Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts and Iminium-Substituted Δ2,3-Butenolides: Synthesis and Reactivity toward Nucleophiles

Article abstract of DOI:10.1055/s-2003-42440

Triflic anhydride reacts regioselectively with the ethoxy-carbonyl- substituted enaminones 6a-h to give the novel 3-trifloxypropene iminium salts 7a-d or iminium-substituted Δ^2,3-butenolides 8a-d and 9a-d in good yields. Hydride reduction of the iminium salts 7a,b affords new 2-dialkylamino-4-trifloxy-but-3-enoates 13a,b, while mild hydrolysis generates 2-oxo-4-trifloxy-butenoates 14a,b. Butenolides 8b,d, and 9c react with methyl hydrazine to afford 4-dialkylamino-pyridazin-3(2H)-ones 12a-c.

Full text of DOI:10.1055/s-2003-42440

PAPER
2679
Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts and Iminium-
Substituted 2,3-Butenolides: Synthesis and Reactivity toward Nucleophiles
A
lkoxycar
o
bonyl-Substi
a
tuted 3-Tri
c
floxypropen
h
e
Iminium
S
i
alts m Nikolai, Gerhard Maas*
Abteilung Organische Chemie I, Universität Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany
Fax +49(731)5022803; E-mail: gerhard.maas@chemie.uni-ulm.de
Received 22 July 2003; revised 8 September 2003
R1
O
R1
N
OTf
Ar
Abstract: Triflic anhydride reacts regioselectively with the ethoxy-
Tf2O
R2
carbonyl-substituted enaminones 6a–h to give the novel 3-trifloxy-
N
R3
Ar
2,3
R2
propene iminium salts 7a–d or iminium-substituted
-
TfO-
R3
butenolides 8a–d and 9a–d in good yields. Hydride reduction of the
iminium salts 7a,b affords new 2-dialkylamino-4-trifloxy-but-3-
enoates 13a,b, while mild hydrolysis generates 2-oxo-4-trifloxy-
butenoates 14a,b. Butenolides 8b,d, and 9c react with methyl hy-
drazine to afford 4-dialkylamino-pyridazin-3(2H)-ones 12a–c.
1
2
∆T or
base
RO
O
Key words: iminium salts, sulfonylations, enamines, reductions
O
R1
Ar
R2N
Ar
R2
N
TfO-
R3
Triflic anhydride (Tf2O) reacts readily with enaminones 1
to yield 3-trifloxypropene iminium triflates 2 which are
useful substrates in nucleophilic vinylic substitution
reactions1,2 as well as intra- and intermolecular SE(Ar) re-
actions.3,4 They are also readily transformed into a wide
range of propyne iminium triflates 3 by -elimination of
triflic acid (HOTf) (Scheme 1).4–6 The NR2R3 moiety in 2
and 3 can be a dialkylamino, morpholino, pyrrolidino or
piperidino group (with R1 = Me, Ph). Also, the iminium
function can be incorporated in a ring system, e.g.
R1–R2 = (CH2)n (n = 3–5) and R3 = Me, homoallyl or
benzyl.1,6,7
4
3
Scheme 1 Tf = CF3SO2
Conjugate addition of secondary amines to alkynylke-
tones 5a,9b,c yielded regio- and stereoselectively ethyl 2-
amino-4-oxo-butenoates 6a–h.10 The H NMR spectra
1
(400 MHz) of compounds 6a,c,g showed remarkably
broadened signals for the pyrrolidine ring, indicating a
partial double bond character for the N–C2 and C3–C4
bond due to -delocalization in the enaminoketone. A
NOESY experiment for 6f suggested the E(2,3),Z(3,4)
stereochemistry (Scheme 2).
In order to extend the applications of conjugated iminium
salts 2 and 3, we wanted to introduce additional function-
alization into propene iminium salts 2. To this end, we
turned our attention to alkoxycarbonyl-substituted enami-
noketones 4. We wondered whether the geminal capto-da-
tive substitution of the enone moiety in 4 would have an
effect on the reactivity and regioselectivity of sulfonyla-
tion with triflic anhydride and whether the presence of an
ester group in the ambident propene iminium moiety of
salts 2 (R1 = COOR) would affect the regioselectivity of a
nucleophilic attack.
When Tf2O was added to cooled solutions of the 2-amino-
4-oxobutenoic acid esters 6a–d in CH2Cl2, the yellow
solutions turned reddish and the moisture-sensitive salts
7a–d were formed in good yield. They could be precipi-
tated completely from the reaction solution by the addi-
tion of Et2O or pentane (Scheme 3). The constitution of
the novel alkoxycarbonyl-substituted 3-trifloxypropene
iminium salts 7 was deduced from their spectroscopic da-
ta. The IR spectra showed medium strong absorptions in
the 1425–1435 cm–1 region, which represent the as(SO2)
stretching vibration of the covalently bound triflate group,
in addition to other diagnostic absorptions of the CF3SO3
moiety in the ranges 1260–1220, 1180–1130, and 1030–
1010 cm–1.1,11,12 In the 19F NMR spectra, the resonance of
the covalent triflate at = –70.2 to –72.7 ppm along with
the signal for the triflate anion (–77.5 to –79.7 ppm rela-
tive to CCl3F) was detected.1,11 A +FAB–MS for 7a
showed a signal at m/z 406 which is attributed to the cation
of salt 7a. The regiochemistry of the electrophilic attack
of Tf2O was indicated by the absence of the 13C resonance
of the carbonyl carbon atom recorded at = 184.5–187.4
ppm for the enaminones 6a–d. The configuration of the
Here, we describe the O-sulfonylation of 2-amino-4-oxo-
butenoates 4 with Tf2O and some reactions of the result-
ing products with nucleophiles.
The required enaminoketones 6 were prepared by analogy
to a published procedure8 that was slightly modified (see
Experimental Part): addition of the alkynyl lithium re-
agent derived from ethyl propiolate to an aromatic alde-
hyde followed by oxidation of the thus formed alcohol
with MnO2 (Scheme 2) yielded the acetylenic ketones 5.
SYNTHESIS 2003, No. 17, pp 2679–2688
x
x.
x
x
.
2
0
0
3
Advanced online publication: 21.10.2003
DOI: 10.1055/s-2003-42440; Art ID: T07403SS
© Georg Thieme Verlag Stuttgart · New York

2680
J. Nikolai, G. Maas
PAPER
Scheme 3
Figure 1
Upon heating to 120 °C for 1 h in CH3CN in a closed
Schlenk tube, salts 7a–d cyclized with elimination of eth-
yl triflate to give the new, intensively orange to red col-
ored 2,3-butenolides 8a–d (Scheme 3) in high yields.
Attempts to induce HOTf elimination from 7a in order to
synthesize alkoxycarbonyl-substituted propyne iminium
salts, using (dimethylaminomethyl)polystyrene as a base,5
were unsuccessful: only an oily residue was isolated, its
1H NMR spectra indicating unselective decomposition of
the substrate under the reaction conditions (r.t., CH2Cl2, 1
h). An IR spectrum of the product mixture did not reveal
the presence of a C≡C bond.
When enaminoketones 6e–h, bearing an electron-rich 3,4-
methylenedioxyphenyl substituent, were reacted with tri-
flic anhydride, the 2,3-butenolides 9a–d were obtained
directly, i.e., the expected 3-trifloxypropene iminium salts
corresponding to 7 eliminate EtOTf readily under the con-
ditions of their synthesis at 20 °C (Scheme 4). The IR
spectra of salts 8a–d and 9a–d show strong absorptions at
1825–1844 cm–1 indicating the presence of a lactone car-
bonyl function. Along with this, the iminium salt nature is
proven by a 13C signal for the iminium carbon at = 174–
175 ppm, the strong and broad IR absorption at 1220–
1260 cm–1 typical for the triflate ion, and the low field
shift of the 1H and 13C NMR resonances for the alkyl sub-
stituents at the iminium nitrogen atom. For 9d, a doubled
set of 1H NMR signals for the alkyl protons of the tetrahy-
droisoquinoline substituent indicates two isomers due to
cis/trans isomerism at the C=N+ bond. According to the
Scheme 2
propene iminium unit in salt 7a was determined as E(1,2),
Z(2,3) by a NOESY experiment (Figure 1). This configu-
ration was also reported for related iminium salts.6,7 Due
to the similar substitution pattern, the same geometry
should apply for all other salts of type 7.
Synthesis 2003, No. 17, 2679–2688 © Thieme Stuttgart · New York

PAPER
Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts
2681
1
intensities of the H signals, both isomers are present in tack of the hydrazine. It should be noted, that derivatives
equal amounts.
of pyridazin-3(2H)-ones are known as pharmaceutically
active substances.15
Tf2O,
CH2Cl2
TfO-
N
–78 °C
r.t.
O
6e−h
O
O
O
9a−d
9
a
b
c
d
O
NEt2
63
N
N
N
N
Yield [%]
84
81
56
Scheme 4
2,3-Butenolides 8 and 9 are rather labile to hydrolysis and
dissolve in reasonable amount without change (vide infra)
only in thoroughly anhyd CH3CN. They may be regarded
as iminium derivatives of 2,3-furandiones. The latter are
readily prepared by cyclodehydration of 2,4-dioxoalkano-
ic acids with thionyl chloride or trifluoroacetic acid anhy-
dride.13 We were not successful in converting salts 8 and
9 into furandiones by selective hydrolysis of the iminium
function. Rather, hydrolysis of 9d in wet CH3CN afforded
in 78% yield the corresponding 2-hydroxy-4-oxo-but-2-
enoic acid 10 (Scheme 5) which was identified by com-
parison of its spectral data with literature data of related 4-
aryl derivatives.14 Attempts to perform a hydride reduc-
tion was hampered by the aforementioned low solubility
of the iminium salts. Only decomposition of the starting
material was observed when the reduction of 8b was tried
with NaBH4 or NaBH3CN in CH3CN and LiAlH4 in
CH2Cl2–THF. Using MeOH as solvent, the only product
that could be isolated after chromatography in 30% yield
was the methyl 2-amino-4-oxobutenoate 11 which stems
from the alcoholysis of the lactone ring (Scheme 5). Ob-
viously, this reaction simply leads back to enaminoesters
of type 4, the starting materials for the synthesis of the
2,3-butenolides (vide supra). Based on the 1H NMR spec-
tra, the same configuration (E) was ascribed to 11 and to
6b.
Scheme 5
In contrast to the iminium butenolides 8 and 9, the imini-
um function of propene iminium salts 7a,b could be re-
duced selectively using LiAlH4 in a mixture of CH2Cl2–
THF, and -aminoesters 13a,b were obtained (Scheme 6).
The Z configuration was suggested by a NOESY experi-
ment. The considerably lower yield of 13a compared to
13b may be a result of the lower reactivity of the pyrroli-
dinium salt towards hydride addition due to the better sta-
bilization of the quaternary nitrogen atom in the
pyrrolidine ring than in the morpholine ring. Amines
13a,b are stable in substance at 0 °C. In CHCl3 solution at
ambient temperature, unspecific decomposition accompa-
nied by formation of ionic triflate (19F: = –76 ppm) oc-
curred within 24–36 h. The lability of the covalently
bound triflate group was also seen from the +FAB–MS
spectra for 13a,b which show a signal for [M+ – TfO] be-
ing the strongest fragmentation peak.
Interestingly, our new iminium-substituted 2,3-buteno-
lides reacted with methyl hydrazine to yield the 4-dialkyl-
amino-pyridazin-3(2H)-ones 12 (Scheme 5). The identity
of the latter was derived from their NMR and mass spec-
troscopic data. Their constitution was determined with the
help of a gs-HMBC NMR experiment which showed a
3J(C,H) correlation peak between the N-methyl group at
= 3.87 ppm and the carbonyl signal of the pyridazinone
ring at
= 157.1 ppm. One may speculate that the low
C
yields for 12a and 12c are related to the more electron-rich
aryl groups in their precursor salts, and that the 4-fluo-
rophenyl group in 8d activates the conjugate position of
the , -unsaturated iminium moiety for nucleophilic at-
Synthesis 2003, No. 17, 2679–2688 © Thieme Stuttgart · New York

2682
J. Nikolai, G. Maas
PAPER
Hydrolysis of salts 7b and 7d in CH2Cl2–H2O yielded the butenolides under the conditions tested, the reduction and
2-oxo-4-trifloxy-butenoic acid esters 14a,b (Scheme 6). hydrolysis of the 3-trifloxypropene iminium salts gives
This reaction parallels an earlier synthesis giving
-
access to -amino esters or -keto esters connected with a
formylvinyl triflates from the hydrolysis of 3-trifloxypro- vinyl triflate moiety being a potential substrate in transi-
pene iminium salts.2a Compounds 14a,b (Z configuration tion-metal mediated cross-coupling reactions. Last but not
2,3
according to a NOESY experiment) represent an uncom- least, the reaction of methyl hydrazine with the novel
-
mon combination of functional groups; up to now, only a butenolides afforded a simple access to 4-dialkylamino-
dichlorovinyl analogue of compound 14a (i.e. Cl instead pyridazin-3(2H)-ones.
of OTf and Ph) has been prepared.16 The compounds
could be stored in substance at –20 °C for several weeks
All reactions, except hydrolyses, involving moisture sensitive com-
but decomposed in CHCl3 at room temperature within a
day. Again, as for 13a,b the loss of the covalent triflate
seems to initiate the degradation process: heating of 14a
in wet THF at 80 °C resulted in hydrolysis of the vinyl tri-
flate function and afforded ethyl 2-oxo-4-hydroxy-4-
phenylbutenoate after column chromatography, the iden-
tity of which was established by NMR and MS spectros-
copy and by comparison with published data.17
pounds were carried out in rigorously dried glassware under Ar.
Et2O was distilled from Na and stored under Ar. CH2Cl2 and
CH3CN were dried over P4O10, distilled and stored under Ar. THF
(p.a.) was purchased from Merck (Darmstadt, Germany) and was
used without further purification. NMR spectra were recorded at
303 K on a Bruker DRX 400 spectrometer operating at 400.13 MHz
for 1H, 100.61 MHz for 13C, and 376.31 MHz for 19F. TMS (0 ppm)
1
served as internal standard for H spectra, and a solvent signal
[ (CDCl3) = 77.0, (CD3CN) = 118.2, (acetone-d6) = 206.3] for
13C spectra. CCl3F ( = 0 ppm) served as external capillary stan-
F
dard for 19F spectra. Assignments of 13C chemical shifts are based
on comparison with literature data for 3-trifloxypropene iminium
salts1 and on DEPT 135, gs-HMBC and gs-HMQC experiments
when necessary. NOESY spectra for 6f, 7a, 13b, and 14a were re-
corded with 300 ms mixing time. IR spectra were measured on a
Bruker Vector 22 FT-IR spectrophotometer. Melting points were
determined on a Büchi B-540 apparatus (heating rate 2 °C/min) and
are uncorrected. Microanalyses were performed at Fachbereich
Chemie, Universität Kaiserslautern, with a Perkin–Elmer Analyzer
2400 CHN. FAB–MS spectra were recorded on a Finnigan TSQ
7000 instrument and GC–MS spectra on a Finnigan SSQ 7000 in-
strument at the Sektion Massenspektrometrie, Universität Ulm. 3-
Nitrobenzyl alcohol (m-NBA) was used as the matrix for the FAB-
MS spectra.
EtO
EtO
LiAlH4,
O
O
CH2Cl2/THF
N
OTf
N
OTf
-78 °C
r.t.
TfO-
H
H
7a,b
13a,b
7, 13
a
b
O
N
N
N
Yield [%]
48
92
NMR data of compounds 5, 6, 8 and 9 are given in Tables 1 and 2.
Ethyl 4-Oxo-4-phenyl-but-2-ynoate (5a)
EtO
H
To a stirred solution of ethyl propiolate (9.61 g, 10.0 mL, 98.0
mmol) in Et2O (100 mL) was added at –100 °C a BuLi solution
(43.0 mL, 108 mmol, 2.5 M in hexane) within 30 min. The resulting
crème colored suspension was stirred for 1 h at –100 °C and a solu-
tion of benzaldehyde (10.4 g, 9.90 mL, 98.0 mmol) in Et2O (50 mL)
was added slowly. The reaction mixture was slowly brought to –20
°C and poured onto a mixture of crushed ice and glacial AcOH (10
mL). The organic layer was separated, washed twice with concd
NH4Cl solution, and dried over Na2SO4. The solvent was evaporat-
ed and the resulting brown oil was taken up in CH2Cl2 (50 mL) and
added slowly to a slurry of MnO2 (60.0 g) in CH2Cl2 (100 mL) at 0
°C. Stirring was continued at 25 °C for 3 h. After filtration over a
plug of Celite, the solvent was removed to yield 15.5 g of crude
product. Distillation at 120 °C/10–3 mbar afforded 9.38 g (47%) of
5a as yellow oil.
EtO
H
O
O
CH2Cl2/H2O
O
N
OTf
O
OTf
TfO-
X
X
7b: X = H
7d: X = F
14a: X = H, 96%
14b: X = F, 80%
Scheme 6
In summary, we have presented the synthesis of novel
alkoxycarbonyl-substituted 3-trifloxypropene iminium
salts from 2-amino-4-oxo-butenoic acid esters with Tf2O.
It is notable that the presence of an ester function does not
affect the successful O-sulfonylation of the enaminoke-
tone moiety and that the resulting 3-trifloxypropene imin-
ium unit is compatible with the presence of an ester group
in the same molecule within certain limits. The participa-
tion of the ester group in a 1,5-cyclization leading to imi-
nium-substituted 2,3-butenolides requires strong heating
but is facilitated by an electron-donating aryl substituent
adjacent to the trifloxy group. Although we could not
achieve a reduction of the iminium function in these
IR (film): 1715 (s, C=O-ester), 1650 (s, C=O), 1231 (vs), 1004 (s)
cm–1.
Anal. Calcd for C12H10O3 (202.21): C, 71.28; H, 4.98. Found: C,
71.37; H, 5.15.
Ethyl 4-(4-Fluorophenyl)-4-oxo-but-2-ynoate (5b)
From ethyl propiolate (9.61 g, 10.0 mL, 98.0 mmol) and 4-fluo-
robenzaldehyde (12.2 g, 10.3 mL, 98.0 mmol). Yield: 12.1 g (55%)
of crude product. Column chromatography [silica gel, cylohexane–
EtOAc (5:1)] afforded an analytically pure sample of 5b as yellow
oil.
Synthesis 2003, No. 17, 2679–2688 © Thieme Stuttgart · New York

PAPER
Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts
2683
IR(film): 1716 (s, C=O-ester), 1635 (s, C=O), 1594 (s), 1233 (vs),
1153 (s), 1007 (s) cm–1.
Anal. Calcd for C17H21NO5 (319.35): C, 63.94; H, 6.63; N 4.39.
Found: C, 63.96; H, 6.62; N, 4.08.
19F NMR (CDCl3): = –99.8.
Ethyl (E)-4-(Benzo[1,3]dioxol-5-yl)-2-(morpholin-4-yl)-4-oxo-
but-2-enoate (6f)
From 5c (2.95 g, 12.0 mmol) and morpholine (1.04 g, 1.04 mL, 12.0
mmol). Yield: 3.03 g (76%), beige solid; mp 153 °C.
Anal. Calcd for C12H9FO3 (220.20): C, 65.45; H, 4.12. Found: C,
65.40; H, 4.17.
Ethyl 4-(Benzo[1,3]dioxol-5-yl)-4-oxo-but-2-ynoate (5c)
IR (KBr): 1737 (s, C=O-ester), 1639 (m), 1605 (s), 1537 (br, s),
1430 (br, s), 1347 (s), 1247 (s), 1209 (s) cm–1.
From ethyl propiolate (9.61 g, 10.0 mL, 98.0 mmol) and piperonal
(14.7 g, 98.0 mmol). Yield after oxidation with MnO2 at 0 °C: 15.4
g (64%) of crude product. Crystallization from Et2O at 0 °C afford-
ed an analytically pure sample of 5c as a yellow powder; mp 52 °C.
Anal. Calcd for C17H19NO6 (333.34): C, 61.25; H, 5.75; N 4.20.
Found: C, 61.23; H, 5.74; N, 4.18.
IR (KBr): 2229 (w, C≡C), 1715 (vs, C=O-ester), 1635 (s, C=O),
1595 (s), 1504 (s), 1492 (m), 1446 (s), 1277 (vs), 1116 (s), 1003 (m)
cm–1.
Ethyl (E)-4-(Benzo[1,3]dioxol-5-yl)-2-(pyrrolidin-4-yl)-4-oxo-
but-2-enoate (6g)
From 5c (2.95 g, 12.0 mmol) and pyrrolidine (0.85 g, 0.98 mL, 12.0
mmol). Yield: 3.19 g (84%), beige solid; mp 148 °C.
Anal. Calcd for C13H10O5 (246.22): C, 63.42; H, 4.09. Found: C,
63.42; H 4.09.
IR (KBr): 1726 (s, C=O-ester), 1620 (m), 1597 (s), 1523 (vs), 1489
(s), 1438 (s), 1340 (s), 1242 (vs), 1229 (vs), 1023 (s) cm–1.
Ethyl (E)-4-Oxo-4-phenyl-2-(pyrrolidin-1-yl)-but-2-enoate (6a)
To a solution of 5a (3.24 g, 16.0 mmol) in THF (25 mL) at –78 °C
was added pyrrolidine (1.14 g, 1.33 mL, 16.0 mmol). The solution
was slowly brought to r.t. and the solvent was removed. The oily
residue was taken up in Et2O and 6a was precipitated with pentane
under vigorous stirring as a yellow solid (3.18 g, 73%); mp 137 °C.
Anal. Calcd for C17H19NO5 (317.34): C, 64.34; H, 6.03; N 4.41.
Found: C, 64.31; H, 6.06; N, 4.26.
Ethyl (E)-4-(Benzo[1,3]dioxol-5-yl)-2-(3,4-dihydro-1H-isoquin-
olin-2-yl)-4-oxo-but-2-enoate (6h)
From 5c (2.70 g, 11.0 mmol) and 1,2,3,4-tetrahydroisoquinoline
(1.46 g, 1.40 mL, 11.0 mmol). Yield: 3.79 g (91%), beige to yellow
solid; mp 65 °C.
IR (KBr): 1734 (vs, C=O-ester), 1623 (s), 1526 (vs), 1456 (s), 1344
(s), 1204 (vs), 950 (s) cm–1.
Anal. Calcd for C16H19NO3 (273.33): C, 70.31; H, 7.01; N 5.12.
Found: C, 70.28; H, 6.99; N, 5.06.
IR (KBr): 1729 (m, C=O-ester), 1600 (m), 1521 (s), 1433 (s), 1236
(s), 1184 (s), 1035 (m) cm–1.
Ethyl (E)-2-(Morpholin-4-yl)-4-oxo-4-phenyl-but-2-enoate (6b)
From 5a (3.45 g, 17.1 mmol) and morpholine (1.49 g, 1.49 mL, 17.1
mmol). Yield: 3.31 g (67%), beige-colored solid; mp 75 °C.
Anal. Calcd for C22H21NO5 (379.42): C, 69.65; H, 5.58; N 3.69.
Found: C, 69.51; H, 5.88; N, 3.71.
(Z)-1-[1-Ethoxycarbonyl-3-phenyl-3-(trifluoromethylsulfo-
nyl)oxy-allylidene]pyrrolidinium Trifluoromethanesulfonate
(7a)
To a solution of 6a (0.80 g, 2.93 mmol) in CH2Cl2 (15 mL) at –78
°C was added triflic anhydride (0.83 g, 0.50 mL, 2.93 mmol) in one
portion. The solution was slowly brought to r.t. Under vigorous stir-
ring, a canary yellow solid was precipitated with Et2O. The solid
was washed with Et2O (2 × 10 mL) to afford 7a (1.15 g, 71%); mp
105 °C.
IR (KBr): 1729 (s, C=O-ester), 1635 (s), 1541 (br, vs), 1211 (s), 930
(s) cm–1.
Anal. Calcd for C16H19NO4 (289.33): C, 66.42; H, 6.62; N, 4.84.
Found: C, 66.39; H, 6.66; N, 4.80.
Ethyl (E)-4-(4-Fluorophenyl)-4-oxo-2-(pyrrolidin-1-yl)-but-2-
enoate (6c)
From 5b (4.45 g, 20.2 mmol) and pyrrolidine (1.44 g, 1.67 mL, 20.2
mmol). Yield: 3.70 g (64%), yellow solid; mp 103 °C.
IR (KBr): 1754 (s, C=O-ester), 1577 (s), 1428 (s), 1258 (vs), 1228
(vs), 1030 (s) cm–1.
IR (KBr): 1736 (s, C=O-ester), 1624 (m), 1589 (s), 1530 (vs), 1503
(vs), 1346 (s), 1204 (vs), 953 (m) cm–1.
19F NMR (CDCl3): = –108.4.
1H NMR (CD3CN): = 1.44 (t, 3J = 6.8 Hz, 3 H, CH3), 2.23 (mc, 4
3
H, NCH2CH2), 4.27 (mc, 4 H, NCH2), 4.59 (q, J = 6.8 Hz, 2 H,
CH3), 6.96 (s, 1 H, Hvinyl), 7.63 (t, 2 H, Hm-Ph), 7.66 (t, 1 H, Hp-Ph),
7.86 (d, 2 H, Ho-Ph).
Anal. Calcd for C16H18FNO3 (291.32): C, 65.97; H, 6.23; N 4.81.
Found: C, 66.03; H, 6.27; N, 4.80.
13C NMR (CD3CN): = 13.0 (CH3), 24.0 and 24.6 (NCH2CH2),
58.1 and 58.6 (NCH2), 66.0 (OCH2), 110.7 (CHvinyl), 118.3 (q,
1JCF = 323.0 Hz, CF3SO3cov) 128.1 (Co-Ph), 129.6 (Cm-Ph), 130.2
(Cipso), 134.2 (Cp-Ph), 158.3 (C=COTf), 159.6 (COOEt), 160.5
(C=N+); signal for CF3SO3– was not detected.
Ethyl (E)-4-(4-Fluorophenyl)-2-(morpholin-4-yl)-4-oxo-but-2-
enoate (6d)
From 5b (5.70 g, 25.9 mmol) and morpholine (2.26 g, 2.26 mL, 25.9
mmol). Yield: 4.80 g (60%), yellow solid; mp 86 °C.
19F NMR (CD3CN): = –79.6 (TfO–), –72.7 (TfOcov).
MS (+FAB, m-NBA): m/z = 406 (99) [M+ – OTf], 256 (52), 228
IR (KBr): 1733 (s, C=O-ester), 1633 (s), 1597 (s), 1531 (vs), 1505
(s), 1442 (s), 1209 (vs), 1155 (s), 1117 (s), 931 (s) cm–1.
19F NMR (CDCl3): = -104.4.
(100).
Anal. Calcd for C16H18FNO4 (307.32): C, 62.53; H, 5.90; N 4.56.
Found: C, 62.54; H, 5.92; N, 4.52.
Anal. Calcd for C18H19F6NO8S2 (555.47): C, 38.92; H, 3.45; N 2.52.
Found: C, 38.93; H, 3.46; N, 2.52.
Ethyl (E)-4-(Benzo[1,3]dioxol-5-yl)-2-diethylamino-4-oxo-but-
2-enoate (6e)
From 5c (2.95 g, 11.9 mmol) and diethylamine (0.87 g, 1.23 mL,
11.9 mmol). Yield: 3.35 g (88%), beige solid; mp 115 °C.
(Z)-4-[1-Ethoxycarbonyl-3-phenyl-3-(trifluoromethylsulfo-
nyl)oxy-allylidene]morpholin-4-ium Trifluoromethane-
sulfonate (7b)
From 6b (1.65 g, 5.66 mmol) and triflic anhydride (1.59 g, 0.95 mL,
5.66 mmol). Yield: 2.41 g (74%), yellow solid; mp 120 °C.
IR (KBr): 1734 (s, C=O-ester), 1605 (s), 1530 (vs), 1251 (s), 1215
(s) cm–1.
Synthesis 2003, No. 17, 2679–2688 © Thieme Stuttgart · New York

2684
J. Nikolai, G. Maas
PAPER
Table 1 1H and 13C NMR Data for Compounds 5 and 6
Compound
1H (CDCl3)
13C (CDCl3)
(ppm), J (Hz)
(ppm), J (Hz)
5a
5b
1.37 (t, 3J = 7.2, 3 H, CH3), 4.35 (q, 3J = 7.2, 2 H, CH2), 7.52 13.8 (CH3), 62.9 (OCH2), 79.6 and 80.3 (C≡C), 128.8, 129.6,
(t, 2 H, Hm-Ph), 7.67 (t, 1 H, Hp-Ph), 8.11 (t, 2 H, Ho-Ph 135.0, 135.5, 152.1 (COOEt), 176.0 (C=O)
)
1.38 (t, 3J = 7.2, 3 H, CH3), 4.36 (q, 3J = 7.3, 2 H, CH2), 7.21 13.8 (CH3), 62.9 (OCH2), 79.2 and 80.6 (C≡C), 116.1 (2JCF
(mc, 2 H, HPh), 8.16 (mc, 2 H, HPh)
22.4, Cm-Ph), 132.0 (4JCF = 2.7, Ci-Ph), 132.4 (3JCF = 9.9, Co-Ph),
152.0 (COOEt), 166.9 (1JCF = 258.5, Cp-Ph), 174.4 (C=O)
=
5c
6a
1.37 (t, 3J = 7.2, 3 H, CH3), 4.34 (q, 3J = 7.2, 2 H, CH2), 6.08 13.7 (CH3), 62.7 (OCH2), 79.6 and 79.7 (C≡C), 102.3
(s, 2 H, OCH2O), 6.92 (d, 3J = 8.2, 1 H, Hm-Ph), 7.51 (d, 4J = (OCH2O), 107.7, 108.1, 127.9, 130.7, 148.4, 152.1, 160.9
1.6, 1 H, Ho -Ph), 7.78 (dd, 3J = 8.2, 4J = 1.6, 1 H, Ho-Ph
)
(COOEt), 173.8 (C=O)
1.42 (t, 3J = 7.1, 3 H, CH3), 2.00 (br signal, 4 H, NCH2CH2), 13.9 (CH3), 24.6 (br, NCH2CH2), 25.1 (br, NCH2CH2), 48.3
3.35 (br, 2 H, NCH2), 3.49 (br, 2 H, NCH2), 4.50 (q, 3J = 7.1, (NCH2), 62.1 (OCH2), 91.5 (C-3), 127.4, 128.0, 131.0, 139.7,
2 H, CH2), 5.66 (s, 1 H, 3-H), 7.38–7.46 (m, 3 H, Hm,p-Ph), 7.90 153.0 (NC=C), 166.1 (COOEt), 186.6 (C=O)
(d, 2 H, Ho-Ph
)
6b
6c
6d
6e
1.39 (t, 3J = 7.2, 3 H, CH3), 3.32–3.34 (m, 4 H, NCH2), 3.77– 13.8 (CH3), 47.3 (NCH2), 62.3 (NCH2CH2O), 65.8 (OCH2),
3.79 (m, 4 H, NCH2CH2O), 4.47 (q, 3J = 7.2, 2 H, OCH2),
92.7 (CHvinyl), 127.5, 128.1, 131.5, 139.3, 155.1 (NC=C),
5.91 (s, 1 H, Hvinyl), 7.40–7.47 (m, 3 H, Hm,p-Ph), 7.88 (d, 2 H, 165.7 (COOEt), 187.4 (C=O)
Ho-Ph
)
1.43 (t, 3J = 7.2, 3 H, CH3), 2.00 (br, 4 H, NCH2CH2), 3.37
(br, 2 H, NCH2), 3.50 (br, 2 H, NCH2), 4.51 (q, 3J = 7.2, 2 H, vinyl), 115.0 (d, 2JCF = 21.6, Cm-Ph), 129.8 (d, 3JCF = 9.1, Co-Ph),
CH2), 5.61 (s, 1 H, Hvinyl), 7.08 (mc, 3 H, HPh), 7.92 (mc, 2 H, 135.9 (d, 4JCF = 3.0, Cipso), 153.2 (NC=C), 164.0 (1JCF
HPh) 250.9, Cp-Ph), 166.0 (COOEt), 185.1 (C=O)
13.9 (CH3), 25.2 (br, NCH2CH2), 62.1 (br, NCH2), 91.0 (CH-
=
1.41 (t, 3J = 7.2, 3 H, CH3), 3.33–3.36 (m, 4 H, NCH2), 3.79– 13.8 (CH3), 47.3 (NCH2), 60.2 (NCH2CH2O), 65.8 (OCH2),
3.81 (mc, 4 H, NCH2CH2O), 4.48 (q, 3J = 7.2, 2 H, OCH2),
92.2 (CHvinyl), 115.1 (d, 2JCF = 21.6, Cm-Ph), 129.9 (d, 3JCF
=
5.86 (s, 1 H, Hvinyl), 7.08 (mc, 2 H, HPh), 7.90 (mc, 2 H, HPh) 7.6, Co-Ph), 135.6 (d, 4JCF = 3.0, Cipso), 155.2 (NC=C), 164.0
(d, 1JCF = 252.4, Cp-Ph), 165.5 (COOEt), 185.8 (C=O)
1.26 (t, 3J = 7.1, 6 H, 2 × CH3), 1.40 (t, 3J = 7.2, 3 H, CH3),
12.6 (CH3), 13.7 (CH3), 44.9 (NCH2), 61.9 (OCH2), 90.3
3.31 (q, 3J = 7.1, 4 H, NCH2), 4.48 (q, 3J = 7.2, 2 H, OCH2), (CHvinyl), 101.2 (OCH2O), 107.4, 107.8, 122.6, 134.8, 147.6,
5.65 (s, 1 H, Hvinyl), 5.99 (s, 2 H, OCH2O), 6.79 (d, 3J = 8.1, 148.0, 154.4 (NC=C), 165.8 (COOEt), 185.1 (C=O)
1 H, Hm-Ph), 7.38 (d, 4J = 1.7, 1 H, Ho -Ph), 7.45 (dd, 3J = 8.2,
4J = 1.7, 1 H, Ho-Ph
)
6f
1.38 (t, 3J = 7.2, 3 H, CH3), 3.29–3.31 (mc, 4 H, NCH2), 3.76– 13.8 (CH3), 47.3 (NCH2), 62.2 (OCH2), 65.9 (NCH2CH2O),
3.79 (m, 4 H, NCH2CH2O), 4.45 (q, 3J = 7.2, 2 H, CH2), 5.82 92.6 (CHvinyl), 101.5 (OCH2O), 107.5, 107.8, 123.0, 134.0,
(s, 1 H, Hvinyl), 5.99 (s, 2 H, OCH2O), 6.79 (d, 3J = 8.1, 1 H, 147.8, 150.5, 154.9 (NC=C), 165.8 (COOEt), 185.7 (C=O)
Hm-Ph), 7.38 (d, 4J = 1.6, 1 H, Ho -Ph), 7.46 (dd, 3J = 8.1, 4J =
1.6, 1 H, Ho-Ph
)
6g
6h
1.40 (t, 3J = 7.2, 3 H, CH3), 2.00 (br signal, 4 H, NCH2CH2), 13.9 (CH3), 25.0 (NCH2CH2), 25.5 (NCH2CH2), 48.3
3.2–3.6 (br signals, 4 H, NCH2), 4.48 (q, 3J = 7.2, 2 H, CH2), (NCH2CH2), 91.5 (CHvinyl), 101.3 (OCH2O), 107.5, 108.0,
5.67 (s, 1 H, Hvinyl), 5.99 (s, 2 H, OCH2O), 6.79 (d, 3J = 8.1, 122.8, 134.6, 147.7, 150.1, 152.9 (NC=C), 166.0 (COOEt),
1 H, Hm-Ph), 7.41 (d, 4J = 1.6, 1 H, Ho -Ph), 7.47 (dd, 3J = 8.2, 185.1 (C=O)
4J = 1.6, 1 H, Ho-Ph
1.42 (t, 3J = 7.2, 3 H, CH3), 2.96 (t, 3J = 5.8, 2 H, 4-Hisoqu),
)
13.9 (CH3), 28.9 (C-4isoqu), 45.6 (C-3isoqu), 48.8 (C-1isoqu),
3.56 (t, 3J = 5.8, 2 H, 3-Hisoqu), 4.47 (s, 2 H, 1-Hisoqu), 4.52 (q, 62.2 (OCH2), 91.5 (CHvinyl), 101.4 (OCH2O), 107.5, 107.9,
3J = 7.2, 2 H, OCH2), 5.81 (s, l H, Hvinyl), 5.99 (s, 2 H,
OCH2O), 6.80 (d, 3J = 8.2, 1 H, Hm-Ph), 7.10–7.26 (m, 4 H,
Hisoqu), 7.42 (d, 4J = 1.6, 1 H, Ho -Ph), 7.50 (dd, 3J = 8.2, 4J =
122.9, 126.1, 126.7, 127.1, 128.2, 131.6, 134.1, 134.3, 147.7,
150.3, 154.5 (NC=C), 165.9 (COOEt), 185.5 (C=O)
1.6, 1 H, Ho-Ph
)
IR (KBr): 1756 (vs, br, C=O-ester), 1640 (s), 1429 (s), 1251 (s),
1228 (s), 1031 (s) cm–1.
1H NMR (CD3CN): = 1.43 (t, 3J = 7.1 Hz, 3 H, CH3), 4.04-4.10
(m, 4 H, NCH2), 4.25-4.26 (m, 2 H, NCH2CH2O), 4.33–4.36 (m, 2
H, NCH2CH2O), 4.59 (q, 3J = 7.1 Hz, 2 H, CH2), 7.24 (s, 1 H, Hvinyl),
7.63 (t, 2 H, Hm-Ph), 7.75 (t, 1 H, Hp-Ph), 7.87 (d, 2 H, Ho-Ph).
13C NMR (CD3CN): = 13.9 (CH3), 57.7 and 58.5 (NCH2), 64.3
(OCH2), 67.5 and 68.0 (CH2O), 110.3 (CHvinyl), 128.7 (Co-Ph), 130.5
(Cm-Ph), 130.9 (Cipso), 135.2 (Cp-Ph), 157.4 (C=COTf), 158.8 (COO-
Et), 161.5 (C=N+); signals for CF3SO3cov and CF3SO3– were not de-
tected.
19F NMR (CD3CN): = –77.5 (TfO–), –70.3 (TfOcov).
Synthesis 2003, No. 17, 2679–2688 © Thieme Stuttgart · New York

PAPER
Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts
2685
Anal. Calcd for C18H19F6NO9S2 (571.47): C, 37.83; H, 3.35; N 2.45.
Found: C, 37.59; H, 3.35; N, 2.45.
4-(2-Oxo-5-phenyl-furan-3-ylidene)morpholin-4-ium Trifluo-
romethanesulfonate (8b)
From 7b (2.74 g, 4.80 mmol) dissolved in CH3CN (25 mL). Yield:
1.80 g (95%), red-brown solid; mp 140 °C (dec.).
(Z)-1-[1-Ethoxycarbonyl-3-(4-fluorophenyl)-3-(trifluorometh-
ylsulfonyl)oxy-allylidene]pyrrolidinium Trifluoromethane-
sulfonate (7c)
To a solution of 6c (1.43 g, 4.90 mmol) in CH2Cl2 (15 mL) at –78
°C was added triflic anhydride (2.76 g, 1.65 mL, 9.80 mmol) in one
portion. Stirring was continued at this temperature for 1 h. The so-
lution was brought to r.t. and stirred for 1 h at 25 °C. Under vigorous
stirring, pentane was added. The resulting oil was washed with
Et2O–pentane (1:1) (2 × 25 mL) to afford 7c as a brownish oil.
Yield: 2.23 g (79%).
IR (KBr): 1828 (m, C=O), 1736 (m), 1593 (s), 1562 (s), 1453 (s),
1249 (vs, br, TfO–), 1043 (s), 1030 (s), 1009 (s) cm–1.
Anal. Calcd for C15H14F3NO6S (393.34): C, 45.80; H, 3.59; N 3.56.
Found: C, 45.20; H, 3.59; N, 3.73.
1-[5-(4-Fluorophenyl)-2-oxo-furan-3-ylidene]-pyrrolidinium
Trifluoromethanesulfonate (8c)
Salt 7c (1.60 g, 2.80 mmol) dissolved in CH3CN (10 mL) was heat-
ed at 120 °C for 1 h in a thick-walled Schlenk tube. Pentane was
added under vigorous stirring and the resulting oil was washed with
Et2O–pentane (1:1) (2 × 10 mL). Upon treating with CH2Cl2, the oil
solidified to afford 8a as a yellow solid, which was washed with
CH2Cl2 (10 mL). Yield: 1.02 g (93%); mp 168 °C (dec.).
IR (film): 1749 (m, C=O-ester), 1630 (m), 1598 (m), 1508 (m),
1432 (m), 1218 (s), 1160 (s), 1132 (s), 1028 (s) cm–1.
3
1H NMR (CD3CN): =1.44 (t, J = 7.1 Hz, 3 H, CH3), 2.18–2.30
3
(m, 4 H, NCH2CH2), 4.20–4.35 (m, 4 H, NCH2), 4.58 (q, J = 7.1
Hz, 2 H, CH2), 6.93 (s, 1 H, Hvinyl), 7.38 (m, 2 H, HPh), 7.90 (m, 2
H, HPh).
IR (KBr): 1844 (m, C=O), 1677 (m), 1591 (vs), 1571 (vs), 1505 (s),
1284 (s), 1242 (vs, TfO–), 1170 (s), 1008 (m) cm–1.
13C NMR (CD3CN): = 13.8 (CH3), 24.8 and 25.4 (NCH2CH2),
58.9 and 59.4 (NCH2), 66.8 (OCH2), 111.5 (CHvinyl), 117.8 (d,
Anal. Calcd for C15H13F4NO5S (395.33): C, 45.57; H, 3.31; N 3.54.
Found: C, 45.39; H, 3.30; N, 3.53.
4
2JCF = 22.8 Hz, Cm-Ph), 131.8 (d, JCF = 9.5 Hz, Cipso), 134.2 (d,
3JCF = 9.9 Hz, Co-Ph), 159.0 (C=COTf), 159.2 (COOEt), 161.4
(C=N+), 166.8 (d, 1JCF = 255.1 Hz, Cp-Ph); signals for CF3SO3cov and
CF3SO3– were not detected.
4-[5-(4-Fluorophenyl)-2-oxo-furan-3-ylidene]-morpholin-4-
ium Trifluoromethanesulfonate (8d)
Salt 7d (0.29 g, 0.50 mmol) dissolved in CH3CN (5.0 mL) was heat-
ed at 120 °C for 1 h in a thick-walled Schlenk tube. Under vigorous
stirring a red-brown solid was precipitated with Et2O. The solid was
washed with Et2O (2 × 5 mL) to afford 0.18 g (90%) of 8d; mp 145
°C (dec.).
19F NMR (CD3CN): = –105.4 (PhF), –79.7 (TfO–), –72.7 (TfOcov).
Anal. Calcd for C18H18F7NO8S2 (573.46): C, 37.70; H, 3.16; N 2.44.
Found: C, 38.09; H, 3.40; N, 2.44.
(Z)-1-[1-Ethoxycarbonyl-3-(4-fluorophenyl)-3-(trifluorometh-
ylsulfonyl)oxy-allylidene]morpholin-4-ium Trifluoromethane-
sulfonate (7d)
From 6d (1.76 g, 5.70 mmol) and triflic anhydride (3.21 g, 1.92 mL,
11.4 mmol). Yield: 3.09 g (91%), yellow solid; mp 172 °C (dec.).
IR (KBr): 1832 (s, C=O), 1666 (m), 1589 (vs), 1569 (vs), 1503 (m),
1249 (vs, br, TfO–), 1028 (s) cm–1.
Anal. Calcd for C15H13F4NO6S (411.33): C, 43.80; H, 3.19; N 3.41.
Found: C, 43.19; H, 3.06; N, 3.42.
IR (KBr): 1759 (s, C=O-ester), 1714 (m), 1628 (s), 1601 (m), 1426
(s), 1249 (s), 1031 (s) cm–1.
[(5-Benzo[1,3]dioxol-5-yl)-2-oxo-furan-3-ylidene]diethylammo-
nium Trifluoromethanesulfonate (9a)
To a solution of 6e (0.29 g, 0.90 mmol) in CH2Cl2 (10 mL) at –78
°C was added triflic anhydride (0.25 g, 0.15 mL, 0.90 mmol) in one
portion. The solution was slowly brought to r.t. Under vigorous stir-
ring, a red solid was precipitated with Et2O. The solid was washed
with Et2O (2 × 5 mL) to afford 0.25 g (63%) of 9a; mp 189 °C (dec.).
1H NMR (CD3CN): = 1.43 (t, 3J = 7.1 Hz, 3 H, CH3), 4.04-4.09
(m, 4 H, Hmorph), 4.24-4.26 (m, 2 H, Hmorph), 4.33–4.35 (m, 2 H,
Hmorph), 4.59 (t, 3J = 7.1 Hz, 2 H, CH2), 7.21 (s, 1 H, Hvinyl), 7.38 (mc,
2 H, HPh), 7.93 (mc, 2 H, HPh).
13C NMR (CD3CN): = 14.1 (CH3), 58.1 and 58.8 (NCH2), 67.8,
IR (KBr): 1830 (m, C=O), 1653 (m), 1565 (vs), 1475 (vs), 1255 (vs,
br, TfO–), 1027 (s) cm–1.
68.2, 68.3 (COOCH2 and NCH2CH2O), 110.7 (CHvinyl), 118.2 (d,
4
2JCF = 23.2 Hz, Cm-Ph), 132.0 (d, JCF = 9.5 Hz, Cipso), 134.3 (d,
3JCF = 10.6 Hz, Co-Ph), 159.1 (C=COTf), 160.6 (COOEt), 164.9
(C=N+), 168.4 (d, 1JCF = 255.8 Hz, Cp-Ph); signals for CF3SO3cov and
CF3SO3– were not detected.
Anal. Calcd for C16H16F4NO7S (423.36): C, 45.39; H, 3.81; N 3.31.
Found: C, 45.06; H, 3.88; N, 3.21.
4-[(5-Benzo[1,3]dioxol-5-yl)-2-oxo-furan-3-ylidene]morpholin-
4-ium Trifluoromethanesulfonate (9b)
From 6f (1.00 g, 3.00 mmol) and triflic anhydride (0.84 g, 0.50 mL,
3.00 mmol). Yield: 1.08 g (83%), orange to red solid; mp 227 °C
(dec.).
19F NMR (CD3CN): = –105.1 (PhF), –79.7 (TfO–), –72.4 (TfOcov).
Anal. Calcd for C18H18F7NO9S2 (589.46): C, 36.68; H, 3.08; N 2.38.
Found: C, 36.96; H, 3.22; N, 2.38.
1-(2-Oxo-5-phenyl-furan-3-ylidene)pyrrolidinium Trifluoro-
methanesulfonate (8a)
IR (KBr): 1830 (m, C=O), 1657 (m), 1562 (vs), 1451 (vs), 1253 (vs,
TfO–), 1029 (s) cm–1.
Salt 7a (0.77 g, 1.40 mmol) dissolved in CH3CN (10 mL) was heat-
ed at 120 °C for 1 h in a thick-walled Schlenk tube. Under vigorous
stirring a red-brown solid was precipitated with Et2O and was
washed with Et2O (2 × 5 mL) to afford 0.42 g (79%) of 8a; mp 150
°C (dec.).
Anal. Calcd for C16H14F3NO8S (437.35): C, 43.94; H, 3.23; N 3.20.
Found: C, 43.84; H, 3.32; N, 3.18.
1-[(5-Benzo[1,3]dioxol-5-yl)-2-oxo-furan-3-ylidene]pyrrolidini-
um Trifluoromethanesulfonate (9c)
From 6g (1.00 g, 3.20 mmol) and triflic anhydride (0.84 g, 0.50 mL,
3.00 mmol). Yield: 0.60 g (45%), orange solid; mp 198 °C (dec.).
IR (KBr): 1832 (m, C=O), 1664 (m), 1593 (s), 1583 (s), 1562 (s),
1451 (m), 1258/1225 (vs, TfO–), 1031 (s) cm–1.
Anal. Calcd for C15H14F3NO5S (377.34): C, 47.75; H, 3.74; N 3.71.
Found: C, 46.70; H, 3.74; N, 3.71.
IR (KBr): 1836 (m, C=O), 1673 (m), 1572 (vs), 1495 (s), 1258 (vs,
TfO–), 1225 (s), 1030 (vs) cm–1.
Synthesis 2003, No. 17, 2679–2688 © Thieme Stuttgart · New York

2686
J. Nikolai, G. Maas
PAPER
Anal. Calcd for C16H14F3NO8S (421.04): C, 45.61; H, 3.35; N 3.32.
Found: C, 45.69; H, 3.45; N, 3.35.
Anal. Calcd for C21H16F3NO7S (483.42): C, 52.18; H, 3.34; N 2.90.
Found: C, 51.85; H, 3.49; N, 2.88.
2-[(5-Benzo[1,3]dioxol-5-yl)-2-oxo-furan-3-ylidene]-1,2,3,4-tet-
rahydroisoquinolinium Trifluoromethanesulfonate (9d)
From 6h (0.50 g, 1.30 mmol) and triflic anhydride (0.37 g, 0.20 mL,
1.30 mmol). Yield: 0.36 g (56%), red solid; mp 200 °C (dec.). Ac-
cording to the 1H NMR spectra, compound 9d is a 50:50 mixture of
cis/trans isomers A and B.
4-Benzo[1,3]dioxol-5-yl-2-hydroxy-4-oxo-but-2-enoic Acid (10)
Salt 9d (0.19 g, 0.40 mmol) was dissolved in CH3CN (10 mL), and
the resulting red solution was stirred at r.t. After 1 h the solution
turned yellow. The solvent was removed at 150 mbar, and the re-
sulting orange solid was extracted with Et2O (2 × 20 mL). The com-
bined organic phases were washed with water (2 × 50 mL) and dried
over Na2SO4. The solvent was removed at 700 mbar to afford a yel-
low solid. Yield: 80 mg (78%); mp 150 °C (dec.).
IR (KBr): 1830 (m, C=O), 1650 (m), 1614 (m), 1561 (s), 1503 (s),
1479 (vs), 1455 (vs), 1251 (vs, br, TfO–), 1029 (s) cm–1.
Table 2 1H, 13C and 19F NMR Data for 2,3-Butenolides 8 and 9
Compound
1H (CD3CN)
(ppm), J (Hz)
13C (CD3CN)
(ppm), J (Hz)
19F (CD3CN)
(ppm)
8a
2.20–2.30 (m, 4 H, NCH2CH2), 4.10–4.20 (m, 2 H, 23.8 and 25.2 (NCH2CH2), 54.6 and 56.9 (NCH2), –79.8 (TfO–)
NCH2), 4.30–4.40 (m, 2 H, NCH2), 7.26 (s, 1 H, 99.7 (CHvinyl), 124.7 (Cp–Ph), 129.7, 130.2, 137.6
Hvinyl), 7.74 (t, 2 H, Hm-Ph), 7.90 (t, 1 H, Hp-Ph), 8.14 (Cipso), 154.9 (C=CPh), 157.0 (C=O), 175.7 (C=N+);
(t, 2 H, Ho-Ph
)
signal for CF3SO3– was not detected
8b
8c
4.02–4.05 (m, 2 H, Hmorph), 4.06–4.09 (m, 2 H,
Hmorph), 4.13–4.16 (m, 2 H, Hmorph), 4.66 (m, 2 H,
50.9 and 55.4 (NCH2), 66.5 (NCH2CH2O), 99.4
(CHvinyl), 124.6 (Cp-Ph), 129.9, 130.3, 138.0 (Cipso),
–77.5 (TfO–)
Hmorph), 7.39 (s, 1 H, Hvinyl), 7.75 (t, 2 H, Hm-Ph), 7.93 156.7 (C=C–Ph) 156.9 (C=O), 175.5 (C=N+); signal
(t, 1 H, Hp-Ph), 8.15 (d, 2 H, Ho-Ph
)
for CF3SO3– was not detected
2.20–2.27 (m, 4 H, NCH2CH2), 4.13–4.16 (m, 2 H, 24.6 and 25.8 (NCH2CH2), 55.4 and 57.5 (NCH2), –98.5 (Ph–F),
NCH2), 4.32–4.35 (m, 2 H, NCH2), 7.26 (m 1 H, 100.2 (CHvinyl), 118.4 (d, 2JCF = 23.2, Cm-Ph), 122.0 –79.4 (TfO–)
Hvinyl), 7.46 (m, 2 H, HPh), 8.21 (m, 2 H, HPh)
(d, 4JCF = 2.7, Cipso), 133.6 (d, 3JCF = 10.6, Co-Ph),
155.5 (C=CPh), 157.5 (C=O), 168.8 (d, 1JCF
=
260.8, Cp-Ph), 174.9 (C=N+); signal for CF3SO3– was
not detected
8d
4.02–4.05 (m, 2 H, Hmorph), 4.06–4.09 (m, 2 H,
51.4 and 55.8 (NCH2), 67.0 (NCH2CH2O), 99.7
–95.9 (Ph–F),
–77.8 (TfO–)
2
Hmorph), 4.12–4.16 (m, 2 H, Hmorph), 4.62–4.66 (m, 2 (CHvinyl), 119.0 (d, JCF = 2.7, Cm-Ph), 121.7 (d,
H, Hmorph), 7.40 (s, 1 H, Hvinyl), 7.47 (m, 2 H, HPh), 4JCF = 2.7, Cipso), 133.8 (d, 3JCF = 9.1, Co-Ph), 157.2
1
8.22 (m, 2 H, HPh)
(C=CPh), 157.4 (C=O), 168.9 (d, JCF = 261.5,
Cp-Ph), 174.7 (C=N+); signal for CF3SO3– was not
detected
9a
9b
9c
9d
1.41 and 1.43 (2 × t, 6 H, 2 × CH3), 3.92 (q, 3J = 7.3, 12.7 (CH3), 13.3 (CH3), 49.3 (NCH2), 53.2 (NCH2), –79.7 (TfO–)
2 H, NCH2), 4.22 (q, 3J = 7.3, 2 H, NCH2), 6.23 (s, 99.0 (CHvinyl), 105.0 (OCH2O), 108.8 (Co-Ph), 111.0
2 H, OCH2O), 7.15 (d, 3J = 8.3, 1 H, Hm-Ph), 7.18 (s, (Cm-Ph), 119.1 (Cipso), 130.1 (Co -Ph), 150.7, 156.8,
1 H, Hvinyl), 7.53 (d, 4J = 1.8, 1 H, Ho -Ph), 7.88 (dd, 158.0, 158.3, 175.4 (C=N+); signal for CF3SO3– was
3J = 8.3, 4J = 1.8, 1 H, Ho-Ph
)
not detected
3.94–3.97 (m, 2 H, Hmorph), 4.00 (s, 4 H, Hmorph),
4.53–4.55 (m, 2 H, Hmorph), 6.24 (s, 2 H, OCH2O),
7.16 (d, 3J = 8.1, 1 H, Hm-Ph), 7.17 (s, 1 H, Hvinyl),
50.9 and 55.2 (NCH2), 67.2 and 67.3 (NCH2CH2O), –79.7 (TfO–)
98.8 (CHvinyl), 105.2 (OCH2O), 108.8 (Co-Ph), 111.1
(Cm-Ph), 119.0 (Cipso), 130.5 (Co -Ph), 150.8, 155.7,
7.51 (d, 4J = 1.9, 1 H, Ho -Ph), 7.88 (dd, 3J = 8.1, 4J = 158.3, 158.7, 175.3 (C=N+); signal for CF3SO3– was
1.9, 1 H, Ho-Ph
)
not detected
2.10–2.25 (m, 4 H, NCH2CH2), 3.95–4.10 (m, 2 H, 23.8 and 25.3 (NCH2CH2), 53.8 and 56.1 (NCH2), –80.8 (TfO–)
NCH2), 4.15–4.30 (m, 2 H, NCH2), 6.21 (s, 2 H,
98.3 (CHvinyl), 104.2 (OCH2O), 107.9 (Co-Ph), 110.1
OCH2O), 7.07 (s, 1 H, Hvinyl), 7.12 (d, 3J = 8.3, 1 H, (Cm-Ph), 118.4 (Cipso), 129.0 (Co -Ph), 149.8, 153.5,
Hm-Ph), 7.49 (d, 4J = 1.8, 1 H, Ho -Ph), 7.83 (dd, 3J = 157.2, 157.6, 174.6 (C=N+); signal for CF3SO3– was
8.3, 4J = 1.8, 1 H, Ho-Ph
)
not detected
3.20 and 3.24 (2 × t, 3J = 6.0, 2 H, NCH2CH2, A, B), 24.5, 27.7 (CH2); 48.5, 50.9, 52.5, 54.8 (NCH2);
4.17 and 4.60 (2 × t, 3J = 6.0, 4 H, NCH2, A, B), 5.13 98.1, 98.4 (CHvinyl); 102.7, 102.8, 104.4, 107.2,
and 5.59 (2 × s, 4 H, NCH2, A, B), 6.25 (s, OCH2O, 107.5, 108.0, 108.4, 110.4, 110.4, 124.9, 125.6,
2 H, A, B), 7.17–7.19 (m, 2 H, Hm-Ph, A, B), 7.20 and 126.6, 126.8, 127.1, 127.6, 128.2, 128.2, 128.2,
–79.8 (TfO–)
7.27 (2 × s, 2 H, Hvinyl, A, B), 7.30–7.36 (m, 4 H,
Hisoqu, A, B), 7.53 (m, 1 H, Ho -Ph, A, B), 7.88–7.91 133.6, 133.8, 150.0, 157.5, 157.9, 174.8 (C=N+);
(m, 1 H, Ho-Ph, A, B)
signal for CF3SO3– was not detected
128.4, 128.6, 129.0, 129.3, 129.9, 130.0, 131.6,
Synthesis 2003, No. 17, 2679–2688 © Thieme Stuttgart · New York

PAPER
Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts
2687
IR (KBr): 3125-2825 (m, br, several bands, COOH), 1730 (m),
1630 (m), 1601 (m), 1454 (m), 1261 (s, br), 1104 (s, br), 1030 (s,
br), 801 (s, br) cm–1.
13C NMR (CDCl3): = 25.4 (NCH2CH2), 40.3 (CH3), 50.0 (NCH2),
100.3 (C-5), 101.3, 105.3, 106.8, 108.2, 120.1, 146.2, 148.1, 148.2,
154.9, 156.8 (C=O).
1H NMR (acetone-d6): 6.04 (OCH2O), 6.90 (d, 3J = 8.1 Hz, 1 H,
MS (GC–EI): m/z = 299 (100) [M+], 256 (41) [M+ – CO], 230 (41).
4
Hm-Ph), 6.91 (s, 1 H, Hvinyl), 7.40 (d, J = 1.9 Hz, 1 H, Ho -Ph), 7.63
(dd, 3J = 8.1 Hz, 4J = 1.9 Hz, 1 H, Ho-Ph).
Ethyl (Z)-4-Phenyl-2-(pyrrolidin-1-yl)-4-(trifluoromethylsulfo-
nyl)oxy-but-3-enoate (13a)
13C NMR (acetone-d6): 97.8 (CHvinyl), 102.7 (OCH2O), 107.3,
108.6, 124.9, 130.0, 148.9, 153.1, 163.5, 169.1, 190.9.
To a solution of 7a (1.00 g, 1.80 mmol) in CH2Cl2 (25.0 mL) was
added a LiAlH4 solution (0.45 mL, 0.45 mmol, 1 M in THF) at –78
°C. The mixture was slowly brought to r.t. and water (100 mL) was
added. The separated organic phase was washed with an aq sat so-
lution of NH4Cl (2 × 50 mL) and dried over Na2SO4. After evapor-
tion of the solvent, 13a was obtained as a yellow oil, which should
be stored at 0 °C. Yield: 0.35 g (48%).
MS (+FAB, m-NBA): m/z = 236 (56) [M+], 191 (100) [M+
–
COOH], 149 (26).
2-Methyl-4-(morpholin-4-yl)-6-phenyl-pyridazin-3(2H)-one
(12a)
To a solution of 8b (1.00 g, 2.50 mmol) in CH3CN (35 mL) was
added at 0 °C methyl hydrazine (0.23 g, 0.26 mL, 5.10 mmol) via a
syringe. The reaction mixture was slowly brought to r.t., and the sol-
vent was removed at 150 mbar. The resulting yellow oil was taken
up in CH2Cl2 and the organic phase was washed twice with water,
once with brine, and dried over Na2SO4. After removing the solvent,
the crude product was chromatographed over silica gel with cyclo-
hexane–acetone (2:1) as eluent; Rf 0.4. Yield: 0.17 g (25%) yellow
solid; mp 110 °C.
IR (film): 1735 (m, C=O-ester), 1418 (m, TfOcov), 1207 (vs), 1136
(vs) cm–1.
1H NMR (CDCl3): = 1.31 (t, 3J = 7.2 Hz, 3 H, CH3), 1.82–1.85 (m,
4 H, NCH2CH2), 2.70-2.80 (m, 4 H, NCH2CH2), 4.23-4.27 (t + d, 3
3
H, OCH2, NCH), 6.08 (d, J = 9.7 Hz, 1 H, Hvinyl), 7.39 (m, 3 H,
HPh), 7.43–7.50 (m, 2 H, HPh).
13C NMR (CDCl3): = 14.1 (CH3), 23.4 (NCH2CH2), 51.1 (NCH2),
61.5 (OCH2), 63.2 (NCH), 118.4 (CHvinyl), 126.4 (Co-Ph), 128.7 (Cm-
Ph), 130.3 (Cipso), 132.6 (Cp-Ph), 148.8 (C=COTf), 169.3 (C=O); sig-
nal for CF3SO3cov was not detected.
IR (KBr): 1635 (s), 1568 (s), 1236 (m), 1218 (m), 1120 (s), 997 (s)
cm–1.
1H NMR (CDCl3): = 3.50-3.55 (pseudo-t, 4 H, NCH2), 3.87 (s, 3
H, CH3), 3.90-3.95 (m, 4 H, NCH2CH2O), 6.73 (s, 1 H, 5-H), 7.44–
7.46 (m, 3 H, HPh), 7.75–7.78 (m, 2 H, HPh).
19F NMR (CDCl3): = –71.5 (TfOcov).
MS (+FAB, m-NBA): m/z = 408 (100) [M+], 258 (70) [M+ – TfO].
13C NMR (CDCl3):
(NCH2CH2O), 107.3 (C-5), 126.1, 128.8 (Co-Ph,m-Ph), 129.1 (Cp-Ph),
=
40.7 (CH3), 48.2 (NCH2), 66.5
Ethyl (Z)-2-(Morpholin-4-yl)-4-phenyl-4-(trifluoromethylsulfo-
nyl)oxy-but-3-enoate (13b)
136.2 (Cipso), 145.5 (C-6), 147.2 (C-4), 157.2 (C=O).
MS (GC–EI): m/z = 271 (56) [M+], 253 (67) [M+ – H2O], 186 (100).
From 7b (1.71 g, 3.00 mmol) and LiAlH4 (0.75 mL, 0.75 mmol, 1
M in THF). Yield: 1.17 g (92%), orange to brown oil which solidi-
fied upon storing at 0 °C; mp 62 °C.
Anal. Calcd for C15H17N3O2 (271.31): C, 66.40; H, 6.32; N 15.49.
Found: C, 66.57; H, 6.41; N, 14.72.
IR (KBr): 1738 (s, C=O-ester), 1413 (s, TfOcov), 1224 (vs), 1117 (s),
1027 (m) cm–1.
6-(4-Fluorophenyl)-2-methyl-4-(morpholin-4-yl)-pyridazin-
3(2H)-one (12b)
From 8d (0.66 g, 1.60 mmol) and methyl hydrazine (0.15 g, 0.17
mL, 3.20 mmol). Rf 0.35, cyclohexane–acetone (2:1). Yield: 0.31 g
(67%) as a yellow solid; mp 138 °C.
1H NMR (CDCl3): = 1.34 (t, 3J = 7.4 Hz, 3 H, CH3), 2.60-2.75 (m,
4 H, NCH2), 3.70-3.80 (m, 4 H, NCH2CH2O), 4.22 (d, 3J = 9.4 Hz,
1 H, NCH), 4.27 (q, 3J = 7.4 Hz, 2 H, CH2), 6.09 (d, 3J = 9.4 Hz, 1
H, Hvinyl), 7.42–7.44 (m, 3 HPh), 7.50–7.53 (m, 2 HPh).
13C NMR (CDCl3): = 14.1 (CH3), 50.5 (NCH2), 61.4 (COOCH2),
64.7 (NCH), 66.7 (NCH2CH2O), 117.3 (CHvinyl), 126.3 (Co-Ph),
128.6 (Cm-Ph), 130.3 (Cipso), 132.4 (Cp-Ph), 149.6 (C=C–OTf), 168.8
(C=O); signal for CF3SO3 cov was not detected.
IR (KBr): 1637 (s), 1580 (s), 1509 (s), 1227 (s), 1125 (s) cm–1.
1H NMR (CDCl3): = 3.50-3.55 (m, 4 H, NCH2), 3.83 (s, 3 H, CH3),
3.90-3.95 (m, 4 H, NCH2CH2O), 6.65 (s, 1 H, 5-H), 7.10–7.14 (m,
2 H, HPh), 7.71–7.75 (m, 2 H, HPh).
19F NMR (CDCl3): = –71.8 (TfOcov).
13C NMR (CDCl3):
=
40.6 (CH3), 48.0 (NCH2), 66.4
MS (+FAB, m-NBA): m/z = 424 (100) [MH+], 274 [M+ – TfO].
(NCH2CH2O), 106.8 (C-5), 115.6 (2JCF = 21 Hz, Cm-Ph), 127.8
(3JCF = 8.7 Hz, Co-Ph), 132.2 (4JCF = 2.9 Hz, Cipso), 144.3 (C-6), 147.1
(C-4), 156.8 (C=O), 163.1 (1JCF = 249.7 Hz, Cp-Ph).
Anal. Calcd for C17H20F3NO6S (423.10): C, 48.22; H, 4.76; N 3.31.
Found: C, 46.90; H, 4.81; N, 3.31. Value for C could not be im-
proved.
MS (GC–EI): m/z = 289 (51) [M+], 271 (72) [M+ – F], 204 (100).
Ethyl (Z)-2-Oxo-4-phenyl-4-(trifluoromethylsulfonyl)oxy-but-
3-enoate (14a)
6-(Benzo[1,3]dioxol-5-yl)-2-methyl-4-(pyrrolidin-1-yl)-py-
ridazin-3(2H)-one (12c)
From 9c (0.74 g, 1.80 mmol) and methyl hydrazine (0.17 g, 0.19
mL, 3.60 mmol). Rf 0.6 (cyclohexane–acetone, 2:1). Yield: 0.10 g
(20%), yellow oil.
To a solution of 7b (1.31 g, 2.30 mmol) in CH2Cl2 (100 mL) was
added water (50 mL). The mixture was vigorously stirred at 25 °C
for 1 h. The organic phase was separated and the aq phase was ex-
tracted with CH2Cl2 (20 mL). After drying over Na2SO4, the organic
solvent was removed at 700 mbar to afford 0.78 g (96%) of 14a as
a yellow oil which solidified at 0 °C; mp 46 °C.
IR (KBr): 1634 (s), 1575 (vs), 1504 (s), 1348 (s), 1243 (s), 1099
(m), 1041 (s) cm–1.
IR (KBr): 1736 (s, C=O-ester), 1703 (s, C=O), 1620 (s), 1433 (s,
TfOcov), 1257 (s), 1227 (vs), 1206 (s), 1139 (s), 1078 (s) cm–1.
1H NMR (CDCl3): = 1.43 (t, 3J = 7.2 Hz, 3 H, CH3), 4.40 (q, 3J =
7.2 Hz, 2 H, CH2), 7.41 (s, 1 H, Hvinyl), 7.51 (t, 2 H, Hm-Ph), 7.54 (t,
1 H, Hp-Ph), 7.71 (d, 2 H, Hp-Ph).
1H NMR (CDCl3): = 1.90-2.00 (m, 4 H, NCH2CH2), 3.65-3.80 (br
signal, 4 H, NCH2), 3.77 (s, 3 H, CH3), 5.99 (s, 2 H, OCH2O), 6.15
(s, 1 H, 5-H), 6.84 (d, 3J = 7.9 Hz, 1 H, Hm-Ph), 7.21 (dd, 3J = 7.9 Hz,
4J = 1.8 Hz, 1 H, Ho-Ph), 7.26 (d, 4J = 1.8 Hz, 1 H, Ho -Ph).
Synthesis 2003, No. 17, 2679–2688 © Thieme Stuttgart · New York

2688
J. Nikolai, G. Maas
PAPER
(2) (a) Singer, B.; Maas, G. Chem. Ber. 1987, 120, 1683.
(b) Rahm, R.; Maas, G. Chem. Ber. 1994, 127, 1295.
(c) Rahm, R.; Maas, G. J. Heterocycl. Chem. 1996, 33, 439.
(3) Maas, G.; Rahm, R.; Schletz, M.; Würthwein, E.-U. J. Org.
Chem. 1994, 59, 6862.
(4) Rahm, R.; Maas, G. Synthesis 1994, 295.
(5) Maas, G.; Singer, B.; Wald, P.; Gimmy, M. Chem. Ber.
1988, 121, 1847.
(6) Neumann, R.; Herz, H. G.; Maas, G. J. Prakt. Chem. 1999,
341, 121.
13C NMR (CDCl3): = 13.9 (CH3), 63.2 (OCH2), 111.3 (CHvinyl),
127.1 (Co-Ph), 129.2 (Cm-Ph), 131.7 (Cipso), 132.8 (Cp-Ph), 157.4
(C=C–OTf), 160.8 (COOEt), 178.2 (C=O); signal for CF3SO3cov
was not detected.
19F NMR (CDCl3): = –71.5 (TfOcov).
MS (+FAB, m-NBA): m/z = 353 (70) [M+], 318 (85), 279 (100).
Anal. Calcd for C13H11F3NO6S (352.28): C, 44.32; H, 3.15. Found:
C, 43.67; H, 3.15.
(7) Reinhard, R.; Maas, G.; Bohrisch, J.; Liebscher, J. Liebigs
Ann. Chem. 1994, 429.
(8) Obrecht, D.; Gerber, F.; Sprenger, D.; Masquelin, T. Helv.
Chim. Acta 1997, 80, 531.
Ethyl (Z)-4-(4-Fluorophenyl)-2-oxo-4-(trifluoromethylsul-
fony)oxy-but-3-enoate (14b)
From 7d (0.41 g, 0.70 mmol) in CH2Cl2 (25 mL) and water (25 mL).
Yield: 0.21 g (80%), yellow solid; mp 65 °C.
(9) For other preparations of 5, see: (a) Santiago, B.; Dalton, C.
R.; Huber, E. W.; Kane, J. M. J. Org. Chem. 1995, 60, 4947.
(b) Ito, H.; Arimoto, K.; Sensui, H.; Hosomi, A. Tetrahedron
Lett. 1997, 38, 3977.
(10) (a) Jones, E. R. H.; Shen, T. Y.; Whiting, M. C. J. Chem. Soc.
1950, 236. (b) Bol’shedvorskaya, R. L.; Pvolova, G. A.;
Alekseeva, N. V.; Vereshchagin, L. I. J. Org. Chem. USSR
1977, 13, 2158.
IR (KBr): 1758 (s, C=O-ester), 1714 (m), 1627 (s), 1600 (s), 1506
(s), 1425 (TfOcov), 1245 (vs), 1211 (vs), 1158 (s), 1085 (s) cm–1.
1H NMR (CDCl3): = 1.42 (t, 3J = 7.1 Hz, 3 H, CH3, 4.37 (q, 3J =
7.1 Hz, 2 H, OCH2), 7.19–7.28 (m, 2 H, HPh), 7.35 (s, 1 H, Hvinyl),
7.70–7.74 (m, 2 H, HPh).
13C NMR (CDCl3): = 13.9 (CH3), 63.2 (OCH2), 111.2 (Cvinyl),
116.7 (d, 2JCF = 14.8 Hz, Cm-Ph), 129.5 (d, 4JCF = 9.1 Hz, Cipso), 136.2
(d, 2JCF = 9.1 Hz, Co-Ph), 156.2 (C=COTf), 160.8 (COOEt), 165.3 (d,
1JCF = 256.2 Hz, Cp-Ph), 178.1 (C=O); signal for CF3SO3cov was not
detected.
(11) Stang, P. J.; Maas, G.; Smith, D. L.; McCloskey, J. A. J. Am.
Chem. Soc. 1981, 103, 4837.
(12) Lin-Vien, D.; Colthup, N. B.; Fately, W. G.; Grasselli, J. G.
Infrared and Raman Characteristic Frequencies of Organic
Molecules; Academic Press: Boston, 1991, 244.
(13) Kappe, C. O.; Kollenz, G.; Wentrup, C. Heterocycles 1994,
38, 779; and references therein.
19F NMR (CDCl3): = –102.5 (Ph–F), –71.4 (TfOcov).
Anal. Calcd for C13H10F3NO6S (370.27): C, 42.17; H, 2.72. Found:
C, 43.91; H, 2.94; C value could not be improved.
(14) Sof’ina, O. A.; Igidov, N. M.; Koz’minykh, E. N.;
Trapeznikova, N. N.; Kasatkina, Yu. S.; Koz’minykh, V. O.
Russ. J. Org. Chem. 2001, 37, 1017.
(15) Sircar, I.; Weishaar, R. E.; Kobylarz, D.; Moos, W. H.;
Bristol, J. A. J. Med. Chem. 1985, 28, 1405.
(16) (a) Levas, M.; Normant, H. C. R. Hebd. Séances Acad. Sci.
Ser. C 1969, 268, 92. (b) Levas, M.; Levas, E.; Normant, H.
C. R. Hebd. Seances Acad. Sci. 1967, 264, 907.
(17) Auger, J.; Belinski, C.; Lalau-Keraly, F.-X.; Nivière, P.;
Payard, M. C. R. Hebd. Seances Acad. Sci. 1976, 282, 93.
Acknowledgment
We wish to thank Birgit Horn (Ulm) for her skillful technical assi-
stance and Elke Biehl (Kaiserslautern) for carrying out the elemen-
tal analyses. J. N. thanks the Land Baden-Württemberg for a
postgraduate fellowship.
References
(1) Singer, B.; Maas, G. Chem. Ber. 1987, 120, 485.
Synthesis 2003, No. 17, 2679–2688 © Thieme Stuttgart · New York