Diastereoselective allylation of α-ketoamides bearing camphor N-tosylpyrazolidinone auxiliary: Efficient synthesis of highly optically active two stereoisomers

Article abstract of DOI:10.1016/j.tet.2005.10.042

Complementary allylation conditions were developed for the synthesis of both diastereomers of tertiary homoallylic alcohols. Treatment of camphor N-tosylpyrazolidinone derived α-ketoamides with allyltributylstannane afforded both the individual homoallyli

Full text of DOI:10.1016/j.tet.2005.10.042

Tetrahedron 62 (2006) 887–893
Diastereoselective allylation of a-ketoamides bearing camphor
N-tosylpyrazolidinone auxiliary: efficient synthesis of highly
optically active two stereoisomers
*
Jung-Hsuan Chen, Uppala Venkatesham, Li-Chen Lee and Kwunmin Chen
Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan 116, ROC
Received 16 September 2005; revised 14 October 2005; accepted 14 October 2005
Available online 9 November 2005
Abstract—Complementary allylation conditions were developed for the synthesis of both diastereomers of tertiary homoallylic alcohols.
Treatment of camphor N-tosylpyrazolidinone derived a-ketoamides with allyltributylstannane afforded both the individual homoallylic
alcohols in high optical purity (up to 98% de) when the reaction was carried out in the presence of Sn(OTf)2 and PdCl2, respectively. The
stereochemical outcome and reversal of stereoselectivity in the reaction are proposed based on 13C NMR and FTIR studies.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
with reversal of stereoselectivity has not been achieved to
date. Here, we wish to report the asymmetric allylation of a
novel camphor auxiliary derived a-ketoamides in the
presence of a Lewis acid. The desired products were
obtained in excellent diastereomeric excess in good to
excellent chemical yields. The facial stereoselectivity and
the stereochemical course of the reactions are discussed.
The development of novel chiral auxiliaries that provide
practical routes for the preparation of synthetically useful
intermediates remains one of the most important fields in
organic synthesis.1 The fact that there are no universal chiral
auxiliaries for all asymmetric transformations is a compel-
ling reasons for discovering novel chiral auxiliaries for
specific reactions.2 From a practical synthetic point of view,
the synthesis of both stereoisomers from the same chiral
resources is attractive and has been a subject of considerable
interest in recent years.3 The reversal of stereochemistry
from a single chiral starting material can be achieved by
careful manipulation of the reaction components, especially
the control of the architecture of the ligand-Lewis acid
complex. The asymmetric allylation of ketones,4 aldehydes5
and imine6 functionalities for the formation of homoallyl
alcohols and homoallyl amines are well documented in the
literature. The corresponding secondary and tertiary
homoallylic alcohols are versatile intermediates that have
been further used in organic synthesis.7 However, allyl
metal addition to a-keto esters and amides is a less well
investigated topic.8 Diastereoselective allylation of
camphor N-phenylpyrazolidinone derived a-ketoamides
was examined recently by us.9 The corresponding
quarternary a-hydroxy carbonyls were obtained with good
to excellent stereoselectivity. However, to the best of our
knowledge, a diastereoselective allylation of a-ketoamides
2. Results and discussion
The preparation of camphor N-tosylpyrazolidinone 4
followed the same synthetic route as described previously
(Scheme 1).2g The treatment of (C)-ketopinic acid 1 with
p-toluenesulfonhydrazide producing the desired hydrazone
2 in nearly quantitative chemical yield. Cyclization was
carried out by treatment with SOCl2 in EtOAc at 75 8C for
4 h. The corresponding C–N double bond was reduced with
NaCNBH3 in acetic acid to give the chiral camphor
N-tosylpyrazolidinone 4 in 75% material yield. The desired
a-ketoamides 5 are readily prepared by coupling the
camphor N-tosylpyrazolidinone 4 with the freshly prepared
a-ketocarboxylic acid chlorides at room temperature in
49–97% yields. It is noteworthy that both camphor
N-tosylpyrazolidinone 4 and camphor N-tosylpyrazoli-
dinone phenylglyoxylate 5a exist as two structural
conformers in the asymmetric unit as indicated by X-ray
crystallographic analyses.10 Two distinct N-invertomers of
camphor N-tosylpyrazolidinone 4 were observed in which
the tosyl group is oriented toward and away from the C7
dimethyl group (Scheme 1, the dihedral angles of NNSCS2P
are K72.0 and C84.18, respectively).11 On the other hand,
Keywords: Allylation; Reversal of stereoselectivity; Chiral auxiliary.
*
Corresponding author. Tel.: C886 2 89315831; fax: C886 2 29324249;
e-mail: kchen@cc.ntnu.edu.tw
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.10.042

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J.-H. Chen et al. / Tetrahedron 62 (2006) 887–893
a probe substrate. No reaction products were obtained when
5a was treated with allyltributylstannane in the absence of a
Lewis acid. Various metal triflates such as Sc(OTf)3,
Sm(OTf)3, Zn(OTf)2 and Eu(OTf)3 were systematically
screened, but resulted in either low to moderate chemical
yields or a low level of diastereoselectivities (data not
shown). A satisfactory result was obtained when the
reaction was carried out in the presence of 2.0 equiv of
Yb(OTf)3 for 24 h (Table 1, entry 1). The stereoselectivity
was further improved to an excellent level when Sn(OTf)2
was employed in a 5 min reaction (entry 2). The
diastereoselectivity was determined by 1H NMR and
HPLC studies of relevant peaks. The absolute stereo-
chemistry of the newly generated stereogenic center in the
major diasteoreomer 6a was assigned to have an R
configuration, deduced from the single crystal X-ray
analysis. Interestingly, the sense of stereoinduction was
reversed with less reactivity when the reaction was carried
out in the presence of PdCl2 and the structure of product 7a
was again confirmed by single crystal X-ray analysis (entry
3). A careful examination of the 1H NMR spectra indicates
that the characteristic C-2 methine proton (camphor
numbering) appears at 3.16 ppm for the R isomer while at
4.32 ppm for the counter S isomer.9,12 The diamagnetic
anisotropy effect of the aromatic substituent may account
for the shielding effect.
Scheme 1. Reagents and conditions: (i) p-toluenesulfonhydrazide, CH2Cl2,
rt, 99%; (ii) SOCl2, EtOAc, 75 8C, 90%; (iii) NaCNBH3, AcOH, rt, 75%;
(iv) RCOCOCl, CH2Cl2, base, rt, 49–97%.
the tosyl group points away from the C7 dimethyl group in
5a, thus avoiding the electrostatic repulsion with the
dicarbonyl groups (the dihedral angles of NNSC2SP are
K69.9 and K83.08, respectively). In addition, the amide
carbonyl group in 5a is oriented away from the N-tosyl
group with the dicarbonyl groups in an s-trans arrangement
(the dihedral angles of COCO are 137.6 and 143.58,
respectively. See supporting information).
Having identified two discrete Lewis acids [Sn(OTf)2 and
PdCl2] that can produce complementary diastereomers of
the allylation reactions, we sought to examine the nature of
the architecture of the chiral auxiliary backbone. Toward
this end, the allylation proceeded smoothly when camphor
N-tosylpyrazolidinone derived 2-thienylglyoxylate 5b
was used under the optimum reaction conditions, providing
6b with excellent selectivity in the presence of Sn(OTf)2
(entry 4). The opposite diasteoreomer with a similar
selectivity was produced when PdCl2 was used (entry 5).
With the desired chiral a-ketoamides 5a–d in hand, we
examined the diastereoselective allylation. The camphor
N-tosylpyrazolidinone phenylglyoxylate 5a was chosen as
Table 1. Diastereoselective allylation of camphor N-tosylpyrazolidinone derived a-ketoamides 5a–d in the presence of a Lewis acida
Me
Me
Me
Me
HO
O
R
R
OH
N
N
N
O
O
N
O
Ts
Ts
6
7
Entry
RZ
Lewis acid
t
Yield (%)b
Configurationc
Ratio (6:7)d
1
2
3
4
5
6
7
8
9
5a
5a
5a
5b
5b
5c
5c
5d
5d
Phenyl
Phenyl
Phenyl
2-Thienyl
2-Thienyl
1-Acetyl-3-indolyl
1-Acetyl-3-indolyl
Ethyl
Yb(OTf)3
Sn(OTf)2
PdCl2
Sn(OTf)2
PdCl2
Sn(OTf)2
PdCl2
Sn(OTf)2
PdCl2
24 h
5 min
24 h
5 min
24 h
5 min
24 h
5 min
24 h
90
92
60
95
88
98
—
95
!10
R
R
S
S
R
91:09
99:01
06:94
99:01
01:99
99:01
—
Rf
—
S
e
89:11
15:85
Ethyl
Rf
a Unless otherwise specified, all reactions were carried out in a solvent [in CH3CN when Sn(OTf)2 was used and in CH2Cl2 when PdCl2 was used] at room
temperature using 5 (0.11 mmol), allyltributylstannane (1.06 mmol) and a Lewis acid (0.22 mmol).
b Total isolated yield (6C7).
c The absolute stereochemistry of the newly generated stereogenic center was deduced by X-ray crystallographic analyses.
d Ratios of diastereomers were determined by 1H NMR analysis of relevant peaks and HPLC analyses of crude products.
e The deacylated compound N-tosylcamphorpyrazolidinone-3-indoloylglyoxylate was isolated in 50%.
f
Absolute stereochemistry are assigned by analogy.

J.-H. Chen et al. / Tetrahedron 62 (2006) 887–893
889
It is noteworthy that, under either reaction conditions, no
desired allylation product was observed with camphor
N-tosylpyrazolidinone derived 3-indoloylglyoxylate. This
was presumably due to the presence of an active hydrogen
atom that decreases the reactivity. This problem was
eliminated when NH protected analogue was used. Thus,
camphor N-tosylpyrazolidinone-1-acetyl-3-indoloylgly-
oxylate 5c upon allylation afforded the expected product
with fairly high yield and selectivity in the presence of
Sn(OTf)2 (entry 6). However, no desired reaction products
were observed when PdCl2 was employed and the
deacylation product was isolated (entry 7). Finally,
the aliphatic substrate 5d efficiently participates in the
reaction, leading to the desired products with good
diastereoselectivity, but the reactivity decreased dramati-
cally when PdCl2 was used as a Lewis acid (entries 8–9).
While, in the case of PdCl2, the electronic rich tosyl group
prevents nucleophilic addition from the si face, leading to
the addition from the top re face.15
3. Conclusion
In conclusion, a new camphor-based chiral auxiliary
N-tosylpyrazolidinone was synthesized, and tested as a
stereocontrolling element in allylation reactions across a
range of substrates. The present work confirms that the
correct choice of Lewis acid is essential in determining the
diastereoselective outcome of the allylation.16 The strongly
chelating Sn(OTf)2 led to the si face addition diastereomer,
while the non-chelating PdCl2 gave the counter diastereo-
mer with allyltributyltin. Further synthetic applications are
currently underway.
The high degree of stereoselectivity and the reversal of
stereoselectivity can be rationalized by the chelation and
non-chelation control of the Lewis acid with a-ketoamides 5
as shown in Figure 1. Among the possible conformations,
the pseudo planar s-trans conformer of the a-dicarbonyl
group in 5 is electronically favored over its s-cis conformer
to avoid electrostatic repulsive interactions between the
adjacent carbonyl groups. This was confirmed by X-ray
crystallographic analyses of 5a,b in the solid states. The
4. Experimental
4.1. General methods
All reagents were used as purchased from the commercial
suppliers without further purification. NMR spectra were
recorded on a Bruker Avance 400 NMR spectrometer
(400 MHz for H, and 100 MHz for 13C). Chemical shifts
1
reversal of stereoselectivity can be explained by simple 13
C
are reported in d ppm referenced to an internal TMS
NMR and FTIR studies. When a mixture of Sn(OTf)2 and 5a
in CD3CN was examined by 13C NMR, no significant
chemical shift difference in the carbonyl region was
observed (!0.05 ppm) in comparison with a spectrum of
the pure substrate.13 This indicates that there is little
chelation of Lewis acid metal atom with the carbonyl
oxygen atoms. In addition, no significant carbonyl group
stretching band changes in the infrared spectrum of the
mixture were observed. However, a new stretching band
standard for H NMR and chloroform-d (d 77.0) for 13C
1
NMR. Optical rotations were measured on a JASCO P-1010
polarimeter. Infrared spectra were recorded on a Perkin-
Elmer FTIR spectrum 500 spectrometer. Only the charac-
teristic peaks are quoted. EI mass spectra were recorded on
Finnigan TSQ-700 at an ionizing energy of 70 eV and
HRMS spectra were recorded on JEOL SX-102A. Routine
monitoring of reactions was performed using silica
gel, glass-backed TLC plates (Merck Kieselgel 60 F254)
and visualized by UV light (254 nm). Analytical high-
performance liquid chromatography was performed on
a JASCO PU-1580 HPLC (ZORBAX analytical NH2
column). Solutions were evaporated to dryness under
reduced pressure with a rotary evaporator and the residue
was purified by flash column chromatography on silica gel
(230–400 mesh) with the indicated eluents. Air and/or
moisture sensitive reactions were performed under usual
inert atmosphere conditions.
corresponding to an S]O group developed at 1272 cmK1
,
which is different from the stretching band of 1240 cmK1 in
5a.14 On the other hand, a mixture of PdCl2 and substrate 5a
give no significant carbonyl signal shift difference or
absorption band changes (carbonyl and sulfonyl groups)
by 13C NMR and FTIR spectroscopy. These data indicate a
strong coordination of the Sn(OTf)2 with sulfonyl oxygen
atoms and this may account for the much faster reaction in
the presence of Sn(OTf)2 in comparison to the use of PdCl2
(5 min vs 24 h). The coordination of the tin to the sulfonyl
group resulted in the rapid release of the nucleophilic allyl
group. The allyl group then attacks the a-carbonyl amide
group from the bottom si face to afford the desired product.
Crystallographic data for the structures in this paper
have been deposited at the Cambridge Crystallographic
Data Center and allocated the deposit numbers CCDC
281384-281390, and 284467.17
4.1.1. 2-(2-Tosylhydrazono)-7,7-dimethylbicyclo[2.2.1]-
heptane-1-carboxylic acid (2). To a solution of (C)-
ketopinic acid 1 (20 g, 109.9 mmol) in CH2Cl2 (300 mL)
was added p-toluenesulfonhydrazide (22.5 g, 120.9 mmol)
in one portion and the mixture was allowed to stir for 4 h
at room temperature. The reaction mixture was diluted
with water (500 mL) and extracted with dichloromethane
(3!500 mL), the organic layer was separated and dried
over anhydrous MgSO4 and concentrated to give ketopinic
acid tosylhydrazone 2 as a white solid (38.1 g; 99%); mp:
114–115 8C. RfZ0.29 (1:1 hexanes/EtOAc). [a]2D7 C47.1
Figure 1. Proposed mechanistic explanation of the diastereoselective
allylation. The stereoview of the Chem3D structure of 5a was generated
from the X-ray crystal coordinates. All hydrogen atoms are omitted for the
sake of clarity.

890
J.-H. Chen et al. / Tetrahedron 62 (2006) 887–893
1
(c 1, CHCl3); H NMR (400 MHz, CDCl3) d 7.81 (d, 2H,
JZ7.6 Hz), 7.74 (br s, 1H, –NH–, D2O exchangeable), 7.35
(d, 2H, JZ7.6 Hz), 2.51–2.39 (m, 2H), 2.43 (s, 3H),
2.09–2.03 (m, 2H), 1.94 (d, 1H, JZ17.4 Hz), 1.68–1.62 (m,
1H), 1.33–1.28 (m, 1H), 1.20 (s, 3H), 0.79 (s, 3H); 13C NMR
(100 MHz, CDCl3) d 171.9, 169.0, 145.0, 134.3, 130.1,
127.9, 61.1, 51.7, 44.3, 33.9, 31.1, 27.5, 21.5, 19.7, 18.3; IR
(neat, cmK1): 3436–2408 (br), 1715, 1597, 1416, 1337,
1166, 1088, 920; HRMS (EI) calcd for C17H22N2O4S
350.1295. Found 350.1283.
H, 6.60; N, 8.20; Crystal data for 4 (colorless crystal,
recrystallized from hexanes/EtOAc) at 25 8C: C17H22N2O3S,
˚
M 334.438, Monoclinic, P21, aZ9.7297(3) A, bZ
3
˚
˚
˚
14.6999(4) A, cZ12.2705(5) A, VZ1714.77(10) A , ZZ4,
DxZ1.295 Mg/m3, mZ0.205 mmK1, 5864 reflections, 415
parameters, RZ0.0643, RwZ0.1547.
4.2. General procedure for the synthesis of compounds
5a–c
Under N2 atmosphere a mixture of benzoylformic acid
(2.25 g, 15.0 mmol) and thionyl chloride (15.27 mL,
209.29 mmol) was refluxed at 75 8C for 2 h and concen-
trated on rotary evaporator to remove SOCl2. The resulting
crude mixture was dissolved in CH2Cl2 (15 mL) and added
to a solution of camphor N-tosylpyrazolidinone 4 (1.0 g,
2.99 mmol) in CH2Cl2 (10 mL). The reaction mixture was
allowed to stir for 15 min and quenched with water (50 mL)
and extracted with CH2Cl2 (3!75 mL). The organic
extracts were combined, dried over anhydrous MgSO4 and
concentrated to give crude products, which were subject to
flash column chromatography eluted with (2:1 hexanes/
EtOAc) afforded the pure product 5a (1.35 g, 97%) as a
white solid.
4.1.2. 10,10-Dimethyl-3-N-tosyl-4-aza-tricyclo[5.2.1.01,5]-
dec-4-en-2-one (3). The above prepared ketopinic acid
tosylhydrazone 2 (20 g, 57.14 mmol) was dissolved in ethyl
acetate (300 mL). To this solution was added thionyl
chloride (15.8 mL, 217.14 mmol) slowly and the reaction
mixture was brought to reflux at 75 8C for 4 h under N2
atmosphere. The reaction mixture quenched with water
(600 mL) and extracted with ethyl acetate (3!600 mL).
The dried MgSO4 extract was concentrated in vacuo and
purified by flash column chromatography, eluted with (1:1
hexanes/EtOAc) afforded the cyclized product 3 as a
colorless solid (17.07 g; 90%).; mp: 83–84 8C. RfZ0.44
1
(1:1 hexanes/EtOAc). [a]2D7 K99.6 (c 1, CHCl3); H NMR
(400 MHz, CDCl3) d 7.93 (d, 2H, JZ7.9 Hz), 7.32 (d, 2H,
JZ7.9 Hz), 2.59 (d, 1H, JZ18.0 Hz), 2.43 (s, 3H),
2.22–2.20 (m, 2H), 2.15 (d, 1H, JZ18.0 Hz), 2.10–2.05
(m, 1H), 1.76–1.69 (m, 1H), 1.52–1.45 (m, 1H), 1.12 (s,
3H), 0.63 (s, 3H); 13C NMR (100 MHz, CDCl3) d 176.2,
172.2, 145.2, 135.3, 129.7, 127.9, 64.0, 50.9, 48.7, 32.2,
26.8, 26.0, 21.5, 18.5, 18.1; IR (neat, cmK1): 3065, 2961,
2923, 2853, 1760, 1747, 1645, 1598, 1455, 1373, 1295,
1258, 1178, 1082, 959, 814, 705; HRMS (EI) calcd for
C17H20N2O3S 332.1189. Found 332.1190; Crystal data for 3
(colorless crystal, recrystallized from hexanes/EtOAc) at
25 8C: C17H20N2O3S, M 332.422, Orthorhombic, P212121,
4.2.1. 10,10-Dimethyl-3-N-tosyl-4-N-(2-oxo-2-phenyl-
acetyl)-tricyclo[5.2.1.01,5]decan-2-one (5a). RfZ0.38 (2:1
hexanes/EtOAc); mp: 179–181 8C. [a]2D7 K194.6 (c 1,
1
CHCl3); H NMR (400 MHz, CDCl3) d 8.15 (d, 2H, JZ
7.6 Hz), 7.92 (s, 2H), 7.65 (t, 1H, JZ7.2 Hz), 7.53 (t, 2H,
JZ7.6 Hz), 7.37 (d, 2H, JZ8.4 Hz), 4.07 (s, 1H), 2.46 (s,
3H), 2.11 (t, 1H, JZ9.8 Hz), 1.95–1.90 (m, 2H), 1.77 (dd,
1H, JZ13.4, 8.2 Hz), 1.26 (s, 3H), 1.26–1.22 (m, 2H), 1.08
(m, 1H), 1.08 (s, 3H); 13C NMR (100 MHz, CDCl3) d 171.3,
162.2, 146.0, 134.4, 133.6, 133.0, 130.5, 130.3, 130.0, 128.6,
128.4, 70.0, 60.0, 52.8, 47.5, 36.1, 28.8, 26.5, 21.6, 20.1,
20.0; IR (neat, cmK1): 3065, 3003, 2964, 2925, 1768, 1680,
1652, 1594, 1483, 1450, 1385, 1241, 1173, 1083, 946, 816,
732; HRMS (EI) calcd for C25H26N2O5S 466.1557. Found
466.1574. Anal. Calcd for C25H26N2O5S: C, 64.36; H, 5.62;
N, 6.00. Found: C, 64.33; H, 5.62; N, 5.75; Crystal data for
5a (colorless crystal, recrystallized from hexanes/EtOAc) at
20 8C: C25H26N2O5S, M 466.54, Monoclinic, P21, aZ
˚
˚
˚
aZ10.1101(2) A, bZ12.9076(3) A, cZ25.9674(8) A, VZ
3
3
K1
˚
3388.67 (15) A , ZZ8, DxZ1.303 Mg/m , mZ0.21 mm
2336 reflections, 416 parameters, RZ0.058, RwZ0.096.
,
4.1.3. 10,10-Dimethyl-3-N-tosyl-4-aza-tricyclo[5.2.1.01,5]-
decan-2-one (4). To a stirred solution of cyclized substrate 3
(5.05 g, 15.21 mmol) in AcOH (75 mL) at room tempera-
ture was added slowly NaBH3CN (13.19 g, 210 mmol). The
reaction mixture was stirred at room temperature for 30 min
until the reaction was completed and diluted with H2O
(750 mL) and extracted with CH2Cl2 (3!600 mL). The
organic layer was dried over anhydrous MgSO4 and
concentrated to give a crude product, which is purified by
flash column chromatography eluted with (2:1 hexanes/
EtOAc) to yield 4 (3.75 g; 75%) as a white solid; mp:
118–119 8C. RfZ0.38 (2:1 hexanes/EtOAc). [a]2D7 C14.4 (c
1, CHCl3); 1H NMR (400 MHz, CDCl3) d 7.93 (d, 2H, JZ
8.0 Hz), 7.32 (d, 2H, JZ8.0 Hz), 5.05 (br s, 1H, –NH–), 3.5
(dd, 1H, JZ8.4, 4.0 Hz), 2.44 (s, 3H), 2.11–2.02 (m, 2H),
1.89–1.80 (m, 2H), 1.66 (dd, 1H, JZ13.2, 8.4 Hz),
1.26–1.15 (m, 2H), 0.94 (s, 3H), 0.76 (s, 3H); 13C NMR
(100 MHz, CDCl3) d 172.3, 145.2, 134.5, 129.4, 128.4,
64.5, 58.9, 52.5, 47.2, 36.4, 29.0, 26.4, 21.6, 20.4, 19.7; IR
(neat, cmK1): 3323, 3302, 2958, 2899, 1757, 1747, 1598,
1481, 1360, 1173, 1075, 863, 817; HRMS (EI) calcd for
C17H22N2O3S 334.1346. Found 334.1350. Anal. Calcd for
C17H22N2O3S: C, 61.05; H, 6.63; N, 8.38. Found: C, 61.07;
˚
˚
˚
10.1710(5) A, bZ11.8910(5) A, cZ19.5700(12) A, VZ
3
3
K1
˚
2360.8(2) A , ZZ4, DxZ1.313 Mg/m , mZ0.176 mm
7815 reflections, 596 parameters, RZ0.1298, RwZ0.1964.
,
4.2.2. 10,10-Dimethyl-3-N-tosyl-4-N-[2-oxo-2-(thiophen-
2-yl)acetyl]-tricyclo[5.2.1.01,5]decan-2-one (5b). White
solid. RfZ0.35 (2:1 hexanes/EtOAc); mp: 180–182 8C.
[a]2D7 K232.7 (c 1, CHCl3); 1H NMR (400 MHz, CDCl3) d
8.13 (d, 1H, JZ3.6 Hz), 7.93 (s, 2H), 7.81 (d, 1H, JZ
4.4 Hz), 7.37 (d, 2H, JZ8.0 Hz), 7.2 (t, 1H, JZ4.4 Hz),
4.11 (d, 1H, JZ6.8 Hz), 2.46 (s, 3H), 2.09–2.06 (m, 1H),
1.94–1.92 (m, 2H), 1.82 (dd, 1H, JZ14.0, 8.4 Hz),
1.26–1.22 (m, 2H), 1.18 (s, 3H), 1.05 (m, 1H), 1.05 (s,
3H); 13C NMR (100 MHz, CDCl3) d 179.1, 174.3, 161.4,
146.0, 139.5, 137.0, 134.6, 129.8, 129.1, 128.9, 128.7, 70.5,
60.3, 52.6, 47.4, 36.8, 28.8, 26.7, 21.8, 20.3, 20.0; IR (neat,
cmK1): 3106, 2997, 2962, 2920, 2884, 1766, 1652, 1596,
1409, 1380, 1357, 1246, 1175, 1083, 1055, 815; HRMS (EI)
calcd for C23H24N2O5S2 472.1127. Found 472.1129. Anal.
Calcd for C23H24N2O5S2: C, 58.45; H, 5.12; N, 5.93. Found:

J.-H. Chen et al. / Tetrahedron 62 (2006) 887–893
891
C, 58.68; H, 5.11; N, 5.88; Crystal data for 5b (colorless
crystal, recrystallized from hexanes/EtOAc) at 20 8C:
products. Further purificatin by flash column chromatog-
raphy eluted with (3:1 hexanes/EtOAc) afforded 6a and 7a
as a white solid (51.42 mg; 92%, ratio of diastereomers
99:01).
C23H24N2O5S2,
˚
M 472.56, Monoclinic, P21, aZ
˚
˚
12.5900(4) A, bZ6.6550(2) A, cZ13.2260(5) A, VZ
3
3
K1
˚
1107.62(6) A , ZZ2, DxZ1.417 Mg/m , mZ0.279 mm
,
3697 reflections, 285 parameters, RZ0.0735, RwZ0.1837.
4.3.1. 10,10-Dimethyl-3-N-tosyl-4-N-[(R)-2-hydroxy-
2-phenylpent-4-enoyl]-tricyclo[5.2.1.01,5]decan-2-one
(6a). RfZ0.54 (2:1 hexanes/EtOAc); mp: 170–172 8C. [a]D27
4.2.3. 10,10-Dimethyl-3-N-tosyl-4-N-[2-(1-acetyl-1H-
indol-3-yl)-2-oxoacetyl]-tricyclo[5.2.1.01,5]decan-2-one
(5c). White solid. RfZ0.59 (2:1 hexanes/EtOAc); mp:
1
C142.0 (c 1, CHCl3); H NMR (400 MHz, CDCl3) d 8.14
(d, 2H, JZ8.0 Hz), 7.54 (d, 2H, JZ7.2 Hz), 7.37 (d, 2H,
JZ8.0 Hz), 7.33–7.26 (m, 3H), 5.92 (m, 1H), 5.35 (d, 1H,
JZ9.6 Hz), 5.28 (d, 1H, JZ16.8 Hz), 3.34 (dd, 1H, JZ
13.2, 5.5 Hz), 3.16 (s, 1H), 3.02 (s, 1H), 2.76–2.73 (m, 1H),
2.46 (s, 3H), 2.46–2.42 (m, 1H), 2.00–1.94 (m, 1H), 1.81–
1.78 (m, 3H), 1.27 (s, 3H), 1.05 (s, 3H), 0.97–0.91 (m, 1H),
0.86–0.81 (m, 1H); 13C NMR (100 MHz, CDCl3) d 171.7,
153.0, 144.8, 139.5, 136.0, 132.6, 129.3, 129.1, 128.4,
128.0, 124.7, 122.1, 78.4, 67.5, 59.0, 55.1, 49.5, 46.3, 41.5,
28.0, 26.2, 21.7, 20.7, 19.7; IR (neat, cmK1): 3530, 3065,
2965, 2884, 1748, 1703, 1450, 1368, 1173, 1083, 814, 739;
HRMS (EI) calcd for C28H32N2O5S 509.2060. Found
509.2053; Crystal data for 6a (colorless crystal, recrystal-
lized from hexanes/EtOAc) at 20 8C: C28H32N2O5S, M
1
194–195 8C; H NMR (400 MHz, CDCl3) d 8.69 (s, 1H),
8.49–8.47 (m, 1H), 8.36–8.34 (m, 1H), 7.94 (s, 2H),
7.48–7.42 (m, 2H), 7.36 (d, 2H, JZ7.6 Hz), 4.22 (s, 1H),
2.75 (s, 3H), 2.46 (s, 3H), 2.12 (td, 1H, JZ11.7, 3.9 Hz),
1.96–1.93 (m, 2H), 1.86 (dd, 1H, JZ13.7, 8.0 Hz),
1.31–1.24 (m, 3H), 1.21 (s, 3H), 1.07 (s, 3H); 13C NMR
(100 MHz, CDCl3) d 180.0, 169.0, 162.2, 146.1, 136.2,
135.9, 129.8, 129.0, 127.1, 126.7, 125.6, 122.0, 117.7,
116.6, 70.7, 60.4, 52.7, 47.6, 29.7, 28.9, 26.7, 23.9, 21.8,
20.3, 20.1; IR (neat, cmK1): 3059, 2962, 2925, 1768, 1732,
1652, 1539, 1448, 1379, 1212, 1175, 1008, 756; HRMS (EI)
calcd for C29H29N3O6S 547.1777. Found 547.1779.
˚
508.62, Monoclinic, P21, aZ8.6460(2) A, bZ
3
4.2.4. 10,10-Dimethyl-3-N-tosyl-4-N-(2-oxobutanoyl)-
tricyclo[5.2.1.01,5]decan-2-one (5d). Under N2 atmosphere
a mixture of 2-ketobutyric acid (3.00 g, 29.30 mmol) and
thionyl chloride (32.1 mL, 440.7 mmol) was refluxed at
75 8C for 2 h and concentrated on rotary evaporator to
remove SOCl2. The resulting crude product was dissolved in
CH2Cl2 (5 mL) and added to a solution of camphor
N-tosylpyrazolidinone 4 (0.20 g, 0.59 mmol) in CH2Cl2
(5 mL). This was added pyridine (2.30 mL, 29.50 mmol)
and the reaction was allowed to stir at room temperature for
12 h. The reaction mixture was then quenched with H2O
(20 mL) and extracted with CH2Cl2 (3!20 mL). The
combined organic extracts dried over anhydrous MgSO4
and the crude products were purified by flash column
chromatography eluted with (2:1 hexane/EtOAc) provided
product 5d (0.12 g; 50%) as a colorless oil. RfZ0.38 (2:1
hexanes/EtOAc); 1H NMR (400 MHz, CDCl3) d 7.81 (d, 2H,
JZ8.2 Hz), 7.40 (d, 2H, JZ8.2 Hz), 3.78 (m, 1H), 3.11 (dq,
1H, JZ19.0, 7.2 Hz), 2.81 (dq, 1H, JZ19.0, 7.2 Hz), 2.48 (s,
3H), 2.03–1.86 (m, 4H), 1.81 (dd, 1H, JZ14.3, 8.2 Hz),
1.26–1.20 (m, 2H), 1.16 (t, 3H, JZ7.2 Hz), 1.16 (s, 3H), 1.03
(s, 3H); 13C NMR (100 MHz, CDCl3) d 197.0, 174.9, 162.3,
146.4, 133.9, 130.0, 128.6, 70.3, 60.0, 52.4, 47.3, 35.2, 31.7,
28.7, 26.6, 21.6, 20.2, 19.8, 6.9; IR (neat, cmK1): 2964, 2941,
2889, 1769, 1726, 1660, 1596, 1458, 1379, 1189, 1175,
1086, 964, 815; HRMS (EI) calcd for C21H26N2O5S
418.1562. Found 418.1560.
˚
˚
˚
11.5040(3) A, cZ13.4890(3) A, VZ1301.10(5) A , ZZ2,
DxZ1.298 Mg/m3, mZ0.165 mmK1, 4476 reflections, 326
parameters, RZ0.0652, RwZ0.1377.
4.3.2. 10,10-Dimethyl-3-N-tosyl-4-N-[(S)-2-hydroxy-
2-phenylpent-4-enoyl]-tricyclo[5.2.1.01,5]decan-2-one
(7a). White solid. RfZ0.46 (2:1 hexanes/EtOAc); mp:
194–195 8C. [a]2D7 K71.3 (c 1, CHCl3); 1H NMR (400 MHz,
CDCl3) d 8.08 (d, 2H, JZ7.8 Hz), 7.67 (d, 2H, JZ7.8 Hz),
7.39–7.28 (m, 5H), 5.94 (m, 1H), 5.32 (d, 1H, JZ10.1 Hz),
5.26 (d, 1H, JZ17.2 Hz), 4.32 (t, 1H, JZ6.2 Hz), 3.27 (dd,
1H, JZ13.4, 6.2 Hz), 2.93 (br s, 1H), 2.66 (dd, 1H, JZ13.4,
8.4 Hz), 2.46 (s, 3H), 2.08–2.02 (m, 1H), 1.89–1.74 (m, 3H),
1.56 (s, 1H), 1.27–1.16 (m, 2H), 0.90 (s, 3H), 0.70 (s, 3H); 13C
NMR (100 MHz, CDCl3) d 174.0, 172.9, 145.2, 140.2, 135.6,
133.0, 129.5, 128.9, 128.1, 127.6, 125.4, 121.9, 78.7, 72.5,
60.3, 51.7, 51.1, 47.0, 39.5, 29.1, 26.5, 21.8, 20.2, 19.5; IR
(neat, cmK1): 3504, 3065, 2965, 2935, 1755, 1668, 1447,
1379, 1295, 1189, 1174, 1086; HRMS (EI) calcd for
C28H32N2O5S 508.2026. Found 508.2009; Crystal data for
7a (colorless crystal, recrystallized from hexanes/EtOAc) at
K73 8C: C28H32N2O5S, M 508.62, Orthorhombic, P212121,
˚
˚
˚
aZ6.3790(2) A, bZ18.5760(6) A, cZ21.1690(8) A, VZ
3
3
K1
˚
2508.45(15) A , ZZ4, DxZ1.347 Mg/m , mZ0.172 mm
4409 reflections, 326 parameters, RZ0.1054, RwZ0.1766.
,
4.3.3. 10,10-Dimethyl-3-N-tosyl-4-N-[(S)-2-hydroxy-2-
(thiophen-2-yl)pent-4-enoyl]-tricyclo[5.2.1.01,5]decan-2-
one (6b). White solid. RfZ0.51 (2:1 hexanes/EtOAc); mp:
163–165 8C. [a]2D7 C122.8 (c 1, CHCl3); 1H NMR
(400 MHz, CDCl3) d 8.11 (d, 2H, JZ8.0 Hz), 7.35 (d, 2H,
JZ8.0 Hz), 7.20 (d, 1H, JZ4.8 Hz), 7.01 (d, 1H, JZ
3.7 Hz), 6.92 (t, 1H, JZ4.8 Hz), 5.89 (m, 1H), 5.36 (d, 1H,
JZ10.1 Hz), 5.31 (d, 1H, JZ17.2 Hz), 3.52 (s, 1H), 3.35
(dd, 1H, JZ13.3, 5.1 Hz), 3.25 (br s, 1H), 2.72–2.65 (m,
2H), 2.44 (s, 3H), 2.06–1.98 (m, 2H), 1.87–1.81 (m, 2H),
1.25 (s, 3H), 1.12–1.06 (m, 1H), 1.06 (s, 3H), 0.97 (t, 1H,
JZ10.0 Hz); 13C NMR (100 MHz, CDCl3) d 177.6, 171.8,
144.9, 144.3, 135.8, 132.0, 129.2, 129.1, 127.3, 125.0,
4.3. Typical procedure for the synthesis of compounds
6a and 7a
To a solution of camphor N-tosylpyrazolidinone derived
a-ketoamide (51.27 mg, 0.11 mmol) in CH3CN (4 mL) was
added allyltributylstannane (0.37 mL, 1.06 mmol) and
tin(II) triflate (91.7 mg, 0.22 mmol). The reaction was
allowed to stir for 5 min at room temperature. The mixture
was quenched with H2O (15 mL) and extracted with CH2Cl2
(3!20 mL). The organic layers were separated and dried
over anhydrous MgSO4 and concentrated to give crude

892
J.-H. Chen et al. / Tetrahedron 62 (2006) 887–893
124.2, 122.4, 78.0, 68.2, 59.0, 55.1, 49.7, 46.3, 41.7, 28.0,
26.2, 21.7, 20.6, 19.7; IR (neat, cmK1): 3516, 2992, 2966,
2884, 1748, 1698, 1452, 1368, 1207, 1173, 1086, 815;
HRMS (EI) calcd for C26H30N2O5S2 514.1591. Found
514.1599; Crystal data for 6b (colorless crystal, recrystal-
lized from hexanes/EtOAc) at K123 8C: C26H30N2O5S2, M
8.2 Hz), 7.35 (d, 2H, JZ8.2 Hz), 6.05 (m, 1H), 5.34 (d, 1H,
JZ10.0 Hz), 5.24 (d, 1H, JZ17.1 Hz), 3.90 (s, 1H), 2.87
(dd, 1H, JZ13.3, 5.2 Hz), 2.67–2.58 (m, 1H), 2.44 (s, 3H),
2.38–2.28 (m, 1H), 2.22–2.11 (m, 2H), 1.98–1.87 (m, 2H),
1.70–1.65 (m, 1H), 1.34 (s, 3H), 1.30–1.23 (m, 3H), 1.13 (s,
3H), 0.93 (t, 3H, JZ7.4 Hz); 13C NMR (100 MHz, CDCl3)
d 171.3, 144.8, 136.0, 132.7, 129.1, 129.0, 121.3, 78.5, 59.1,
46.2, 42.3, 32.1, 28.0, 27.8, 26.3, 21.7, 20.8, 19.8, 17.5,
13.6, 8.2; IR (neat, cmK1): 3535, 2968, 2941, 2884, 1747,
1695, 1597, 1456, 1373, 1295, 1173, 1083, 814, 737; HRMS
(EI) calcd for C24H32N2O5S 460.2032. Found 460.2035.
˚
514.64, Monoclinic, P21, aZ8.5300(3) A, bZ
3
˚
˚
˚
11.2470(4) A, cZ13.4740(7) A, VZ1247.57(9) A , ZZ2,
DxZ1.370 Mg/m3, mZ0.254 mmK1, 4278 reflections, 317
parameters, RZ0.0625, RwZ0.1386.
4.3.4. 10,10-Dimethyl-3-N-tosyl-4-N-[(R)-2-hydroxy-2-
(thiophen-2-yl)pent-4-enoyl]-tricyclo[5.2.1.01,5]decan-
2-one (7b). White solid. RfZ0.41 (2:1 hexanes/EtOAc);
mp: 167–168 8C. [a]2D7 K50.1 (c 1, CHCl3); 1H NMR
(400 MHz, CDCl3) d 8.06 (d, 2H, JZ8.2 Hz), 7.37 (d, 2H,
JZ8.2 Hz), 7.25 (dd, 1H, JZ5.0, 1.0 Hz), 7.17 (dd, 1H, JZ
3.5, 1.0 Hz), 6.95 (dd, 1H, JZ5.0, 3.5 Hz), 5.95 (m, 1H),
5.34 (d, 1H, JZ10.8 Hz), 5.30 (d, 1H, JZ18.0 Hz), 4.34 (s,
1H), 3.25 (dd, 1H, JZ13.6, 7.5 Hz), 3.18 (br s, 1H), 2.89
(dd, 1H, JZ13.6, 7.5 Hz), 2.46 (s, 3H), 2.19–2.16 (m, 1H),
2.09–2.04 (m, 1H), 1.92 (dd, 1H, JZ14.4, 8.1 Hz),
1.87–1.81 (m, 1H), 1.67 (t, 1H, JZ3.7 Hz), 1.30–1.19 (m,
2H), 0.94 (s, 3H), 0.81 (s, 3H); 13C NMR (100 MHz,
CDCl3) d 174.0, 172.8, 145.3, 144.5, 135.4, 132.4, 129.5,
128.9, 126.8, 125.3, 124.4, 122.3, 78.3, 72.8, 60.4,
51.7, 51.5, 47.0, 39.9, 29.1, 26.6, 21.8, 20.3, 19.5; IR
(neat, cmK1): 3501, 3054, 2992, 2961, 1741, 1683, 1380,
1175, 1080, 1039, 936, 827, 752; HRMS (EI) calcd for
C26H30N2O5S2 514.1591. Found 514.1598. Anal. Calcd for
C26H30N2O5S2: C, 60.68; H, 5.88; N, 5.44. Found: C, 60.82;
H, 5.85; N, 5.45; Crystal data for 7b (colorless
crystal, recrystallized from hexanes/EtOAc) at K73 8C:
C26H30N2O5S2, M 514.64, Orthorhombic, P212121, aZ
Acknowledgements
This work was supported by the National Science Council of
the Republic of China (NSC 94-2113-M-003-003) and the
National Taiwan Normal University (ORD 93-C). The
X-ray crystal data were collected and processed by National
Taiwan Normal University are gratefully acknowledged.
References and notes
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˚
˚
˚
9.8170(2) A, bZ12.1720(2) A, cZ21.7010(5) A, VZ
3
3
K1
˚
2593.11(9) A , ZZ4, DxZ1.318 Mg/m , mZ0.244 mm
,
4469 reflections, 316 parameters, RZ0.0531, RwZ0.1272.
4.3.5. 10,10-Dimethyl-3-N-tosyl-4-N-[(R)-2-(1-acetyl-1H-
indol-3-yl)-2-hydroxypent-4-enoyl]-tricyclo[5.2.1.01,5]-
decan-2-one (6c). White solid. RfZ0.60 (2:1 hexanes/
1
EtOAc); mp: 153–155 8C. [a]1D6 C157.3 (c 1, CHCl3); H
NMR (400 MHz, CDCl3) d 8.44 (d, 1H, JZ7.9 Hz), 8.10 (d,
2H, JZ8.2 Hz), 7.96 (d, 1H, JZ7.9 Hz), 7.49 (s, 1H), 7.38
(d, 2H, JZ8.2 Hz), 7.35 (t, 1H, JZ7.9 Hz), 7.26 (t, 1H, JZ
7.9 Hz), 5.94 (m, 1H), 5.35 (d, 1H, JZ10.4 Hz), 5.30 (d,
1H, JZ17.4 Hz), 3.54 (dd, 1H, JZ7.7, 5.1 Hz), 3.43 (dd,
1H, JZ12.6, 4.1 Hz), 3.25 (br s, 1H), 2.80–2.75 (m, 1H),
2.69 (d, 1H, JZ12.6 Hz), 2.61 (s, 3H), 2.47 (s, 3H), 1.98 (td,
1H, JZ12.0, 4.8 Hz), 1.83–1.78 (m, 3H), 1.30–1.26 (m,
1H), 1.16 (s, 3H), 1.03 (s, 3H), 1.00–0.96 (m, 1H); 13C NMR
(100 MHz, CDCl3) d 176.0, 172.2, 168.6, 145.2, 136.4,
135.5, 132.0, 129.3, 129.2, 127.3, 125.5, 123.8, 122.9,
122.1, 121.9, 121.7, 116.5, 77.4, 59.2, 47.4, 46.4, 41.2, 31.5,
28.1, 26.3, 22.6, 21.7, 20.5, 19.7, 14.1; IR (neat, cmK1):
3418, 3080, 2962, 2930, 2894, 1748, 1710, 197, 1451, 1382,
1331, 1225, 1173, 1083, 815; HRMS (EI) calcd for
C32H35N3O6S 589.2247. Found 589.2240.
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4.3.6. 10,10-Dimethyl-3-N-tosyl-4-N-[(S)-2-ethyl-2-
hydroxypent-4-enoyl]-tricyclo[5.2.1.01,5]decan-2-one
(6d). White solid. RfZ0.42 (2:1 hexanes/EtOAc); mp:
138–140 8C; 1H NMR (400 MHz, CDCl3) d 8.10 (d, 2H, JZ

J.-H. Chen et al. / Tetrahedron 62 (2006) 887–893
893
Kobayashi, S. Chem. Commun. 2003, 676–677. (e) Thadani,
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14. In infrared spectra stretching bands shift toward lower
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6183–6185.
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16. The diastereoselective allylation of the camphorsultam derived
phenylglyoxylate was carried out under similar reaction
conditions. The reversal of stereoselectivity was observed
and the results are as follows.
Me
Me
Me
Me
O
O
Allyltributyltin
Lewis acid
Ph
N
N
HO
Ph
O
S
O
S
O
O
O
Sn(OTf)2: β-OH/α -OH = 13:87 (62%)
Zn(OTf)2: β-OH/ α-OH = 86:14 (87%)
10. Lavallee, D. K.; Zeltmann, A. H. J. Am. Chem. Soc. 1974, 96,
5552–5556.
.
11. Yang, K.-S.; Chen, K. J. Org. Chem. 2001, 66, 1676–1679.
12. Additional data for C-2 methine protons are as follows: 6b
(3.52 ppm), 7b (4.34 ppm), 6c (3.54 ppm), and 6d (3.90 ppm).
17. Compounds 3 (CCDC 284467), 4 (CCDC 281390), 5a (CCDC
281384), 5b (CCDC 281386), 6a (CCDC 281385), 6b (CCDC
281387), 7a (CCDC 281388), 7b (CCDC 281389). TOC.