Benzaldehyde → Piperazine

Participants

Reaction Conditions

Reaction Steps

At room temperature, a three-neck flask equipped with a reflux condenser, internal thermometer, dropping funnel and stirrer under protective nitrogen gas was initially charged with 4.6 g of zinc powder (71 mmol) in 40 ml of ethyl acetate. After 1.13 ml of trimethylchlorosilane had been added, the mixture was heated to 50° C. for 15 min and 10 g of 1-phenylhexan-3-one (57 mmol, prepared by base-catalyzed aldol condensation of benzaldehyde and pentan-2-one and subsequent hydrogenation of the 1-phenylhex-1-en-3-one obtained) were added undiluted. Subsequently, 10.4 g of methyl bromoacetate (68 mmol) were added dropwise within 5 min and the temperature was maintained at 60° C. by external cooling. The mixture was then stirred at 55° C. for 10 min (formation of the zinc alkoxide). After cooling to 10° C., 7.4 g of trimethylchlorosilane (68 mmol) were added and the mixture was heated to 40° C. for 30 min. At 20° C., 7.4 g of piperazine (85 mmol) were subsequently added as a solid. The mixture was then stirred at 50° C. for 3 h. After the ethyl acetate solvent had been virtually completely distilled off (recovery of the anhydrous solvent), 40 ml of pentane were added, the suspension was cooled to −20° C. and stirred for 1 h, and the solid formed (complex of zinc bromide chloride and piperazine) was filtered off. The solid was washed three times with 10 ml of pentane. Pentane was distilled off under reduced pressure (recovery of pentane) and the desired product methyl 3-trimethylsiloxy-3-(2″-phenylethyl)caproate was obtained in a yield of 17.4 g (95% of theory) and a purity of >97% (HPLC). The zinc content of the product was 20 ppm (ICP).

Provenance & Evidence