Synthesis of (2R,3S,4S)-4-aryl-3-hydroxyprolinols

Article abstract of DOI:10.1016/j.tet.2006.10.002

Synthesis of (2R,3S,4S)-4-aryl-3-hydroxyprolinols has been established starting from 2-benzyloxymethylpyrrolidin-2-one framework, which is derived from commercially available trans-(2S,4R)-4-hydroxyproline. The single diastereomer having a trans-cis relat

Full text of DOI:10.1016/j.tet.2006.10.002

Tetrahedron 62 (2006) 12334–12339
Synthesis of (2R,3S,4S)-4-aryl-3-hydroxyprolinols
b
a
Meng-Yang Chang,a, Chun-Yu Lin and Tsun-Cheng Wu
*
aDepartment of Applied Chemistry, National University of Kaohsiung, No. 700, Kaohsiung University Road,
Kaohsiung 811, Taiwan, ROC
bDepartment of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, ROC
Received 8 September 2006; revised 29 September 2006; accepted 2 October 2006
Available online 27 October 2006
Abstract—Synthesis of (2R,3S,4S)-4-aryl-3-hydroxyprolinols has been established starting from 2-benzyloxymethylpyrrolidin-2-one frame-
work, which is derived from commercially available trans-(2S,4R)-4-hydroxyproline. The single diastereomer having a trans–cis relative
configuration with C2 and C3 and C3 and C4 is constructed in two one-pot functional group transformations of Grignard addition/dehydration
and epoxidation/isomerization as the key steps in moderate yield.
Ó 2006 Elsevier Ltd. All rights reserved.
Ar
OH
HO
1. Introduction
4 3
2
OH
Based on the structural framework of trans-(2S,4R)-4-
hydroxyproline, it possesses three functional groups that can
be easily modified and they are 1-amino, 2-carboxylate and
4-hydroxy groups.1 The skeleton represents the significant
feature for producing a series of different carbon frameworks
such as monocycles (pyrrole,2a pyrrolidine,2b,c,l piperidine2d
and azanucleoside2e), fused or bridged bicycles (pyrrolizidi-
ne2f or azabicycles2g,h,m), polycycles,2i–k,n macrocycle,2o
etc. using an efficient modification technique.
CO2H
N
N
H
Ts
(2R,3S,4S)-4-aryl-3-hydroxyprolinol trans-(2S,4R)-4-hydroxyproline
Figure 1. Structures of (2R,3S,4S)-4-aryl-3-hydroxyprolinol and trans-
(2S,4R)-4-hydroxyproline.
hydroxyprolinols were investigated (Fig. 1). Our interest in
synthesizing 4-aryl-3-hydroxyprolinol (4-aryl-3-hydroxy-
2-hydroxymethylpyrrolidine) skeleton was piqued on the
different biological properties and because it is with the mo-
tif of 3-hydroxyl group and is a key intermediate for prepar-
ing many important skeletons of substituted piperidines and
prolines.3 Prolinol is an a-aminoalcohol with a unique na-
ture inducing specific electronic and geometric features. The
presence of such a ring in the chemical structure restricts
conformational flexibility, which may efficiently modify
binding affinity to its target. In addition, this peptidomimetic
compound is expected to be more stable to hydrolysis by
metabolic enzymes.
Recently, we have introduced a facile and straightforward
approach toward monocyclic pyrrolidine (anisomycin)2l
and piperidine (a-conhydrine),2m bicyclic bridged 7-azabi-
cyclo[2.2.1]heptane (epibatidine)2n and pyrrolophane (strep-
torubin B core),2o bicyclic fused hexahydro-1H-indol-3-one
(pancracine)2p and acyclic g-amino acid (statin and vigaba-
trinÒ)2q,r skeleton system via some easy functional group
transformations, intramolecular basic alkylation, acidic aldol
condensation, ring-closing metathesis and regioselective
Baeyer–Villiger oxidation of different 2-substituted pyrroli-
din-4-one framework employing trans-(2S,4R)-4-hydroxy-
proline as the starting material.
To demonstrate the synthetic utility of our methodology and
explore the application to the synthesis of 2-substituted pyr-
rolidin-4-one, synthetic studies toward (2R,3S,4S)-4-aryl-3-
2. Results and discussion
2.1. Retrosynthetic analysis of (2R,3S,4S)-4-aryl-3-
hydroxyprolinols 1a–d
Keywords: (2R,3S,4S)-4-Aryl-3-hydroxyprolinols; trans-(2S,4R)-4-Hy-
droxyproline; One-pot reaction; Grignard addition/dehydration; Epoxida-
tion/isomerization.
* Corresponding author. Tel.: +886 7 5919464; fax: +886 7 5919348;
e-mail: mychang@nuk.edu.tw
We now wish to report an easy and straightforward synthesis
of (2S)-2-benzyloxymethylpyrrolidin-4-one 3 leading to four
(2R,3S,4S)-4-aryl-3-hydroxyprolinols 1a–d by two remark-
able one-pot transformations as shown in Scheme 1. One
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.10.002

M.-Y. Chang et al. / Tetrahedron 62 (2006) 12334–12339
12335
is the access to produce (2S)-4-aryl-2-benzyloxymethyl-2,5-
dihydropyrroles 2a–d by the Grignard addition of compound
3 and subsequent boron trifluoride etherate mediated dehy-
dration of the resulting tertiary alcohols. The other is a spe-
cific step from olefins 2a–d to diols 1a–d by stereochemical
epoxidation and followed by boron trifluoride etherate medi-
ated isomerization of the resulting epoxides.
not observed. In the other way, one-pot reaction of ketone
3 with methylmagnesium bromide and followed by dehydra-
tion was also examined. Treatment of 4-hydroxy-4-methyl-
2-benzyloxymethylpyrrolidine yielded 4-methyl-2-benzyl-
oxymethyl-2,5-dihydropyrrole in trace amounts under the
acidic conditions (e.g., boron trifluoride etherate, aluminum
chloride and Dean–Stark distillation). Based on these re-
sults, we envisioned that aryl group is an important substit-
uent, which easily provides a stable benzylic cation in the
dehydration process. However, 4-methyl-2-benzyloxymethyl-
2,5-dihydropyrrole was carried out in 34% yield by the basic
dehydration of this tertiary alcohol with mesyl chloride and
pyridine.
Ar
OH
Ar
O
OH
OBn
OBn
N
N
N
Ts
Ts
Ts
1
2
3
To investigate the relative stereochemistry of diols 1a–d at
C2 and C3 and C3 and C4 positions, epoxidation of olefins
2a–d and isomerization of the resulting epoxides 2aa–da
were studied in the next stage. Epoxidation of model sub-
strate 2a with m-chloroperoxybenzoic acid afforded a sole
epoxide 2aa with three contiguous asymmetric centers in
92% yield. The structural stereochemistry of epoxide 2aa
was determined by single-crystal X-ray analysis (Diagram
1).5 According to the provided epoxide 2aa, we envisioned
that stereoselective epoxidation of olefin 2a was strongly af-
fected by the steric hindrance of 2-benzyloxymethyl group.6
Both 4-phenyl and 2-benzyloxymethyl groups in the struc-
ture of epoxide 2aa could be arranged as cis configuration.
Next, ketone 5a was afforded by the selective isomerization
of trisubstituted epoxide 2aa via hydride shift in 91% yield.7
Therefore, the stereochemical assignment of ketone 5a at C2
and C4 centers was made the trans configuration.
a, Ar=C6H5; b, Ar=2-CH3C6H4; c, Ar=2-CH3OC6H4; d, Ar=3,4-CH2O2C6H3
Scheme 1. Retrosynthetic analysis of (2R,3S,4S)-4-aryl-3-hydroxyprolinols
1a–d.
2.2. Synthesis of (2R,3S,4S)-4-aryl-3-hydroxyprolinols
1a–d
In a previous report,2m–q synthesis of prolinol 4 from trans-
(2S,4R)-4-hydroxyproline provided a 90% overall yield with
purification done only once via a facile four-step reaction.
As shown in Scheme 2, prolinol 4 was first transformed into
ketone 3 (82% yield in two steps) by O-benzylation and
Jones oxidation under the standard conditions. With enough
amounts of ketone 3, conversion of ketone 3 into olefins
2a–d was further examined.
TBSO
O
For the epoxidation of olefins 2c–d with electron-donating
groups, the desired epoxides 2ca–da could not be obtained
and complex products were isolated during silica gel chro-
matography. With the previous experiences in mind,8 we
envisioned that the problem was solved by the one-pot reac-
tion. Therefore, ketones 5a–d were yielded via the one-pot
reaction of olefins 2a–d with the combination of m-chloro-
peroxybenzoic acid and followed by boron trifluoride ether-
ate in 60–84% overall yield. Ketones 5a–d must be purified
by recrystallization from dichloromethane and methanol
because the generated racemic mixture was observed by
the epimerization of C2 or C4 position during silica gel-
mediated chromatographic purification.
1) NaH, BnBr
RMgBr, then
BF3-OEt2
OH
OBn
2) Jones ox.
(two steps 82%)
N
Ts
N
Ts
3
4
Ar
Ar
Ar
OH
O
MCPBA, then
4
1) DIBALH
2
OH
OBn
OBn
BF3-OEt2
2) H2, Pd/C
N
N
Ts
N
Ts
Ts
2a, Ar=C6H5, 73%
5a, 84%
5b, 74%
5c, 68%
5d, 60%
1a, 69%
1b, 63%
1c, 61%
1d, 55%
2b, Ar=2-CH3C6H4, 68%
2c, Ar=4-CH3OC6H4, 60%
2d, Ar=3,4-CH2O2C6H3, 63%
Scheme 2. Synthetic approach toward (2R,3S,4S)-4-aryl-3-hydroxyproli-
nols 1a–d.
Treatment of ketone 3 with different arylmagnesium bro-
mide reagents (a, Ar¼C6H5; b, Ar¼2-CH3C6H4; c, Ar¼4-
CH3OC6H4; d, Ar¼3,4-CH2O2C6H3) in tetrahydrofuran
provided a pair of diastereoisomers (ca. 1:1 ratio) without
any induction onto the stereoselectivity.4a Following this
similar approach, attempts to form a sole tertiary alcohol un-
der a variety of conditions (prolonged reaction time, diverse
temperature, different solvents) were unsuccessful.4
With these results in hand, the direct one-pot conversion for
the reaction of ketone 3 with four arylmagnesium bromide
reagents and subsequent dehydration of the resulting tertiary
alcohols with boron trifluoride etherate yielded compounds
2a–d in 60–73% overall yield. During the one-pot process,
4-aryl-2-benzyloxymethyl-2,3-dihydropyrrole framework was
Diagram 1. X-ray crystallography of epoxide 2aa.

12336
M.-Y. Chang et al. / Tetrahedron 62 (2006) 12334–12339
Briefly, ketones 5a–d were obtained via the stereoselective
epoxidation of olefins 2a–d with m-chloroperoxybenzoic
acid and followed by isomerization of the resulting epoxides
2aa–da with boron trifluoride etherate. Two one-pot proce-
dures of Grignard addition/dehydration and epoxidation/
isomerization were monitored by TLC until the reaction
was completed. The overall simple procedure was achieved
within one working day.
reaction mixture was stirred at refluxed temperature for
20 h. The resulting mixture was cooled to room temperature,
quenched with aqueous ammonium chloride solution (15%,
10 mL) and concentrated. The residue was extracted with
ethyl acetate (3ꢂ150 mL) and the combined organic layers
were washed with brine, dried, filtered and evaporated to af-
ford the crude product. Without further purification, excess
Jones reagent (15 mL) was added to a stirred solution of re-
sulting benzyl compound in acetone (200 mL) at 0 ꢁC. The
mixture was stirred for 20 min and treated with 2-propanol
(10 mL) to destroy the unreacted oxidizing reagent. After
the solvent was removed, the residue was diluted with water
(10 mL) and extracted with diethyl ether (3ꢂ150 mL). The
combined organic layers were dried, filtered and evaporated
to afford crude product. Purification on silica gel (hexane/
ethyl acetate¼4:1) afforded compound 3 (5.9 g, two steps
82%). White solid; mp¼118–119 ꢁC; [a]D25 +41.10 (c 0.21,
CHCl3); IR (CHCl3) 2959, 1766, 1312, 1141, 1094,
688 cmꢀ1; FAB-MS: C19H22NO4S m/z (%)¼91 (100), 155
(19), 224 (36), 238 (52), 360 (M++1, 17); HRMS (ESI,
M++1) calcd for C19H22NO4S 360.1270, found 360.1272;
1H NMR (500 MHz, CDCl3) d 7.72 (d, J¼8.5 Hz, 2H),
7.32–7.26 (m, 5H), 7.16 (d, J¼8.5 Hz, 2H), 4.43 (d,
J¼12.0 Hz, 1H), 4.43–4.38 (m, 1H), 4.37 (d, J¼12.0 Hz,
1H), 3.78 (dd, J¼3.5, 9.5 Hz, 1H), 3.76 (s, 2H), 3.52 (dd,
J¼3.5, 9.5 Hz, 1H), 2.43 (s, 3H), 2.39–2.29 (m, 2H); 13C
NMR (125 MHz, CDCl3) d 209.09, 144.08, 137.39,
135.36, 130.01 (2ꢂ), 128.41 (2ꢂ), 127.75, 127.31 (2ꢂ),
127.07 (2ꢂ), 73.37, 73.22, 56.84, 53.92, 40.47, 21.52;
Anal. Calcd for C19H21NO4S: C, 63.49; H, 5.89; N, 3.90.
Found: C, 63.41; H, 6.01; N, 3.71.
With the requisite ketones 5a–d in hand, we examined the
reduction of ketones 5a–d. When the model substrate 5a
was treated with sodium borohydride or lithium aluminum
hydride under different temperatures, two diastereoisomers
were obtained in a 2:3 ratio. Therefore, reduction of ketone
5a with diisobutylaluminum hydride at ꢀ78 ꢁC afforded the
sole benzyl alcohol 5aa. Other benzyl alcohols 5ba–da were
also afforded by this reduction. Finally, hydrogenolysis of
the benzyl alcohols 5aa–da with a catalytic amount of
10% palladium on activated carbon yielded (2R,3S,4S)-4-
aryl-3-hydroxyprolinols 1a–d. According to the literature
reports,9 the coupling constant (JH3–H4 value) with cis con-
figuration was approximately determined to be about 2.8–
4.2 Hz in the prolinol or proline skeleton.3f,9c,h In compari-
son with the prolinols 1a–d, we believe that the relative
stereochemical centers at C3 and C4 positions were also as-
signed by correlation of the H3–H4 coupling constant (e.g.,
1a, d 4.45, JH3–H4¼4.0 Hz). Thus, the assignment of three
contiguous stereocenters on pyrrolidine framework of com-
pounds 1a–d was made the trans–cis configuration.
3. Conclusion
4.3. A representative procedure with one-pot reaction
for the preparation of olefins 2a–d
In summary, we have developed two one-pot Grignard addi-
tion/dehydration and epoxidation/isomerization as the key
transformations for synthesizing (2R,3S,4S)-4-aryl-3-
hydroxyprolinols 1a–d with potential biological activities.
Further application of this methodology to the synthesis of
4-methyl-3-hydroxyproline (4-HMP), which is the common
constituent of the active echinocandin family,10 is now
underway.
A solution of different arylmagnesium bromide reagents
(1.0 M in tetrahydrofuran, 1 mL, 1.0 mmol) was added to
a stirred solution of ketone 3 (180 mg, 0.5 mmol) in tetra-
hydrofuran (20 mL) at ꢀ78 ꢁC. The reaction mixture was
stirred at room temperature for 2 h. The total procedure
was monitored by TLC until the reaction was completed.
Without further purification, boron trifluoride etherate
(1 mL) was added to a stirred solution of the resulting reac-
tion mixture at 0 ꢁC. The reaction mixture was stirred at
room temperature for 15 min. Saturated sodium bicarbonate
solution (10 mL) was added to the reaction mixture and the
solvent was concentrated under reduced pressure. Water
(2 mL) and ethyl acetate (10 mL) were added to the residue
and the mixture was filtered through a short plug of Celite.
The filtrate was concentrated under reduced pressure. The
residue was extracted with ethyl acetate (3ꢂ20 mL). The
combined organic layers were washed with brine, dried, fil-
tered and evaporated to afford crude product under reduced
pressure to yield the crude compound. Purification on silica
gel (hexane/ethyl acetate¼8:1–4:1) afforded olefins 2a–d in
60–73% overall yield.
4. Experimental
4.1. General
Tetrahydrofuran was distilled prior to use. All other reagents
and solvents were obtained from commercial sources and
used without further purification. Reactions were routinely
carried out under an atmosphere of dry nitrogen with mag-
netic stirring. Products in organic solvents were dried with
anhydrous magnesium sulfate before concentration in vacuo.
4.2. (2S)-2-Benzyloxymethyl-1-(4-methylphenylsulfo-
nyl)pyrrolidin-4-one (3)
A solution of prolinol 4 (7.7 g, 20.0 mmol) in tetrahydrofu-
ran (100 mL) was added to a rapidly stirred suspension of so-
dium hydride (1.60 g, 60%, 40.0 mmol) in tetrahydrofuran
(30 mL). After the reaction mixture was stirred at room tem-
perature for 20 min, a solution of benzyl bromide (5.0 g,
29.0 mmol) in tetrahydrofuran (100 mL) was added. The
4.3.1. 2-Benzyloxymethyl-4-phenyl-1-(4-methylphenyl-
sulfonyl)-2,5-dihydro-1H-pyrrole (2a). Viscous oil; [a]D24
ꢀ12.45 (c 0.043, CHCl3); IR (CHCl3) 2360, 1636, 1345,
1163, 1092, 754, 695 cmꢀ1; FAB-MS: C25H26NO3S m/z
(%)¼91 (100), 137 (28), 154 (20), 298 (6), 420 (M++1,
15); HRMS (ESI, M++1) calcd for C25H26NO3S 420.1633,

M.-Y. Chang et al. / Tetrahedron 62 (2006) 12334–12339
12337
1
found 420.1632; H NMR (500 MHz, CDCl3) d 7.74 (d,
108.23, 105.77, 101.25, 73.96, 73.65, 67.02, 55.93, 21.51.
Anal. Calcd for C26H25NO5S: C, 67.37; H, 5.44; N, 3.02.
Found: C, 67.50; H, 5.70; N, 3.21.
J¼8.5 Hz, 2H), 7.36–7.26 (m, 12H), 6.14 (br d, J¼2.0 Hz,
1H), 4.70–4.65 (m, 1H), 4.62–4.54 (m, 1H), 4.59 (s, 2H),
4.43 (d, J¼14.0 Hz, 1H), 4.03 (dd, J¼4.0, 9.5 Hz, 1H),
3.63 (t, J¼9.5 Hz, 1H), 2.40 (s, 3H); 13C NMR (125 MHz,
CDCl3) d 143.71, 138.13, 137.15, 134.06, 132.35, 129.84
(2ꢂ), 128.64 (2ꢂ), 128.48, 128.40 (2ꢂ), 127.70 (2ꢂ),
127.68, 127.50 (2ꢂ), 125.52 (2ꢂ), 122.14, 73.96, 73.67,
67.13, 55.80, 21.50. Anal. Calcd for C25H25NO3S:
C, 71.57; H, 6.01; N, 3.34. Found: C, 71.68; H, 6.29; N,
3.57.
4.4. A general representative procedure with one-pot
reaction for the preparation of ketones 5a–d
m-Chloroperoxybenzoic acid (70 mg, 75%, 0.3 mmol) was
added to a solution of olefins 2a–d (0.2 mmol) in dichloro-
methane (10 mL). The reaction mixture was stirred at
room temperature for 3–5 h. The total procedure was moni-
tored by TLC until the reaction was completed. Without fur-
ther purification, boron trifluoride etherate (1 mL) was
added to a stirred solution of the resulting epoxides 2aa–
da at 0 ꢁC. The reaction mixture was stirred at room temper-
ature for 15 min. Saturated sodium bicarbonate solution
(10 mL) was added to the reaction mixture and the solvent
was concentrated under reduced pressure. The residue was
extracted with ethyl acetate (3ꢂ20 mL). The combined
organic layers were washed with brine, dried, filtered and
evaporated to afford crude products under reduced pressure.
Recrystallization from dichloromethane and methanol
yielded the ketones 5a–d. Besides ketone 5a, it is worthy
of note that ketones 5b–d are slow in producing some epi-
mers under the deuterated chloroform condition.
4.3.2. 2-Benzyloxymethyl-4-(2-methylphenyl)-1-(4-
methylphenylsulfonyl)-2,5-dihydro-1H-pyrrole (2b).
Viscous oil; [a]2D6 ꢀ12.20 (c 0.01, CHCl3); IR (CHCl3)
2359, 1634, 1160, 668 cmꢀ1; HRMS (ESI, M++1) calcd
for C26H28NO3S 434.1790, found 434.1791; 1H NMR
(500 MHz, CDCl3) d 7.75 (d, J¼8.5 Hz, 2H), 7.36–7.28
(m, 7H), 7.20–7.12 (m, 3H), 7.00 (d, J¼7.5 Hz, 1H), 5.75
(dd, J¼2.0, 4.0 Hz, 1H), 4.76–4.73 (m, 1H), 4.61 (d,
J¼12.0 Hz, 1H), 4.58 (d, J¼12.0 Hz, 1H), 4.44 (ddd,
J¼2.0, 5.0, 14.5 Hz, 1H), 4.36 (dt, J¼2.0, 14.5 Hz, 1H),
3.97 (dd, J¼3.5, 9.0 Hz, 1H), 3.68 (dd, J¼7.0, 9.0 Hz,
1H), 2.42 (s, 3H), 2.17 (s, 3H); 13C NMR (125 MHz,
CDCl3)
d 143.67, 138.17, 138.08, 135.90, 134.26,
132.98, 130.82, 129.77 (2ꢂ), 128.37 (2ꢂ), 127.99,
127.87, 127.63 (3ꢂ), 127.51 (2ꢂ), 125.93, 125.81, 73.81,
73.59, 67.46, 57.92, 21.51, 20.88. Anal. Calcd for
C26H27NO3S: C, 72.03; H, 6.28; N, 3.23. Found: C, 72.19;
H, 6.12; N, 3.44.
4.4.1. 4-Benzyloxymethyl-3-(4-methylphenylsulfonyl)-
1-phenyl-6-oxa-3-aza-bicyclo[3.1.0]hexane (2aa). White
solid; mp¼115–116 ꢁC; [a]D28 +27.48 (c 0.12, CHCl3); IR
(CHCl3) 2925, 2358, 1634, 1453, 1342, 1163, 1096,
814 cmꢀ1; FAB-MS: C25H26NO4S m/z (%)¼91 (100), 298
(20), 328 (15), 436 (M++1, 13); HRMS (ESI, M++1) calcd
for C25H26NO4S 436.1582, found 436.1584; 1H NMR
(500 MHz, CDCl3) d 7.70 (d, J¼8.0 Hz, 2H), 7.32–7.27
(m, 10H), 7.18 (dd, J¼2.0, 8.0 Hz, 2H), 4.58 (d,
J¼11.5 Hz, 1H), 4.52 (d, J¼11.5 Hz, 1H), 4.12 (t,
J¼4.0 Hz, 1H), 4.03 (d, J¼12.5 Hz, 1H), 3.86 (d, J¼
4.0 Hz, 2H), 3.78 (d, J¼12.5 Hz, 1H), 3.60 (s, 1H), 2.43
(s, 3H); 13C NMR (125 MHz, CDCl3) d 143.54, 137.75,
135.36, 133.21, 129.60 (2ꢂ), 128.53, 128.47 (2ꢂ), 128.39
(2ꢂ), 127.78, 127.70 (2ꢂ), 127.53 (2ꢂ), 126.05 (2ꢂ),
73.74, 71.19, 65.99, 65.49, 61.10, 51.35, 21.60. Anal. Calcd
for C25H25NO4S: C, 68.94; H, 5.79; N, 3.22. Found: C,
69.03; H, 5.92; N, 3.51. Single-crystal X-ray diagram:
crystal of epoxide 2aa was grown by slow diffusion of ethyl
acetate into a solution of compound 2aa in dichloromethane
to yield colorless prism. The compound crystallizes in
4.3.3. 2-Benzyloxymethyl-4-(4-methoxyphenyl)-1-(4-
methylphenylsulfonyl)-2,5-dihydro-1H-pyrrole (2c). Vis-
cous oil; [a]2D6 +61.67 (c 0.01, CHCl3); IR (CHCl3) 2922,
2358, 1652, 1515, 1344, 1162, 1094, 817, 590 cmꢀ1
;
HRMS (ESI, M++1) calcd for C26H28NO4S 450.1739, found
450.1740; 1H NMR (500 MHz, CDCl3) d 7.73 (d, J¼8.5 Hz,
2H), 7.38–7.27 (m, 7H), 7.22 (d, J¼9.0 Hz, 2H), 6.85 (d,
J¼9.0 Hz, 2H), 6.00 (br d, J¼2.0 Hz, 1H), 4.66–4.64 (m,
1H), 4.59 (s, 2H), 4.54 (ddd, J¼2.0, 5.0, 13.5 Hz, 1H),
4.40 (dt, J¼2.0, 13.5 Hz, 1H), 4.02 (dd, J¼4.0, 9.0 Hz,
1H), 3.80 (s, 3H), 3.62 (t, J¼8.5 Hz, 1H), 2.40 (s, 3H); 13C
NMR (125 MHz, CDCl3) d 159.72, 143.63, 138.17,
136.55, 134.08, 129.80 (2ꢂ), 128.37 (2ꢂ), 127.68 (2ꢂ),
127.64, 127.48 (2ꢂ), 126.81 (2ꢂ), 125.08, 119.90, 113.98
(2ꢂ), 74.07, 73.64, 67.09, 55.89, 55.29, 21.48. Anal. Calcd
for C26H27NO4S: C, 69.46; H, 6.05; N, 3.12. Found: C,
69.61; H, 5.83; N, 3.35.
˚
the monoclinic crystal system. a¼7.778(16) A, b¼
3
˚
˚
˚
16.074(3) A, c¼18.523(4) A, V¼2315.7(8) A , Z¼4,
4.3.4. 2-Benzyloxymethyl-4-(3,4-dioxymethylenephenyl)-
1-(4-methylphenylsulfonyl)-2,5-dihydro-1H-pyrrole
(2d). Viscous oil; [a]2D6 ꢀ38.32 (c 0.007, CHCl3); IR
(CHCl3) 2360, 1635, 1558, 668 cmꢀ1; HRMS (ESI, M++1)
calcd for C26H26NO5S 464.1532, found 464.1535; 1H
NMR (500 MHz, CDCl3) d 7.73 (d, J¼8.5 Hz, 2H), 7.38–
7.27 (m, 7H), 6.81 (d, J¼1.5 Hz, 1H), 6.75 (d, J¼8.0 Hz,
1H), 6.70 (dd, J¼1.5, 8.0 Hz, 1H), 5.97 (d, J¼2.0 Hz, 1H),
5.95 (s, 2H), 4.66–4.61 (m, 1H), 4.59 (s, 2H), 4.50 (ddd,
J¼2.0, 5.0, 14.0 Hz, 1H), 4.37 (d, J¼14.0 Hz, 1H), 4.01
(dd, J¼4.0, 9.0 Hz, 1H), 3.63 (t, J¼8.5 Hz, 1H), 2.40 (s,
3H); 13C NMR (125 MHz, CDCl3) d 148.00, 147.83,
143.69, 138.14, 136.68, 134.07, 129.83 (2ꢂ), 128.40 (2ꢂ),
127.70 (2ꢂ), 127.68, 127.50 (2ꢂ), 126.67, 120.65, 119.47,
dcalcd¼1.249 mg/m3, absorption coefficient 0.170 mmꢀ1
,
F(000)¼920, 2q range (2.20–25.99ꢁ), wR2¼0.1304.
4.4.2. 2-Benzyloxymethyl-4-phenyl-1-(4-methylphenyl-
sulfonyl)pyrrolidin-3-one (5a). White solid; mp¼124–
125 ꢁC; [a]D27 ꢀ4.05 (c 0.037, CHCl3); IR (CHCl3) 2358,
1764, 1348, 1165, 1091, 815, 662, 549 cmꢀ1; FAB-MS:
C25H26NO4S m/z (%)¼91 (100), 155 (11), 314 (29), 328
(10), 341 (15), 436 (M++1, 11); HRMS (ESI, M++1) calcd
for C25H26NO4S 436.1582, found 436.1584; 1H NMR
(500 MHz, CDCl3) d 7.75 (d, J¼8.0 Hz, 2H), 7.36–7.23
(m, 10H), 7.03 (dd, J¼2.0, 8.0 Hz, 2H), 4.52 (d,
J¼12.0 Hz, 1H), 4.47 (d, J¼12.0 Hz, 1H), 4.23 (dd,
J¼9.0, 9.5 Hz, 1H), 4.09 (dd, J¼2.5, 10.0 Hz, 1H), 3.94

12338
M.-Y. Chang et al. / Tetrahedron 62 (2006) 12334–12339
(dd, J¼2.0, 10.0 Hz, 1H), 3.81 (dd, J¼9.0, 9.5 Hz, 1H), 3.77
(dd, J¼2.0, 2.5 Hz, 1H), 3.52 (dd, J¼9.0, 9.5 Hz, 1H), 2.45
(s, 3H); 13C NMR (125 MHz, CDCl3) d 208.44, 144.26,
137.66, 134.54, 133.54, 129.93 (2ꢂ), 128.91 (2ꢂ), 128.36
(2ꢂ), 128.05 (2ꢂ), 127.78, 127.70 (2ꢂ), 127.69, 127.44
(2ꢂ), 73.66, 70.24, 64.70, 53.37, 51.60, 21.57. Anal. Calcd
for C25H25NO4S: C, 68.94; H, 5.79; N, 3.22. Found: C,
68.61; H, 5.89; N, 3.57.
organic layers were washed with brine, dried, filtered and
evaporated to afford crude benzyl alcohols 5aa–da under
reduced pressure. Palladium (10%) on activated carbon
(30 mg) was added to a stirred solution of the resulting
benzyl alcohols 5aa–da in methanol (10 mL). Hydrogen
was bubbled into the mixture for 10 min and stirring of the
reaction mixture was continued for 10 h at room tempera-
ture. The catalyst was filtered through a short plug of Celite
and washed with methanol (2ꢂ20 mL). The combined or-
ganic layers were evaporated to afford crude products. Puri-
fication on silica gel (hexane/ethyl acetate¼2:1–1:1)
afforded diols 1a–d.
4.4.3. 2-Benzyloxymethyl-4-(2-methylphenyl)-1-(4-
methylphenylsulfonyl)pyrrolidin-3-one (5b). Viscous oil;
[a]2D7 ꢀ2.31 (c 0.01, CHCl3); IR (CHCl3) 2360, 1771,
1346, 1159, 1088, 760 cmꢀ1; HRMS (ESI, M++1) calcd
for C26H28NO4S 450.1739, found 450.1743; 1H NMR
(300 MHz, CDCl3) d 7.77 (d, J¼8.1 Hz, 2H), 7.32–7.25
(m, 7H), 7.20–7.13 (m, 3H), 6.99 (d, J¼7.2 Hz, 1H), 4.50
(d, J¼10.8 Hz, 1H), 4.44 (d, J¼10.8 Hz, 1H), 4.27 (dd, J¼
9.0, 9.6 Hz, 1H), 4.06 (dd, J¼2.4, 10.2 Hz, 1H), 3.96 (dd,
J¼2.4, 10.2 Hz, 1H), 3.85 (dd, J¼9.0, 9.6 Hz, 1H), 3.80
(dd, J¼2.4, 2.7 Hz, 1H), 3.50 (dd, J¼9.0, 9.6 Hz, 1H),
2.45 (s, 3H), 2.15 (s, 3H); Anal. Calcd for C26H27NO4S:
C, 69.46; H, 6.05; N, 3.12. Found: C, 69.87; H, 6.39; N, 3.43.
4.5.1. 2-Hydroxymethyl-4-phenyl-1-(4-methylphenylsul-
fonyl)pyrrolidin-3-ol (1a). White solid; mp¼158–159 ꢁC;
[a]2D8 +23.82 (c 0.019, CHCl3); IR (CHCl3) 3430, 2358,
1634, 1339, 1160, 1089, 663 cmꢀ1
;
FAB-MS:
C18H22NO4S m/z (%)¼91 (100), 136 (13), 154 (10), 316
(30), 341 (5), 348 (M++1, 7); HRMS (ESI, M++1) calcd
for C18H22NO4S 348.1269, found 348.1267; 1H NMR
(500 MHz, CDCl3) d 7.79 (d, J¼8.0 Hz, 2H), 7.37–7.26
(m, 5H), 7.13 (d, J¼8.5 Hz, 2H), 4.45 (t, J¼4.0 Hz, 1H),
4.14 (dd, J¼5.5, 12.0 Hz, 1H), 4.11 (dd, J¼4.0, 12.0 Hz,
1H), 3.92 (dd, J¼11.5, 12.0 Hz, 1H), 3.88 (dd, J¼8.0,
11.5 Hz, 1H), 3.76 (dd, J¼4.0, 10.0 Hz, 1H), 2.66 (ddd,
J¼4.0, 8.0, 12.0 Hz, 1H), 2.46 (s, 3H), 1.68 (br s, 2H); 13C
NMR (125 MHz, CDCl3) d 144.08, 134.74, 134.17, 130.01
(2ꢂ), 128.79 (2ꢂ), 128.27 (2ꢂ), 127.65, 127.53 (2ꢂ),
75.68, 65.57, 62.63, 51.07, 48.65, 21.58. Anal. Calcd for
C18H21NO4S: C, 62.23; H, 6.09; N, 4.03. Found: C, 62.50;
H, 6.23; N, 4.30.
4.4.4. 2-Benzyloxymethyl-4-(4-methoxyphenyl)-1-(4-
methylphenylsulfonyl)pyrrolidin-3-one (5c). Viscous oil;
[a]2D9 ꢀ12.53 (c 0.006, CHCl3); IR (CHCl3) 2355, 1761,
1345, 1162, 1090, 766 cmꢀ1; HRMS (ESI, M++1) calcd
for C26H28NO5S 466.1688, found 466.1689; 1H NMR
(300 MHz, CDCl3) d 7.78 (d, J¼8.1 Hz, 2H), 7.39–7.18
(m, 7H), 6.85 (d, J¼9.0 Hz, 2H), 6.63 (d, J¼9.0 Hz, 2H),
4.50 (d, J¼10.8 Hz, 1H), 4.43 (d, J¼10.8 Hz, 1H), 4.22
(dd, J¼9.0, 9.6 Hz, 1H), 4.08 (dd, J¼2.4, 10.2 Hz, 1H),
3.94 (dd, J¼2.4, 10.2 Hz, 1H), 3.79 (s, 3H), 3.80–3.76 (m,
2H), 3.27 (dd, J¼9.0, 9.6 Hz, 1H), 2.46 (s, 3H). Anal. Calcd
for C26H27NO5S: C, 67.08; H, 5.85; N, 3.01. Found: C,
66.83; H, 5.60; N, 2.84.
4.5.2. C3 isomer of compound 1a. Viscous oil; [a]2D8 +10.68
(c 0.009, CHCl3); IR (CHCl3) 3432, 2916, 2849, 1636, 1159,
543 cmꢀ1; FAB-MS: C18H22NO4S m/z (%)¼91 (100), 136
(18), 154 (16), 316 (26), 341 (8), 348 (M++1, 6); HRMS
(ESI, M++1) calcd for C18H22NO4S 348.1269, found
348.1268; 1H NMR (500 MHz, CDCl3) d 7.76 (d,
J¼8.0 Hz, 2H), 7.38 (d, J¼8.0 Hz, 2H), 7.30–7.23 (m,
3H), 7.07 (d, J¼8.5 Hz, 2H), 4.18 (dd, J¼5.0, 12.0 Hz,
1H), 4.04 (dd, J¼8.0, 9.5 Hz, 1H), 3.98 (dd, J¼3.0,
12.0 Hz, 1H), 3.88 (dd, J¼8.0, 10.0 Hz, 1H), 3.75 (ddd,
J¼4.5, 5.0, 8.0 Hz, 1H), 3.39 (dd, J¼9.5, 10.0 Hz, 1H),
3.05 (dd, J¼10.0, 10.0 Hz, 1H), 2.48 (s, 3H), 2.10 (br s,
2H); 13C NMR (125 MHz, CDCl3) d 144.19, 137.49,
132.94, 129.95 (2ꢂ), 128.86 (2ꢂ), 127.72 (2ꢂ), 127.57,
127.37 (2ꢂ), 77.55, 62.73, 61.33, 51.70, 49.98, 21.60.
Anal. Calcd for C18H21NO4S: C, 62.23; H, 6.09; N, 4.03.
Found: C, 62.42; H, 5.83; N, 4.32.
4.4.5. 2-Benzyloxymethyl-4-(3,4-dioxymethylenephenyl)-
1-(4-methylphenylsulfonyl)pyrrolidin-3-one (5d). Vis-
cous oil; [a]2D9 ꢀ16.32 (c 0.008, CHCl3); IR (CHCl3) 2356,
1760, 1350, 1160, 1095 cmꢀ1; HRMS (ESI, M++1) calcd
for C26H26NO6S 480.1481, found 480.1481; 1H NMR
(300 MHz, CDCl3) d 7.79 (d, J¼8.1 Hz, 2H), 7.39–7.25
(m, 5H), 7.20–7.16 (m, 2H), 6.78 (d, J¼8.1 Hz, 1H), 6.52
(d, J¼1.2 Hz, 1H), 6.43 (dd, J¼1.2, 8.1 Hz, 1H), 5.96 (s,
2H), 4.38 (d, J¼10.8 Hz, 1H), 4.36 (d, J¼10.8 Hz, 1H),
4.18 (dd, J¼9.0, 9.6 Hz, 1H), 4.03 (dd, J¼2.4, 10.2 Hz,
1H), 3.96 (dd, J¼2.4, 10.2 Hz, 1H), 3.76 (dd, J¼9.0,
9.6 Hz, 1H), 3.75 (dd, J¼1.8, 2.4 Hz, 1H), 3.22 (dd,
J¼9.0, 9.6 Hz, 1H), 2.42 (s, 3H).
4.5.3. 2-Hydroxymethyl-4-(2-methylphenyl)-1-(4-
methylphenylsulfonyl)pyrrolidin-3-ol (1b). White solid;
mp¼167–168 ꢁC; [a]D27 +16.67 (c 0.009, CHCl3); IR
(CHCl3) 3428, 2920, 1635, 1338, 1160, 1091, 661,
545 cmꢀ1; HRMS (ESI, M++1) calcd for C19H24NO4S
4.5. A representative procedure for the preparation of
diols 1a–d
A solution of diisobutylaluminum hydride (1.0 M in hexane,
0.3 mmol) was added to a solution of ketones 5a–d
(0.1 mmol) in tetrahydrofuran (10 mL) at ꢀ78 ꢁC. The
reaction mixture was stirred at ꢀ78 ꢁC for 3 h. The total
procedure was monitored by TLC until the reaction was
completed. Methanol (0.5 mL) was added to the reaction
mixture and the solvent was concentrated under reduced
pressure. The residue was diluted with water (15 mL) and
extracted with ethyl acetate (3ꢂ20 mL). The combined
1
362.1426, found 362.1427; H NMR (500 MHz, CDCl3)
d 7.80 (d, J¼8.0 Hz, 2H), 7.37 (d, J¼8.0 Hz, 2H), 7.19–
7.14 (m, 4H), 4.40 (br s, 1H), 4.11 (br s, 2H), 3.97 (t,
J¼12.0 Hz, 1H), 3.87 (dd, J¼5.0, 10.5 Hz, 1H), 3.76 (dd,
J¼7.0, 12.0 Hz, 1H), 2.78 (br s, 1H), 2.72–2.67 (m, 1H),
2.46 (s, 3H), 2.03 (br s, 1H), 2.01 (s, 3H); 13C NMR
(125 MHz, CDCl3) d 144.07, 136.52, 134.40, 132.27,
130.84, 129.95 (2ꢂ), 127.62, 127.58 (2ꢂ), 127.48, 126.21,

M.-Y. Chang et al. / Tetrahedron 62 (2006) 12334–12339
12339
Pauwels, R.; Andries, K.; Janssen, M. A. C.; Janssen, P. A. J.
J. Med. Chem. 1995, 38, 771; (l) Chang, M. Y.; Chen, S. T.;
Chang, N. C. Heterocycles 2003, 60, 1203; (m) Chang, M. Y.;
Kung, Y. H.; Chen, S. T. Tetrahedron 62, in press. (n) Chang,
M. Y.; Chen, H. P. Heterocycles 2005, 65, 1705; (o) Chang,
M. Y.; Pai, C. L.; Chen, H. P. Tetrahedron Lett. 2005, 46,
7705; (p) Chang, M. Y.; Chen, H. P.; Lin, C. Y.; Pai, C. L.
Heterocycles 2005, 60, 1999; (q) Chang, M. Y.; Kung,
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Chang, M. Y.; Lin, C. Y.; Ong, C. W. Heterocycles 2006,
68, 2031.
73.49, 65.70, 62.66, 50.82, 45.19, 21.53, 19.36. Anal. Calcd
for C19H23NO4S: C, 63.13; H, 6.41; N, 3.88. Found: C,
63.38; H, 6.80; N, 3.61.
4.5.4. 2-Hydroxymethyl-4-(4-methoxyphenyl)-1-(4-
methylphenylsulfonyl)pyrrolidin-3-ol (1c). Viscous oil;
[a]2D6 +25.57 (c 0.009, CHCl3); IR (CHCl3) 3455, 2920,
1611, 1515, 1340, 1160, 1033, 817 cmꢀ1; HRMS (ESI,
M++1) calcd for C19H24NO5S 378.1375, found 378.1377;
1H NMR (500 MHz, CDCl3) d 7.78 (d, J¼8.0 Hz, 2H),
7.35 (d, J¼8.0 Hz, 2H), 7.05 (d, J¼8.5 Hz, 2H), 6.85 (d,
J¼8.5 Hz, 2H), 4.38 (br s, 1H), 4.11 (br s, 2H), 3.89–3.80
(m, 2H), 3.78 (s, 3H), 3.76–3.73 (m, 1H), 2.94 (br s, 1H),
2.64–2.59 (m, 1H), 2.46 (s, 3H), 2.42 (br s, 1H); 13C NMR
(125 MHz, CDCl3) d 159.01, 144.03, 134.19, 129.98 (2ꢂ),
129.31 (2ꢂ), 127.53 (2ꢂ), 126.43, 114.21 (2ꢂ), 75.65,
65.56, 62.63, 55.28, 51.28, 47.92, 21.57. Anal. Calcd for
C19H23NO5S: C, 60.46; H, 6.14; N, 3.71. Found: C, 60.22;
H, 6.29; N, 3.90.
3. (a) Mauger, A. B. J. Org. Chem. 1981, 46, 1032; (b) Blanco,
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3593; (b) Koskinen, A. M. P.; Schwerdtfeger, J.; Edmonds, M.
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(c) Krapcho, J.; Turk, C.; Cushman, D. W.; Powell, J. R.;
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J. Med. Chem. 1988, 31, 1148; (d) Dormoy, J.-R. Synthesis
1982, 753.
5. CCDC 619819 (compound 2aa) contains the supplementary
crystallographic data for this paper. This data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html
(or from the CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: 44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk).
6. Roa, L. F.; Gnecco, D.; Galindo, A.; Teran, J. L.; Bernes, S.
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Tetrahedron Lett. 1989, 30, 5607.
4.5.5. 2-Hydroxymethyl-4-(3,4-dioxymethylenephenyl)-
1-(4-methylphenylsulfonyl)pyrrolidin-3-ol (1d, rotamer).
Viscous oil; [a]2D6 +10.39 (c 0.008, CHCl3); IR (CHCl3)
3445, 2933, 1504, 1338, 1160, 1037, 663 cmꢀ1; HRMS
(ESI, M++1) calcd for C19H22NO6S 392.1168, found
392.1171; 1H NMR (300 MHz, CDCl3) d 7.78 (d,
J¼8.4 Hz, 2H), 7.39 (d, J¼8.4 Hz, 2H), 6.77 (d, J¼8.1 Hz,
1H), 6.63 (br s, 1H), 6.52 (dd, J¼1.2, 8.1 Hz, 1H), 5.97 (s,
2H), 4.39 (br s, 1H), 4.16 (br s, 2H), 3.97–3.93 (m, 1H),
3.85–3.80 (m, 2H), 3.73–3.69 (m, 1H), 2.83 (br s, 1H),
2.66–2.62 (m, 1H), 2.45 (s, 3H).
Acknowledgements
The authors would like to thank the National Science Coun-
cil (NSC-95-2113-M-390-003-MY2) of the Republic of
China for financial support. We also thank Prof. Michael
Y. Chiang (National Sun Yat-Sen University) for structural
determination of epoxide 2aa by X-ray diffraction analysis.
References and notes
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