Highly diastereoselective hetero-Diels-Alder reaction of buta-1,3-diene with N-glyoxyloyl-(2R)-bornane-10,2-sultam: An efficient synthesis of homochiral (S)-3-[2-{(methylsulfonyl)oxy}ethoxy]-4-(triphenylmethoxy)-1-butanol methanesulfonate

Article abstract of DOI:10.1016/S0957-4166(02)00746-2

The influence of Lewis acid on the diastereoselectivity of [4+2] cycloaddition of buta-1,3-diene to N-glyoxyloyl-(2R)-bornane-10,2-sultam was investigated and high levels of asymmetric induction were achieved. (S)-3-[2-{(Methylsulfonyl)oxy}ethoxy]-4-(trip

Full text of DOI:10.1016/S0957-4166(02)00746-2

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 14 (2003) 239–244
Highly diastereoselective hetero-Diels–Alder reaction of
buta-1,3-diene with N-glyoxyloyl-(2R)-bornane-10,2-sultam:
an efficient synthesis of homochiral
(S)-3-[2-{(methylsulfonyl)oxy}ethoxy]-4-(triphenylmethoxy)-
1-butanol methanesulfonate
Małgorzata Kosior,a Małgorzata Malinowska,a Julita Jo´z´wik,a Jean-Claude Cailleb and
Janusz Jurczaka,c,
*
aDepartment of Chemistry, Warsaw University, Pasteura 1, 02-093 Warsaw, Poland
bPPG-SIPSY, Z.I. La Croix Cadeau B.P. 79, 49242, Avrille Cedex, France
cInstitute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
Received 24 October 2002; accepted 7 November 2002
Abstract—The influence of Lewis acid on the diastereoselectivity of [4+2] cycloaddition of buta-1,3-diene to N-glyoxyloyl-(2R)-
bornane-10,2-sultam was investigated and high levels of asymmetric induction were achieved. (S)-3-[2-
{(Methylsulfonyl)oxy}ethoxy]-4-(triphenylmethoxy)-1-butanol methanesulfonate were synthesized in 15% overall yield, applying
as a crucial step the above-mentioned [4+2] cycloaddition catalyzed by ZnBr2. © 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
pressure.9 Thus, we examined the diastereoselective
reaction of 6 with 8, as a potential route to enantiomer-
ically pure (S)-3-[2-{(methylsulfonyl)oxy}ethoxy]-4-
(triphenylmethoxy)-1-butanol methanesulfonate 4.
Naturally occurring indolocarbazoles, such as stau-
rosporine 11 and rebeccamycin 22 are known to be
inhibitors of protein kinase C (PKC), which regulates
vascular function.3 Recently, Jirousek et al.4 have iden-
tified a family of macrocyclic bisindolylmaleimides of
type 3 that are competitive, reversible inhibitors of
PKC. The promising biological and pharmacological
properties of compounds 3 encouraged Faul et al.5 to
synthesize them in enantiomerically pure form. A ret-
rosynthetic analysis (Scheme 1) shows that the crucial
intermediate for the synthesis is homochiral compound
4,4,5 which could be readily obtained from (S)-trityl-
2. Results
Our preliminary studies concerning the diastereoselec-
tive [4+2] cycloaddition of buta-1,3-diene 6 to chiral
glyoxylates10 suggested that this process requires opti-
mization. We first studied N-glyoxyloyl-(2R)-bornane-
10,2-sultam 8 as a chiral heterodienophile (Scheme 2) in
an effort to assess the influence of Lewis acids on this
reaction.
oxymethyl-3,6-dihydro-2H-pyran
5
via ozonolysis.6
Compound (S)-5 could be synthesized via enantioselec-
tive hetero-Diels–Alder reaction of buta-1,3-diene 6
with trityloxyacetaldehyde 7 or in its diastereoselective
version using, for example, N-glyoxyloyl-(2R)-bornane-
10,2-sultam 87 a highly activated heterodienophile con-
taining the efficient chiral auxiliary 11.8 Unfortunately,
the reaction of 6 with nonactivated heterodienophile 7
failed, even when it was carried out under very high
The hetero-Diels–Alder reactions of 6 with 8 were
carried out in methylene chloride at room temperature
in the presence of several Lewis acids: BF3·Et2O, AlCl3,
TiCl4, SnCl4, ZnCl2 and ZnBr2. The results are col-
lected in Table 1.
In all cases a mixture of distereoisomers (2%S)-9 and
(2%R)-9 was obtained. The highest diastereoselectivity
and the best yields were obtained when the reaction was
* Corresponding author.
0957-4166/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(02)00746-2

240
M. Kosior et al. / Tetrahedron: Asymmetry 14 (2003) 239–244
Scheme 1.
carried out in the presence of ZnBr2 (Table 1, entry 6).
Similar diastereoselectivity was found for ZnCl2 and for
the high-pressure experiment11 (Table 1, entries 5 and 7,
respectively) but in both cases, the yields were slightly
lower. Separation of the diastereoisomers was success-
fully executed using flash silica chromatography. X-Ray
structural analysis (Fig. 1) showed that the configura-
tion of the newly formed stereogenic center at C-2% was
(2%S) for the major diastereoisomer.
Table 1. Asymmetric [4+2]cycloaddition of 6 to 8
Figure 1. ORTEP diagram of (2%S)-9.
Entry Lewis acid Pressure Yield Diastereoisomeric ratio
(bar)
(%)
(2%S)-9:(2%R)-9
Having in hand a very good method for the synthesis of
diastereoisomerically pure compound (2%S)-9, we pur-
sued the synthesis of (S)-3-[2-{(methylsulfonyl)oxy}
1
2
3
4
5
6
7
BF3·Et2O
AlCl3
TiCl4
SnCl4
ZnCl2
ZnBr2
–
1
1
1
1
1
1
64
57
51
57
57
66
50
7:3
7:3
8:2
8:2
9:1
9:1
9:1
ethoxy]-4-(triphenylmethoxy)-1-butanol
methanesul-
fonate (4). Separate reduction of diastereoisomers (2%S)-
9 and (2%R)-9 with lithium aluminum hydride afforded
the respective enantiomerically pure (>99% ee) alcohols
(S)-10 and (R)-10 in a good yield. Then enantiomeric
10 000

M. Kosior et al. / Tetrahedron: Asymmetry 14 (2003) 239–244
241
Scheme 2. Reagents and conditions: (a) i. ZnBr2 (cat), CH2Cl2, −78°C“rt, 24 h; ii. Chromatographic separation; (b) LiAlH4, Et2O,
0°C“rt, 2 h; (c) TrCl, CH2Cl2, DMAP (cat), Et3N, 0°C, 12 h; (d) i. O3, CH2Cl2:MeOH (1:1 v/v), −50°C, 1 h; ii. NaBH4, 0.05
N NaOHaq; (e) MsCl, Et3N, CH2Cl2, 0°C, 2 h.
purities were confirmed by GC experiments using a
chiral column. Protection of the (S)-10 hydroxy group
using trityl chloride, gave (S)-5 in excellent yield; its
configuration was established by X-ray structural anal-
ysis (Fig. 2). Compound (S)-5 was then subjected to
ozonolysis, followed by reduction with sodium borohy-
dride to afford diol (S)-12. Treatment of diol (S)-12
with methanesulfonyl chloride gave the desired com-
pound (S)-4 in 15% overall yield.
3. Conclusions
The highly stereoselective synthesis of (S)-3-[2-
{(methylsulfonyl)oxy}ethoxy]-4-(triphenylmethoxy)-1-
butanol methanesulfonate 4 proceeds in 15% yield over
five steps, starting from N-glyoxyloyl-(2R)-bornane-
10,2-sultam 8. During the course of our studies we
found that the [4+2]cycloaddition of buta-1,3-diene 6 to
8 is Lewis acid dependent. The best results were
obtained for ZnBr2 as the catalyst. We also found that
the [4+2]cycloaddition of 6 to 8 can be successfully
conducted under high-pressure conditions in the
absence of a Lewis acid.
4. Experimental
4.1. General
Melting points were determined on a Kofler hot-stage
apparatus with a microscope, and are uncorrected. All
reported NMR spectra were recorded with a Varian
Unity plus spectrometer at 500 (1H NMR) and 125 (13C
NMR) MHz. Chemical shifts are reported as l values
relative to TMS peak defined at l=0.00 (1H NMR) or
l=0.0 (13C NMR). IR spectra were obtained on a
Perkin–Elmer 1640 FTIR spectrometer. Mass spectra
were obtained on an AMD 604 Intectra instrument
using the EI or LSIMS techniques, or on a Mariner
Figure 2. ORTEP diagram of (S)-5.

242
M. Kosior et al. / Tetrahedron: Asymmetry 14 (2003) 239–244
BioSystem unit using the ESI technique. Optical rota-
tions were recorded using a Perkin–Elmer 241 polar-
imeter with a thermally jacketed 10 cm cell. X-Ray
analysis was performed on a Kuma KM4CCD k-axis
diffractometer with graphite-monochromated Mo Ka
radiation. Elemental analysis (C, H, and N) were per-
formed by the ‘in-house’ analytical service. Analytical
TLC was carried out on commercially prepared plates
coated with 0.25 mm of Merck Kieselgel 60. Prepara-
tive flash silica chromatography was performed using
Merck Kieselgel 60 (230–400 mesh). GC experiments
were carried out on a Hewlett–Packard 5890 apparatus
equipped with a FID detector and b-Dex 225 chiral
column (30 m×0.25 mm I.D.).
4.2.4. Diastereoisomer (2%S)-9. Mp 189–191°C; [h]2D0=
−193.3 (c 1, CHCl3); 1H NMR (500 MHz, CDCl3,
27°C, TMS): l=0.97 (s, 3H), 1.13 (s, 3H), 1.34–1.47
(m, 2H), 1.85–1.96 (m, 3H), 1.99–2.04 (m, 1H), 2.10–
2.14 (dd, 1H, J1=8 Hz, J2=14 Hz), 2.27–2.35 (m, 1H),
2.41–2.47 (m, 1H, J1=1.5 Hz, J2=3.5 Hz, J3=15 Hz),
3.47 (AB, 2H, J1=13.5 Hz), 3.96 (dd, 1H, J1=4.75 Hz,
J2=7.75 Hz), 4.27–4.39 (m, 2H), 4.71 (dd, 1H, J1=3
Hz, J2=10.25 Hz), 5.74–5.77 (m, 1H, J1=1.5 Hz, J2=
10.5 Hz), 5.81–5.85 (m, 1H); 13C NMR (125 MHz,
CDCl3, 27°C, TMS): l=19.9, 20.7, 26.4, 28.6, 32.7,
38.1, 44.5, 47.9, 48.7, 53.1, 65.0, 65.8, 72.8, 122.7, 126.1,
170.63; IR (KBr): w=1054, 1135, 1337, 1713, cm−1; MS
(EI LR) m/z=325 (M)+ (1.6%), 244 (10.9%), 177
(15.0%), 135 (23.4%), 93 (15.5%), 83 (100%), 82
(32.8%), 75 (48.1%), 55 (51.6%), 41 (10.8%). Anal. calcd
for C16H23NSO4: C, 59.05; H, 7.12; N, 4.30; S, 9.85.
Found: C, 58.79; H, 7.25; N, 4.14; S, 9.65%.
All chemicals were used as received unless otherwise
noted. Reagents grade solvents were dried and distilled
prior to use. N-Glyoxyloyl-(2R)-bornane-10.2-sultam
was prepared according to the literature procedure.7
4.3. Transformation of (2%S)-9 into (S)-5
4.2. [4+2]Cycloaddition of buta-1,3-diene (6) to N-
glyoxyloyl-(2R)-bornane-10,2-sultam (8)
To a solution of LiAlH4 (0.03 mol) in diethyl ether (80
mL), the enantiomerically pure (2%S)-9 (0.06 mol) dis-
solved in dry CH2Cl2 (10 mL) was added dropwise, and
a reaction mixture was stirred for 2 h. After usual
work-up, a post-reaction mixture was filtered, and
filtrate was dried with MgSO4. After evaporation of
CH2Cl2, addition of hexane to the residue caused pre-
cipitation of sultam 11 which was filtered off, and
hexane was removed by distillation. The residue was
diluted with dry CH2Cl2 (500 mL) and treated with
trityl chloride (0.07 mol) in the presence of catalytic
amount of DMAP. A solution was cooled (0°C) and
Et3N (0.07 mol) was added in a stream of argon. After
12 h stirring, a post-reaction mixture was washed with
brine (100 mL), dried with Na2SO4, and solvents were
evaporated. The residue was then directly subjected to
flash silica chromatography using hexane/ethyl acetate
(30:1) as an eluent. Overall yield of (S)-5 counted on
(2%S)-9 was 60%.
4.2.1. Lewis acid-catalyzed reaction, typical procedure.
The heterodienophile 8 (0.1 mol) was dissolved in dry
CH2Cl2 (100 mL) and added to a suspension of ZnBr2
(0.1 mol) in CH2Cl2 (100 mL), and the mixture was
stirred for 1 h at room temperature. Then the mixture
was cooled to −78°C and buta-1,3-diene (6, 0.3 mol)
was added dropwise, and it was stirred for additional
24 h at rt. After evaporation of solvents, the residue
was chromatographed on a silica-gel column using a
hexane/acetone/ethyl acetate (2.5:3:1 v/v/v) system to
give two diastereoisomerically pure products (2%S)-9
and (2%R)-9 in a ratio of 9:1 with 69% overall yield.
4.2.2. High-pressure reaction, typical procedure.11 In a
Teflon ampoule was placed a solution of buta-1,3-diene
(6, 2 mmol) and heterodienophile 8 (1 mmol) in dry
CH2Cl2 (2 mL). The ampoule was subjected to a high-
pressure apparatus and compressed up to 10 kbar for
48 h. After decompression, the post-reaction mixture
was purified on a silica-gel column as in Section 4.2.1 to
afford two pure diastereoisomers (2%S)-9 and (2%R)-9 in
a 9:1 ratio with 50% overall yield.
4.3.1. Alcohol (S)-10. [h]2D0=−147.4 (c 1.02, CDCl3);
>99% ee (determined by GC on chiral column b-dex
1
225); H NMR (500 MHz, CDCl3, 27°C, TMS): l=
1.87–1.93 (m, 1H), 2.06–2.14 (m, 1H), 2.18–2.53 (m,
1H; –OH), 3.56–3.60 (m, 1H), 3.65–3.69 (m, 1H), 3.67–
3.70 (m, 1H), 4.22–4.24 (m, 2H), 5.67–5.76 (m, 1H),
5.80–5.85 (m, 1H); 13C NMR (125 MHz, CDCl3, 27°C,
TMS): l=26.5, 65.6, 65.7, 74.1, 123.7, 126.2; IR (film):
w=1641, 3393 cm−1; MS (ESI HR): calcd for
[C6H10O2Na]+ 137.0573, found 137.0579.
4.2.3. Diastereoisomer (2%R)-9. Mp 144–145°C; [h]2D0=
1
−32 (c 1, CHCl3); H NMR (500 MHz, CDCl3, 27°C,
TMS): l=0.99 (s, 3H), 1.21 (s, 3H), 1.32–1.43 (m, 2H),
1.85–1.97 (m, 3H), 2.09 (dd, 1H, J1=8 Hz, J2=13.5
Hz), 2.14–2.19 (m, 1H), 2.24–2.31 (m, 1H), 2.47–2.55
(m, 1H), 3.47 (AB, 2H, J1=13.5 Hz), 3.95 (dd, 1H,
J1=5 Hz, J2=7.75 Hz), 4.23–4.33 (m, 2H), 4.60 (dd,
1H, J1=3.25 Hz, J2=10.5 Hz), 5.71–5.75 (m, 1H, J1=
10 Hz), 5.83–5.88 (m, 1H); 13C NMR (125 MHz,
CDCl3, 27°C, TMS): l=19.9, 21.3, 26.3, 26.4, 33.3,
38.6, 45.0, 47.8, 48.6, 53.3, 65.8, 66.1, 72,7, 123.2, 125.7,
170.2; IR (KBr): w=1080, 1138, 1332, 1691 cm−1; MS
(EI LR) m/z=325 (M)+ (2.0%), 244 (10.3%), 177
(10.6%), 135 (21.9%), 93 (15.3%), 83 (100%), 82
(31.3%), 55 (51.6%), 41 (13.6%). Anal. calcd for
C16H23NSO4: C, 59.05; H, 7.12; N, 4.30; S, 9.85.
Found: C, 59.02; H, 7.16; N, 4.27; S, 9.70%.
4.3.2. Alcohol (R)-10. [h]1D5=+140.7 (c 1, CDCl3); >99%
1
ee (determined by GC on chiral column b-dex 225); H
NMR and 13C NMR were the same as in Section 4.3.1.
4.3.3. Compound (S)-5. Mp 124–126°C; [h]2D1=−74.2 (c
1
1, CDCl3); H NMR (500 MHz, CDCl3, 25°C, TMS):
l=2.00–2.11 (m 2H), 3.02–3.05 (m, 1H), 3.27 (dd, 1H,
J1=6 Hz, J2=10 Hz), 3.77 (sextet, 1H), 4.18–4.26 (m,
2H), 5.67–5.74 (m, 1H), 5.79–5.83 (m, 1H), 7.23 (q, 3H,
J1=7.5 Hz), 7.29 (t, 6H, J1=7.5 Hz), 7.47 (d, 6H,
J1=7.5 Hz); 13C NMR (125 MHz, CDCl3, 25°C, TMS):

M. Kosior et al. / Tetrahedron: Asymmetry 14 (2003) 239–244
243
l=28.1, 65.9, 66.7, 73.0, 86.4, 123.9, 126.3, 126.9,
127.8, 128.7, 144.1; IR (KBr) w=1595 cm−1; MS (ESI
HR): calcd for [C25H24O2Na]+ 379.1674, found
379.1674.
The structure was solved by direct methods12 and
refined using SHELXL.13 The refinement was based on
F2 for all reflections except those with very negative F2.
Weighted R factors wR and all goodness-of-fit S values
are based on F2. Conventional R factors are based on F
with F set to zero for negative F2. The Fo2>2s(Fo2)
criterion was used only for calculating R factors and is
not relevant to the choice of reflections for the refine-
ment. The R factors based on F2 are about twice as
large as those based on F. All hydrogen atoms were
located from a differential map and refined isotropi-
cally. Scattering factors were taken from Tables 6.1.1.4
and 4.2.4.2 in Ref. 14.
4.4. (S)-3-(2-Hydroxyethoxy)-4-(triphenylmethoxy)-1-
butanol (12)
Compound (S)-5 was subjected to ozonolysis which
was carried out at −50°C in a mixture of solvents
CH2Cl2/MeOH (1:1 v/v), and in the presence of Sudan
indicator. After 2 h of ozonolysis, when the color of the
indicator was changed, the reaction mixture was treated
with cooled (0–5°C) solution of NaBH4 (2.2 equiv.) in
0.05N NaOHaq. When the addition was completed, the
temperature of the reaction mixture was allowed to rise
to rt, and was stirred for an additional 12 h. After that
a post-reaction mixture was concentrated and washed
with water. An organic layer was dried with MgSO4
and solvents were evaporated to give (S)-12 as an oil
with 50% yield.
Crystallographic data (excluding structural factors) for
the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data
Centre under the deposition numbers CCDC 194388
and 194387 for (2%S)-9 and (S)-5, respectively.
Compound
(2%S)-9:
C16H23NSO4,
M=325.41,
orthorhombic, a=7.921(2), b=12.786(3), c=16.148(3)
3
,
,
A, space group P212121, V=1635.4(6) A , Z=4, Dc=
1.322 Mg m−3, v(Mo Ka)=0.215 mm−1, T=293 K,
16501 reflections measured, 16501 unique reflections
(Rint=0.1285), which were used in all calculations.
Compound (S)-12: [h]2D1=−20.7 (c 1.01, CDCl3); 1H
NMR (500 MHz, CDCl3, 25°C, TMS): l=1.76 (q, 2H,
J1=6.0 Hz), 2.47 (br s, 2H; -OH), 3.15 (dd, 1H, J1=
4.25 Hz, J2=10 Hz), 3.21 (dd, 1H, J1=6.0 Hz, J2=10.0
Hz), 3.64–3.60 (m, 1H), 3.68–3.75 (m, 4H), 3.73–3.82
(m, 2H), 7.22–7.26 (m, 3H), 7.28–7.31 (m, 6H), 7.43–
7.46 (m, 6H); 13C NMR (125 MHz, CDCl3, 25°C,
TMS): l=34.4, 60.3, 62.3, 66.2, 71.8, 78.5, 86.9, 127.1,
127.8, 128.7, 143.9; IR (film CH2Cl2) w=1597, 3370
cm−1; MS (LSIMS HR): calcd for [C25H28O4Na]+
415.18853, found 415.18901.
Data/parameters: 16501/202. The final R1=0.0639 (all
3
,
data). Residual electron density: 0.201 and −0.172 e A .
Compound (S)-5: C25H24O2, M=356.44, monoclinic,
,
a=9.5656(19), b=10.602(2), c=19.905(4) A, space
3
−3
,
group P21, V=1963.1(7) A , Z=4, Dc=1.206 Mg m ,
v(Mo Ka)=0.075 mm−1, T=293 K, 25391 reflections
measured, 25391 unique reflections (Rint=0.1220),
which were used in all calculations. Data/parameters:
25391/488. The final R1=0.0563 (all data). Residual
electron density: 0.137 and −0.153 e A .
4.5. (S)-3-[2-{(Methylsulfonyl)oxy}ethoxy]-4-(triphenyl-
methoxy)-1-butanol methanesulfonate (4)
3
,
Diol (S)-12 was dissolved in 50 mL of dry CH2Cl2, the
solution was cooled to 0°C, and after addition of Et3N
(0.03 mol), mesyl chloride (0.03 mol) was added. After
additional stirring at 0–5°C for 2 h, the reaction mix-
ture was washed with water (2×20 mL), and treated
with brine (20 mL). An organic layer was dried with
MgSO4, and solvents were evaporated. The solid
residue was recrystallized from a mixture of heptane/
ethyl acetate, to afford the pure product (S)-4 in 80%
yield, which is thermally unstable.5 1H and 13C NMR
spectra are identical with those obtained by Lilly
Research Laboratories.5
Acknowledgements
The authors thank Dr. M. Asztemborska, Institute of
Physical Chemistry of the Polish Academy of Sciences,
Warsaw, for carrying out the GC experiments. X-Ray
measurements were undertaken in the Crystallographic
Unit of the Physical Chemistry Laboratory at the
Chemistry Department of the Warsaw University.
Financial support from the Polish Committee for Scien-
tific Research (Grant 7 T09A 136 21) and from PPG
Industries Inc is gratefully acknowledged.
4.6. X-Ray structure determination of (2%S)-9 and (S)-5
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time of 15 s. The data were corrected for Lorentz and
polarization effects. No absorption correction was
applied. Data reduction and analysis were carried out
with the Kuma Diffraction (Wrocław) programs.
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