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 Synthesis of (+)-(1R,2S,3R)-Tetracarbonyl[(1-3η)-1-(phenylsulfonyl)but-2-en-1-yl]iron(1+) tetrafluoroborate
  • Synthesis of (+)-(1R,2S,3R)-Tetracarbonyl[(1-3η)-1-(phenylsulfonyl)but-2-en-1-yl]iron(1+) tetrafluoroborate
  • (+)-(1R,2S,3R)-Tetracarbonyl[(1-3η)-1-(phenylsulfonyl)but-2-en-1-yl]iron(1+) tetrafluoroborate could be made from the following synthesis routes.

    A. (+)-(E,1R,3S)-Tetracarbonyl[(3-(benzyloxy)-1-(phenylsulfonyl)-η2-but-1-ene]iron(0). A flame-dried, 250-mL Schlenk-flask equipped with a septum, magnetic stirring bar and a balloon filled with carbon monoxide is charged with 3.03 g (10.0 mmol) of (-)-(E,S)-3-(benzyloxy)-1-butenyl phenyl sulfone and 4.73 g (13.0 mmol) of nonacarbonyldiiron [Fe2(CO)9]. The reagents are suspended in 150 mL of anhydrous hexane and the orange suspension is stirred for 3 days at room temperature under an atmosphere of carbon monoxide and with exclusion of light. The reaction mixture is diluted with anhydrous diethyl ether (ca. 100 mL) and transferred via canula to an air-free filter containing a short column of Celite by means of a flame-dried inert gas frit and filtered under an atmosphere of argon. The bright yellow filtrate is collected in a 1000-mL, flame-dried Schlenk-flask. The filter column is washed with anhydrous diethyl ether until the filtrate becomes colorless. The clear yellow solution of the neutral complex is concentrated under reduced pressure in a room temperature water bath to between a third and a quarter of the original volume by means of a medium pressure vacuum pump and is then fractionally crystallized at -25°C in a freezer. The pale yellow precipitate is washed with anhydrous hexane pre-cooled to -25°C under an atmosphere of argon and dried under reduced pressure at room temperature by means of a high vacuum pump with the exclusion of light to afford 1.88-3.05 g (40-65%) of a moderately air sensitive pale yellow crystalline solid.

    B. (+)-(1R,2S,3R)-Tetracarbonyl[(1-3η)-1-(phenylsulfonyl)but-2-en-1-yl]iron(1+) tetrafluoroborate 1. A flame-dried, 50-mL Schlenk-flask equipped with a septum and an argon balloon is charged with 1.88 g (4.0 mmol) of (+)-(E,1R,3S)-tetracarbonyl[(1-2η)-3-(benzyloxy)-1-(phenylsulfonyl)-but-1-ene]iron(0) and the complex is dissolved in 15 mL of anhydrous diethyl ether under an atmosphere of argon. The bright yellow solution is taken up into a syringe under an atmosphere of argon and filtered through a PTFE-syringe filter into a flame-dried, 100-mL Schlenk flask equipped with a magnetic stirring bar, a septum and an argon balloon. The solution is diluted with anhydrous diethyl ether to give a total volume of 50-70 mL and then warmed to 30°C by means of a water bath. , (HBF4), 0.7 mL (4.8 mmol) of a 54% solution of HBF4 in diethyl ether is added dropwise by means of a syringe to the rapidly stirring solution. After ca. 2 hr, the precipitate is filtered off under an atmosphere of argon using an inert gas frit. The precipitate is washed with anhydrous diethyl ether until the filtrate becomes colorless (3 × 10-20 mL). The residue is dried for ca. 12 hr under reduced pressure at room temperature using a high vacuum pump to yield 1.73 g (96%) of a pale yellow solid. Normally the complex is obtained in spectroscopically and analytically pure form (by 1H and 13C NMR, elemental analysis) and can be used without further purification for nucleophilic addition reactions. If necessary, the complex can be further purified by re-precipitation from nitromethane solution with the addition of excess cold diethyl ether . The dry complex should be stored at -25°C in a freezer under an atmosphere of argon and may be handled for short periods in air.


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