Organic Syntheses, Coll. Vol. 10, p.718 (2004); Vol. 76, p.275 (1999).
of vitamin D2
). A 2-L photo-reaction vessel equipped with a quartz immersion well
, a thermometer
, an argon-inlet tube
, a mineral oil outlet-bubbler
, a mechanical stirrer
, and supported in an adequately sized Dewar
, is charged with
13.5 g (34 mmol) of ergosterol
) (Note 2)
1.31 g (6.8 mmol) of ethyl p-dimethylaminobenzoate
1.7 L of tert-butyl methyl ether (tert-BuOMe)
. The mixture is stirred at room temperature overnight with gentle bubbling of argon
. A 450-watt Hanovia medium-pressure mercury lamp
is inserted into the well, through which a fast stream of water is continuously passed (Note 5)
. The solution is cooled in a dry ice-ethanol bath
and stirred vigorously (Note 6)
. When the temperature of the solution reaches 0°C, the lamp is turned on, and irradiation is continued at 0°C to −20°C for 4 hr (Note 7)
. The lamp is turned off, a solution of
75 mg (0.34 mmol) of 9-acetylanthracene
3 mL of tert-BuOMe
is added to the solution, and a uranium filter
is inserted into the arc housing (Note 10)
. After 10 min, the lamp is started again, and the mixture is irradiated at 0°C to −20°C for 1 hr through the uranium filter (Note 11)
. The cold, pale yellow solution of pre-vitamin 2
thus obtained (Note 12)
is transferred to a 3-L, round-bottomed flask
and concentrated at 20-25°C under reduced pressure. The residue is transferred again to a 500-mL, round-bottomed flask
using tert-BuOMe to allow quantitative transfer. The solution is concentrated and dried at room temperature under high vacuum (1 mm) for 30 min to give approximately 15.4 g
of a yellow resin. The flask is filled with argon
and equipped with a magnetic stirrer
Methanol (100 mL)
is added, and the mixture is shaken to give a stirrable suspension. The suspension is then stirred for 45 min at room temperature and stored in a freezer overnight. After the mixture is stirred at −30°C (Note 13)
for 30 min, it is quickly filtered through a 60-mL sintered-glass funnel of coarse porosity
. The collected solid is washed with
20 mL of cold methanol
Ergosterol (1.83 g, 14%
recovery, mp 145-151°C
, 99.4% pure) is recovered by washing this solid with absolute
ethanol (30 mL at room temperature)
. The filtrate and cold-methanol wash are transferred to a 500-mL, round-bottomed flask equipped with a magnetic stirrer, an argon-inlet tube, and a reflux condenser
. The flask is flushed with argon
, and the orange solution is heated under reflux for 6 hr (Note 15)
and then stirred at 35-40°C overnight (Note 16)
. The mixture is concentrated at 30°C under reduced pressure, and the residual methanol
is removed by coevaporation with
50 mL of toluene
at 30°C to give approximately 14.6 g
of an orange-tan oil. The flask is filled with argon
and then equipped with a magnetic stirrer. The residue is dissolved in
40 mL of pyridine
, and the solution is cooled in an ice-water bath
3,5-dinitrobenzoyl chloride (9.0 g, 39 mmol)
is added in small portions over 5 min followed by
20 mL of pyridine
to rinse the walls of the flask, and the mixture is stirred at 0°C for 20 min. The very thick suspension obtained is shaken and then allowed to stand at 0°C for a further 20 min, whereupon
methanol (30 mL)
is added to the cold mixture. The mixture is allowed to stand at 0°C for 5 min, and then it is shaken for about 5 min to give a stirrable suspension. After the orange suspension is stirred at 0°C for 1.5 hr, it is diluted by the dropwise addition of
150 mL of methanol
over 15 min and stirred at 0°C for another hour. The yellow solid is collected by filtration, washed with
50 mL of ice-cold methanol
, and dried at room temperature under high vacuum for 2 hr. The yellow-orange solid is transferred to a 250-mL, round-bottomed flask
equipped with a magnetic stirrer and an argon-inlet tube. The flask is flushed with argon
, and the solid is suspended in
50 mL of absolute ethanol
. The suspension is stirred at room temperature for 15 min and at 0°C for 45 min. The solid is collected by filtration, washed with
20 mL of cold methanol
, and dried at room temperature under high vacuum overnight to give 8.3-10.1 g
) of 3
as a yellow solid, mp 139-141°C
) (Note 18)
and (Note 19)
The reactor is available from Ace Glass Inc. [reaction vessel (#7851-17)
, immersion well (#7854-28, 290 mm)
, Teflon bearing (#8066-24)
, and stirring shaft (#8068-303)
]. It is similar to that shown in Figure 1 (Org. Synth., Coll. Vol. V
with an additional stirring chamber. The submitter used a 4-mm I.D. tube
for an argon-inlet in order to avoid clogging; the tube should reach near to the bottom of the vessel. The checkers used a 20 × 45-cm (ID × height) Dewar
, available from Cole-Parmer Instrument Co. #H-03774-54).
Ergosterol (1), obtained from Aldrich Chemical Company, Inc.
, ε 8,030 at 282 nm in EtOH), was purified before use as follows:
24.4 g of 1
was suspended in
200 mL of ethanol (EtOH)
, and the mixture was stirred at room temperature for 3 hr prior to filtration. The collected solid was washed with
40 mL of EtOH
and dried under high vacuum (1.0 mm) to give
19.3 g (79% recovery) of 1
as a white solid (mp 147-153°C
, ε 11,900 at 282 nm in EtOH). The submitter observed that when 1
purchased from Kaneka Co. (mp 147-153°C
, ε 11,560 at 282 nm in EtOH) was used as received, a better quality of vitamin D2
) (mp 114-115°C
, 99.8% pure) was obtained in a better overall yield of 48%
based on the recovered ergosterol
). The checkers used
ergosterol obtained from Acros Organics
), which was purified as described above (mp 154-158°C
The overnight stirring with bubbling of argon
to remove oxygen
is probably too long, but was done simply for convenience, thereby allowing the irradiation to be carried out the next day. The checkers found that 4 hr was sufficient.
Water flow must be very fast to avoid freezing, which could result in breakage of the photochemical reactor and generation of a hazardous situation. Water flow should be monitored continuously during the course of the reaction.
Efficient stirring is necessary to achieve relatively homogeneous temperature distribution throughout the reaction mixture. The submitter recommends that the mixture be kept below 0°C to prevent thermal isomerization of 1
to vitamin D2
, which produces a variety of photoproducts upon irradiation.
The checkers monitored the reaction temperature at 5-min intervals and added dry ice to the bath each time the temperature approached 0°C. Approximately 30 pounds of dry ice are required over the 4-hr irradiation period. Using 1
H NMR analyses, the submitter judged the conversion to be 80-85% after 4 hr of irradiation with the apparatus described. After 3 hr, a 1:2:1 mixture of 1
:tachy-isomer (see Discussion) was obtained. The diagnostic peaks in the 1
H NMR spectra are listed in Table. The Rf
values on silica gel TLC using 1:4 EtOAc-hexane are as follows: 1
(0.34), tachy-isomer (0.34), 2
(0.42), ethyl p-dimethylaminobenzoate
(0.47), and 9-acetylanthracene
(0.53), using short wave UV detection.
THE CHEMICAL SHIFTS OF DIAGNOSTIC PEAKS IN 1H NMRa
5.39 (m), 5.57 (m)
5.48 (m), 5.67 (d, 11 Hz), 5.93 (d, 11 Hz)
5.67 (m), 6.00 (d, 16 Hz), 6.71 (d, 16 Hz)
a The chemical shifts are reported in ppm relative to CHCl3 (7.25) in CDCl3 as an internal standard.
9-Acetylanthracene was purchased from Aldrich Chemical Company, Inc.
and used as received.
A cylindrical uranium filter (31-mm O.D., 2.5-mm thickness)
was obtained from Houde Glass Co., Inc.
Caution! The lamp is very hot.
The lamp should be allowed to cool for 10 min before restarting to prevent damage.
Based on 1
H NMR analyses, the photosensitized isomerization of the tachy-isomer into 2
was complete after 40 min of irradiation (see Discussion).
The submitter recommends that pre-isomer (2
) and vitamin D2
) not be exposed to air at room temperature for more than 30 min, since these compounds are relatively easily oxidized by air.
The checkers used a dry ice-ethylene glycol bath
The checkers cooled the methanol
to −70°C in a dry ice-acetone bath
After 3 hr of reflux, the ratio of 2
was ca. 1:3, whereas after 6 hr, it reached about 1:5.
At this point, the ratio of 2
was greater than 1:6.
3,5-Dinitrobenzoyl chloride was purchased from Aldrich Chemical Company, Inc.
pyridine (A.C.S. certified) was obtained from Fisher Scientific Co.
They are used as received.
The elemental analysis and spectral properties of 3
are as follows: Anal. Calcd for C35
: C, 71.16; H, 7.85; N, 4.74. Found: C, 71.05; H, 7.89; N, 4.58; IR (KBr) cm−
: 1733, 1546, 1342
H NMR (CDCl3
) δ: 0.56 (s, 3 H), 0.82 (d, 3 H, J = 6.5), 0.84 (d, 3 H, J = 6.5), 0.92 (d, 3 H, J = 6.8), 1.02 (d, 3 H, J = 6.6), 1.25-2.17 (m, 16 H), 2.32 (m, 1 H), 2.50 (m, 1 H), 2.59 (dd, 1 H, J = 12.2 and 6.8), 2.73 (dd, 1 H, J = 12.2 and 4.5), 2.80 (dd, 1 H, J = 8.8 and 3.5), 4.91 (bs, 1 H), 5.13 (bs, 1 H), 5.20 (m, 2 H), 5.31 (m, 1 H), 6.06 (d, 1 H, J = 11.1), 6.28 (d, 1 H, J = 11.1), 9.13 (d, 2 H, J = 2.1), 9.22 (t, 1 H, J = 2.1)
C NMR (CDCl3
) δ: 12.2 (q), 17.5 (q), 19.5 (q), 19.8 (q), 21.0 (q), 22.1 (t), 23.5 (t), 27.7 (t), 28.9 (t), 31.7 (t), 32.0 (t), 33.0 (d), 40.3 (d and t), 41.9 (t), 42.7 (d), 45.8 (s), 56.3 (d), 74.8 (d), 113.2 (t), 117.1 (d), 122.1 (d), 123.0 (d), 129.3 (d), 131.9 (d), 133.1 (s), 134.3 (s), 135.4 (d), 143.1 (s), 143.8 (s), 148.5 (s), 161.8 (s)
(one doublet was not observed).
The submitter indicates that HPLC analysis of the product shows its purity to be 97.3% (with 0.3% of ergosteryl 3,5-dinitrobenzoate
). HPLC conditions for this unchecked analysis are as follows: column: Chromegasphere SI-60 (3μ,15-cm × 5-mm) (purchased from ES Industries); mobile phase: 5% EtOAc in heptane
(1 mL/min); detection: 275 nm. The retention times of 3
and ergosteryl 3,5-dinitrobenzoate
are 4.90 and 3.83 min, respectively. Those of the other impurities are 4.20, 4.55, 6.17, and 8.67 min. The checkers observed traces of pyridine
in the 1
H NMR spectrum of the product.
The checkers cooled this solution in an ice-water bath.
The elemental analysis and the spectral properties of 4
are as follows: Anal. Calcd for C28
O: C, 84.79; H, 11.18. Found: C, 84.89; H, 11.17. UV (EtOH) λmax
264 nm (ε 18,450);
H NMR (CDCl3
) δ: 0.55 (s, 3 H), 0.82 (d, 3 H, J = 6.5), 0.84 (d, 3 H, J = 6.5), 0.91 (d, 3 H, J = 6.5), 1.01 (d, 3 H, J = 6.7), 1.2-2.5 (m, 19 H), 2.57 (dd, 1 H, J = 11.6 and 3.5), 2.81 (broad d, 1 H, J = 9.0), 3.95 (m, 1 H), 4.82 (bs, 1 H), 5.04 (bs, 1 H), 5.20 (m, 2 H), 6.05 (d, 1 H, J = 11.2), 6.23 (d, 1 H, J = 11.2)
; The OH hydrogen
was not observed;
C NMR (CDCl3
) δ: 12.2 (q), 17.5 (q), 19.5 (q), 19.8 (q), 21.0 (q), 22.1 (t), 23.4 (t), 27.7 (t), 28.9 (t), 31.8 (t), 33.0 (d), 35.0 (t), 40.3 (d and t), 42.7 (d), 45.6 (s), 45.8 (t), 56.3 (d), 69.1 (d), 112.3 (t), 117.4 (d), 122.3 (d), 131.8 (d), 134.9 (s), 135.5 (d), 142.1 (s), 144.0 (s)
(one doublet was not observed).
The submitter indicates that HPLC analysis of the product shows the purity to be 99.7% (with 0.1% of ergosterol
). The HPLC conditions for this unchecked analysis are as follows: column: Chromegasphere SI-60 (3μ, 15-cm × 5-mm)
(purchased from ES Industries); mobile phase: 5% EtOAc in heptane
(2 mL/min); detection: 275 nm. The retention times of 1
are 19.54 and 16.27 min, respectively. The checkers observed signals due to a trace olefinic contaminant in the 1
H NMR of the product at δ 6.47 and 5.95.
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
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