)ethoxyphenylmagnesium bromide, 1.30 M THF (prepared from 0.512 g (21.1 mmol) of Mg and 5.21 g of the corresponding aryl bromide), was added dropwise over 20 minutes. After the addition was complete, the reaction mixture was stirred at reflux for an additional 30 min and then cooled to room temperature. The reaction mixture was then poured into a mixture of 35 mL each of MTBE (methyl t-butyl ether) and aqueous 1 M sodium citrate, and the mixture was vigorously stirred for 15 min. The aqueous phase was drained from the mixture, and the remaining organic phase treated with 35 mL of 6 N NaOH. The resulting mixture was then vigorously stirred at 50° C. for 3 h, then cooled to room temperature. An additional 35 mL each of MTBE and water were added in order to break the emulsion that had formed. The aqueous phase was discarded and the remaining organic phase was extracted twice with 10.5 mL of 3 N HCl. The combined acidic aqueous extracts were diluted with 15 mL of water and then extracted twice with 10 mL chlorobenzene. The combined chlorobenzene extracts were extracted twice with 20 mL of 0.5 N HCl, and then once with 20 mL of brine. The organic phase was then concentrated by distillation at atmospheric pressure, with a total of 9 mL of distillate being collected (2 mL of this distillate was water). The remaining solution in the distillation pot was then allowed to cool slowly with stirring to room temperature (at about 55° C. a flocculent solid separated from the solution), and then cooled further to 0-5° C. The mixture was held at 0-5° for 1 h, then the solid was collected by filtration and washed with a small amount of MTBE. Drying under reduced pressure gave 5.39 g the hydrochloride salt of 1-{4-[2-(pyrrolidin-N-yl)ethoxy]-6-methoxy-3,4-dihydronaphthalene as a white solid (80% yield on 6-methoxy-1-tetralone).

Provenance & Evidence