Triazolopyridines. Part 25: Synthesis of new chiral ligands from [1,2,3]triazolo[1,5-a]pyridines

Article abstract of DOI:10.1016/j.tet.2007.07.101

The synthesis of new chiral triazolopyridine ligands possessing fluorescent properties is described. The triazolo ring opening was studied in order to obtain new chiral 2,6-disubstituted pyridines. A preliminary coordination assay with Zn(II) is also pres

Full text of DOI:10.1016/j.tet.2007.07.101

Tetrahedron 63 (2007) 10479–10485
Triazolopyridines. Part 25: Synthesis of new chiral ligands
from [1,2,3]triazolo[1,5-a]pyridines*
a,
Belen Abarca, Rafael Ballesteros, Rafael Ballesteros-Garrido,
a
a,b
*
ꢀ
Franc¸oise Colobertb, and Frederic R. Leroux
ꢀ ꢀ
b
*
a
´
Departamento de Quꢀımica Orgaꢀnica, Facultad de Farmacia, Universidad de Valencia, Avda. Vicente Andres Estelles s/n,
´
46100 Burjassot, Valencia, Spain
b
´ ´
Laboratoire de stereochimie associe au CNRS, Universite Louis Pasteur (ECPM), 25 rue Becquerel, 67089 Strasbourg, France
´
´
Received 4 July 2007; revised 20 July 2007; accepted 23 July 2007
Available online 2 August 2007
Abstract—The synthesis of new chiral triazolopyridine ligands possessing fluorescent properties is described. The triazolo ring opening was
studied in order to obtain new chiral 2,6-disubstituted pyridines. A preliminary coordination assay with Zn(II) is also presented.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
starting with 2b the unexpected reaction products reveal an
interesting structural feature. By an experimental (1H
NMR) and theoretical (DFT) studies,1,12 we have dem-
onstrated that there is a ring–chain–ring isomerization of
3-(2-pyridyl)-[1,2,3]triazolo[1,5-a]pyrid-7-ylderivatives (A)
into 6-{[1,2,3]triazolo[1,5-a]pyrid-3-yl}-2-pyridyl deriva-
tives (B). The A/B ratio depends on the electronic properties
of the substituent in the 7-position (Scheme 1). Electron-do-
nating substituents favour the A form, electron-withdrawing
substituents the B form, and only in the case where the sub-
stituent is a methyl group both forms are present (75% of A
and 25% of B).
The pyridine ring can be found as structural motif in a large
number of chiral ligands used in asymmetric catalysis,2 and
molecular recognition chemistry.3 Pyridines and 2,20-bipyr-
idines are common donor ligands.4 Jones and some of us
have reported on the synthesis of interesting 2,6-disubsti-
tuted pyridines5 and bipyridines,6 using [1,2,3]triazolo[1,5-
a]pyridines as synthons. We have also reported many aspects
of the chemistry of [1,2,3]triazolo[1,5-a]pyridines,7 their
fluorescent behaviour,8 application in the field of magnetic
materials9,10 and in the preparation of fluorescent sensors.11
However, there are no studies dealing with the preparation of
chiral triazolopyridines. Due to our interest in the chemistry
of triazolopyridines, we have now prepared new chiral com-
pounds possessing fluorescent properties. The triazolo ring
opening reaction affording chiral 2,6-disubstituted pyridines
has also been studied as well as a preliminary coordination
assay with Zn(II).
R
R
R
i
E
N
N
N
N
N
N
N
N
N
E
Li
2a, b
1a R = Me
1b R = 2-Pyridyl
i = n-BuLi, Toluene,-40 ºC, 15 min.
2. Results and discussion
N
N
We had reported that the regioselective metalation of
[1,2,3]triazolo[1,5-a]pyridines (1a and b) with n-BuLi in
toluene at ꢀ40 ꢁC gives the 7-lithioderivatives 2a and b,
which react subsequently with a number of electrophiles to
give 7-substituted triazolopyridines from 2a.5,6b However,
N
N
N
N
N
N
N
N
N
N
E
E
E
B
A
Scheme 1.
*
See Ref. 1.
Keywords: N-Heterocycles; Triazolopyridines; Chiral fluorescent ligands.
* Corresponding authors. Tel.: +34963544933; fax: +34963544939; e-mail:
belen.abarca@uv.es
Using this methodology and with chiral electrophiles such
as (ꢀ)-fenchone or (R)-(+)-menthyl-p-toluenesulfinate, we
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.07.101

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B. Abarca et al. / Tetrahedron 63 (2007) 10479–10485
have now obtained the corresponding chiral alcohols 3 (80%)
1
and 4 (in B form, evidenced by H, 13C NMR and COSY
N
N
experiments) (88%) as well as the chiral sulfoxides 5 and 6
(also in B form) (Scheme 2).
N
N
2a
N
Li
N
N
N
N
N
N
Nu
7
N
S
H
7
p-Tol
N
O
N
N
5
N
N
N
N
(-)fenchone
or
N
O
OH
N
N
N
Nu
N
R
N
OH
N
2b
N
4 (from 2b)
N
3 (from 2a)
N
Li
N
N
N
N
N
N
(R)- pTolS(O)OMenthyl
8
7
S
Li
H
p-Tol
O
N
N
N
6
2a R = Me
2b R = 2-Pyridyl
N
N
N
N
N
or
N
N
S
p-Tol
S
O
Scheme 3.
p-Tol
6 (from 2b)
O
5 (from 2a)
Scheme 2.
transcription proteins.19 Also, the role of Zn2+ in neurobio-
logy has received significant attention.20 In this regard, we
are interested to develop chemosensors for Zn2+ ions. In
a preliminary study, we have used the alcohol 4 to obtain
a Zn(II) complex by reaction with zinc chloride. FABMS
supports the formation of 1:1 [Zn(4)]2+–Cl2 aggregate. The
emissive property of the complex presents a bathochromic
shift of the fluorescence emission at 392 nm and 398 nm
(lexc 331 nm), which appears at 409 nm. Encouraged by
our preliminary results, we presently investigate the optical
properties of these new chiral ligands.
The alcohols 3 and 4 were formed as optically pure diaste-
reomers, as was evidenced by 1H NMR analysis. The prefer-
ential nucleophilic attack of 7-lithiotriazolopyridine to the
carbonyl group of fenchone from the sterically less hindered
side occurs according to the Felkin–Ahn model.13
Although chiral sulfoxides arevery important compounds for
asymmetric synthesis14 and asymmetric catalysis,15 the syn-
thesis of enantiomerically pure triazolopyridine sulfoxides
was so far unknown. Queguiner et al.16 had shown that sulf-
ꢀ
oxides of p-deficient heterocycles can be obtained with ex-
cellent enantiomeric excesses by the Andersen method,17
usingorganometallic intermediates and chiral menthyl-p-tol-
uenesulfinates as electrophiles. We have studied the reaction
of 7-lithio-triazolopyridines 2a and b with (R)-(+)-menthyl-
p-toluenesulfinate, employing either normal or reverse addi-
tion at ꢀ40 ꢁC under different concentrations using toluene
or tetrahydrofuran as solvent. The best conditions (see Exper-
imental 3), afforded 5 and 6 in a low yield of 20% and 16%,
respectively, with 97% ee (determined by HPLC). Concom-
itant formation of the dimerized compounds 7 (56%) and 8
(26%) was observed. Previously 76a and 81 were obtained
in lower yields as secondary compounds in lithiation reac-
tions. In our opinion the higher yield of dimerized side-prod-
ucts is due to a higher reactivity of in situ generated sulfoxide,
which reacts with the lithiated intermediates 2a and b by
nucleophilic substitution. This reactivity pattern is well
established in pyridine chemistry (Scheme 3).18
3-Substituted-[1,2,3]triazolo[1,5-a]pyridines react with
electrophiles by a triazol ring opening reaction with loss of
nitrogen yielding 2,6-disubstituted pyridines.21 We have
studied now the triazole ring opening reaction of the chiral al-
cohols 3 and 4 with the aim to obtain chiral 2,6-disubstituted
pyridines. The reactions were performed with acetic acid,
2.5 M sulfuric acid and selenium dioxide as electrophiles.
Treatment of compound 3 with aqueous sulfuric acid gave the
alcohol 9 (60%) as a diastereoisomeric mixture, de 5% (de-
termined by NMR), and with acetic acid, the acetate 11
(75%, de 5%) was obtained. The chiral fenchyl group is too
far from the triazolopyridine 3-position for chiral induction.
In both cases small quantities of the elimination product, the
vinylpyridine 10, was formed. Under the usual conditions for
treatment with selenium dioxide (i.e., 2.5 M sulfuric acid,
80 ꢁC, 24 h)21b no reaction was observed. However, in
p-xylene at reflux temperature, the known pyridine 1222
was obtained, probably due to a total oxidation followed by
decarboxylation of compound 13 (Scheme 4).
We had demonstrated that the conjugation of a triazolopyr-
idine group with an aryl or heteroaryl group gives highly ef-
ficient fluorescent compounds.8 Derivatives 4 and 6 are new
examples of fluorescent triazolopyridines. The alcohol 4
emitted at 409 nm and sulfoxide 6 at 387 nm and 404 nm
when excited at 331 nm in CHCl3 solution.
The alcohol 4 is more stable and does not react with sulfuric
acid, acetic acid or selenium dioxide under the conditions
described for reaction with 3. When 4 was treated with acetic
acid at reflux a diastereoisomeric mixture (de 3.5%) of ace-
tates 14 was obtained in 42% yield (Scheme 5).
Another interesting application of triazolopyridines is their
capacity to coordinate with metals, and behave as chemosen-
sors for metal ions or anionic species.11 The Zn2+ ion is an
essential component of many enzymes, and plays an impor-
tant role in maintaining the key structural features of gene
According to our hypothesis, the unusual stability of the
alcohol 4 can be explained by an intramolecular hydrogen
bond between the hydroxyl group and the lone pairs of the
pyridine and N3-triazole nitrogen atoms (in analogy to a

B. Abarca et al. / Tetrahedron 63 (2007) 10479–10485
10481
+
+
*R
*R
*R
N
*R
N
N
N
OAc
OH
11
10
9
10
(75%)
(17%)
(60%)
(10%)
CH3
N
H2SO4,
100 °C, 23 h
AcOH, 80 ºC, 5 h
N
N
SeO2 / H2SO4
80 ºC, 24 h
SeO2 / p-Xylene,
150 ºC, 72 h
OH
3
*R
*R
N
12
= *R
N
O
13
OH
(22%)
Scheme 4.
N
N
O
OH
R = H; H2SO4, 2.5M
24 h, 100 ºC
R = CH3; H2SO4, 2.5M
24 h, 100 ºC
N
N
+ 17 (38%)
N
R1
N
N
18 (13%)
R = H; AcOH
24 h, 80 ºC
N
4
R = H
15 R = CH3
OR
R = CH3; AcOH
50 h, 115 ºC
R = H; AcOH
6 h, 115 ºC
R = H
N
N
N
SeO2 / H2SO4
80 ºC, 24 h
+
O
OAc
OAc
N
N
N
N
O
R2
17 (60%)
= R2
OCH3
R2
16 (26%)
R1
14 (42%)
N
= R1
OH
R1
Scheme 5.
proton sponge).23 This hypothesis was supported by the
treatment of ether 15 with acetic acid at reflux. In this case,
the corresponding diastereoisomeric mixture (de 4%) of ac-
etates 16 (26%) and ketones 17 (60%) was obtained. Thermal
decomposition of diarylmethyl acetates to form ketones has
been reported.24 Reaction with sulfuric acid gave two ketone
products, 17 (38%) as major product (probably obtained by
oxidation of the initial alcohol intermediate) and the amazing
cyclofenchone 18 (13%). The formation of 18 can be ex-
plained by the formation, in acid media, of a norbornyl cation
as has been reported by Vonwiller25 in fenchyl chemistry.
The new chiral dipyridyl ketones 17 and 18 could be very in-
teresting compounds as building block in cluster chemistry.26
This possibility is currently under investigation.
AC300 MHz in CDCl3 as solvent. COSY experiments were
done for all compounds. HRMS (EI) determinations were
made using a VG Autospec Trio 1000 (Fisons). Ultraviolet
spectra were recorded on a Shimadzu UV-2101 instrument.
Fluorescence spectra were recorded on a Spectrofluorimeter
P.T.I. (Photon Technology International) instrument. Optical
rotation measurements were determined on a Perkin–Elmer
241 polarimeter at room temperature in CHCl3 solution.
HPLC determinations were done in a Waters HPLC system
with Mallinkrodt–Baker Chiralcel OD-H column. All the
lithiation reactions were done under inert atmosphere and
dry solvents.27
3-Methyl-[1,2,3]triazolo[1,5-a]pyridine 1a and 3-(2-pyr-
idyl)-[1,2,3]triazolo[1,5-a] pyridine 1b were prepared as
described elsewhere.28–30,6b
3. Experimental
3.1. General
3.2. General procedure for lithiation of
[1,2,3]triazolo[1,5-a]pyridines 1a and b
Melting points were determined on a Kofler heated stage and
are uncorrected. NMR spectra were recorded on a Bruker
To a solution of the corresponding [1,2,3]triazolo[1,5-a]pyr-
idines 1a and b (1 equiv) in anhydrous toluene at ꢀ40 ꢁC,

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B. Abarca et al. / Tetrahedron 63 (2007) 10479–10485
a solution of n-butyllithium in hexane (2.5 M) (1.1 equiv)
was added with stirring. A deep red colour developed. The
mixture was kept at ꢀ40 ꢁC (15 min).
3.4. Reaction with (R)-(D)-menthyl-p-toluenesulfinate
The lithiated triazolopyridines 2a and b were poured by
double-needle over a solution of (R)-(+)-menthyl-p-toluene-
sulfinate (1.5 equiv) in dry toluene (1.5 mL). The mixture
was left at ꢀ40 Cꢁ (2 h) and allowed at room temperature
overnight, a colour change to yellow was observed. Then it-
was treated with a saturated solution of ammonium chloride
(15 mL). The organic layer was separated and the aqueous
layer extracted with dichloromethane (3ꢂ20 mL). After dry-
ing over anhydrous Na2SO4 and evaporation of the organic
solvents, a residue was obtained. The residue was purified
by chromatotron using hexane/ethyl acetateas eluent, starting
material and menthol were obtained in the first fractions. The
amount of reactants and yields are given for each compound.
3.3. Reaction with (–)-fenchone
The corresponding mixture was treated with a dry toluene
solution (10 mL) of (ꢀ)-fenchone (excess) recently dis-
tilled. Then was left at ꢀ40 Cꢁ (2 h) and allowed at
room temperature overnight, a colour change to yellow
was observed. Then was treated with a saturated solution
of ammonium chloride (15 mL). The organic layer was
separated and the aqueous layer extracted with dichloro-
methane (3ꢂ20 mL). After drying over anhydrous
Na2SO4 and evaporation of the organic solvents, a residue
was obtained. The crude product was washed with hexane
and filtered. Purification by recrystallization from ethyl
acetate/hexane gave compounds 3 or 4 as white solids.
The amount of reactants and yields are given for each
compound.
3.4.1. (R)-3-Methyl-7-(toluene-4-sulfinyl)-[1,2,3]triazolo-
[1,5-a]pyridine 5. Compound 1a (153 mg, 1.15 mmol),
toluene (10 mL), n-BuLi (0.5 mL) and (R)-(+)-menthyl-
p-toluenesulfinate (490 mg). Compound 5 (60.5 mg, 20%)
was obtained as a white solid. Mp 145 ꢁC (AcOEt/Hex 1:7).
[a]2D0 +281.6 (c 0.39, CHCl3). HRMS found for M+
3.3.1. (1R,2S,4S)-1,3,3-Trimethyl-2-[70-(30-methyl[1,2,3]-
triazolo[1,5-a]pyridyl)]bicyclo[2.2.1]hept-2-ol 3. Com-
pound 1a (2 g, 15.03 mmol), toluene (120 mL), n-BuLi
(6.6 mL), (ꢀ)-fenchone (5 g). Compound 3 (3.8 g, 88%)
was obtained as a white solid. Mp 113 ꢁC (AcOEt/Hex
1:7). [a]2D0 ꢀ144.6 (c 1.2, CHCl3). HRMS found for M+
1
271.0778; C14H13N3OS requires 271.0779. H NMR d 7.89
(d, J¼8.2 Hz, 2H), 7.71 (dd, J1¼6.9 Hz, J2¼1 Hz, 1H), 7.65
(dd, J1¼8.9 Hz, J2¼1 Hz, 1H), 7.38 (dd, J1¼8.9 Hz,
J2¼6.9 Hz, 1H), 7.22 (d, J¼8.2 Hz, 2H), 2.58 (s, 3H), 2.30
(s, 3H). 13C NMR d 143.04 (C), 141.29 (C), 137.84 (C),
135.19 (C), 132.08 (CH), 129.92 (C), 126.28 (CH), 123.88
(CH), 118.88 (CH), 111.68 (CH), 21.47 (CH3), 10.35 (CH3).
EM (EI) m/z (%) 273 (3), 271 (40), 243 (63), 226 (35), 195
(30), 139 (100), 120 (36), 104 (60), 91 (42), 77 (67). 7,70-
Bis(3-methyl[1,2,3]triazolo[1,5-a]pyridine) 7 (81 mg, 56%)
was obtained as a fluorescent yellow solid mp 238–240 ꢁC.6a
1
285.1824; C17H23N3O requires 285.1841. H NMR d 7.44
(dd, J1¼7.8 Hz, J2¼1.8 Hz, 1H), 7.14 (dd, J1¼7.8 Hz,
J2¼7.2 Hz, 1H), 7.10 (dd, J1¼7.2 Hz, J2¼1.8 Hz, 1H),
6.67 (s, 1OH), 2.53–2.50 (m, 1H), 2.18 (dd, J1¼10.5 Hz,
J2¼2.1 Hz, 1H), 1.78–1.67 (m, 2H), 1.45–1.29 (m, 2H),
1.31 (s, 3H), 1.26 (s, 3H), 1.15 (ddd, J1¼12.6 Hz,
J2¼12.6 Hz, J3¼3.9 Hz, 1H), 0.24 (s, 3H). 13C NMR
d 141.16 (C), 133.83 (C), 132.74 (C), 123.60 (CH), 115.02
(C), 114.26 (CH), 83.62 (C), 51.86 (C), 48.87 (CH), 45.97
(C), 42.00 (CH2), 35.52 (CH2), 26.94 (CH2), 24.64 (CH3),
22.82 (CH3), 18.14 (CH3), 10.27 (CH3). UV lmax (log 3)
(CHCl3) 294 (4.89), 312 (4.72). EM (EI) m/z (%) 285 (50),
257 (58), 242 (23), 229 (50), 214 (28), 174 (41), 160 (55),
105 (62), 104 (100).
3.4.2. (R)-3-[6-(Toluene-4-sulfinyl)-pyridin-2-yl]-[1,2,3]-
triazolo[1,5-a]pyridine 6. Compound 1b (153 mg,
0.79 mmol), toluene (10 mL), n-BuLi (0.34 mL) and (R)-
(+)-menthyl-p-toluenesulfinate (345 mg). Compound
6
(41 mg, 15%) was obtained as a white solid. Mp 167–170 ꢁC
(AcOEt/Hex 1:7). [a]D20 +15.5 (c 1.2, CHCl3). HRMS found
for M+ 334.0904; C18H14N4OS requires 334.0888. 1H NMR
d 8.69 (d, J¼7.0 Hz, 1H), 8.37 (d, J¼8.9 Hz, 1H), 8.27
(dd, J1¼7.2 Hz, J2¼1.8 Hz, 1H), 7.91 (dd, J1¼7.1 Hz,
J2¼7.8 Hz, 1H), 7.88 (dd, J1¼7.8 Hz, J2¼1.8 Hz, 1H),
7.65 (d, J¼8.1 Hz, 2H), 7.33 (dd, J1¼7.0 Hz, J2¼8.9 Hz,
1H), 7.2 (d, J¼8.1 Hz, 2H), 7.0 (dd, J1¼7.0 Hz,
J2¼6.9 Hz, 1H), 2.30 (s, 3H). 13C NMR d 165.00 (C),
152.40 (C), 141.90 (C), 141.26 (C), 138.67 (CH), 136.16
(C), 132.19 (C), 129.93 (CH), 126.96 (CH), 125.42 (CH),
125.35 (CH), 121.19 (CH), 120.84 (CH), 116.74 (CH),
116.05 (CH), 21.82 (CH3). UV lmax (log 3) (CHCl3) 240
(4.45), 275 (4.42), 331 (4.46). EM (EI) m/z (%) 336 (3),
334 (40), 306 (75), 258 (65), 215 (10), 199 (5), 183 (86),
167 (100), 139 (80), 113 (20), 91 (44), 78 (47). 7,70-Bis(3-
(2-pyridyl)-[1,2,3]triazolo[1,5-a]pyridine) 8 (80 mg, 26%)
was obtained as a fluorescent yellow solid mp >300 ꢁC.1
3.3.2. (1R,2S,4S)-1,3,3-Trimethyl-2-(6-[1,2,3]triazolo-
[1,5-a]pyridin-3-yl-pyridin-2-yl)-bicyclo[2.2.1]hept-2-ol
4. Compound 1b (1.07 g, 8.7 mmol), toluene (80 mL), n-
BuLi (4 mL), (ꢀ)-fenchone (4 g). Compound 4 (2.46 g,
80%) was obtained as a white solid. Mp 144–146 ꢁC
(AcOEt/Hex 1:7). [a]D20 ꢀ69 (c 0.66, CHCl3). HRMS found
1
for M+ 348.1915; C21H24N4O requires 348.1950. H NMR
d 8.70 (d, J¼6.9 Hz, 1H), 8.34 (d, J¼7.9 Hz, 1H), 8.16 (d,
J¼8.3 Hz, 1H), 7.72 (dd, J1¼J2¼7.9 Hz, 1H), 7.40 (d,
J¼7.9 Hz, 1H), 7.32 (dd, J1¼6.9 Hz, J2¼8.3 Hz, 1H), 6.99
(dd, J1¼J2¼6.9 Hz, 1H), 5.89 (br s, 1OH), 2.35–2.15 (m,
2H), 1.90–1.75 (m, 1H), 1.50–1.41 (m, 1H), 1.33 (d,
J¼10.5 Hz, 1H), 1.20–1.18 (m, 1H), 1.00 (s, 6H), 0.82 (m,
1H), 0.45 (s, 3H). 13C NMR d 161.55 (C), 149.09 (C),
136.98 (C), 136.16 (CH), 131.56 (C), 126.80 (CH), 125.47
(CH), 121.56 (CH), 120.09 (CH), 118.54 (CH), 115.77
(CH), 84.07 (C), 55.77 (C), 48.81 (CH), 46.02 (C), 41.89
(CH2), 32.61 (CH2), 26.28 (CH3), 24.27 (CH2), 21.64
(CH3), 17.14 (CH3). UV lmax (log 3) (CHCl3) 290 (4.75),
313 (4.93), 324 (4.92). EM (EI): m/z (%) 348 (25), 320
(30), 292 (100), 169 (80).
3.5. (1R,2S,4S)-3-[6-(2-Methoxy-1,3,3-trimethyl-
bicyclo[2.2.1]hept-2-yl)pyridin-2-yl]-[1,2,3]triazolo-
[1,5-a]pyridine 15
To a stirred solution of 2-[6-([1,2,3]triazolo[1,5-a]pyridin-3-
yl)pyridin-2-yl]-1,3,3-trimethylbicyclo[2.2.1]heptan-2-ol 4

B. Abarca et al. / Tetrahedron 63 (2007) 10479–10485
10483
(348 mg, 1 mmol, 1 equiv) in THF (11 mL), NaH (100 mg,
4.10 mmol, 4.10 equiv) was added at 25 ꢁC. After being
stirred for 30 min, iodomethane (0.569 g, 4.00 mmol,
0.56 mL) was added, and the resulting mixture was stirred
for 16 h at 25 ꢁC, monitored by TLC. Then saturated aque-
ous NH4Cl (5 mL) solution was added to quench the reac-
tion, the resulting mixture was extracted with CH2Cl2
(3ꢂ50 mL). The organic extracts were combined, washed
with brine, dried over Na2SO4, filtered and concentrated.
Column chromatography (silica, ethyl acetate/cyclohexane
gradient) provided 0.343 mg (95%) of 15 as a white solid.
Mp 127–130 ꢁC. [a]D20 7.7 (c 1, CHCl3). HRMS found for
M+ 362.2096; C22H26N4O requires 362.2107. 1H NMR
d 8.81 (d, J¼9.07 Hz, 1H), 8.76 (d, J¼6.98 Hz, 1H), 8.26
(d, J¼7.80 Hz, 1H), 7.75 (dd. J1¼J2¼7.90 Hz, 1H), 7.41
(d, J¼7.93 Hz, 1H), 7.35 (dd. J1¼6.60 Hz, J2¼8.90 Hz,
1H), 7.03 (dd, J1¼J2¼6.64 Hz, 1H), 3.23 (s, 3H), 3.05 (d,
J¼8.61 Hz, 1H), 2.15 (m. 1H), 2.89 (m, 1H), 1.7 (d,
J¼4.21 Hz, 1H), 1.5 (m, 2H), 1.31 (m, 2H), 1.04 (s, 3H),
0.38 (s, 3H). 13C NMR d 162.4 (C), 149.8 (C), 138.2 (C),
136.1 (CH), 131.5 (C), 125.9 (CH), 125.3 (CH), 121.8
(CH), 121.0 (CH), 117.8 (CH), 115.6 (CH), 90.0 (C), 54.7
(OCH3), 52.3 (C), 48.8 (CH), 48.5 (C), 44.4 (CH2), 32,2
(CH2), 29.1 (CH3), 25.1 (CH2), 21.6 (CH3), 20.7 (CH3).
EM (EI) m/z (%) 362 (27), 347 (64), 319 (64), 281 (36),
221 (50), 195 (24), 168 (75), 167 (38), 81 (100), 78 (65).
(m, 2H), 1.33 (d, J¼10.2 Hz, 2H), 1.13 (ddd, J1¼J2¼
12.3 Hz, J3¼4.5 Hz, 2H), 0.99 (s, 3H), 0.98 (s, 3H), 0.97
(s, 3H), 0.95 (s, 3H), 0.38 (s, 3H), 0.35 (s, 3H). 13C NMR
d 170.22/170.14 (C), 161.84/161.82 (C), 157.34/157.25 (C),
135.88/135.57 (CH), 121.75/121.63 (CH), 117.73/117.63
(CH), 83.56 (C), 72.55/72.49 (C), 51.62/51.57 (CH), 48.76
(CH), 45.92 (C), 41.84/41.73 (CH3), 32.43/32.31 (CH2),
29.09 (CH2), 24.36/24.22 (CH2), 22.13 (CH), 21.19/21.15
(CH3), 20.84/20.48 (CH3), 20.36/20.22 (CH3), 17.11/17.08
(CH3). EM (EI) m/z (%) 317 (10), 236 (85), 176 (20), 81 (100).
3.6.2. (1R,2S,4S)-1,3,3-Trimethyl-2-(6-vinylpyridin-2-
yl)-bicyclo[2.2.1]hept-2-ol 10. Purified by chromatotron
with ethyl acetate/hexane (15 mg, 17% oil colourless).
HRMS found for M+ 257.1779; C17H23NO2 requires
257.1779. 1H NMR d 7.60 (dd, J1¼7.8 Hz, J2¼7.5 Hz,
1H), 7.39 (d, J¼7.8 Hz, 1H), 7.16 (d, J¼7.5 Hz, 1H), 6.76
(dd, J1¼17.4 Hz, J2¼12 Hz, 1H), 6.20 (dd, J1¼17.4 Hz,
J2¼1.5 Hz, 1H), 5.45 (dd, J1¼12 Hz, J2¼14.5 Hz, 1H),
2.32–2.15 (m, 2H), 1.87–1.7(m, 2H), 1.5–1.37 (m, 1H),
1.29 (dd, J1¼1.5 Hz, J2¼12 Hz, 1H), 1.18 (br s, 1OH),
1.06 (ddd, J1¼J2¼12.6 Hz, J3¼4.8 Hz, 2H), 0.92 (s, 3H),
0.90 (s, 6H), 0.39 (s, 3H). 13C NMR d 152.56 (C), 152.41
(C), 136.30 (CH), 135.64 (CH), 122.01 (CH), 119.07
(CH), 118.00 (CH2), 83.528 (C), 48.80 (CH), 45.96 (C),
42.01 (CH2), 32.52 (CH2), 29.69 (C), 29.29 (CH), 24.38
(CH2), 24.41 (CH3), 22.28 (CH3), 17.17 (CH3). EM (EI)
m/z (%) 257 (15), 242 (15), 229 (35), 176 (100), 160 (82),
153 (12), 104 (45), 81 (60), 77 (18).
3.6. General procedure for ring opening reactions of
triazolopyridines 3, 4 and 15 with AcOH
A solution of the corresponding triazolopyridine in glacial
acetic acid (10 mL) was heated (see conditions in Table 1).
The solution was neutralized with saturated aqueous solu-
tion of sodium bicarbonate and extracted with dichloro-
methane. The organic solvent was dried and evaporated.
The residue was purified by silica column chromatography
or chromatotron. The products, yields and conditions of pu-
rification are given for each compound.
3.6.3. [6-(2-Hydroxy-1,3,3-trimethylbicyclo[2.2.1]hept-
2-yl)pyridin-2-yl](pyridin-2-yl) methyl acetate 14.
Diastereomeric mixture 3.5% de (1R,2S,4S,10S) and
(1R,2S,4S,10R). Silica column chromatography eluted with
ethyl acetate/cyclohexane (91.1 mg, 42%, colourless oil).
HRMS found 380.2108 for M+; C23H28N2O3 requires
1
380.2100. H NMR d 8.53 (m, 2H), 7.67 (m, 4H), 7.51
(dd, J1¼J2¼8.0 Hz, 2H), 7.40 (m, 4H), 7.18 (m, 2H), 6.87
(s, 1H), 6.85 (s, 1H), 2.21 (s, 3H), 2.20 (s, 3H), 1.82–1.72
(m, 4H), 1.43 (m, 2H), 1.28 (m, 2H), 1.10 (m, 2H), 0.95
(s, 3H), 0.93 (s, 3H), 0.85 (s, 3H), 0.82 (s, 3H), 0.26 (s,
3H), 0.23 (s, 3H). 13C NMR d 169.9/169.9 (C), 157.9 (C),
155.0/154.9 (C), 149.3/149.2 (CH), 136.6 (CH), 136.1 (CH),
122.9/122.8 (CH), 122.5/122.2 (CH), 121.9/121.7 (CH),
119.8/119.2 (CH), 83.7 (C), 78.2 (CH), 48.1(CH), 46.0/
45.9 (C), 41.8 (CH3), 32.5/32.4 (CH2), 28.8/28.7 (CH3),
24.3 (CH2), 22.0/21.9 (CH3), 21.1/21.0 (CH3), 17.1/17.0
(CH). EM (EI) m/z (%) 380 (7), 321 (27), 320 (100), 299
(30), 292 (31), 283 (30).
3.6.1. 1-[6-(2-Hydroxy-1,3,3-trimethylbicyclo[2.2.1]hept-
2-yl)-pyridin-2-yl] ethyl acetate 11. Diastereomeric mix-
ture, 5% de (1R,2S,4S,10S) and (1R,2S,4S,10R). Purified by
chromatotron with ethyl acetate/hexane (132 mg, 75%, col-
ourless oil). HRMS found for M+ 317.1986; C19H27N3O
1
requires 317.1990. H NMR d 7.62 (dd, J1¼7.8 Hz, J2¼
7.5 Hz, 2H), 7.40 (d, J¼7.8 Hz, 1H), 7.41 (d, J¼7.8 Hz,
1H), 7.17 (d, J¼7.5 Hz, 1H), 7.16 (d, J¼7.5 Hz, 1H), 5.92–
5.84 (m, 2H), 2.35–2.20 (br m, 2H), 2.11 (s, 3H), 2.10 (s,
3H), 1.90–1.7 (m, 4H), 1.55 (d, J¼6.6 Hz, 6H), 1.51–1.41
Table 1
Starting material
(mg, mmol)
Reactant/solvent
t (h)/T (ꢁC)
Product (mg, %)
3 (102, 0.35)
3 (160, 0.56)
3 (100, 0.35)
3 (100, 0.35)
H2SO4/H2O
AcOH
SeO2/H2SO4
SeO2/p-xylene
23/100
5/80
24/80
72/140
9 (52, 60); 10 (10, 10)
11 (132, 75); 10 (15, 17)
No reaction
12 (18, 22)
4 (109, 0.30)
4 (110, 0.31)
4 (197, 0.57)
4 (100, 0.29)
H2SO4/H2O
AcOH
AcOH
24/100
24/80
6/115
No reaction
No reaction
14 (91, 42)
No reaction
SeO2/H2SO4
24/100
15 (150, 0.42)
15 (148, 0.40)
H2SO4/H2O
AcOH
24/100
50/115
18 (17, 13); 17 (55, 38)
16 (40, 26); 17 (83, 60)

10484
B. Abarca et al. / Tetrahedron 63 (2007) 10479–10485
3.6.4. [6-(2-Methoxy-1,3,3-trimethylbicyclo[2.2.1]hept-
2-yl)pyridin-2-yl](pyridin-2-yl) methyl acetate 16.
Diastereomeric mixture, 4% de (1R,2S,4S,10S) and
(1R,2S,4S,10R). Silica column chromatography eluted with
ethyl acetate/cyclohexane (40 mg, 26%, yellow oil).
HRMS found 394.2254 for M+; C24H30N2O3 requires
394.2256. 1H NMR d 8.54 (m, 2H), 7.69 (ddd, J1¼
J2¼7.71 Hz, J3¼1.75 Hz, 2H), 7.61 (dd, J1¼J2¼7.57 Hz,
2H), 7.57 (dd, J1¼J2¼8.80 Hz, 2H), 7.32 (dd, J1¼2.98 Hz,
J2¼7.64 Hz, 2H), 7.28 (d, J¼7.98 Hz, 2H), 7.17 (m, 2H),
6.91/6.89 (s, 2H), 3.12/3.11 (s, 6H), 2.51 (m, 2H), 2.21 (s,
6H), 2.05–1.96 (m, 2H), 1.83–1.73 (m, 2H), 1.54–1.36 (m,
4H), 1.18 (s, 3H), 1.15 (s, 3H), 1.12–1.07 (m, 2H), 1.00
(m, 2H), 0.92 (s, 6H), 0.08 (s, 3H), 0.05 (s, 3H). 13C NMR
d 170/169 (C), 162.3/162.2 (C), 158.5 (C), 155.6/155.5
(C), 149.9/149.0 (CH), 136.4 (CH), 136.0 (CH), 122.8/
122.7 (CH), 122.7/122.5 (CH), 122.0/121.9 (CH), 118.9/
118.7 (CH), 89.9 (C), 78.7/78.6 (CH), 54.6 (CH3), 52.4/
52.3 (C), 48.4/48.3 (C), 48.4 (CH3), 44.3/44.2 (CH2), 31.7
(CH2), 28.8/28.7 (CH3), 25.3 (CH2), 21.2/21.1 (CH3),
20.0/19.8 (CH3), 14.1 (CH). EM (EI) m/z (%) 394 (16),
380 (30), 379 (100), 319 (31), 314, (20), 313 (96).
(ddd, J1¼J2¼12.9 Hz, J3¼4.8 Hz, 2H), 1.00 (s, 3H), 0.99
(s, 3H), 0.98 (s, 6H), 0.40 (s, 3H), 0.39 (s, 3H). 13C NMR
d 162.11 (C), 161.19 (C), 136.62 (CH), 121.90/121.84
(CH), 117.71 (CH), 84.24 (C), 70.09/69.93 (CH), 52.45/
52.36 (C), 49.24 (CH), 46.47 (C), 42.39 (CH2), 32.92
(CH2), 29.55/29.52 (CH), 24.80/24.68 (CH2), 24.41 (CH3),
22.55 (CH3), 17.58 (CH3). EM (EI) m/z (%) 275 (8), 260
(12), 194 (100), 178 (71). In the first fraction 10 (10 mg,
10%) was obtained.
3.7.2. Pyridin-2-yl [6-(2,7,7-trimethyltricyclo[2,2,1,
2,6]hept-1-yl)pyridin-2-yl] methanone 18. Silica column
0
chromatography with ethyl acetate/cyclohexane as eluent.
Brown oil (17 mg, 13%). HRMS found for M+ 318.1733;
C21H22N2O requires 318.1732. 1H NMR d 8.73 (d, J¼
4.34 Hz, 1H), 8.06 (d, J¼7.82 Hz, 1H), 7.90 (dd, J1¼
7.67 Hz, J2¼0.98 Hz, 1H), 7.83 (ddd, J1¼J2¼7.71 Hz,
J3¼1.7 Hz, 1H), 7.74 (dd, J1¼J2¼7.79 Hz, 1H), 7.43 (m,
1H), 7.35 (dd, J1¼7.86 Hz, J2¼1.00 Hz, 1H), 1.82 (m,
2H), 1.53 (m, 1H), 1.40 (s, 1H), 1.32 (m, 1H), 1.22 (m, 1H),
1.07 (s, 3H), 1.00 (s, 3H), 0.86 (s, 3H). 13C NMR d 193.4
(C]O), 159.0 (C), 154.7 (C), 153.5 (C), 149.1 (CH),
136.0 (CH), 127.3 (CH), 127.2 (CH), 125.7 (CH), 125.6
(CH), 121.3 (CH), 46.8 (C), 44.1 (CH), 42.0 (C), 38.6 (CH2),
32.2 (CH2), 29.4 (C), 27.1 (CH3), 22.6 (CH3), 21.7 (CH3),
14.0 (CH). EM (EI) m/z (%) 318 (100), 303 (60), 277 (34),
212 (20), 78 (20). Further elution gave 17 (55.1 g, 38%).
3.6.5. (1R,2S,4S)-[6-(2-Methoxy-1,3,3-trimethylbicy-
clo[2.2.1]hept-2-yl)pyridin-2-yl](pyridin-2-yl) meth-
anone 17. Silica column chromatography eluted with ethyl
acetate/cyclohexane (83.1 mg, 60% colourless oil). HRMS
found for M+ 350.1995; C22H26N2O2 requires 350.1994.
1H NMR d 8.68 (m, 1H), 7.95 (dd, J1¼7.62 Hz, J2¼
1.09 Hz, 1H), 7.94–7.79 (m, 3H), 7.06 (dd, J1¼7.99 Hz,
J2¼1.10 Hz, 1H), 7.44–7.40 (m, 1H), 3.15 (s, 3H), 2.31
(m, 1H), 2.01 (m, 1H), 1.83–1.73 (m, 1H), 1.54–1.36 (m,
3H), 1.18 (s, 3H), 1.14–1.04 (m, 1H), 0.98 (s, 3H), 0.30 (s,
3H). 13C NMR d 194.4 (C]O), 162.2 (C), 155.8 (C),
152.5 (C), 148.9 (CH), 136.2 (CH), 136.1 (CH), 126.0 (CH),
125.3 (CH), 123.9 (CH), 121.6 (CH), 90.0 (C), 54.6 (CH3),
52.2 (C), 48.5 (C), 48.4 (CH3), 44.4 (CH2), 31.6 (CH2),
29.1 (CH3), 24.4 (CH2), 21.6 (CH3), 19.9 (CH3), 14.1 (CH).
EM (EI) m/z (%) 350 (13), 335 (50), 269 (100), 78 (18).
3.8. Ring opening reaction of triazolopyridines 3 and 4
with SeO2
Method A: a suspension of triazolopyridine 3 or 4 and sele-
nium dioxide (2 equiv) in sulfuric acid (10 mL, 2.5 M) was
heated (see conditions in Table 1). Method B: a suspension
of 3 and selenium dioxide (2 equiv) in p-xylene was heated
(see conditions in Table 1). Then the corresponding mixture
was filtered and the filtrate neutralized with a saturated aque-
ous solution of sodium hydrogencarbonate and extracted
with dichloromethane. The organic solvent was dried and
evaporated. The residue was purified by chromatotron to ob-
tain 12 (22%).
3.7. General procedure for ring opening reactions of
triazolopyridines 3, 4 and 15 with sulfuric acid
3.9. Synthesis of Zn(4)Cl2
A solution of the corresponding triazolopyridine in aqueous
sulfuric acid (10 mL, 2.5 M) was heated (see conditions
in Table 1). The solution was neutralized with a saturated
aqueous solution of sodium bicarbonate and extracted with
dichloromethane. The organic solvent was dried and evapo-
rated. The residue was purified by silica column chromato-
graphy or chromatotron. With 4 no reaction was observed.
The products, yields and conditions of purification are given
for each compound.
To a solution of (1R,2S,4S)-1,3,3-trimethyl-2-(6-[1,2,3]tri-
azolo[1,5-a]pyridin-3-yl-pyridin-2-yl)-bicyclo[2.2.1]hept-2-
ol 4 (50 mg, 0.14 mmol) in dichloromethane (20 mL), a solu-
tion of Cl2Zn in ether (0.15 mL, 1 M) was added. A yellow
solution was formed and was stirred (30 min) at room tem-
perature. Evaporation of the solvent gives a yellow oil that
was washed with hot ethyl acetate. The oil obtained has
1
identical H and 13C NMR in DMSO-d6 that the ligand 4.
HRMS (FAB) found for M+ 447.093; C21H24N4OClZn
requires 447.093. MS m/e (%) 454 (3), 453 (16), 452 (17),
451 (62), 450 (31), 449 (92), 448 (25), 447 (100). UV lmax
(log 3) (MeOH) 225 (2.5), 270 (2.47), 311 (2.56), 320 (2.57).
3.7.1. 2-[6-(1-Hydroxy-ethyl)-pyridin-2-yl]-1,3,3-trime-
thylbicyclo[2.2.1]hept-2-ol 9. Diastereomeric mixture 5%
de (1R,2S,4S,10S) and (1R,2S,4S,10R). Purified by chromato-
tron with ethyl acetate/hexane (52 mg, 60% colourless oil).
HRMS found for M+ 275.1889; C17H25NO2 requires
275.1885. 1H NMR d 7.65 (dd, J1¼7.8 Hz, J2¼7.5 Hz,
2H), 7.43 (d, J¼7.8 Hz, 2H), 7.18 (d, J¼7.5 Hz, 2H), 4.88
(d, J¼6.6 Hz, 2H), 3.2 (br s, 2OH), 2.28 (m, 4H), 1.87–
1.78 (m, 4H), 1.5 (d, J¼6.6 Hz, 3H), 1.49 (d, J¼6.6 Hz,
3H), 1.51–1.48 (m, 2H), 1.35 (d, J¼9.3 Hz, 2H), 1.17
Acknowledgements
ꢀ
We are much grateful to the Ministerio de Educacion y Cien-
cia (Spain) (Project CTQ2006-15672-C05-03) for its finan-
cial support, and to the SCSIE for the realization of the

B. Abarca et al. / Tetrahedron 63 (2007) 10479–10485
10485
18. (a) Kawai, T.; Furukawa, N.; Oae, S. Tetrahedron Lett. 1984,
25, 2549–2552; (b) Furukawa, N.; Shibutani, T.; Furihara, H.
Tetrahedron Lett. 1987, 28, 5845–5848; (c) Vinishi, J.;
Tanaka, T.; Wakabayashi, S.; Oae, S. Tetrahedron Lett. 1990,
31, 4625–4628; (d) Furukawa, N.; Ogawa, S.; Matsumura,
K.; Furihara, Y. H. J. Org. Chem. 1991, 56, 6341–6348; (e)
Shibutani, T.; Furihara, H.; Furukawa, N. Tetrahedron Lett.
1991, 32, 2947–2948.
19. (a) Vallee, B. L.; Falchuk, K. H. Physiol. Rev. 1993, 73, 79–
188; (b) Berg, J. M.; Shi, Y. Science 1996, 271, 1081–1085.
20. Bush, A. I. Curr. Opin. Chem. Biol. 2000, 4, 184–191.
21. (a) Jones, G.; Sliskovic, R.; Foster, B.; Rogers, J.; Smith, A. K.;
Wong, M. I.; Yarhan, A. C. J. Chem. Soc., Perkin Trans. 1 1981,
78–81; (b) Jones, G.; Mouat, D. J.; Tonkinson, D. J. Chem.
Soc., Perkin Trans. 1 1985, 2719–2723; (c) Abarca, B.;
Ballesteros, R.; Rodrigo, G.; Jones, G.; Veciana, J.; Vidal-
Gancedo, J. Tetrahedron 1998, 54, 9785–9790.
ꢁ
HRMS spectra. R.B.-G. wants to thank the Ministere de
l’Education Nationale, de la Recherche et de la Technologie
(France) for a predoctoral fellowship.
ꢀ
References and notes
1. Last part in the series: Abarca, B.; Ballesteros, R.; Chadlaoui,
M. Tetrahedron 2004, 60, 5785–5792.
2. Chelucci, G. Chem. Soc. Rev. 2006, 35, 1230–1243 and refer-
ences cited therein.
3. Lehn, J.-M. Supramolecular Chemistry, Concepts and
Perspectives; VCH: Weinheim, 1995.
4. (a) Reedijk, J. Comprehensive Coordination Chemistry;
Wilikinson, S. G., Ed.; Pergamon: London, 1987; Vol. 2; (b)
Constable, E. C. Metals and Ligand Reactivity; VCH: Weinheim,
1996.
5. Jones, G.; Sliskovic, R. J. Chem. Soc., Perkin Trans. 1 1982,
967–971.
22. Genov, M.; Kostova, K.; Dimitrov, V. Tetrahedron: Asymmetry
1997, 8, 1869–1876.
6. (a) Jones, G.; Pitman, M. A.; Lunt, E.; Lyghgoe, D. J.; Abarca,
B.; Ballesteros, R.; Elmasnouy, M. Tetrahedron 1997, 53,
8257–8268; (b) Abarca, B.; Ballesteros, R.; Elmasnaouy, M.
Tetrahedron 1998, 54, 15287–15292.
23. Staab, H. A.; Saupe, T. Angew. Chem., Int. Ed. Engl. 1988, 27,
865–879.
24. Pawel, J.; Serafinowski, M.; Garland, B. J. Am. Chem. Soc.
2003, 125, 962–965.
7. Abarca, B. J. Enzyme Inhib. Med. Chem. 2002, 17, 359–367
and references cited therein.
25. Scott, M.; Starling, S.; Vonwiller, C.; Joost, N.; Reek, H. J. Org.
Chem. 1998, 63, 2262–2272.
ꢀ
8. Abarca, B.; Aucejo, R.; Ballesteros, R.; Blanco, F.; Garcıa-
26. (a) Papaefstathiou, G. S.; Perlepes, S. P. Comments Inorg.
Chem. 2002, 23, 249–274; (b) Boudalis, A. K.; Donnadieu,
B.; Nastopoulos, V.; Clemente-Juan, J. M.; Mari, A.; Sanakis,
Y.; Tuchagues, J.-P.; Perlepes, S. P. Angew. Chem. 2004, 116,
2316–2320; Angew. Chem., Int. Ed. 2004, 43, 2266–2270; (c)
Tsohos, A.; Dionyssopoulou, S.; Raptopoulou, C. P.; Terzis,
A.; Bakalbassis, E. G.; Perlepes, S. P. Angew. Chem. 1999,
111, 1036–1038; Angew. Chem., Int. Ed. 1999, 38, 983–985;
(d) Papaefstathiou, G. S.; Perlepes, S. P.; Escuer, A.; Vicente,
R.; Font-Bardia, M.; Solans, X. Angew. Chem. 2001, 113,
908–910; Angew. Chem., Int. Ed. 2001, 40, 884–886; (e)
Papaefstathiou, G. S.; Escuer, A.; Vicente, R.; Font-Bardia,
M.; Solans, X.; Perlepes, S. P. Chem. Commun. 2001, 2414–
2415.
Espan˜a, E. Tetrahedron Lett. 2006, 47, 8101–8103.
9. Niel, V.; Gaspar, A. B.; Mun˜oz, M. C.; Abarca, B.; Ballesteros,
R.; Real, J. A. Inorg. Chem. 2003, 42, 4782–4788.
10. Boudalis, A. K.; Raptpoulo, C. P.; Abarca, B.; Ballesteros, R.;
Chadlaoui, M.; Tuchagues, J.-P.; Terzis, A. Angew. Chem., Int.
Ed. 2006, 45, 432–435.
ꢀ
11. Chadlaoui, M.; Abarca, B.; Ballesteros, R.; Ramırez de
ꢀ
Arellano, C.; Aguilar, J.; Aucejo, R.; Garcıa-Espan˜a, E.
J. Org. Chem. 2006, 71, 9030–9034.
12. Abarca, B.; Alkorta, I.; Ballesteros, R.; Blanco, F.; Chadlaoui,
M.; Elguero, J.; Mojarrad, F. Org. Biomol. Chem. 2005, 3,
3905–3910.
ꢀ
13. (a)Cherest, M.;Felkin, H.;Prudent, N.TetrahedronLett. 1968, 9,
2199–2204; (b) Ahn, N. T. Top. Curr. Chem. 1980, 88, 145–162.
ꢀ
14. Hanquet, G.; Colobert, F.; Lanners, S.; Solladie, G. Arkivoc
27. Perrin, D.; Armarego, L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: Oxford, 1988.
2003, 7, 328–401.
15. Pellissier, H. Tetrahedron 2007, 63, 1297–1330.
28. Boyer, J. H.; Borgers, R.; Wolford, L. T. J. Am. Chem. Soc.
1957, 79, 678–680.
ꢀ
16. Pollet, P.; Turk, A.; Ple, N.; Queguiner, G. J. Org. Chem. 1999,
ꢀ
29. Bower, J. D.; Ramage, G. R. J. Chem. Soc. 1957, 4506–4510.
30. Battaglia, L. P.; Carcelli, M.; Ferraro, F.; Mavilla, L.; Pellizzi,
C.; Pellizzi, G. J. Chem. Soc., Dalton Trans. 1994, 2651–
2654.
64, 4512–4515.
17. Andersen, K. K.; Gaffield, W.; Papanikolaou, N. E.; Foley,
J. W.; Perkins, R. I. J. Am. Chem. Soc. 1964, 86, 5637–5646.