Synthesis of novel halopyridinylboronic acids and esters. Part 2: 2,4, or 5-Halopyridin-3-yl-boronic acids and esters

Article abstract of DOI:10.1016/S0040-4020(02)00283-1

This paper describes a general method for the synthesis and the isolation of novel 2,4, or 5-halopyridin-3-yl-boronic acids and esters 4, 7, 10, 13, 15. These compounds are prepared taking into account a regioselective halogen-metal exchange using nBuLi or a regioselective ortho-lithiation using lithium diisopropylamide and subsequent quenching with triisopropylborate starting from appropriate mono or dihalopyridines. All substrates studied to date provided a single regioisomeric boronic acid or ester product. Additionally, these compounds have been found to undergo Pb-catalyzed coupling with a range of arylhalides and authorize a strategy to produce new pyridines libraries.

Full text of DOI:10.1016/S0040-4020(02)00283-1

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 3323±3328
Synthesis of novel halopyridinylboronic acids and esters.
Part 2: 2,4, or 5-Halopyridin-3-yl-boronic acids and estersq
a
a
a
b
Â
Alexandre Bouillon, Jean-Charles Lancelot, Valerie Collot, Philippe R. Bovy
and Sylvain Raulta,p
a
 Â
Centre d'Etudes et de Recherche sur le Medicament de Normandie, UFR des Sciences Pharmaceutiques, 5 rue Vaubenard,
14032 Caen Cedex, France
b
Á
Sano®-Synthelabo Recherche, 10 rue des Carrieres, 92500 Rueil-Malmaison, France
Received 22 January 2002; revised 22 February 2002; accepted 11 March 2002
AbstractÐThis paper describes a general method for the synthesis and the isolation of novel 2,4, or 5-halopyridin-3-yl-boronic acids and
esters 4, 7, 10, 13, 15. These compounds are prepared taking into account a regioselective halogen±metal exchange using nBuLi or a
regioselective ortho-lithiation using lithium diisopropylamide and subsequent quenching with triisopropylborate starting from appropriate
mono or dihalopyridines. All substrates studied to date provided a single regioisomeric boronic acid or ester product. Additionally, these
compounds have been found to undergo Pd-catalyzed coupling with a range of arylhalides and authorize a strategy to produce new pyridines
libraries. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Aiming at studying mild and ¯exible strategies to design
new pyridines libraries, we focused on a general method
for the synthesis of new pyridinylboronic acids usable in
combinatorial approaches. For this reason, we particularly
studied the synthesis of new halopyridinylboronic acids
likely to offer a double reactivity, via their boronic moiety
and their halogen atom. We recently published the synthesis
and the isolation of novel 6-halopyridin-3-yl-boronic acids
and esters I1 and demonstrated that these compounds were
stable, easy to purify and to handle. In the second part of this
work, we now report the synthesis, the isolation and the
reactivity of new 2,4, or 5-halopyridin-3-yl-boronic acids
and esters II, III and IV.
The successful methods of preparation of 6-halopyridin-3-
yl-boronic acids and esters I prompted us to apply them to
the synthesis of various different isomers II, III and IV
bearing an halogen atom in 2, 4 or 5 position.
2.1. 2-Halopyridin-3-yl-boronic acids and esters
On these bases our ®rst attempts were carried out starting
from 2-chloro-3-bromopyridine 1 and 2-chloro-3-iodo-
pyridine 2 prepared according to reported procedures2,3
from 3-amino-2-chloropyridine.
Thus, bromine±lithium exchange and iodine±lithium
exchange4,5 were carried out in ether at 2788C with
q For Part 1, see Ref. 1.
Keywords: halopyridinylboronic acids; halogen±metal exchange; directed
ortho-metalation.
Corresponding author. Tel.: 133-2-31-93-41-69; fax: 133-2-31-93-11-
p
Scheme 1. Obtention of boronic acid 4a and ester 4b via HMe or via DoM.
88; e-mail: rault@pharmacie.unicaen.fr
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00283-1

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A. Bouillon et al. / Tetrahedron 58 (2002) 3323±3328
Table 1. Yields of halopyridinylboronic acids and esters, 4, 7 and 10
Compounds
2-X
3-X
Boronic acid
Yield (%)
Boronic ester
Yield (%)
1
2
3
5
6
9
Cl
Cl
Cl
Br
Br
F
Br
I
H
Br
H
H
4a
4a
4a
7a
7a
10a
66
62
63
60
45
63
4b
4b
4b
7b
7b
10b
70
68
65
56
53
58
nBuLi followed by the reaction with triisopropylborate,
known to give better results than other borates6 (Scheme 1).
2-chloro-3-lithiopyridine. Quenching this anion at low
temperature with triisopropylborate B(OiPr)3 gave the
expected boronic acid 4a carrying out the work-up avoiding
the formation of pyridinium salts. Performing the in situ
transesteri®cation with pinacol gave the corresponding
ester 4b in 65% yield (Table 1).
In order to obtain either the boronic acid or the correspond-
ing pinacol ester we used the same method as for 6-halo-
pyridin-3-yl-boronic acids and esters.1 At the end of the
reaction from 1 or 2, the boronic acid 4a was obtained
with 62±66% yield after a work-up avoiding the formation
of pyridinium salts. Namely, the mixture was quenched by
slow addition of 5% aqueous NaOH solution and the result-
ing aqueous layer neutralized by careful addition of aqueous
HCl to prevent protodeboronation.7 The boronic acid 4a is
stable, easy to purify and to handle as a white solid.
The same reactions were performed via halogen±metal
exchange (HMe) with 2,3-dibromopyridine 5, prepared
according to Scheme 2with 30% overall yield, or from
commercial 2-bromopyridine
metalation (DoM) (Scheme 3).
6 via directed ortho-
In the case of 2,3-dibromopyridine 5, conditions of the
reaction that are low temperature and slight excess of
nBuLi had to be strictly monitored in order not to induce
halogen dance.13 With these precautions, we were able to
isolate in moderate yields boronic acid 7a and, after trans-
esteri®cation the corresponding ester 7b (Scheme 3 and
Table 1).
On the other hand, considering the amphoteric character of
this acid which could be problematic for further use, we
studied the direct formation of its pinacol ester, using
Coudret's procedure.8 These conditions applied to 1 and 2
yielded 70 and 68%, respectively, of the corresponding
pinacol ester 4b (Scheme 1, Table 1).
Using the fact that the expected boronic moiety was in
ortho-position from the halogen atom, we also tried a
more direct method taking into account the fact that
ortho-lithiation of p-de®cient heterocycles is now fully
described.9,10 2-Chloropyridine 3 was easily and regio-
selectively deprotonated by lithium diisopropylamide
(LDA) at 2708C for 3 h in THF to give corresponding
2,3-disubstituted pyridines.11
The directed deprotonation of 2-bromopyridine 6 followed
by transmetalation has been described by Karig et al. for
aryl zinc preparation.14 The same conditions and further
quenching with B(OiPr)3 gave 7a in 45% yield and 7b in
53% yield.
As for ¯uoro isomers, the most reliable reported procedure15
for the preparation of 3-bromo-2-¯uoropyridine 8 uses
directed metalation of 2-¯uoropyridine followed by action
of bromine. Even if HMe has already been described on
3-bromo-2-¯uoropyridine 8 with good yields,16 we did not
A ®rst attempt of pyridylboronic acid synthesis was already
described by Achab et al.12 starting from 2,6-dichloro-
pyridine deprotonated by LDA in THF at 2788C and
quenched by trimethylborate. In our case, commercially
available 2-chloropyridine 3 was directly metalated in
ether (to make the lithiopyridine precipitate to improve
the conversion and make easier further treatment) at
2608C by one equivalent of LDA prepared in situ by the
action of nBuLi on diisopropylamine (Scheme 1). Lithiation
took place regioselectively at position 3 to afford the
Scheme 3. Obtention of 7a and 7b via HMe or DoM.
Scheme 2. Preparation of 2,3-dibromopyridine 5.
Scheme 4. Obtention of 10a and 10b via DoM.

A. Bouillon et al. / Tetrahedron 58 (2002) 3323±3328
3325
The versatility of this functionalization is enhanced by the
4-halogen reactivity toward various nucleophiles.
2.3. 5-Halopyridin-3-yl-boronic acids and esters
As far as 3,5-dihalogenopyridines are concerned, we per-
formed the HMe onto commercial 3,5-dibromopyridine 14
as already described.24,25 The now usual method gave success-
fully the boronic acid 15a and the ester 15b without changing
the conditions for HMe (nBuLi, ether, 2788C) (Scheme 6).
Scheme 5. Obtention of 13a and 13b.
Table 2. Yields of halopyridinylboronic acids and esters 13
Compounds
3-X
4-X
Boronic acid
Yield (%)
Boronic ester
Yield (%)
11
12
Br
H
Cl
Cl
13a
13a
25
43
13b
13b
20
41
want to multiply reaction steps, so we decided to prepare
pyridylboronic acid 10a and corresponding ester 10b by
action of LDA in ether at 2608C onto commercially
available 2-¯uoropyridine 9 (Scheme 4).
The yields were good as illustrated in Scheme 6, and no
disubstituted product was observed even with increased
proportions of nBuLi (2equiv.) or longer reaction time for
HMe (2h).
Directed ortho-lithiation of 2-¯uoropyridine has been
described with good yield17 using LDA. In our case the
yields given in Table 1 con®rmed that it was not necessary
to prepare 8 in order to have better yields. We thus obtained
already described18 10a in similar yields, although all the
other compounds are, to our knowledge, new ones.
This tends to prove that boronic acid and ester are fully
compatible with pyridine without the uncertainty caused
by the use of corresponding salts.26
2.4. Suzuki couplings
As illustrated in Scheme 7, the boronic acids a and the esters
b were ef®ciently coupled with sterically hindered, electron-
rich, or electron-poor aryl halides under standard Suzuki-
type conditions,27,28 furnishing a range of unknown biaryls
not easily accessible, as for example 16±18.
2.2. 4-Halopyridin-3-yl-boronic acids and esters
Another ®eld of interest concerns the potential effect of
halogens on the basic character of pyridine nitrogen. So,
we purposed two types of experiment to verify the stability
of these new types of pyridyl-boron derivatives. In fact, does
the inductive effect of an halogen atom change the pKa of
the pyridine nitrogen to avoid problems of stability due to
interactions between boron and amines?19
The yields for cross-coupling were generally good, and the
resulting arylpyridines 16±18 were isolated following
column chromatography. Interestingly, no `homocoupled'
products with halopyridin-3-yl-boronic acid or esters acting
as both the aryl boronic and aryl bromide fragments were
Thus, experiments were performed with 3-bromo-4-chloro-
pyridine 11 prepared according to reported procedure20
from 3-bromopyridine.
The boronic acid 13a and the corresponding ester 13b were
prepared by HMe with limited yields (Scheme 5, Table 2).
So, we really preferred to perform a DoM on 4-chloro-
pyridine 12. Indeed, this has been studied extensively21±23
and proceed with very great regioselectivity. Carrying out
the metalation by LDA in ether at 2608C gave medium
yields of stable compounds, proving that the effect of the
halogen does not play the role of base moderator.
Scheme 6. Obtention of 15 via HMe.
Scheme 7. Suzuki cross-couplings of pyridylboronic acids a or esters b.

3326
A. Bouillon et al. / Tetrahedron 58 (2002) 3323±3328
observed. A detailed study of these Suzuki cross-coupling
reactions will be published elsewhere.
58C. Extraction with ethyl acetate, evaporation of the
organic layer and recrystallization from Et2O gave pure
4a, 7a, 15a.
A discussion concerning the choice between the two
different approaches either HMe or DoM starting from
mono or polyhalogenated pyridines will be discussed at
the end of this general study.
3.2.1. 2-Chloro-3-pyridylboronic acid (4a). White solid;
mp 1608C. IR(KBr): 2979, 2930, 1582, 1562, 1451, 1387,
1
1255, 1101, 1041, 839, 799, 749, 659 cm21. H NMR (d6-
DMSO) d 8.53 (s, 2H), 8.33 (dd, Jˆ2.1, 4.8 Hz, 1H), 7.81
(dd, Jˆ2.1, 7.3 Hz, 1H), 7.33 (dd, Jˆ4.8, 7.3 Hz, 1H). 13C
NMR (d6-DMSO) d 152.4, 149.7, 143.1, 122.3. Anal. calcd
for C5H5BClNO2: C, 38.16; H, 3.20; N, 8.90. Found: C,
38.25; H, 3.12; N, 8.80.
It will be very important to recognize the dual role of such
compounds. Further experiments concerning the double
reactivity of these compounds are currently under investiga-
tion in order to use these new starting materials in the
production of new pyridine libraries. These results will be
published elsewhere.
3.2.2. 2-Bromo-3-pyridylboronic acid (7a). White solid;
dec 2108C. IR(KBr): 3096, 1585, 1552, 1415, 1380, 1340,
1130, 1083, 1024, 802, 738, 642 cm21 1H NMR (d6-
.
DMSO) d 8.63 (d, Jˆ2.0 Hz, 1H), 8.47 (s, 2H), 7.98 (dd,
Jˆ8.0, 2.0 Hz, 1H), 7.62 (d, Jˆ8 Hz, 1H). Anal. calcd for
C5H5BBrNO2: C, 29.76; H, 2.50; N, 6.94. Found: C, 29.82;
H, 2.37; N, 6.76.
3. Experimental
3.1. General procedures
Commercial reagents were used as received without addi-
tional puri®cation. Melting points were determined on a
Ko¯er melting point apparatus and are uncorrected. IR spec-
tra were taken with a Genesis Series FTIR spectrometer. 1H
NMR (400 MHz) and 13C NMR (100 MHz) were recorded
on a JEOL Lambda 400 Spectrometer. Chemical shifts are
expressed in parts per million down®eld from tetramethyl-
silane as an internal standard. The mass spectra (MS) were
taken on a JEOL JMS GCMate spectrometer at a ionizing
potential of 70 eV. Thin-layer chromatography (TLC) was
performed on 0.2mm precoated plates of silica gel 60F-264
(Merck). Visualization was made with ultraviolet light.
Column chromatography was carried out using silica gel
60 (0.063±0.2mm) (Merck). Elemental analyses for new
compounds were performed at the `Institut de Recherche
en Chimie Organique Fine' (Rouen).
3.2.3. 5-Bromo-3-pyridylboronic acid (15a). White solid;
dec 2108C. IR(KBr): 3083, 2958, 1578, 1545, 1433, 1410,
1355, 1318, 1286, 1185, 1096, 1037, 1011, 859, 758,
1
714 cm21. H NMR (d6-DMSO) d 8.81 (s, 1H), 8.70 (s,
1H), 8.56 (s, 2H), 8.26 (s, 1H). Anal. calcd for
C5H5BBrNO2: C, 29.76; H, 2.50; N, 6.94. Found: C,
29.92; H, 2.22; N, 7.11.
3.3. General procedure for the synthesis of pyridyl-
boronic acids via a DoM
To a slurry of freshly distilled diisopropylamine (1.2equiv.)
in 150 mL of anhydrous ether cooled to 08C was added
dropwise to a 2.5 M solution of nBuLi (1.25 equiv.). The
mixture was allowed to react at 08C during 30 min, and then
cooled to 2608C. A solution of halopyridine (1 equiv.) in
50 mL of anhydrous ether was then added dropwise in order
to keep the internal temperature at 2608C. The resulting
colored mixture was allowed to react at this temperature
over 45 min. A solution of triisopropylborate (1.25 equiv.)
in 50 mL of anhydrous ether was then added and the mixture
allowed to warm to room temperature and left to react for an
additional hour. The mixture was quenched by slow addi-
tion of 5% aqueous NaOH solution (150 mL). The resulting
aqueous layer was collected and acidi®ed to pH 6±7 by
dropwise addition of 3N HCl (<70 mL), keeping the inter-
nal temperature below 58C. Extraction with ethyl acetate,
evaporation of the organic layer and recrystallization from
Et2O gave pure 4a, 7a, 10a and 13a.
3-Bromo-2-chloropyridine, 2-chloro-5-iodopyridine and 3-
bromo-4-chloropyridine were prepared according to
reported procedures.2,3,20 2-Fluoropyridine and 2-chloro-
pyridine were purchased from Acros Organics and were
used without further puri®cation. 4-Chloropyridine hydro-
chloride was purchased from Acros Organics, dissolved in
sodium hydroxide and extracted with CH2Cl2. Drying the
organic phase with MgSO4, ®ltering and concentrating
under reduced pressure gave pure 4-chloropyridine which
was used immediately.
3.2. General procedure for the synthesis of
pyridylboronic acids via a HMe
To a slurry of 2.5 M solution of nBuLi (1.2equiv.) in
anhydrous ether (150 mL), cooled to 2788C, was added to
a solution of dihalopyridine (1 equiv.) in anhydrous ether
(100 mL). The resulting dark colored mixture was allowed
to react at this temperature over 1 h. A solution of triiso-
propylborate (1.2equiv.) in anhydrous ether was then added
in 10 min and the mixture allowed to warm to room
temperature and left to react for an additional hour. The
mixture was quenched by slow addition of 5% aqueous
NaOH solution (150 mL). The resulting aqueous layer was
collected and acidi®ed to pH 6±7 by dropwise addition of
3N HCl (<70 mL), keeping the internal temperature below
3.3.1. 2-Fluoro-3-pyridylboronic acid (10a). White solid;
mp 1728C. IR(KBr): 3390, 3100, 1602, 1570, 1405, 1309,
1163, 1066, 829, 755 cm21. 1H NMR (d6-DMSO) d 8.44 (s,
2H), 8.22 (dd, Jˆ4.4, 2.1 Hz, 1H), 8.06 (dq, Jˆ9.2, 7.2,
2.1 Hz, 1H), 7.29 (dq, Jˆ7.2, 4.4, 2.9 Hz, 1H). 13C NMR
(d6-DMSO)
d
165.5 (d, Jˆ229.6 Hz), 148.8 (d,
Jˆ14.8 Hz), 147.0 (d, Jˆ9.0 Hz), 121.4 (d, Jˆ4.1 Hz).
Anal. calcd for C5H5BFNO2: C, 42.62; H, 3.58; N, 9.94.
Found: C, 42.51; H, 3.38; N, 9.72.
3.3.2. 4-Chloro-3-pyridylboronic acid (13a). White solid;
mp 1608C. IR(KBr): 3390, 3100, 1602, 1570, 1405, 1309,

A. Bouillon et al. / Tetrahedron 58 (2002) 3323±3328
3327
1163, 1066, 829, 755 cm21. 1H NMR (d6-DMSO) d 8.59 (s,
2H), 8.52 (s, 1H), 8.46 (d, Jˆ5.4 Hz, 1H), 7.44 (d,
Jˆ5.4 Hz, 1H). Anal. calcd for C5H5BClNO2: C, 38.16;
H, 3.20; N, 8.90. Found: C, 38.44; H, 3.41; N, 8.62.
in 150 mL of anhydrous ether cooled to 08C was added
dropwise to a 2.5 M solution of nBuLi (1.25 equiv.). The
mixture was allowed to react at 08C during 30 min, and then
cooled to 2608C. At this time, a solution of halopyridine
(1 equiv.) in 50 mL of anhydrous ether was added dropwise
in order to keep the internal temperature at 2608C. The
resulting colored mixture was allowed to react at this
temperature over 45 min. A solution of triisopropylborate
(1.25 equiv.) in 50 mL of anhydrous ether was then added
and the mixture was allowed to warm to room temperature
and left to react for an additional hour. A solution of anhy-
drous pinacol (1.35 equiv.) in 75 mL of anhydrous ether was
added and, after 10 min, a solution of glacial acetic acid
(1.05 equiv.) in anhydrous ether (50 mL). The mixture
was allowed to react for 2h, then ®ltered through Celite,
and extracted by 5% aqueous NaOH solution (200 mL). The
resulting aqueous layer was collected and acidi®ed down to
pH 6±7 by dropwise addition of 3N HCl (<90 mL), keeping
the internal temperature below 58C. Extraction with ether,
evaporation of the ethereal layer and puri®cation by column
chromatography on silica gel for oils or recrystallization for
solids gave 4b, 7b, 15b, 10b and 13b.
3.4. General procedure for the synthesis of
pyridylboronic esters via a HMe
To a slurry of 2.5 M solution of nBuLi (1.2equiv.) in
150 mL of anhydrous ether, cooled to 2788C, was added
a solution of dihalopyridine (1 equiv.) in anhydrous ether
(100 mL). The resulting dark colored mixture was allowed
to react at this temperature over 1 h. A solution of triiso-
propylborate (1.2equiv.) in 50 mL of anhydrous ether was
then added dropwise and the mixture was allowed to warm
to room temperature and left to react for an additional hour.
A solution of anhydrous pinacol (1.35 equiv.) in 75 mL of
anhydrous ether was added and, after 10 min, a solution of
glacial acetic acid (1.05 equiv.) in anhydrous ether (50 mL).
The mixture was allowed to react for 2h, then ®ltered
through Celite, and extracted by 5% aqueous NaOH solution
(200 mL). The resulting aqueous layer was collected and
acidi®ed down to pH 6±7 by dropwise addition of 3N
HCl (<90 mL), keeping the internal temperature below
58C. Extraction with Et2O, evaporation of the ethereal
layer and puri®cation by column chromatography on silica
gel for oils or recrystallization for solids gave 4b, 7b and
15b.
3.5.1. 2-[3-(2-Fluoro)pyridine]-4,40,5,50-tetramethyl-1,3-
dioxaborolane (10b). Amber solid; mp ,508C. IR(KBr):
2981, 2935, 1602, 1565, 1423, 1361, 1323, 1212, 1146,
1128, 1046, 850, 817, 774, 665 cm21 1H NMR (d6-
.
DMSO) d 8.43 (d, Jˆ2.0 Hz, 1H), 8.16 (dt, Jˆ8.2,
2.1 Hz, 1H), 7.18 (dd, Jˆ8.2, 2.1 Hz, 1H), 1.29 (s, 12H).
13C NMR (d6-DMSO) d 166.1 (d, Jˆ240.2 Hz), 151.0 (d,
Jˆ14.8 Hz), 148.5 (d, Jˆ6.6 Hz), 121.8 (d, Jˆ4.1 Hz),
84.2, 24.6. Anal. calcd for C11H15BFNO2: C, 59.23; H,
6.78; N, 6.28. Found: C, 59.45; H, 6.90; N, 6.37.
3.4.1. 2-[3-(2-Chloro)pyridine]-4,40,5,50-tetramethyl-1,3-
dioxaborolane (4b). Amber solid; mp ,508C. IR(KBr):
2979, 2933, 1578, 1553, 1455, 1393, 1358, 1317, 1131,
1
1061, 1042, 857, 827, 755, 731, 668 cm21. H NMR (d6-
DMSO) d 8.46 (dd, Jˆ2.1, 4.8 Hz, 1H), 8.01 (dd, Jˆ2.1,
7.4 Hz, 1H), 7.41 (dd, Jˆ4.8, 7.4 Hz, 1H), 1.30 (s, 12H). 13C
NMR (d6-DMSO) d 154.3, 151.8, 145.8, 122.5, 84.4, 24.5.
Anal. calcd for C11H15BClNO2: C, 55.16; H, 6.31; N, 5.85.
Found: C, 55.32; H, 6.41; N, 6.03.
3.5.2. 2-[3-(4-Chloro)pyridine]-4,40,5,50-tetramethyl-1,3-
dioxaborolane (13b). White solid; mp 1208C. IR(KBr):
2969, 2925, 1597, 1553, 1450, 1397, 1156, 1034, 876,
1
826, 764, 660 cm21. H NMR (d6-DMSO) d 8.69 (s, 1H),
8.57 (d, Jˆ5.4 Hz, 1H), 7.51 (d, Jˆ5.4 Hz, 1H), 1.30 (s,
12H). 13C NMR (d6-DMSO) d 156.1, 152.9, 148.4, 124.8,
84.4, 24.6. Anal. calcd for C11H15BClNO2: C, 55.16; H,
6.31; N, 5.85. Found: C, 55.29; H, 6.41; N, 5.93.
3.4.2. 2-[3-(2-Bromo)pyridine]-4,40,5,50-tetramethyl-1,3-
dioxaborolane (7b). Yellow oil; IR(KBr): 2979, 2932,
1578, 1550, 1450, 1384, 1354, 1125, 1037, 962, 855, 824,
802, 747, 714, 667 cm21. 1H NMR (d6-DMSO) d 8.40 (dd,
Jˆ2.1, 4.8 Hz, 1H), 7.89 (dd, Jˆ2.1, 7.4 Hz, 1H), 7.42 (dd,
Jˆ4.8, 7.4 Hz, 1H), 1.29 (s, 12H). 13C NMR (d6-DMSO) d
152.2, 146.2, 145.3, 123.0, 84.8, 24.7. Anal. calcd for
C11H15BBrNO2: C, 46.53; H, 5.32; N, 4.93. Found: C,
46.65; H, 5.47; N, 4.88.
Acknowledgements
Â
The authors thank the Conseil Regional de Basse-
Â
Normandie and FEDER (Fonds Europeens de Developpe-
ment Economique Regional) for their ®nancial support.
Â
Â
3.4.3. 2-[3-(5-Bromo)pyridine]-4,40,5,50-tetramethyl-1,3-
dioxaborolane (15b). White solid; mp 608C; IR(KBr):
3084, 3038, 2975, 2927, 1578, 1435, 1409, 1354, 1318,
References
1
1286, 1184, 1106, 1037, 860, 735, 714 cm21. H NMR
(d6-DMSO) d 8.79 (s, 1H), 8.70 (s, 1H), 8.09 (s, 1H),
1.30 (s, 12H). 13C NMR (d6-DMSO) d 152.6, 152.5,
143.6, 120.4, 84.4, 24.5. Anal. calcd for C11H15BBrNO2:
C, 46.53; H, 5.32; N, 4.93. Found: C, 46.71; H, 5.48; N,
5.11.
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