Toluene → 4-(4'-Fluoro-biphenyl-4-yl)-piperazine-1-carboxylic acid tert-butyl ester

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Reaction Steps

4-Bromo-4′-fluorobiphenyl (4.46 g, 17.8 mmol), N-tert-butoxycarbonyl piperazine (3.97 g, 21.3 mmol), sodium tert-butoxide (2.39 g, 24.9 mmol), racemic 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (rac-BINAP) (0.082 g, 0.131 mmol), bis-(dibenzylideneacetone)palladium (0) (0.041 g, 0.045 mmol) and dry toluene (45 mL) were stirred at 80° C. under nitrogen atmosphere for six hours. The warm mixture was filtered, the solids were washed twice with warm toluene and the filtrate was concentrated in vacuo giving an orange-red crude, which was stirred with ether (50 mL) for two hours. The solid was filtered off, washed with small volumes of ether and dried in vacuo at 45° C. over night to give 5.57 g (88% yield) of tert-butyl 4-(4′-fluoro[1,1′-biphenyl]-4-yl)-1-piperazinecarboxylate. This product (5.52 g, 15.5 mmol) was dissolved in dioxane (150 mL) and stirred with 4M hydrochloric acid (8.1 mL) at RT over night. Concentrated hydrochloric acid (3.0 mL) was added and stirring was continued at 45° C. for 1.5 hours and at 60° C. for 1 hour. The solution was concentrated to dryness and the solid was triturated with ether (100 mL), filtered, washed with small volumes of ether and dried in vacuo at 45° C. for two hours to give 5.26 g (103% yield) of 1-(4′-fluoro[1,1′-biphenyl]-4-yl)piperazine dihydrochloride as a light-yellow salt.

Provenance & Evidence