Novel partial synthetic approaches to replace carbons 2,3,4 of steroids. A methodology to label testosterone and progesterone with 13C in the steroid A ring. Part 1

Article abstract of DOI:10.1016/S0040-4020(00)00966-2

A synthetic route to replace A ring carbon atoms 2, 3 and 4 of steroid hormones is described. Readily available testosterone propionate or progesterone, respectively, are degraded to the corresponding 10-formyl-5-oxo-des-A intermediates, in a first stage to the preparation of 2,3,4-(¹³C₃)-labeled steroids. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00966-2

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 9957±9965
Novel Partial Synthetic Approaches to Replace Carbons 2,3,4 of
Steroids. A Methodology to Label Testosterone and Progesterone
with C in the Steroid A Ring. Part 1
13
*
Isa G. J. de Avellar and Friedrich W. Vierhapper
È È È
Institut fur Organische Chemie der Universitat Wien, Wahringerstrasse 38, A-1090 Wien, Austria
Received 10 January 2000; revised 10 October 2000; accepted 11 October 2000
AbstractÐA synthetic route to replace A ring carbon atoms 2, 3 and 4 of steroid hormones is described. Readily available testosterone
propionate or progesterone, respectively, are degraded to the corresponding 10-formyl-5-oxo-des-A intermediates, in a ®rst stage to the
preparation of 2,3,4-(13C3)-labeled steroids. q 2000 Elsevier Science Ltd. All rights reserved.
Stable isotope labeled compounds are widely employed in
pharmacological and clinical research. Their emergence as
®rst-choice tracers and standards results from their ethical
acceptability compared to the radioactive analogs and from
the sensitivity of the methods in which they are employed.1,2
Stable isotope labeled steroid hormones are needed in the
development of de®nitive gas chromatography±mass spec-
trometry quantitation methods and are used in metabolic,
kinetic and clinical studies, especially in those conducted
with human subjects.3 It is essential that the labels are
retained during metabolic processes, during chemical and
analytical treatment of the samples, and that isotopic effects
are negligible. Therefore, the choice of the label and its site
are of ®rst importance. In most cases 13C is the ideal label,
especially if it is introduced into the steroid skeleton rather
than into the more susceptible 17-side chain.
Results and Discussion
The route of synthesis described here comprises the clea-
vage of the steroid A ring of testosterone and progesterone,
respectively, and the degradation of three carbon atoms to
the key 10-formyl-5-oxo-des-A intermediates 1 and 2.
Reconstruction of the steroidal A ring is then achieved by
incorporation of a C3 unit5 unto these intermediates by reac-
tion with the stabilized ylide, 1-triphenyl-phosphoranyli-
dene-2-propanone. The use of a 13C labeled reagent
conveniently leads to the desired labeled compounds. The
reconstruction of the 13C labeled steroid hormones is
described in the following paper in this issue.6
Two general approaches may be considered when synthe-
sizing steroid hormones labeled with 13C: partial synthesis,
in which part of the steroid nucleus is replaced with a
labeled synthon, or total synthesis. Partial synthesis labeling
procedures offer the advantage of shorter synthetic path-
ways and readily available steroid starting materials. By
these procedures, however, not more than two 13C atoms
have been previously introduced in the steroid A ring,4 a
most attractive labeling site. We now describe a novel
partial synthesis developed for the preparation of
(2,3,4-13C3) testosterone and progesterone.
Our initial attempt to degrade the A ring of testosterone to
the 10-formyl-5-oxo-des-A derivate is depicted in Scheme 1.
Ozonolysis of testosterone propionate 3 was conducted in
ethyl acetate at 2788C, followed by overnight treatment
with hydrogen peroxide, produced the keto acid 4.7 The
key step in this route is the oxidative decarboxylation8 of
the keto acid 4, leading to the terminal alkene 5, which after
another ozonolysis would generate the desired intermediate
6. Our initial attempt for oxidative decarboxylation was by
lead tetraacetate in the presence of catalytic amounts of
cupric acetate and pyridine, which had been successfully
applied in steroid synthesis.9 Low yields of the conversions
(16±42%) after many attempts of optimization discouraged
us from this route. An alternative procedure for oxidative
Keywords: steroids; degradation; labeling.
* Corresponding author. Tel.: 143-1-4277-52106; fax: 143-1-4277-9521;
e-mail: friedrich.vierhapper@univie.ac.at
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00966-2

9958
I. G. J. de Avellar, F. W. Vierhapper / Tetrahedron 56 (2000) 9957±9965
Scheme 1. Reagents and conditions: A: O3, then H2O2. B: Pb(OAc)4, Cu(OAc)2, pyridine, re¯uxing benzene. C: IBDA, Cu(OAc)2, pyridine, re¯uxing
benzene. D: O3, Me2S.
Scheme 2. Reagents and conditions: A: O3, then H2O2. B: KOH, CH3OH/H2O, re¯ux. C: CH2N2. D: HOCH2CH2OH, (CH3O)3CH, PTSA. E: LDA, PhSeSePh,
then H2O2. F: TBDMSiCl, imidazole. G: O3, Me2S. H: CH3CO2H/H2O, re¯ux.

I. G. J. de Avellar, F. W. Vierhapper / Tetrahedron 56 (2000) 9957±9965
9959
Scheme 3. Reagents and conditions: A: O3, then H2O2. B: CH2N2. C: HOCH2CH2OH, (CH3O)3CH, PTSA. D: LDA, PhSeSePh. E: CH2Cl2±H2O2, pyridine.
F: O3, Me2S. G: CH3CO2H/H2O, re¯ux
decarboxylation with iodosobenzene diacetate (IBDA) and
catalytic amounts of cupric acetate (previously used to
prepare alkenes from primary and secondary carboxylic
acids derivates of steroidal substrates10) also afforded a
very modest yield (34%).
led to a mixture of predominantly starting material and
only about 20% of the desired a,b-unsaturated ketal ester
1
10 (ratio estimated by H NMR).
Protection of the 17b-hydroxy group by treatment of 9 with
dimethyl-tert-butylsilyl chloride and imidazole in dimethyl-
formamide13 afforded the silyl ether 11 (99%). Treatment of
this compound with lithium diisopropylamide and reaction
of the lithium enolate with diphenyldiselenide followed by
oxidation with hydrogen peroxide yielded the unsaturated
ester 12 (94%). Two-carbon-degradation to the 10-formyl
derivate was achieved by ozonolysis of 12 followed by
reductive treatment of the ozonide with dimethyl sul®de.
Compound 13 was obtained in 85% yield. Simultaneous
deacetalization of the C-5 carbonyl and cleavage of the
dimethyl-tert-butylsilyl ether to the corresponding alcohol
was done by treatment of 13 with aqueous acetic acid at
re¯ux temperature,14 providing compound 1 in excellent
yield (98%). The overall yield of 10-formyl-5-oxo-des-A-
testosterone 1 from 3 by the above procedure was 44%.
Another synthetic route was therefore employed for the
removal of the three adjacent carbons of the steroid nucleus
to obtain the desired intermediate 1 (Scheme 2). Starting
with testosterone propionate 3, ozonolysis of the enone
moiety followed by hydrolysis of the 17b-propionate
group of 4 gave the keto acid 7 in good overall yield
(76%). Reaction of this product with diazomethane quanti-
tatively afforded the keto ester 8. The 5-keto group was
protected as an ethylenedioxyacetal group giving the ketal
ester 9 (74%). Dehydrogenation of the ketal ester 9 would
lead to an a,b-unsaturated carboxylic functionality, from
which a second ozonolysis would effect the necessary
further cleavage of two carbon atoms to obtain a 10-formyl
group.
Conversion of ketones and esters to their a,b-unsaturated
derivates can be done at mild conditions and in high yields
by selenation followed by selenoxide elimination.11 In our
case selenation of ketal ester 9 with diphenyldiselenide,
followed by oxidation of the crude selenated material,12
An analogous procedure was employed for the A ring degra-
dation of progesterone (Scheme 3). Ozonolysis of the enone
group accounts for the removal of the ®rst carbon. The crude
keto acid 14 was treated with diazomethane in methanol
and the keto ester 15 was isolated in 79% yield after

9960
I. G. J. de Avellar, F. W. Vierhapper / Tetrahedron 56 (2000) 9957±9965
Scheme 4. Reagents and conditions: A: LiCH2CN.
chromatography. Protection of the keto groups at C-5 and
C-20 was accomplished by reaction with ethylene glycol,
trimethyl orthoformate and p-toluenesulfonic acid.15 The
diketal ester 16 was isolated as a white crystalline solid
after radial chromatography on silica gel in 84% yield. Sele-
nation of compound 16 was accomplished by reaction with
lithium diisopropylamide in dry THF and treatment of the
resulting enolate with diphenyldiselenide. The a-phenylse-
leno ester 17 was isolated after radial chromatography in
91% yield as a mixture of diastereomers. Oxidation of 17
with subsequent selenoxide elimination to give the a,b-
unsaturated ester was performed using pyridine as a buffer
to avoid hydrolysis of the C-20 ketal group under the
slightly acidic aqueous condition of the oxidation. The
desired a,b-unsaturated diketal ester 18 was isolated in
84% yield after radial chromatography. Further degradation
of the A ring residue to the 10-formyl diketal derivate was
accomplished by ozonolysis of 18 followed by treatment of
the ozonide with dimethyl sul®de. Compound 19 was
obtained in 96% yield after radial chromatography.
yield) (Scheme 4). The low yield of this conversion,
however, discouraged us from further attempts towards
the potential route dehydration±hydrogenation±methyl-
ation and ®nally deprotection and cyclization.
In summary, we think that the synthetic routes presented
here are an ef®cient way to eliminate the carbon atoms 2,
3 and 4 in the A rings of testosterone and progesterone. The
reaction sequence can be easily adapted for use with a
number of other steroid hormones. The 10-formyl-5-oxo-
des A derivatives are well suited for reconstruction of the
A rings; if suitably labeled components are used, this leads
to 13C-labeled testosterone and progesterone.6
Experimental
Melting points were determined using a Reichert Ko¯er
melting point microscope and are uncorrected. NMR spectra
were recorded at room temperature (in CDCl3 unless other-
wise indicated); internal references were (CH3)4Si (d 0.00)
Deprotection of the carbonyl groups at C-5 and C-20 could
be acchieved by re¯uxing compound 19 in 50% aqueous
acetic acid solution to give 10-formyl-5-oxo-des-A-pro-
gesterone 2, in 85% yield. The overall yield of 2 from
progesterone was 41%.
1
and CDCl3 (d 77.00), respectively. H NMR spectra were
recorded on either a Bruker WM 250 or a Bruker AM 400
operating at 250 MHz and 400 MHz, respectively. 13C NMR
spectra (62.9 and 100 MHz) were also recorded on these
instruments. Mass spectra were recorded on a quadrupole
mass spectrometer MS 800 (Frisons Instruments) connected
to a gas chromatograph GC 800 series (Carlo Erba Instru-
ments). Column was a DB-1 fused silica capillary column
(15 m£0.32 mm ID), ®lm thickness 0.25 mm. MS-con-
ditions were 70 eV ionization energy, scan 50±600. The
high resolution mass spectrum of 2 was recorded on a
mass spectrometer 8230 (Finnigan, MAT) with direct inlet
and 70 eV ionization energy (EI).
The three-step procedure employed to accomplish A-ring
reconstruction starting with the formyl ketones 1 and 2 is
described in the following paper in this issue6. The use of
compound 19 as an alternative starting material for the
reconstruction of ring A of progesterone was also con-
sidered. Attempts to condense aldehyde 19 with 1-tri-
phenylphosphoranylidene-2-propanone in xylene under
re¯ux were unsuccessful. Reaction of 19 with diethyl
2-oxopropylphosphonate, which was attempted in a variety
of procedures, also met with failure; the unreacted ketal
aldehyde 19 was recovered from the reaction mixtures.
Elemental analyses were carried out by Mikroanalytisches
Laboratorium, Institut fuÈr Physikalische Chemie der
È
Universitat Wien.
Reconstruction of the ring A starting by reaction of 19 with
lithium ethyl acetate16 with subsequent incorporation of a
third carbon was also considered, but conversion of the
carbonyl compound 19 into the corresponding b-hydroxy
ester could not be achieved.
Solvents were puri®ed by standard methodology. Reactions
requiring anhydrous conditions were carried out under
either dry nitrogen or argon atmospheres. THF was distilled
from sodium-benzophenone prior to use. Flash chroma-
tography was performed using Merck silica gel 0.040±
0.063 mm. Radial chromatography was carried out on a
Chromatotron 8924 from Harrison Research, using rotors
coated with Merck silica gel 60 PF-254 with calcium sulfate
in various layer thickness (1,2 or 4 mm). Ozonolysis was
performed by a Welsbach ozonizator using dry air as
oxygen source.
Since the addition to the 10-formyl group of 19 appeared to
be seriously disfavored by steric hindrance, it seemed
reasonable that a smaller and sterically less demanding
nucleophile like acetonitrile anion17 would be more effec-
tive in performing the addition. In fact, treatment of 19 with
cyanomethyllithium gave the anticipated adduct 20 (39%

I. G. J. de Avellar, F. W. Vierhapper / Tetrahedron 56 (2000) 9957±9965
9961
17b-Propionoxy-5-oxo-3,5-seco-4-norandrostan-3-oic
acid (4). A solution of testosterone propionate (2.028 g,
5.89 mmol) in ethyl acetate (100 mL) was oxidized by
passing ozone through the solution at 2788C. The progress
of the reaction was followed by TLC. As soon as the testos-
terone propionate had reacted, the excess ozone was ¯ushed
by a stream of nitrogen. To the ozonized solution hydrogen
peroxide (30%, 25 mL) and water (5 mL) were added and
the biphasic reaction mixture was stirred overnight at room
temperature. The aqueous phase was then removed, the
organic phase was washed with water (2£30 mL), extracted
with ice cold 1% sodium hydroxide solution (4£25 mL).
Each portion of the basic extract was immediately acidi®ed
with cold 5% hydrochloric acid solution and the resulting
suspension was extracted with diethyl ether (3£80 mL). The
organic phase was dried over anhydrous magnesium sulfate,
®ltered, the solvent was evaporated and the product was
dried under vacuum to give a crystalline white solid
(1.863 g, 87%). The product was used in the next step
without further puri®cation; dH (400 MHz, CDCl3/TMS)
0.83 (s, 3H, 18-CH3), 1.09 (s, 3H, 19-CH3), 4.60 (t, 1H,
17-CH); dC (100.6 MHz) 214.5 (C-5), 179.3 (C-3), 174.5
(OCvOCH2CH3), 82.1 (C-17).
mixed in dry benzene (40 mL) under an atmosphere of dry
nitrogen. The reagents were stirred for 15 min at room
temperature to effect solution. The ®rst portion of IBDA
(0.500 g, 1.55 mmol) was then added and the reaction
mixture was heated to re¯ux. To the reaction mixture four
additional portions of IBDA (0.505 g, 1.57 mmol; 0.500 g,
1.55 mmol; 0.517 g, 1.60 mmol and 0.513, 1.59 mmol)
were added every 90 min, and the mixture was re¯uxed
for 8 h. The reaction mixture was then washed with 5%
hydrochloric acid solution (3£20 mL) and water (2£
20 mL), dried over anhydrous magnesium sulfate, ®ltered
and concentrated. The residue was submitted to ¯ash
chromatography (silica gel, elution with 5±50% ethyl
acetate in petroleum ether) to yield 0.167 g (0.524 mmol,
34%) of alkene 5. The methyl ester of the acid 4, methyl
17b-propionoxy-5-oxo-3,5-seco-4-norandrostan-3-oate, was
also isolated from the reaction mixture as an oil (0.175 g,
0.462 mmol, 30%), dH (400 MHz, CDCl3/ TMS) 3.65 (s,
3H, CH3O), 4.60 (t, 1H, 17-CH); dC (62.9 MHz, CDCl3/
TMS) 214.2 (C-5), 174.4 (C-3), 174.3 (OCOCH2CH3),
82.1 (C-17), 51.5 (CH3O).
17b-Hydroxy-5-oxo-3, 5-seco-4-norandrostan-3-oic acid
(7). To the acid 4 (1.498 g, 4.11 mmol), prepared as
described above, 70 mL of a solution of potassium
hydroxide (1.0 g) in aqueous methanol (60 mL methanol,
10 mL water) was added. The mixture was heated to re¯ux
for 3 h under nitrogen. The mixture was diluted with
distilled water (140 mL), the resulting mixture was acidi®ed
and extracted with ether (4£100 mL). The organic phase
was dried over anhydrous magnesium sulfate, ®ltered, the
solvent evaporated to yield 1.116 g (3,62 mmol, 88%) of the
product 7 as a white crystalline solid. Overall yield from
testosterone propionate was 76%. The product was used in
the next step without further puri®cation. An analytical
specimen was obtained by recrystallization from ethyl
acetate±petroleum ether, colorless crystals, mp 203±
2058C (literature,7 mp 195±1978C, literature,18 mp 204±
2058C); dH (400 MHz, CDCl3/ TMS) 3.58 (t, 1H, 17-CH),
1.07 (s, 3H, 19-CH3), 0.74 (s, 3H, 18-CH3); dC (100.6 MHz,
CDCl3/ TMS) 215.4 (C-5), 176,9 (C-3), 81.1 (C-17), 17.5
(C-19), 10.9 (C-18).
17b-Propionoxy-2, 5-seco-3, 4-dinorandrost-1-en-5-one
(5). (a) Oxidative decarboxylation of acid 4 with lead tetra-
acetate. In a three neck round bottom ¯ask equipped with
condenser, the acid 4 (0.226 g, 0.620 mmol), cupric acetate
(0.34 mmol), pyridine (0.3 mL) and dry benzene were
stirred at room temperature under dry nitrogen. To the
mixture the ®rst portion of lead tetraacetate (0.560 g,
1.26 mmol) was added. The resulting dark green solution
was stirred at room temperature in the dark for 30 min. The
mixture was heated to re¯ux for 1 h and 45 min, then the
second portion of lead tetraacetate was added (0.289 g,
0.652 mmol). The reaction mixture was re¯uxed for an
additional 1 h and 45 min and the third portion of lead tetra-
acetate (0.264 g, 0.569 mmol) was added; heating was
continued for another 1 h and 30 min. The mixture was
allowed to cool to room temperature and 2.5 mL of ethylene
glycol and water (20 mL) were added. The organic phase
was separated, diluted with ethyl acetate (30 mL), washed
with 10% solution of nitric acid (3£20 mL) and water
(3£15 mL). The unchanged acid 4 was recovered by
extracting the organic phase with ice cold 1% sodium
hydroxide solution followed by reacidi®cation and solvent
extraction. The organic neutral extract, containing the
desired alkene 5 was dried over anhydrous magnesium sul-
fate, ®ltered, evaporated and the residue chromatographed
(silica gel, elution with 5% ethyl acetate in petroleum ether)
to yield 83 mg (0.26 mmol, 42%) of 5 as an oil that crystal-
lized on standing, mp (prisms from benzene±pentane) 119±
1228C (Found: C, 75.17; H, 9.46. C20H30O3 requires: C,
75.43; H, 9.50%), dH (400 MHz, CDCl3/ TMS) 0.84 (s,
3H, 18-CH3), 4.59 (t, 1H, 17-CH), 5.02 (d, 1H, 2-CH),
5.24 (d, 1H, 2-CH), 5.76 (dd, 1H, 1-CH); dC (100.6 MHz,
CDCl3/ TMS) 214.1 (C-5), 174.4 (O2CCH2CH3), 141.6 (C-
1), 114.5 (C-2), 82.0 (C-17). From the organic acidic extract
78 mg of unchanged acid 4 were recovered.
Methyl 17b-hydroxy-5-oxo-3, 5-seco-4-norandrostan-3-
oate (8). To a solution of the keto acid 7 (0.720 g,
2.33 mmol) in methanol (15 mL) a solution of diazo-
methane in diethyl ether was added until the bright yellow
color persisted. The excess diazomethane was removed by
passing a stream of dry nitrogen through the solution, and
the mixture was concentrated. The residue was submitted to
chromatography on silica gel (20 g of silica gel, elution with
20±40% ethyl acetate in petroleum ether) to give the keto
ester 8 as a viscous colorless oil in quantitative yield:
C19H30O4 MS (EI): m/z: 322 (M1,1.00%), 236 (100%); dH
(400 MHz, CDCl3/ TMS) 3.62 (s, 3H, MeO), 3.59 (t, 1H,
17-CH), 1.07 (s, 3H, 19-CH3), 0.77 (s, 3H, 18-CH3). dC
(100.6 MHz, CDCl3/ TMS) 214.4 (C-5), 174.3 (C-3), 81.2
(C-17), 56.5 (MeO), 20.3 (C-19), 10.9 (C-18).
Methyl 17b-hydroxy-5, 5-ethylenedioxy-3,5-seco-4-
norandrostan-3-oate(9). The keto ester 8 (2.815 g,
8.73 mmol) was stirred overnight at room temperature
with trimethyl orthoformate (20 mL), ethylene glycol
(b) Oxidative decarboxylation of acid 4 with iodosobenzene
diacetate (IBDA). The acid 4 (0.565 g, 1.55 mmol), cupric
acetate (0.060 g, 0.33 mmol) and pyridine (1,1 mmol) were

9962
I. G. J. de Avellar, F. W. Vierhapper / Tetrahedron 56 (2000) 9957±9965
(20 mL) and p-toluenesulfonic acid (0.150 g). The mixture
was diluted with ethyl acetate and the solution was washed
with 5% sodium hydrogen carbonate solution. The organic
phase was dried over anhydrous magnesium sulfate, ®ltered,
concentrated and the residue was chromatographed (silica
gel, elution with 18% ethyl acetate in petroleum ether)
affording 2.371 g (6.45 mmol, 74%) of ketal ester 9, mp
(colorless crystals from benzene±pentane) 152±1548C
(Found: C, 68.81; H 9.36. C21H34O5 requires: C, 68.82; H,
9.35%); dH (400 MHz, CDCl3/ TMS) 3.88 (m, 4H,
±OCH2CH2O±), 3.61 (s, 3H, OMe), 3.59 (t, 1H, 17-CH),
2.54 (m, 1H, 2-CH), 2.29 (m, 1H, 2-CH), 0.969 (s, 3H,
19-CH3), 0.715 (s, 3H, 18-CH3); dC (100.6 MHz, CDCl3/
TMS) 175.3 (C-3), 113.7 (C-5), 81.7 (C-17), 64.1 and
63.9 (±OCH2CH2O±), 51.4 (CH3O), 18.0 (C-19), 11.1
(C-18).
hydrogen carbonate solution (30 mL), saturated sodium
chloride solution (30 mL), dried over anhydrous magnesium
sulfate, ®ltered and evaporated to yield a bright orange
crystalline solid. The crude product weighed 1.869 g. In
another run, the phenylseleno intermediate, methyl 17b-
(tert-butyldimethylsilyloxy)-2-phenylseleno-5,5-ethylene-
dioxy-3,5-seco-4-norandrostan-3-oate, was puri®ed by
radial chromatography (4 mm silica gel coated rotor, elution
with 5% ethyl acetate in petroleum ether) and isolated as
yellow crystals: dH (400 MHz, CDCl3/TMS) 7.60±7.58 (m,
2H, aromatic protons), 7.27±7.25 (m, 3H, aromatic protons)
3.92±3.63 (m, 4H, ±OCH2CH2O±) 3.53 (s, 3H, MeO), 3.48
(t, 1H, 17-CH), 2.58 (dd, 1H, 2-CH), 0.93 (s, 3H, 19-CH3),
0.86 (s, 9H, Me3±C±Si), 0.65 (s, 3H, 18-CH3), 0.0001 and
20.0015 (2s, 3H each, Me2±Si); dC (100.6 MHz, CDCl3/
TMS) 174.4 (C-3), 135.8, 129.2, 128.9, 128.4 (aromatic
carbons), 113.1 (C-5), 81.7 (C-17), 63.4 and 63.4
(±OCH2CH2O±), 51.7 (MeO), 25.9 (Me3±C±Si), 18.1 (Me3±
C±Si), 17.7 (C-19), 11.3 (C-18), 24.5 and 24.8 (Me2±Si).
Methyl 17b-(tert-butyldimethylsilyloxy)-5,5-ethylene-
dioxy-3,5-seco-4-norandrostan-3-oate (11). To a stirred
solution of the ketal ester 9 (1.329 g, 3.63 mmol) in
dimethylformamide (14 mL), imidazole (0.957 g, 14.05
mmol) and tert-butyldimethylsilyl chloride (1.06 g,
7.03 mmol) were added. The mixture was stirred overnight
at room temperature. Water (15 mL) was added and the
mixture was extracted with ethyl acetate. The organic
extract was washed with 1 N hydrochloric acid (30 mL),
water (20 mL) and brine (20 mL), then dried over anhydrous
magnesium sulfate, ®ltered and concentrated. The oily
residue was chromatographed (silica gel, elution with 5%
ethyl acetate in petroleum ether) yielding 1.722 g of product
11 (3.58 mmol, 99 %) as a colorless oil which crystallized
when left standing, mp (colorless crystals from pentane)
87±898C (Found: C, 67.61; H, 10.23. C27H48O5Si requires:
C, 67.45; H, 10.06%). dH (400 MHz, CDCl3/ TMS) 3.90 (m,
4H, ±OCH2CH2O±), 3.64 (s, 3H, OMe), 3.55 (t, 1H,
17-CH), 2.57 (m, 1H, 2-CH) and 2.32 (m, 1H, 2-C±H),
0.99 (s, 3H, 19-CH3), 0.86 (s, 9H, Me3±C±Si), 0.70 (s,
3H, 18-CH3), 0.0007 and 20.0060 (2s, 3H each, Me2±Si);
dC (100.6 MHz, CDCl3/ TMS) 175.4 (C-3), 113.9 (C-5),
81.7 (C-17), 64.2 and 64.0 (±OCH2CH2O±), 51.4 (OMe),
25.8 (Me3±C±Si), 18.2 (C-19), 18.1 (Me3±C±Si), 11.4
(C-18), 24.5 and 24.8 (Me2±Si).
Oxidation/elimination of the phenylseleno group. A solution
of the crude a-phenylseleno ester derivate (1.869 g) in
dichloromethane (15 mL) was stirred in a three necked
round bottom ¯ask equipped with thermometer, re¯ux
condenser and addition funnel. It was cooled in an ice
bath and a solution of hydrogen peroxide (30%, 2 mL) in
water (2 mL) was added dropwise. After addition was
complete, the temperature of the reaction mixture rose
quickly to 208C, dropping thereafter. The ice bath was
removed and the reaction mixture was stirred brie¯y at
room temperature. Progress of the reaction was checked
by TLC. The reaction mixture was transferred to a sepa-
ration funnel with 5% sodium hydrogen carbonate solution
(30 mL) and extracted with dichloromethane. The extract
was dried over magnesium sulfate, ®ltered, evaporated,
and the residue was submitted to radial chromatography
(rotor coated with silica gel, 4 mm layer, elution with
5±10% ethyl acetate in petroleum ether) to yield 1.032 g
(2.15 mmol, 94%) of product 12, mp (colorless crystals
from pentane) 85±888C (Found: C, 67.69; H 9.91.
C27H46O5Si requires: C, 67.74; H 9.68%); dH (400 MHz,
CDCl3/ TMS) 7.00 (d, 1H, 1-CH, Jˆ16 Hz), 5.80 (d, 1H,
2-CH, Jˆ16 Hz), 3.82 (m, 4H, ±OCH2CH2O±), 3.71 (s, 3H,
OMe), 3.52 (t, 1H, 17-CH), 1.14 (s, 3H, 19-CH3), 0.85 (s,
9H, Me3±C±Si), 0.67 (s, 3H, 18-CH3), 20.022 (s, 6H, Me2±
Si); dC (100.6 MHz, CDCl3/ TMS) 167.3 (C-3), 155.4 (C-1),
121.0 (C-2), 112.5 (C-5), 81.6 (C-17), 65.2 (±OCH2CH2O±),
51.4 (OMe), 25.8 (Me3±C±Si), 18.1 (Me3±C±Si), 13.6
(C-19), 11.4 (C-18), 24.5 and 24,8 (Me2±Si).
Methyl 17b-(tert-butyldimethylsilyloxy)-5,5-ethylene-
dioxy-3,5-seco-4-norandrost-1-en-3-oate (12). (a) Prepa-
ration of the a-phenylseleno carboxylic ester derivate,
17b (tert-butyldimethylsilyloxy)-2-phenylseleno-5,5-ethyl-
enedioxy-3,5-seco-4-norandrostan-3-oate: To
a three-
necked round bottom ¯ask equipped with two septa inlets,
magnetic stirring, addition funnel and nitrogen inlet were
added freshly distilled anhydrous THF (4 mL) and diiso-
propylamine (0.4 mL, 2.85 mmol). The solution was cooled
in a dry ice±isopropanol bath, and was treated with n-butyl-
lithium in hexane (15% solution, 1.75 mL, 2.87 mmol) for
25 min. The saturated ketal ester 11 (1.106 g, 2.30 mmol) in
4 mL THF was then slowly added dropwise. After stirring
for 25 min, diphenyldiselenide (0.888 g, 2.84 mmol) in
4 mL dry THF was added quickly. The solution was stirred
at 2788C for 30 min and then allowed to come to room
temperature over a 2 h period. The reaction was then
quenched by adding saturated ammonium chloride solution
(30 mL), extracted with ethyl acetate, washed with 1 N
hydrochloric acid (30 mL), water (30 mL), 5% sodium
17b-(tert-Butyldimethylsilyloxy)-10-formyl-5,5-ethylene-
dioxy-des-A-androstane (13). A solution of the a,b-
unsaturated ketal ester 12 (0.164 g, 0.343 mmol) in
dichloromethane±methanol solution (2:1.15 mL) was
treated with ozone at 2788C until all starting material had
been consumed, as indicated by TLC. After excess ozone
had been removed by a stream of nitrogen, an excess of
dimethyl sul®de (2 mL, 27 mmol) was added and the
reaction mixture was allowed to warm gradually and was
then stirred overnight at room temperature19. The mixture
was then diluted with dichloromethane, washed with 5%
sodium hydrogen carbonate solution (2£20 mL) and brine,
dried over anhydrous magnesium sulfate, ®ltered and the

I. G. J. de Avellar, F. W. Vierhapper / Tetrahedron 56 (2000) 9957±9965
9963
solvent was evaporated. The residue, a crystalline white
solid, was chromatographed (silica gel, elution with 5%
ethyl acetate in petroleum ether) to give 0.123 g
(0.291 mmol, 85%) of the aldehyde 13, a crystalline white
solid, mp (colorless needles from pentane) 144±1458C
(Found: C, 68.13; H, 9.91. C24H42O4Si requires: C, 68.20;
H, 10.02%); dH (400 MHz, CDCl3/ TMS) 9.65 (s, 1H, alde-
hydic proton at C-1), 3.93±3.78 (m, 4H, ±OCH2CH2O±),
3.55 (t, 1H, 17-CH), 1.12 (s, 3H, 19-CH3), 0.853 (s, 9H,
Me3±C±Si), 0.68 (s, 3H, 18-CH3), 20.02 (s, 6H, Me2±
Si); dC (100.6 MHz, CDCl3/ TMS) 207.2 (C-1), 113.0
(C-5), 81.6 (C-17, 64.7 and 64.6 (±OCH2CH2O±), 25.8
(Me3±C±Si), 18.0 (Me3±C±Si), 11.4 (C-19), 10.6 (C-18),
24.53 and 24.9 (Me2±Si).
2.652 g (7.612 mmol, 79%) of the keto ester 15 as a color-
less oil. C21H32O4: MS (EI), m/z (%)ˆ348 (M1 1.55%), 262
(100%); dH (400 MHz, CDCl3/ TM) 3.59 (s, 3H, OMe), 205
(s, 3H, 21-CH3), 1.04 (s, 3H, 19-CH3), 0.61 (s, 3H, 18-CH3).
dC (100.6 MHz, CDCl3/ TMS) 214.0 (C-5), 208.9 (C-20),
174.1 (C-3), 63.3 (C-17), 51.4 (OMe), 20.2 (C-19), 13.2
(C-18).
Methyl 5,5,20,20-bis (ethylenedioxy)-3,5-seco-4-nor-
pregnan-3-oate (16). The diketo ester 15 (2.350 g,
6.74 mmol) was stirred overnight at room temperature
with trimethyl orthoformate (15 mL), ethylene glycol
(15 mL) and p-toluenesulfonic acid (65 mg). The mixture
was then diluted with dichloromethane and washed with 5%
sodium hydrogen carbonate solution, dried over anhydrous
magnesium sulfate, ®ltered, concentrated and the residue
was submitted to radial chromatography on silica gel
(4 mm layer rotor coated with silica gel, elution with
5±15% ethyl acetate in petroleum ether) affording 2.475 g
(5.67 mmol, 84%) of the bisketal ester 16 as a crystalline
white solid, mp (colorless crystals from pentane) 115±
1178C (Found: C, 68.60; H, 9.43. C25H40O6 requires: C,
68.78; H, 9.23%); dH (400 MHz, CDCl3/TMS) 3.87 (m,
8H, ±OCH2CH2O±), 3.60 (s, 3H, OMe), 2.52 and 2.29 (m
both, 1H each, 2-CH2), 1.24 (s, 3H, 21-CH3), 0.91 (s, 3H,
19-CH3), 0.72 (s, 3H, 18-CH3); dC (100.6 MHz, CDCl3/
TMS) 175.2 (C-3), 113.7 (C-5), 11.7 (C-20), 65.1, 64.0,
63.8 and 63.1 (2£±OCH2CH2O±), 58.2 (C-17), 51.2
(OMe), 18.0 (C-19), 12.9 (C-18).
17b-Hydroxy-10-formyl-5-oxo-des-A-androstane (10-
formyl-5-oxo-des-A-testosterone) (1). The ketal aldehyde
13 (0.1134 g, 0.268 mmol) was suspended in a mixture of
glacial acetic acid, THF and water (3:1:1; 4.5 mL) and
stirred overnight. Aqueous acetic acid was added (50% solu-
tion, 2 mL) and the mixture was heated to re¯ux (oil bath
temperature 1208C) for 40 min, after which no more starting
protected aldehyde could be detected by TLC. The mixture
was allowed to cool to room temperature, brine (20 mL) was
added and the mixture was thoroughly extracted with ethyl
acetate. The organic extract was washed with 5% sodium
hydrogen carbonate solution (15 mL), dried over mag-
nesium sulfate, ®ltered, concentrated and the residue was
chromatographed (silica gel, elution with 20% ethyl acetate
in petroleum ether) to afford 1 (69.8 mg, 0.264 mmol, 98%)
as a white crystalline solid, mp (colorless crystals from ben-
zene) 133±1348C (Found: C, 72.61; H, 8.96. C16H24O3
requires: C, 72.69; H, 9.15%). MS (EI), m/z (%)ˆ236
(100) M1228, 221 (56), 218 (19), 185 (14). No trace of
the M1-peak could be detected. dH (400 MHz, CDCl3/
TMS) 9.51 (s, 1H, CHO), 3.67 (t, 1H, 17-CH), 2.52 and
2.34 (dt, ddd respectively, 1H each, 6-CH2), 1.27 (s, 3H,
19-CH3), 0.79 (s, 3H,18-CH3); dC (100.6 MHz, CDCl3/
TMS) 212.4 (C-5), 201.1 (C-1), 81.1 (C-17), 62.0 (C-10),
49.9 (C-14), 46.0 (C-9), 42.8 (C-13), 37.9 (C-6), 35.6
(C-12), 34.8 (C-8), 30.6 (C-7), 29.8 (C-16), 23.2 (C-15),
21.3 (C-11), 12.7 (C-19), 11.0 (C-18).
Methyl 2-phenylseleno-5,5,20,20-bis(ethylenedioxy)-3,5-
seco-4-norpregnan-3-oate (17). To a three-neck round
bottom ¯ask equipped with septum inlet, magnetic stirring,
addition funnel and nitrogen inlet were added anhydrous
THF (4 mL) and diisopropyl amine (0.45 mL, 3.19 mmol).
The resulting solution was cooled in a dry ice±isopropanol
bath and treated with n-butyllithium in hexane (15%
solution, 2.0 mL, 3.28 mmol) for 30 min. The bisketal
ester 16 (0.997 g, 2.28 mmol) in THF (5 mL) was then
added dropwise and the reaction mixture was stirred at
2788C for another 30 min. Diphenyldiselenide (0.995 g,
3.19 mmol) in THF (2 mL) was quickly added and the reac-
tion mixture was stirred at 2788C for 1 h, allowed to warm
slowly to room temperature (over 1 h period), and then
quenched by adding saturated ammonium chloride solution.
After extraction with ethyl acetate the organic phase was
washed with 5% sodium hydrogen carbonate solution, dried
over anhydrous magnesium sulfate, ®ltered and the residue
was submitted to radial chromatography (silica gel coated
rotor, 4 mm layer, elution with 5±30% ethyl acetate in
petroleum ether), giving 1.225 g (2.071 mmol, 91%) of
compound 17 as a pale yellow solid. Compound 17 was
isolated as a diastereoisomeric mixture, in which the two
diastereoisomers are approximately in a ratio of 4 to 1: dH
(400 MHz, CDCl3/TMS) 7.61±7.58 (m, 2H, aromatic
protons), 7.29±7.26 (m, 3H aromatic protons), 3.98±3.77
(m, 8H, ±OCH2CH2O±), 3.53 and 3.48 (both s, 3H OMe,
relative proportion 4: 1), 2.58 (dd, 1H, CH±SePh), and 2.3
(dd, 1H, CH±SePh),1.28 and 1.26 (both s, 3H, 21-CH3),
0.96 and 0.95 (both s, 3H, 19-CH3), 0.74 and 0.73 (both s,
3H, 18-CH3); dC (100.6 MHz, CDCl3/TMS; relative inten-
sities, in a maximum of 10.00, are given) C-3, 174.8 (0.38)
and 174.5 (1.73); C-5, 113.5 (0.72) and 113.1 (2.24); C-20,
Methyl 5,20-dioxo-3,5-seco-4-norpregnan-3-oate (15). A
solution of progesterone (3.02 g, 9.60 mmol) in ethyl
acetate (100 mL) was treated with a stream of ozone until
no starting material could be detected by TLC (30 min). The
excess ozone was purged with air, and hydrogen peroxide
(30% solution, 25 mL) and water (5 mL) were added to the
reaction mixture. The biphasic mixture was stirred over
night at room temperature. The organic layer was then sepa-
rated, washed with water, concentrated to 1/3 of its initial
volume and extracted with saturated sodium carbonate solu-
tion (3£30 mL). The basic extract was acidi®ed with 10%
hydrochloric acid solution and extracted with ethyl acetate.
The organic phase was dried over magnesium sulfate,
®ltered and concentrated to yield the keto acid 14 as a
white foam. The crude keto acid was dissolved in methanol
(20 mL) and treated with diazomethane until the bright
yellow color of the solution persisted. The excess of diazo-
methane was discharged, the solvent was evaporated and the
residue submitted to chromatography (silica gel; elution
with 10±25% ethyl acetate in petroleum ether) giving

9964
I. G. J. de Avellar, F. W. Vierhapper / Tetrahedron 56 (2000) 9957±9965
111.8 (2.94); C-17, 58.2 (5.18) and 58.2 (1.48); OMe, 51.7
(1.02) and 51.7 (3.73); C-19 17.4 (2.56) and 16.6 (1.28);
C-18, 13.4 (1.35) and 12.9 (5.12). Aromatic carbons: 135.7
(8.89), 135.7 (2.80), 129.1 (0.85), 128.8 (10.00) and 128.8
(3.69), 128.4 (5.24). Ethylenedioxy groups are also to some
extent affected, since 6 signals were detected: 65.2 (4.77),
64.0 (2.90), 63.4 (5.40), 63.3 (5.24), 63.2 (6.04), 63.1 (2.49).
(C-20), 65.1, 64.7, 64.5, 63.1 (2£±OCH2CH2O±), 58.1
(C-17), 13.0 (C-19) and 10.6 (C-18).
10-Formyl-5,20-dioxo-des-A-pregnane
(10-formyl-5-
oxo-des-A-progesterone) (2). The bisketal aldehyde 19
(0.755 g, 1.99 mmol) was suspended in a 50% aqueous
solution of acetic acid (14 mL) and heated to re¯ux until
all the starting material had been consumed (oil bath
temperature 1258C, 30 min). The mixture was then diluted
with ethyl acetate and washed with brine (30 mL), with 5%
sodium hydrogen carbonate solution (2£30 mL), dried over
magnesium sulfate, ®ltered and concentrated. The residue
was submitted to chromatography on silica gel (¯ash
chromatography, 20 g silica gel, elution with 10±15%
ethyl acetate in petroleum ether) to give 0.492 g (1.69
mmol, 85%) of the bis-keto aldehyde 2 as a white crystalline
solid: mp (colorless crystals from benzene±pentane) 140±
1428C (Found: C, 74.16; H, 9.24. C18H26O3 requires: C,
74.45; H, 9.02%). MS (EI), m/z (%)ˆ262 (100) M1228,
247 (52), 201 (46). As for 1, no trace of the M1-peak could
be detected. For both compounds the largest peak was due to
the loss of a fragment with mass 28. High resolution mass
spectrometry for 2 showed this fragment to correspond to
C17H26O2 (calculated 262.1927; found 262.1933) and thus
resulting from the loss of CO. dH (400 MHz, CDCl3/ TMS)
9.51 (s, 1H, CHO), 2.54 (m, 2H, 17-CH and 6-H), 2.34 (ddd,
1H, the other 6-H), 2.10 (s, 3H, 21-CH3), 1.25 (s, 3H, 19-
CH3), 0.66 (s, 3H, 18-CH3); dC (100.6 MHz, CDCl3/ TMS)
212.5 (C-5), 208.8 (C-20), 201.4 (C-1), 63.1 (C-17), 62.3
(C-10), 55.6 (C-14), 45.6 (C-9), 44.0 (C-13), 38.1 (C-6),
37.9 (C-12), 34.0 (C-8), 31.3 (C-21), 30.6 (C-7), 24.2
(C-15), 22.6 (C-16), 22.2 (C-11), 13.2 (C-18), 12.3
(C-19). The assignments for C-6 and C-12 are uncertain.
Methyl 5,5,20,20-bis (ethylenedioxy)-3,5-seco-4-nor-
pregn-1-en-3-oate (18). To a solution of the a-phenyl-
seleno ester 17 (1.164 g, 1.97 mmol) in dichloromethane
(15 mL) in a three necked round bottom ¯ask (equipped
with condenser, thermometer, addition funnel, magnetic
stirring) pyridine was added (0.5 mL) and the solution was
cooled in an ice bath. To the cooled mixture a solution of
hydrogen peroxide (30% solution, 2 mL) in water (1 mL)
was added dropwise. When the addition was complete, the
temperature of the reaction mixture rose rapidly to 108C,
dropping thereafter. The cooling bath was removed and
stirring was continued at room temperature for 30 min.
The mixture was diluted with dichloromethane and washed
with 5% sodium hydrogen carbonate solution. The organic
phase was dried with anhydrous magnesium sulfate, ®ltered
and concentrated to give an off-white solid. The crude
product was then submitted to radial chromatography on
silica gel±silver nitrate coated rotor (2 mm layer, elution
with 5±10% ethyl acetate in petroleum ether) to give
0.717 g (1.65 mmol, 84%) of the a,b-unsaturated ester 18
as a white powder: mp (colorless crystals from benzene±
pentane) 188±1908C (Found: C, 68.88; H, 8.58. C25H38O6
requires: C, 69.10; H, 8.81%.); dH (400 MHz, CDCl3/ TMS)
7.01 (d, 1H, J 16.2, 1-HCv), 5,08 (d, 1H, Jˆ16.2 Hz,
2-HCv), 3.96±3,81 (m, 8H, ±OCH2CH2O±), 3.71 (s, 3H,
OMe), 1.26 (s, 3H, 21-CH3), 1.14 (s, 3H, 19-CH3), 0.73 (s,
3H, 18-CH3); dC (100.6 MHz, CDCl3/ TMS) 167.3 (C-3),
155.4 (C-1), 121.0 (C-2), 112.5 (C-5), 111.8 (C-20), 65.2
and 63.1 (±OCH2CH2O±), 58.1 (C-17), 51.3 (OMe), 13.0
(C-18).
1-Hydroxy-2-cyano-5,5,20,20-bis(ethylenedioxy)-2,5-seco-
3,4-dinor-pregnane (20). To a three neck round bottom
¯ask equipped with septa inlet, magnetic stirring and
addition funnel freshly distilled anhydrous THF (1 mL)
was added under an atmosphere of dry nitrogen. The ¯ask
was cooled by a dry ice±isopropanol bath, and n-butyl-
lithium (15% solution in hexane, 0.50 mL, 0.82 mmol)
was added, followed by 10% acetonitrile solution in anhy-
drous THF (0.40 mL, 0.75 mmol). The mixture was stirred
for 45 min and the ketal aldehyde 19 (0.220 g, 0.581 mmol),
in THF (2 mL), was added dropwise. Stirring was continued
for 45 min and the reaction was quenched with 10% ammo-
nium chloride solution (10 mL) and extracted with ether
(2£25 mL). The ether extract was dried over anhydrous
magnesium sulfate, ®ltered and concentrated. The residue
was submitted to radial chromatography (silica gel coated
rotor, 2 mm layer, elution with 15±30% ethyl acetate in
petroleum ether) affording 0.096 g of the adduct 20
(0.229 mmol, 39%, diastereoisomeric mixture) as a color-
less oil: dH (400 MHz, CDCl3/TMS) 4.2 to 3.9 (m, 9H,
1-C±(OH)±Hand ±OCH2±CH2O±), 2.95 to 2.5 (m, 2H,
CH2±CN), 1.25 (s, 3H, 21-CH3), 1.15 (s, 3H, 19-CH3),
0.75 (s, 3H, 18-CH3); dC (100.6 MHz, CDCl3/TMS) 119.4
and 115.3 (CN), 114.0 and 113.6 (C-5), 111.7 and 111.6
(C-20), 73.2 and 72.8 (C-1), 65.1, 65.0, 63.8, 63.6, 63.17,
63.13, 63.09, and 63.07 (±OCH2±CH2O±), 15.6 and 15.3
(C-19), 12.9 and 12.8 (C-18), and unchanged compound 19
(85 mg, 0.224 mmol). Yield based on unrecovered bisketal
aldehyde 19 is 64%.
10-Formyl-5,5,20,20-bis(ethylenedioxy)-des-A-pregnane
(19). The a,b-unsaturated keto ester 18 (0.565 g,
1.30 mmol) in a dichloromethane±methanol solution (2:1,
15 mL) was cooled in a dry ice±isopropanol bath and
treated with a stream of ozone until no starting material
remained (30 min). Excess ozone was then removed by a
stream of nitrogen, dimethyl sulphide (2.0 mL, 27.2 mmol)
was added to the solution at 2788C, and the resulting
mixture was allowed to come to room temperature and
was stirred overnight. The mixture was then diluted with
dichloromethane (30 mL), washed with 5% sodium hydro-
gen carbonate solution (30 mL), dried over anhydrous
magnesium sulfate, ®ltered and evaporated to yield a
white crystalline solid. The crude ozonolysis product was
submitted to radial chromatography (silica gel coated rotor,
2 mm layer, elution with 5±10% ethyl acetate in petroleum
ether), yielding 0.471 g (1.24 mmol, 96%) of the ketal
aldehyde 19 as a white crystalline solid: mp (colorless
crystals from benzene±pentane) 160±1628C (Found: C,
69.64; H, 9.28. C22H34O5 requires: C, 69.81; H, 9.05%);
dH (400 MHz, CDCl3/ TMS) 9.96 (s, 1H, CHO), 3.91±
3.79 (m, 8H, 2£±OCH2CH2O±), 1.26 (s, 3H, 21-CH3),
1.11 (s, 3H, 19-CH3) and 0.74 (s, 3H, 18-CH3); dC
(100.6 MHz, CDCl3/TMS) 207.3 (C-1), 113.0 (C-5), 111.8

I. G. J. de Avellar, F. W. Vierhapper / Tetrahedron 56 (2000) 9957±9965
9965
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