Synthesis of 3-exo-aroylhexahydroindoles via sequential gold(I)-catalyzed claisen-type rearrangement-epimerization reactions of cis -4-[ N -Tosyl- N -(3-arylprop-2-ynyl)amino]cyclohex-2-en-1-ols

Article abstract of DOI:10.1055/s-0033-1339129

A two-step process for the synthesis of 3-exo-aroylhexahydroindoles is described. cis-4-[N-Tosyl-N-(3-arylprop-2-ynyl)amino]cyclohex-2-en-1-ols were cycloisomerized with a catalytic amount of chloro(triphenylphosphine)gold(I)/ silver(I) hexafluoroantimonate (AuPPh₃Cl/AgSbF₆); subsequent base treatment of the crude mixture provided 3-exo- aroylhexahydroindoles in good yields and complete stereoselectivity. A key step involving a 9-endo-dig attack of the hydroxyl group onto the gold-activated alkyne is proposed. The resulting allyl vinyl ether intermediate underwent a gold-assisted [3,3]-sigmatropic rearrangement to form 3-exo-3- aroylhexahydroindole derivatives. Georg Thieme Verlag Stuttgart. New York.

Full text of DOI:10.1055/s-0033-1339129

2220▌
PAPER
paper
Synthesis of 3-exo-Aroylhexahydroindoles via Sequential Gold(I)-Catalyzed
Claisen-Type Rearrangement–Epimerization Reactions of cis-4-[N-Tosyl-N-
(3-arylprop-2-ynyl)amino]cyclohex-2-en-1-ols
Synthesis of 3-exo-Aroylhexahydroindoles
Chia-Jung Liang, Xuan-Yi Jiang, Ming-Chang P. Yeh*
Department of Chemistry, National Taiwan Normal University, 88 Ding-Jou Road, Section 4, Taipei 11677, Taiwan, R. O. C.
Fax +886(2)29324249; E-mail: cheyeh@ntnu.edu.tw
Received: 18.03.2014; Accepted after revision: 22.04.2014
tion reaction to prepare 3-exo-aroylhexahydroindole
Abstract: A two-step process for the synthesis of 3-exo-aroylhexa-
derivatives
from
cis-4-[N-tosyl-N-(3-arylprop-2-
hydroindoles is described. cis-4-[N-Tosyl-N-(3-arylprop-2-
ynyl)amino]cyclohex-2-en-1-ols were cycloisomerized with a cata-
lytic amount of chloro(triphenylphosphine)gold(I)/silver(I) hexa-
ynyl)amino]cyclohex-2-en-1-ols (3). The reaction path
leading to 3-aroylhexahydroindoles may be initiated with
fluoroantimonate (AuPPh3Cl/AgSbF6); subsequent base treatment a nucleophilic 9-endo-dig addition of the hydroxy group
onto the gold-activated alkyne,12 providing an allyl vinyl
ether intermediate which undergoes a gold-assisted [3,3]-
of the crude mixture provided 3-exo-aroylhexahydroindoles in good
yields and complete stereoselectivity. A key step involving a 9-
endo-dig attack of the hydroxyl group onto the gold-activated
sigmatropic rearrangement to furnish the heterobicyclic
alkyne is proposed. The resulting allyl vinyl ether intermediate un-
derwent a gold-assisted [3,3]-sigmatropic rearrangement to form 3-
skeleton.
exo-3-aroylhexahydroindole derivatives.
our previous work
Key words: alcohols, alkynes, cyclization, ethers, indoles
O
OH
OH
Ar
Ph3PAuCl (5 mol%)
AgOTf (5 mol%)
Ar
(1)
(2)
Ts
N
Nitrogen-containing heterobicycles are of great interest
because of their ubiquity and wide range of biological ac-
tivities.1 Transition metal-assisted hydroamination of un-
saturated C–C bonds has been widely employed in the
construction of hexahydroindole scaffolds. Several efforts
towards the synthesis of hexahydroindoles include the zir-
conium-promoted reductive cyclization of N-benzyl-N-
(cyclohex-2-enyl)propargylamines,2 the palladium-cata-
lyzed intramolecular olefin allylation of N-containing 1-
acetoxy-2,7-dienes,3a the palladium-catalyzed cou-
pling/cyclization reaction of cyclic N-containing 1,6-
enynes with aryl halides,3b the nickel-catalyzed intramo-
lecular allylation/carbonylation of N-containing dienyl
acetates,4 the gold(I)-catalyzed double cyclization of 3,7-
dienylsulfonamide,5a and the gold(I)-catalyzed intramo-
lecular 1,4-hydroamination of cyclic 1,3-dienes.5b In our
previous study (Scheme 1),6 we reported a gold-catalyzed
Claisen-type rearrangement7–10 of cyclic 8-aryl-5-aza-2-
en-7-yn-1-ols, leading to azaspirocyclic ketones in 90%
yield as a 1:1 mixture of diastereomers (1).6 Similar re-
sults were obtained upon treatment of the acyclic ana-
CH2Cl2, r.t., 3 min
ref. 6
N
Ts
O
Ph3PAuCl (10 mol%)
AgOTf (10 mol%)
Ar
Ar
Ts
CH2Cl2, r.t., 5 h
ref. 11
N
N
Ts
this work
OH
O
1. Au/Ag cat.
2. base
Ar
(3)
Ar
N
Ts
TsN
Scheme 1 Gold-catalyzed Claisen-type rearrangements of nitrogen-
containing enynols
We began our studies with the parent cis-4-[N-tosyl-N-(3-
phenylprop-2-ynyl)amino]cyclohex-2-en-1-ol
(1a),
which is available by epoxidation of cyclohexa-1,3-diene
with m-chloroperoxybenzoic acid (see Supporting Infor-
mation for details).13–15 Compound 1a was subjected to
various catalysts and sets of conditions (Table 1). When
exposed to chloro(triphenylphosphine)gold(I)/silver(I)
trifluoromethanesulfonate (AuPPh3Cl/AgOTf, 10 mol%)
in dichloromethane at 20 °C for 24 hours, 1a formed 3-
benzoylhexahydroindole 2a in only 5% isolated yield
with low exo/endo stereoselectivity (exo-2a/endo-2b =
3:2, entry 1). Unfortunately, 1a decomposed upon heating
in the presence of the chloro(triphenylphos-
phine)gold(I)/silver(I) trifluoromethanesulfonate (10
mol%) catalyst system in dichloromethane at 40 °C (entry
2). No reaction occurred when chloro(triphenylphos-
logues (Z)-8-aryl-5-azaoct-2-en-7-yn-1-ols with
a
catalytic amount of the gold cationic species, affording
cis-3-acyl-4-alkenylpyrrolidines (2).11 We envision that
introducing an N-(3-arylpropargyl)-N-tosylamine tether
at the C-4 position of the cyclohex-2-en-1-ol ring should
lead to fused heterobicyclic skeletons under gold-cata-
lyzed conditions (3). Herein, we describe a sequential
gold(I)-catalyzed Claisen-type rearrangement–epimeriza-
SYNTHESIS 2014, 46, 2220–2224
Advanced online publication: 02.06.2014
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0033-1339129; Art ID: ss-2014-f0190-op
© Georg Thieme Verlag Stuttgart · New York

PAPER
Synthesis of 3-exo-Aroylhexahydroindoles
2221
phine)gold(I)/silver(I) bis(trifluoromethanesulfonyl)im- the temperature to 80 °C in 1,2-dichloroethane provided
ide (AuPPh3Cl/AgNTf2, 10 mol%) was used as the 2a in 2 min with a 2:3 exo/endo selectivity in 77% yield.
catalyst system (entry 3). The use of silver(I) hexafluoro- (entry 8). The use of toluene at either 25 or 80 °C dimin-
antimonate (AgSbF6) as the silver salt additive with ished the yield of 2a (entries 9 and 10). Switching to sil-
chloro(triphenylphosphine)gold(I) (10 mol%) in di- ver(I) hexafluorophosphate (10 mol%) as the silver salt
chloromethane at 20 °C for 30 minutes delivered exo-2a additive in 1,2-dichloroethane at 80 °C led to 2a in only
and endo-2b in 55% yield (exo/endo = 1:1, entry 4). De- 6% yield (entry 11). Employing the N-heterocyclic carbe-
lightfully, the cycloisomerization reaction was completed ne gold catalyst IPrAuCl [IPr = 1,3-bis(diisopropylphe-
in four minutes when 1a was reacted with chloro(triphen- nyl)imidazol-2-ylidene] with silver(I) hexafluoro-
ylphosphine)gold(I) and silver(I) hexafluoroantimonate antimonate in dichloromethane at 40 °C for 24 hours
(10 mol%) in dichloromethane at 40 °C, generating exo- failed to improve the yield and stereoselectivity of 2a (en-
2a and endo-2b with 2:3 exo/endo selectivity in 78% yield try 12). Moreover, the Brønsted acid trifluoromethanesul-
(entry 5). When 1a was treated with the same catalyst sys- fonimide (Tf2NH, entry 13), was ineffective and gave 2a
tem in dichloromethane at 0 °C, the reaction required a in only 11% yield. Subjecting 1a to gold(III) chloride (10
longer time (3 h) and produced the same amounts of exo mol%), silver(I) hexafluoroantimonate (10 mol%), or
and endo isomers in 68% yield (entry 6).
platinum(II) chloride (10 mol%) in dichloromethane at
40 °C led predominantly to the recovery of 1a in each case
(entries 14−16). Thus, entry 5 (10 mol% of AuPPh3Cl and
AgSbF6, CH2Cl2, 40 °C) was chosen as the optimal reac-
tion conditions. It is of note that the corresponding trans-
4-[N-tosyl-N-(3-phenylprop-2-ynyl)amino]cyclohex-2-
en-1-ol (3) failed to undergo cycloisomerization with var-
ious gold(I)/silver(I) catalyst systems.
Table 1 Optimization of Catalyst and Conditions
OH
O
O
conditions
Ph
+
Ph
Ph
N
N
TsN
1a
Ts
Ts
exo-2a
endo-2a
Although the exo/endo selectivity was poor in all cases,
the mixture of exo and endo isomers can be separated eas-
ily by simple flash column chromatography over silica
gel. Structural assignments for exo-2a and endo-2a were
Entry Catalyst
(10 mol%)
Conditions
Yield Ratio
(%)a exo/endob
1
established by their H NMR spectral data. The stereo-
1
2
3
4
5
6
7
8
9
AuPPh3Cl, AgOTf CH2Cl2, 20 °C, 24 h
AuPPh3Cl, AgOTf CH2Cl2, 40 °C, 6 h
AuPPh3Cl, AgNTf2 CH2Cl2, 20 °C, 12 h
5
0
0
3:2
–
chemistry assignment for endo-2a was based on the char-
acteristic upfield shift, δ = 4.96, of the vinyl proton at C-
4, while the vinyl proton at C-4 of exo-2a appears at δ =
5.42. The observed upfield shift of the vinyl proton for
endo-2a may result from a shielding effect of the endo-
benzoyl moiety. These assignments were further secured
by X-ray diffraction analysis of both exo-2a and endo-
2a.16
–
AuPPh3Cl, AgSbF6 CH2Cl2, 20 °C, 30 min 55
AuPPh3Cl, AgSbF6 CH2Cl2, 40 °C, 4 min 78
1:1
2:3
1:1
3:2
2:3
3:2
3:2
1:1
1:1
3:2
–
AuPPh3Cl, AgSbF6 CH2Cl2, 0 °C, 3 h
AuPPh3Cl, AgSbF6 DCE, 25 °C, 2 h
AuPPh3Cl, AgSbF6 DCE, 80 °C, 2 min
AuPPh3Cl, AgSbF6 toluene, 25 °C, 5 h
68
44
77
22
Since endo-2a can be epimerized to the thermodynamical-
ly more stable exo-2a under basic conditions, it would be
practical to obtain the exo isomer exclusively by treatment
of the crude exo and endo mixture with base after the ini-
tial cycloisomerization reaction. Thus, 1a was treated
with the catalyst system (10 mol% AuPPh3Cl/AgSbF6) in
dichloromethane at 40 °C for six minutes. The crude mix-
ture was then filtered through a pad of Celite. The filter
cake was eluted with dichloromethane (ca. 10 mL). The
solvent was removed and the resulting residue was sub-
jected to potassium hydroxide in dichloromethane–etha-
nol (1:1) at 40 °C for five minutes to give exo-2a as the
only isomer in 73% yield after flash column chromatogra-
phy (silica gel). As shown in Table 2, exo-2a–l were ob-
tained in 55–83% yield (over two steps).
10 AuPPh3Cl, AgSbF6 toluene, 80 °C, 2 min 39
11 AuPPh3Cl, AgPF6
12 IPrAuCl, AgSbF6
13 Tf2NH
DCE, 80 °C, 12 h
6
30
11
0
CH2Cl2, 40 °C, 24 h
CH2Cl2, 20 °C, 12 h
CH2Cl2, 20 °C, 12 h
CH2Cl2, 40 °C, 24 h
CH2Cl2, 20 °C, 24 h
14 AuCl3
15 AgSbF6
0
–
16 PtCl2
0
–
a All reactions were conducted under N2 and yields were obtained after
flash column chromatography over silica gel.
b Determined by 400 MHz 1H NMR analysis of the crude reaction
mixture.
As shown in Table 2, substrates bearing an electron-neu-
tral or -rich arene at the alkyne terminus were found to be
successful, affording the desired 3-aroylhexahydroindoles
exo-2a–g in yields of 55–78% over two steps (entries
1−7). It was found that a bromine atom at the C-4 position
of the phenyl ring (1h) has no influence on the catalytic
activity, as exo-2h was isolated in 83% yield (entry 8).
Changing the solvent to 1,2-dichloroethane afforded 2a in
44% yield (exo:endo = 3:2) (Table 1, entry 7). Increasing
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 2220–2224

2222
C.-J. Liang et al.
PAPER
Table 2 Sequential Gold(I)-Catalyzed Cycloisomerization–Epi-
merization Reactions of 1
OH
1. AuPPh3Cl (10 mol%)
OH
AgSbF6 (10 mol%)
CH2Cl2, 40 °C
2–15 min
O
R
TsN
1m R = H
Ar
2. KOH (1.5 equiv)
EtOH–CH2Cl2 (1:1)
40 °C, 5 min
Ar
1n R = Me
X
X
exo-2
Figure 1 Structures of 1m and 1n
1
Entry Ar
Substrate
X
Yield (%)a
the trans isomer 3 indicates that the 9-endo-dig process
could only take place when the hydroxyl and alkyne moi-
eties are on the same face of the six-membered ring.
Subsequently, a gold-assisted [3,3]-sigmatropic rear-
rangement of 4 gives the bicyclic intermediate 5 contain-
ing a carbon–gold bond at the α-position of the carbonyl
group. The cis stereochemistry of the fused bicycle 5 is
fixed by the vinylgold moiety aligned to the face of the
six-membered ring where the tether resides. Deprotona-
tion and tautomerization of 5 gives oxygen-bound gold
enolate 6. Protonation of enolate 6 provides hexahydroin-
dole 2 as a mixture of exo/endo isomers and regenerates
the gold(I) catalyst into the catalytic cycle. However, a
stepwise reaction involving an activation of the allylic al-
cohol by gold(I) cannot be ruled out.17 Addition of the al-
lylgold moiety and the hydroxyl residue across the alkyne
followed by tautomerization of the resulting enol furnish-
es exo/endo-2.
1
2
Ph
1a
1b
1c
1d
1e
1f
NTs
73 (exo-2a)
75 (exo-2b)
58 (exo-2c)
55 (exo-2d)
70 (exo-2e)
57 (exo-2f)
78 (exo-2g)
83 (exo-2h)
25 (exo-2i)b
15 (exo-2j)b
80 (exo-2k)
56 (exo-2l)
4-MeC6H4
3-MeC6H4
4-PhC6H4
1-naphthyl
4-MeOC6H4
3-MeOC6H4
4-BrC6H4
3-EtO2CC6H4
4-O2NC6H4
Ph
NTs
3
NTs
4
NTs
5
NTs
6
NTs
7
1g
1h
1i
NTs
8
NTs
9
NTs
10
11
12
1j
NTs
1k
1l
NSO2Ph
NSO2Mes
Ph
In summary, we have described a practical and convenient
synthesis of 3-exo-aroylhexahydroindoles by gold-cata-
lyzed cycloisomerization of 4-[N-tosyl-N-(3-arylprop-2-
ynyl)amino]cyclohex-2-en-1-ols and subsequent epi-
merization with base. The advantages of this method are
a. Yields were obtained after column chromatography over silica gel.
b Products were obtained after gold-catalyzed cyclization followed by
separation by column chromatography over silica gel.
However, the presence of an electron-withdrawing ester
or nitro substituent on the phenyl ring, for example in 1i
and 1j, resulted in the alkyne being less reactive, deliver-
ing the corresponding 3-aroylhexahydroindoles exo-2i
and exo-2j in 25 and 15% yield, respectively, after gold-
catalyzed cyclization/epimerization and purification by
column chromatography over silica gel. (entries 9 and 10).
Other nitrogen-protecting groups such as phenyl sulfon-
ate, in 1k (entry 11), and 2,4,6-trimethylphenyl sulfonate,
in 1l (entry 12), were readily allowed and afforded exo-2k
and exo-2l in 80 and 56% yield, respectively. Unfortu-
nately, treatment of substrates having a hydrogen or meth-
yl group at the alkyne terminus, for example 1m and 1n
(Figure 1), with the gold catalyst (AuPPh3Cl and AgSbF6)
in dichloromethane gave a complex mixture of unidenti-
fied products in both cases.
AuLCl
OH
O
AgSbF6
Ar
Ar
TsN
+AuL
N
H+
1
Ts
–SbF6
exo/endo-2
Ar
HO
LAu+
LAuO
Ar
TsN
N
Ts
6
9-endo-dig
– H+
HO+
The postulated reaction path for the formation of 2 via
gold(I)-catalyzed cycloisomerization of 1 is depicted in
Scheme 2. First, coordination of the alkyne to the cationic
gold center, generated from chloro(triphenylphos-
phine)gold(I) and silver(I) hexafluoroantimonate, forms
the gold(I)–alkyne species. Attack of the cis-hydroxyl
group onto the gold-activated alkyne in a 9-endo-dig fash-
Ar
H
Ar
+
O
LAu
AuL
N
TsN
Ts
5
[3,3]-sigmatropic
rearrangement
4
ion provides the allyl vinyl ether intermediate 4. There- Scheme 2 A plausible mechanism for the formation of hexahydroin-
dole 2
fore, the failure of gold-catalyzed cycloisomerization of
Synthesis 2014, 46, 2220–2224
© Georg Thieme Verlag Stuttgart · New York

PAPER
Synthesis of 3-exo-Aroylhexahydroindoles
2223
HRMS (ESI): m/z [M + Na]+ calcd for C22H23NO3NaS: 404.1297;
found: 404.1307.
short reaction times, mild reaction conditions, and good
yields. Further studies to reveal the reaction path are cur-
rently underway in our laboratory.
Sequential Gold(I)-Catalyzed Cycloisomerization–Epimeriza-
tion of cis-4-[N-Tosyl-N-(3-arylprop-2-ynyl)amino]cyclohex-2-
en-1-ols; General Procedure (II)
All reactions were performed with oven-dried glassware under a N2
atmosphere. All organic solvents were dried by passing through a
column of alumina. Melting points were determined in open capil-
laries and are uncorrected. 1H NMR spectra were obtained with 400
and 500 MHz spectrometers. The chemical shifts are reported in
ppm with either TMS (δ = 0.00) or CHCl3 (δ = 7.26) as internal stan-
dard. 13C NMR spectra were recorded on 100 and 125 MHz spec-
trometers with CDCl3 (δ = 77.0) as the internal standard. IR spectra
were recorded of samples prepared as CH2Cl2 solutions. Mass spec-
tra were determined by using a spectrometer operating at an ioniza-
tion potential of 70 eV. High-resolution mass spectra were obtained
on a double-focusing mass spectrometer.
To a solution of the crude mixture of exo-2a and endo-2a, obtained
from General Procedure (I), in CH2Cl2 (2 mL) and EtOH (2 mL)
was added KOH (0.017 g, 0.30 mmol) and then the mixture was
heated to 40 °C. The mixture was stirred at 40 °C until no trace of
the endo isomer was detected by TLC (ca. 5 min). The reaction mix-
ture was then extracted with H2O (5 mL) and CH2Cl2 (3 × 5 mL).
The crude oil was purified by flash column chromatography (silica
gel, EtOAc–hexanes, 1:20); this afforded exo-2a as the only product
isolated.
Yield: 55 mg (0.145 mmol, 73%).
The analytical data of exo-2a are consistent with those obtained pre-
viously.
Gold(I)-Catalyzed Cycloisomerization Reaction of cis-4-[N-To-
syl-N-(3-arylprop-2-ynyl)amino]cyclohex-2-en-1-ols; General
Procedure (I)
Acknowledgment
To a solution solution of 1a (80 mg, 0.2 mmol) in CH2Cl2 (2 mL)
were added Ph3PAuCl (10 mg, 0.02 mmol) and AgSbF6 (7 mg, 0.02
mmol) at 40 °C under an atmosphere of N2. The reaction mixture
was stirred until 1a was consumed, as monitored by TLC. The reac-
tion mixture was filtered through a bed of Celite and concentrated
to give the crude mixture, which was purified by flash column chro-
matography (silica gel, EtOAc–hexanes, 5:95) to give exo-2a and
endo-2a.
This work has been supported by the National Science Council
(NSC 101-2113-M-003-002-MY3) and the National Taiwan Nor-
mal University.
Supporting Information for this article is available online
at
http://www.thieme-connect.com/products/ejournals/journal/
10.1055/s-00000084, including complete experimental procedures,
exo-3-Benzoyl-1-tosyl-2,3,3a,6,7,7a-hexahydro-1H-indole (exo-
analytical data, NMR spectra, and X-ray diffraction analyses.SunogIoifrmipntSartunpIgpfmiron
o
rtai
t
2a)
Yield: 24 mg (0.063 mmol, 31%); white solid; mp 151−152 °C.
Crystals suitable for X-ray diffraction analysis were grown from References
CH2Cl2 and hexanes.
IR (CH2Cl2): 3029, 2924, 1682, 1598, 1449, 1345, 1165, 1039 cm–1.
(1) (a) Baldwin, S. W.; Debenham, J. S. Org. Lett. 2000, 2, 99.
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1H NMR (500 MHz, CDCl3): δ = 7.88−7.84 (m, 2 H), 7.69 (d, J =
8.2 Hz, 2 H), 7.60 (t, J = 7.4 Hz, 1 H), 7.47 (t, J = 8.0 Hz, 2 H), 7.29
(d, J = 8.0 Hz, 2 H), 5.81 (dtt, J = 9.9, 2.5, 2.1 Hz, 1 H), 5.42 (d, J =
9.9 Hz, 1 H), 3.89−3.84 (m, 1 H), 3.84−3.77 (m, 2 H), 3.27 (t, J =
9.2 Hz, 1 H), 2.71 (br s, 1 H), 2.44 (s, 3 H), 2.25−2.15 (m, 2 H),
2.11−2.02 (m, 1 H), 1.85−1.76 (m, 1 H).
13C NMR (125 MHz, CDCl3): δ = 197.7, 143.6, 136.1, 134.0, 133.8,
129.8, 129.6, 128.8, 128.5, 127.5, 125.1, 58.4, 51.2, 50.1, 41.7,
27.9, 23.0, 21.5.
ESI-MS: m/z = 404.1 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C22H23NO3NaS: 404.1297;
found: 404.1305.
endo-3-Benzoyl-1-tosyl-2,3,3a,6,7,7a-hexahydro-1H-indole
(endo-2a)
Yield: 36 mg (0.094 mmol, 47%); white solid; mp 152−153 °C.
Crystals suitable for X-ray diffraction analysis were grown from
CH2Cl2 and hexanes.
IR (CH2Cl2): 3028, 2919, 1678, 1598, 1340, 1157, 1091 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.82−7.77 (m, 4 H), 7.57 (t, J =
7.4 Hz, 1 H), 7.44 (d, J = 8.0 Hz, 2 H), 7.36 (d, J = 8.1 Hz, 2 H),
5.93−5.85 (m, 1 H), 4.96 (d, J = 10.2 Hz, 1 H), 4.12 (br s, 1 H), 3.78
(t, J = 11.2 Hz, 1 H), 3.66 (dd, J = 11.8, 6.9 Hz, 1 H), 3.42 (dt, J =
10.6, 7.0 Hz, 1 H), 3.23 (br s, 1 H), 2.46 (s, 3 H), 2.37−2.30 (m, 1
H), 2.27−2.17 (m, 1 H), 1.90 (d, J = 17.2 Hz, 1 H), 1.67−1.59 (m, 1
H).
13C NMR (125 MHz, CDCl3): δ = 197.5, 143.5, 136.4, 135.4, 133.5,
132.2, 129.8, 128.8, 127.9, 127.5, 122.0, 59.5, 48.9, 48.9, 42.5,
26.0, 21.5, 19.6.
(3) (a) Oppolzer, W.; Gaudin, J.-M.; Bedoya-Zurita, M.; Hueso-
Rodriguez, J.; Raynham, T. M.; Robyr, C. Tetrahedron Lett.
1988, 29, 4709. (b) Meng, T.-J.; Hua, Y.-M.; Sun, Y.-J.;
Zhu, T.; Wang, S. Tetrahedron 2010, 66, 8648.
(4) Oppolzer, W.; Bedoya-Zurita, M.; Switzer, C. Y.
Tetrahedron Lett. 1988, 29, 6433.
ESI-MS: m/z = 404.1 [M + Na]+.
© Georg Thieme Verlag Stuttgart · New York
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© Georg Thieme Verlag Stuttgart · New York