A.
Diethyl 5-methylcoprost-3-en-3-yl phosphate. A dry,
100-ml., three-necked flask equipped with a magnetic stirring bar, a
pressure-equalizing dropping funnel, a
nitrogen inlet tube, and a
rubber septum is charged with
384 mg. (0.00201 mole) of copper(I) iodide (Note
1) and
20 ml. of anhydrous diethyl ether (Note
2). After the reaction vessel has been flushed with
nitrogen, a static oxygen-free
nitrogen atmosphere is maintained in the reaction vessel throughout the remainder of the reaction. The reaction mixture is cooled in an
ice bath and an ether solution, containing
0.0040 mole of methyllithium (Note
3), is added with a hypodermic syringe, dropwise and with stirring. As the
methyllithium is added, the initial yellow precipitate of polymeric
methylcopper(I) redissolves, forming a colorless to pale-yellow solution of
lithium dimethylcuprate (Note
4). To the resulting cold solution is added, dropwise and with stirring over 20 minutes, a solution of
576 mg. (0.00150 mole) of cholest-4-en-3-one (Note
5) in
20 ml. of ether (Note
2). During the addition of the enone, a yellow precipitate of polymeric
methylcopper(I) separates from the reaction solution. After the addition is complete, the cooling bath is removed, and the reaction mixture is stirred for 2 hours at room temperature. The dropping funnel is replaced with a second dry dropping funnel which contains a loose plug of glass wool above the stopcock. The reaction mixture is again cooled in an ice bath and a mixture of
4.0 ml. of triethylamine (Note
6) and
2.00 g. (0.0115 mole) of diethyl phosphorochloridate (Note
7) is added from the dropping funnel to the reaction mixture, rapidly and with stirring. After this addition, the cooling bath is removed, and stirring is continued for one hour. Saturated aqueous
sodium hydrogen carbonate is added to hydrolyze any remaining organometallic reagents before the reaction mixture is transferred to a
separatory funnel and washed successively with two
50-ml. portions of cold (0°) 1 M ammonium hydroxide and a 50-ml. portion of water. The aqueous washes are extracted in turn with a
30-ml. portion of ether. The combined
ether solutions are dried over anhydrous
sodium sulfate and concentrated with a
rotary evaporator. A solution of the residual liquid in
3 ml. of ether is applied to a
2.5 cm. by 15 cm. chromatographic column packed with a slurry of
50 g. of silica gel (Note
8) in
ether. The column is eluted with
ether. After the first 70 ml. of eluent has been collected and discarded, the next
120 ml. of ether eluent is collected and concentrated with a rotary evaporator, yielding
420–480 mg. of crude phosphate ester (Note
9), a colorless liquid, sufficiently pure for use in the following procedure.