Substituted pyridylamide ligands in microwave-accelerated Mo(0)-catalysed allylic alkylations

Article abstract of DOI:10.1055/s-2002-33345

Novel 4- and 6-substituted bis-pyridylamides were prepared by microwave accelerated nucleophilic substitution of the 4- and 6-halo substituted derivatives of the parent ligand 1a. The ligands were used in the asymmetric allylation of cinnamyl carbonate catalysed by Mo(O) in which the 4-chloro- and 4-pyrrolidyl substituted ligand derivatives exhibited high regioselectivity (74:1 and 88:1, respectively) and enantioselectivity (96% ee), whereas 6-substituted ligands afforded no product under the same conditions. Other allylic substrates were used to explore the generality of the procedure.

Full text of DOI:10.1055/s-2002-33345

SPECIAL TOPIC
1601
Substituted Pyridylamide Ligands in Microwave-Accelerated
Mo(0)-Catalysed Allylic Alkylations
M
icrowave-Accela
s
rate
d
Mo
c
(0)-Catalys
a
edAllylic
A
r
lkylations Belda, Christina Moberg*
Department of Chemistry, Organic Chemistry, KTH, 100 44 Stockholm, Sweden
Fax +46(8)7912333; E-mail: kimo@kth.se
Received 21 May 2002
Abstract: Novel 4- and 6-substituted bis-pyridylamides were pre-
pared by microwave accelerated nucleophilic substitution of the 4-
O
O
NH HN
and 6-halo substituted derivatives of the parent ligand 1a. The
ligands were used in the asymmetric allylation of cinnamyl carbon-
ate catalysed by Mo(0) in which the 4-chloro- and 4-pyrrolidyl sub-
stituted ligand derivatives exhibited high regioselectivity (74:1 and
88:1, respectively) and enantioselectivity (96% ee), whereas 6-sub-
stituted ligands afforded no product under the same conditions. Oth-
er allylic substrates were used to explore the generality of the
procedure.
N
N
1a
Figure 1 The structure of the bis-pyridylamide 1a
We wanted to study the generality of our findings and ex-
plore whether a more selective catalyst could be prepared
by further modification of the electronic properties of the
pyridine nitrogen atoms of the ligand. Moreover, since
this kind of ligands can be used in other asymmetric catal-
ysed processes10 we wanted to develop a facile synthesis
for derivatives of 1a.
Key words: molybdenum, allylations, asymmetric catalysis, pyr-
idylamides, microwaves
Allylic alkylations catalysed by Mo(0) complexes have
become of great interest since they afford selectively the
more substituted product when non-symmetrical allylic
substrates are used, as opposed to most Pd(0)-catalysed
allylations.1 After Trost’s findings that pyridylamide 1a
(Figure 1) served as an efficient ligand in asymmetric al-
lylations catalysed by Mo(0),2 a number of other ligands
have been developed including bis(dihydrooxazoles),3
bipyridines4 and C1-symmetric pyridylamides.5
The strategy that we previously employed for the synthe-
sis of the different bis(pyridylamide) ligands was based
either on the reaction of the corresponding substituted py-
ridine-2-carboxylic acid with a coupling reagent or, alter-
natively, on making the acid chloride to activate the
carboxylic function, followed by condensation with the
chiral diamine. This route requires first the preparation of
the substituted pyridine-2-carboxylic acid, which is acces-
sible from a multistep synthesis and a tedious workup pro-
cedure for the isolation of the amphoteric picolinic acid
derivative. Since the ability of - and -halopyridines to
undergo nucleophilic substitution is well known,11 we
thought that the corresponding 4- or 6-halosubstituted
ligand derivatives would constitute versatile building
blocks giving access to a series of other substituted
ligands by direct nucleophilic substitution. Thus, we pre-
pared 1b by treating 4-chloropyridine-2-carboxylic acid
as its sulfuric/hydrobromic acid salt with N,N -carbonyl-
diimidazole (CDI)12 in THF at 50 °C in the presence of
K2CO3 and then adding the diamine at once to give the
ligand derivative. The analogue 1c was prepared in a sim-
ilar fashion but using commercially available 6-bromopy-
ridine-2-carboxylic acid (Scheme 1).
As part of our work on microwave accelerated highly se-
lective transition metal catalysed reactions,6 we explored
the allylation catalysed by Mo(0) and developed a conve-
nient and robust reaction procedure for the microwave ac-
celerated reaction of cinnamyl carbonate with sodium
dimethyl malonate using Mo(CO)6, ligand 1a and N,O-
bis(trimethylsilyl)acetamide (BSA) under air, that afford-
ed the product with high regio- and enantioselectivity.7
Due to our interest in pyridylamides,8 we decided to pre-
pare derivatives of 1a and study the influence of subtitu-
ents in the pyridine rings on the outcome of the catalytic
reaction.9 Our results showed that electronic effects were
important. Thus, an electron-withdrawing subtituent (4-
nitro) in the pyridine rings resulted in a less selective cat-
alyst. On the other hand, a higher regio- and enantioselec-
tivity was obtained by using a ligand with an electron-
donating group (4-methoxy) in the pyridine rings. Steric
effects were also important and a ligand with a methyl
group in the 6 position of the pyridine rings afforded a cat-
alyst exhibiting poor activity and selectivity.
Then, direct nucleophilic substitution was accomplished
in a few minutes by heating the substrate 1b or 1c with the
appropriate nucleophile in a microwave cavity to afford
the corresponding derivatives in essentially quantitative
isolated yield after workup and removal of the volatiles
under vacuum (Scheme 2).
Synthesis 2002, No. 11, Print: 22 08 2002.
Art Id.1437-210X,E;2002,0,11,1601,1606,ftx,en;C01902SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881
We also synthesised the ligand 1f with 3-hydroxy substi-
tuted pyridine rings, to explore the effect of substituents in

1602
O. Belda, C. Moberg
SPECIAL TOPIC
R1
N
O
O
O
O
1) Oxalyl chloride
DMF cat., CH2Cl2, 0 ºC
OH
NH HN
1) CDI
HO
NH HN
OH
R1
N
N
R1
R2
CO2H
2)
N
CO2H
2)
N
N
R2
R2
1f
H2N
NH2
H2N
NH2
R1= -Cl R2= -H
or
R1= -Cl R2= -H 1b 54%
R1= -H R2= -Br 1c 54%
31%
R1= -H R2= -Br
Scheme 3
Scheme 1
active catalyst. Representative examples of temperature
profile of the microwave accelerated alkylations
(Figure 2) favour a temperature of 160–170 °C for the re-
action, which is then generally used.
other positions, from commercially available 3-hydroxy-
pyridine-2-carboxylic acid by preparation of the acid
chloride using oxalyl chloride and its subsequent reaction
with (1R,2R)-1,2-diaminocyclohexane (Scheme 3). We
attempted to make the 3-methoxy substituted derivative
by methylation of 1f, but to our surprise no product could
be obtained using different methods and conditions.
With these new ligands in hand, we performed the micro-
wave accelerated Mo(0)-catalysed allylation of 3-phenyl-
prop-2-enyl carbonate (2a) using sodium dimethyl
malonate as the nucleophile (Table 1). As previously ob-
served, when a ligand containing electron-donating sub-
stitutents in the 4-position of the pyridine rings was used,
a catalyst exhibiting higher regioselectivity was produced.
Thus, ligands 1b and 1d afforded the product with an ex-
cellent branched to linear ratio (74:1 and 88:1, respective-
ly) although the enantioselectivity was slightly lower than
for the parent ligand. It can also be noted that the ligand
1d afforded a catalyst with lower activity, all starting ma-
terial being consumed only after 12 minutes of reaction at
170 °C. On the other hand, when ligands 1c, 1e and 1f
were used, no reaction occurred. We have already shown,9
that a ligand bearing a methyl group in the 6 position of
the pyridine rings afforded a less reactive and less selec-
tive catalyst, and it can thus be concluded that ligands
with 6-substituted pyridine rings give rise to catalysts with
low activity. Whether this is due to steric or electronic fac-
tors is not clear. In the case of 1f, the introduction of an
additional donor atom in the ligand might result in an in-
Figure 2 Representative examples of temperature profile of the
microwave accelerated alkylations.
Having found easily available 1b as a highly regioselec-
tive ligand for the allylation of 3-phenylprop-2-enyl car-
bonate using sodium dimethyl malonate as nucleophile,
we decided to explore the reaction of other allylic carbon-
ates.
First we studied the reaction of 4-substituted cinnamyl
substrates 2a–d (Table 2). Again, we found that the ligand
1b afforded the corresponding branched product with
higher regioselectivity than 1a. It can also be noted that
the substituents on the phenyl ring in the substrate have an
O
O
NH
O
O
NH HN
NH HN
160 °C
10 min
N
N
N
N
Cl
N
N
Cl
1b
1d
>99%
O
O
O
O
NH HN
MeONa/MeOH
140 °C, 15 min
NH HN
N
N
Br
N
N
Br
OMe
MeO
1c
1e
>99%
Scheme 2
Synthesis 2002, No. 11, 1601–1606 ISSN 0039-7881 © Thieme Stuttgart · New York

SPECIAL TOPIC
Microwave-Accelarated Mo(0)-Catalysed Allylic Alkylations
1603
Table 1 Allylation of 2a Using Ligands 1a–f
MeO2C
CO2Me
+
O
4 % Mo(CO)6 , Ligand
CH2(CO2Me)2, NaCH(CO2Me)2, BSA
O
O
branched
THF, µ−waves
CO2Me
CO2Me
2a
linear
Ligand
1a
Temp (°C)
160
Time (min)
Yield (%)a
Regioselectiviyb
ee (%)c
6
6
80
89
0
19:1
74:1
–
98
96
–
1b
165
1c
160
6
1d
170
12
6
91
0
88:1
–
96
–
1e
160
1f
160
6
0
–
–
a Isolated yield.
b Determined by GC-MS.
c Determined by chiral HPLC using a Daicel OD-H (0.46 cm Ø 25 cm) column.
Table 2 Allylation of 2a–d Using Ligands 1a and 1b
MeO2C
CO2Me
+
O
4 % Mo(CO)6 , Ligand
R
CH2(CO2Me)2, NaCH(CO2Me)2, BSA
O
O
branched
THF, µ−waves
R
CO2Me
CO2Me
R= -H
R= -Cl
R= -CF3
R= -OMe
2a
2b
2c
2d
R
linear
R
Ligand
1a
Temp (°C)
160
Time (min)
Yield (%)a
Regioselectivityb
ee (%)c
98
H
5
6
6
6
6
6
6
6
80
89
51
86
50
66
59
79
19:1
74:1
32:1
47:1
11:1
22:1
51:1
57:1
H
1b
165
96
Cl
1a
165
96
Cl
1b
165
90
CF3
CF3
MeO
MeO
1a
165
99
1b
165
96
1°
165
98
1b
165
94
a Isolated yield.
b Determined by GC-MS.
c Determined by chiral HPLC using a Daicel OD-H (0.46 cm
25 cm) column.
Synthesis 2002, No. 11, 1601–1606 ISSN 0039-7881 © Thieme Stuttgart · New York

1604
O. Belda, C. Moberg
SPECIAL TOPIC
effect on the selectivity of the nucleophilic attack. Thus, 4-pyrrolidyl substituted ligands afforded the products
an electron-donating group in the phenyl ring afforded the with considerably higher regioselectivity than the parent
product with a higher branched to linear ratio whereas the ligand and with 96% ee. Furthermore, when using other
opposite was found for an electron-withdrawing group. allylic carbonates in the reaction, the catalyst derived
As seen before for the model substrate 2a, the enantiose- from the 4-chloro substituted ligand yielded the product
lectivity of the product obtained when using ligand 1b with higher regioselectivity than the catalyst derived from
was slightly lower than when using the parent ligand.
the parent ligand, which is of interest for synthetic pur-
poses.
We also compared ligands 1a and 1b using different race-
mic 4-phenyl substituted methyl carbonate derivatives of
1-arylprop-2-en-1-ols 3a–c (Table 3). Unfortunately, we
were not able to include the 4-methoxy substituted deriv-
ative in this reaction series due to its thermal instability.
The results show once more that 1b affords the corre-
sponding branched product with higher regioselectivity
than 1a. Furthermore, in analogy to what has been shown
previously,2a the ratio between branched and linear prod-
ucts obtained for substrates 2a–d differs slightly when us-
ing the isomeric carbonates 3a–c as substrates in the
reaction. Enantioselectivities using ligand 1b for sub-
strates 3a–c were moderate to good, varying from 74 to
90% ee depending on the substrate. It has recently been
shown13 that a kinetic resolution takes place when using
this kind of substrates. In THF, a significant memory ef-
fect is operating with the slowly reacting enantiomer pro-
viding the product with lower ee than the fast reacting
enantiomer. This results in lower product ee when the re-
actions are run to completion.
Allylic carbonates 2a–d and 3a–c were prepared according to pre-
viously published procedures.14 THF was distilled over Na/ben-
zophenone and CH2Cl2 over CaH2. The microwave heating was
performed with a Smith Creator™ single mode cavity from Person-
al Chemistry AB, Uppsala, Sweden. Unless otherwise noted, all 1H
and 13C NMR spectra were recorded in CDCl3 at 500 and 125.7
MHz, respectively. Chemical shifts are reported in ppm relative to
the solvent as internal standard.
4-Chloropyridine-2-carboxylic Acid Mixed Salt
Into a flame dried 250 mL flask a mixture of pyridine-2-carboxylic
acid (10 g, 0.08 mol) and anhyd NaBr15 (17 g, 0.16 mol) was re-
fluxed in SOCl2 (50 mL) for 22 h. The initially dark green mixture
changed to a dark red colour. Excess SOCl2 was removed by rota-
tory evaporation and the residue was dissolved in CH2Cl2 (200 mL)
and filtered through Celite to remove any insoluble material. The re-
sulting red solution was transferred into a three-necked 1 L flask
equipped with a thermometer, a mechanical stirrer and an addition
funnel. The solution was cooled to –5 °C and H2O (200 mL) was
added dropwise while stirring vigorously, keeping the temperature
between –5 and 2 °C. The solution changed to orange in colour with
In summary, we have developed a simple route towards 4- formation of a white precipitate. The mixture was further stirred at
r.t. for 25 h and then concentrated under rotatory evaporation. Com-
and 6-substituted pyridylamide ligands. The ligands were
plete removal of H2O was achieved by successively adding toluene
used in the microwave accelerated allylation of cinnamyl
to the wet solid and evaporating under reduced pressure. The solid
carbonates catalysed by Mo(0) in which the 4-chloro and
was recrystallised from a minimum amount of EtOH to give 9.6 g
Table 3 Allylation of 3a–c Using Ligands 1a and 1b
O
MeO2C
CO2Me
+
O
O
4 % Mo(CO)6 , Ligand
R
CH2(CO2Me)2, NaCH(CO2Me)2, BSA
branched
R
(±)
THF, µ−waves
CO2Me
CO2Me
R= -H
R= -Cl
R= -CF3
3a
3b
3c
R
linear
R
Ligand
Temp (°C)
165
Time (min)
Yield (%)a
Regioselectivity
ee (%)c
96
H
1a
1b
1a
1b
1a
1b
6
6
6
6
6
6
76
89
78
70
48
52
13:1
69:1
26:1
34:1
10:1
20:1
H
165
86
Cl
Cl
CF3
CF3
165
96
165
74
165
98
165
90
a Isolated yield.
b Determined by GC-MS.
c Determined by chiral HPLC using a Daicel OD-H (0.46 cm
25 cm) column.
Synthesis 2002, No. 11, 1601–1606 ISSN 0039-7881 © Thieme Stuttgart · New York

SPECIAL TOPIC
Microwave-Accelarated Mo(0)-Catalysed Allylic Alkylations
1605
(48%) of a yellow product consisting of a 0.57:0.43 mixture of the
sulphuric and hydrobromic acid salts (according to elemental anal-
ysis).
1H NMR (DMSO-d6): = 12.17 (2 H, br s), 8.70 (1 H, d, J = 4.9
Hz), 8.08 (1 H, d, J = 1.6 Hz), 7.83 (1 H, dd, J = 4.9, 1.6 Hz).
br s), 3.29 (4 H, br s), 2.19 (1 H, br s), 1.98 (4 H, br s), 1.79 (1 H, br
s), 1.43 (2 H, br s).
13C NMR: = 165.9, 152.9, 150.3, 148.5, 108.6, 106.0, 53.4, 47.6,
33.1, 25.7, 25.2.
(1R,2R)-1,2-Bis[(6-methoxypyridine)-2-carboxyamido]cyclo-
hexane (1e)
A suspension of 1c (50 mg, 0.1 mmol) and solid MeONa (54 mg,
1.0 mmol) in MeOH (2 mL) was heated in the microwave cavity at
140 °C for 15 min. H2O (4 mL) was added to the resulting solution
and the turbid mixture was extracted with CH2Cl2 (3 5 mL). The
13C NMR (DMSO-d6): = 165.8, 151.6, 150.7, 145.3, 128.0, 125.7.
Anal. Calcd for C6H5.57Br0.43ClNO4.28S0.57: C, 29.02; H, 2.24; Br,
13.84; Cl, 14.28; N, 5.64; O, 27.58; S, 7.35. Found: C, 28.59; H,
2.16; Br, 13.92; Cl, 14.50; N, 5.52; O, 27.18; S, 7.06.
(1R,2R)-1,2-Bis[(4-chloropyridine)-2-carboxyamido]cyclohex-
ane (1b)
combined organic extracts were dried (Na2SO4) and the solvent
20
evaporated to afford 38 mg (>99%) of the pure product; [ ]D
–
A suspension of 4-chloropyridine-2-carboxylic acid mixed salt (1.0
g, 4.03 mmol), 1,1 -carbonyldiimidazol (649 mg, 4.0 mmol) and
K2CO3 (553 mg, 4.0 mmol) in THF (5 mL) was heated at 50 °C un-
der N2 for 1 h. Then (1R,2R)-1,2-diaminocyclohexane (223 mg,
1.96 mmol) was added at once and the reaction mixture was stirred
at 50 °C for a further 1 h. H2O (20 mL) was added to the cold mix-
ture and the resulting suspension was extracted with CH2Cl2 (3 10
mL). The combined organic extracts were dried (Na2SO4) and the
solvent evaporated. The crude product was purified by column
chromatography on silica gel (eluent: 20% EtOAc–hexanes) to
101.3 (c = 1.07, CHCl3).
1H NMR: = 8.12 (1 H, br d, J = 6.1 Hz), 7.62 (2 H, m), 6.80 (1 H,
d, J = 8.54 Hz), 4.01 (3 H, s), 4.00 (1 H, br s), 2.24 (1 H, br s), 1.82
(1 H, br s), 1.44 (2 H, br s).
13C NMR: = 165.1, 163.2, 147.5, 139.8, 115.7, 114.6, 54.1, 54.0,
32.9, 25.2.
Anal. Calcd for C20H24N4O4: C, 62,49; H, 6,29; N, 14,57. Found: C,
62,28; H, 6,39; N, 14,45.
20
yield 408 mg (54%) of the pure product; [ ]D –12.1 (c = 0.24,
CHCl3).
(1R,2R)-1,2-Bis[(3-hydroxypyridine)-2-carboxyamido]cyclo-
hexane (1f)
1H NMR: = 8.43 (1 H, d, J = 5.9 Hz), 8.17 (1 H, br s), 8.07 (1 H,
d, J = 1.8 Hz), 7.37 (1 H, dd, J = 5.9, 1.8 Hz), 4.06 (1 H, br s), 2.20
(1 H, br s), 1.86 (1 H, br s), 1.47 (2 H, br s).
13C NMR: = 163.8, 151.6, 149.5, 146.0, 126.5, 123.1, 53.9, 32.9,
25.2.
Oxalyl chloride (0.5 mL, 5.9 mmol) was added to a suspension of
3-hydroxypyridine-2-carboxylic acid (0.72 g, 5.2 mmol) and a cat-
alytic amount of DMF in anhyd CH2Cl2 (5 mL) at 0 °C. The result-
ing suspension was stirred at 0 °C for 1 h. The mixture was
concentrated under vacuum to give an almost colourless solid that
was immediately suspended in anhyd CH2Cl2 (5 mL). To the result-
ing suspension, a solution of (1R,2R)-1,2-diaminocyclohexane (294
mg, 2.6 mmol) and ethyldiisopropylamine (2.7 mL, 15.6 mmol) in
CH2Cl2 (5 mL) was added at 0 °C and the mixture was stirred for 14
h. Evaporation of the solvent afforded the crude product. Purifica-
tion by liquid chromatography on silica gel (eluent: hexanes–
EtOAc, 5:1) yielded 284 mg (31%) of the pure product; [ ]D20 –91.4
(c = 0.14, CHCl3).
1H NMR: = 12.06 (1 H, s), 8.33 (1 H, br s), 8.09 (1 H, d, J = 4.9
Hz), 7.33 (1 H, dd, J = 8.5, 4.9 Hz), 7.26 (1 H, d, J = 8.5 Hz), 4.06
(1 H, br s), 2.27 (1 H, br s), 1.92 (1 H, br s), 1.52 (2 H, br s).
13C NMR: = 169.5, 158.1, 140.0, 131.6, 129.0, 126.3, 53.5, 32.7,
25.1.
Anal. Calcd for C18H18Cl2N4O2: C, 54.97; H, 4.61; N, 14.25. Found:
C, 54.85; H, 4.77; N, 14.16.
(1R,2R)-1,2-Bis[(6-bromopyridine)-2-carboxyamido]cyclohex-
ane (1c)
A suspension of 6-bromopyridine-2-carboxylic acid (200 mg, 1
mmol) and 1,1 -carbonyldiimidazol (195 mg, 1.2 mmol) in THF (1
mL) was heated at 50 °C under N2 for 1 h. Then (1R,2R)-1,2-diami-
nocyclohexane (57 mg, 0.5 mmol) was added at once and the reac-
tion mixture was stirred at 50 °C as described for 1b. The crude
product was recrystallized from EtOH to yield 130 mg (54%) of the
pure product as white needles; [ ]D20 –193.8 (c = 1.1, CHCl3).
1H NMR: = 8.07 (1 H, d, J = 7.3 Hz), 8.02 (1 H, d, J = 6.1 Hz),
7.61 (1 H, dd, J = 7.3 Hz), 7.52 (1 H, d, J = 7.3 Hz), 4.02 (1 H, br
s), 2.20 (1 H, br d, J = 11.0 Hz), 1.83 (1 H, br s), 1.46 (2 H, br s).
Microwave-Assisted Allylic Alkylations; General Procedure
Two different stock solutions were prepared: Solution-N, contain-
ing the nucleophile, sodium dimethyl malonate in THF, was made
by adding dimethyl malonate (880 L, 7.7 mmol) to a suspension of
60% NaH in mineral oil (27 mg, 0.68 mmol) in THF (10 mL). So-
lution-S, containing the corresponding allylic substrate, was pre-
pared by dissolving the allylic carbonate 2 or 3 (7.1 mmol) in THF
(10 mL). The appropriate ligand 1 (0.034 mmol) and Mo(CO)6 (6.9
mg, 0.026 mmol) were transferred to a SmithProcess Vial™. Solu-
tion-N (1 mL, 0.77 mmol of the nucleophile), Solution-S (1 mL,
0.71 mmol of the substrate) and BSA (208 L) were added in this
order and the sample was microwave heated to the appropriate tem-
perature for the indicated time. Directly after reaction, the reaction
mixture (dark coloured) was diluted with Et2O to a total volume of
10 mL (a precipitate appeared). The yellow-orange solution was fil-
tered and analysed by GC-MS. Purification of the crude product
was achieved by column chromatography on silica gel (eluent:
EtOAc–hexanes). The structures of all products were confirmed by
comparison with published spectroscopic data14,16 and GC-MS
analyses.
13C NMR: = 163.6, 151.3, 140.6, 139.8, 131.0, 121.7, 54.1, 32.8,
25.2.
Anal. Calcd for C18H18Br2N4O2: C, 44.84; H, 3.76; N, 11.62. Found:
C, 44.71; H, 3.82; N, 11.59.
(1R-2R)-1,2-Bis[(4-N-pyrrolidylpyridine)-2-carboxyamido]cy-
clohexane (1d)
A solution of 1b (100 mg, 0.25 mmol) in pyrrolidine (2.5 mL) was
heated in the microwave cavity at 160 °C for 10 min. The reaction
mixture was concentrated under vacuum and the residue was dis-
solved in CHCl3 (5 mL). The organic solution was washed with aq
20% K2CO3 solution (2 5 mL) and dried (Na2SO4). Evaporation
of the solvent afforded a yellowish solid. Further evaporation of
pyrrolidine in a desiccator under vacuum afforded the pure product;
yield: 116 mg (>99%); [ ]D20 +70.1 (c = 0.16, CHCl3).
1H NMR: = 8.24 (1 H, br d, J = 6.1 Hz), 8.07 (1 H, d, J = 6.1 Hz),
7.21 (1 H, d, J = 2.4 Hz), 6.32 (1 H, dd, J = 6.1, 2.4 Hz), 4.00 (1 H,
Synthesis 2002, No. 11, 1601–1606 ISSN 0039-7881 © Thieme Stuttgart · New York

1606
O. Belda, C. Moberg
SPECIAL TOPIC
(6) (a) Bremberg, U.; Larhed, M.; Moberg, C.; Hallberg, A. J.
Org. Chem. 1999, 64, 1082. (b) Kaiser, N.-F.; Bremberg,
U.; Larhed, M.; Moberg, C.; Hallberg, A. J. Organomet.
Chem. 2000, 603, 2. (c) Bremberg, U.; Lutsenko, S.; Kaiser,
N.-F.; Larhed, M.; Hallberg, A.; Moberg, C. Synthesis 2000,
1004. (d) Lutsenko, S.; Moberg, C. Tetrahedron: Asymmetry
2001, 12, 2529.
Acknowledgements
This work was supported by the Swedish Foundation for Strategic
Research.
References
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