Selective synthesis of mono- and distannylpyridines from chloropyridinols via an SRN1 mechanism

Article abstract of DOI:10.1016/j.jorganchem.2010.08.032

A selective two-step synthesis of either mono- or distannylated pyridines from commercially available pyridinols, involving its conversion to the corresponding diethyl pyridyl phosphates (pyDEP) followed by the reaction with Me₃SnNa in liquid ammonia, is described. The results obtained clearly indicate that the reactions proceed through an unimolecular radical nucleophilic substitution mechanism (S_RN1) with intermediacy of a monosubstitution product.

Full text of DOI:10.1016/j.jorganchem.2010.08.032

Journal of Organometallic Chemistry 695 (2010) 2578e2585
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Selective synthesis of mono- and distannylpyridines from chloropyridinols via
an SRN1 mechanism
,1
*
*
Gustavo F. Silbestri, Marcos J. Lo Fiego, María T. Lockhart , Alicia B. Chopa
INQUISUR, Departamento de Química, Universidad Nacional del Sur, Avenida Alem 1253, 8000 Bahía Blanca, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
A selective two-step synthesis of either mono- or distannylated pyridines from commercially available
pyridinols, involving its conversion to the corresponding diethyl pyridyl phosphates (pyDEP) followed by
the reaction with Me3SnNa in liquid ammonia, is described.
The results obtained clearly indicate that the reactions proceed through an unimolecular radical
nucleophilic substitution mechanism (SRN1) with intermediacy of a monosubstitution product.
Ó 2010 Elsevier B.V. All rights reserved.
Received 16 July 2010
Received in revised form
17 August 2010
Accepted 24 August 2010
Available online 23 September 2010
Dedicated to Professor Pelayo Camps on the
occasion of his 65th birthday.
Keywords:
Bis(trimethylstannyl)pyridines
Diethyl chloropyridyl phosphates
SRN
1
(Trimethylstannyl)pyridines
(Trimethylstannyl)sodium
1. Introduction
In connection with the synthetic importance of organotin
compounds, we are involved in searching new routes for their
Heterocyclic compounds are of great interest because of their
role as versatile building blocks in the synthesis of more complex
structures. Among them, pyridine is the most common heterocyclic
ring found in natural products [1] as well as in biologically active
compounds [2], and plays an extraordinary diverse role as chelating
ligand in transition metal chemistry [3]. These facts have made
functionalized pyridines attractive goals for synthesis over more
than three decades and justify continuous interest in the devel-
opment of new synthetic routes [4].
Over the past two decades the synthesis and application of
organotin intermediates has become a significant aspect in organic
heterocyclic chemistry. For example, much supramolecular archi-
tectures are based on ligands synthesized through a Stille-type
carbonecarbon bond-forming reaction [5]. This reaction has been
widely employed owing to its versatile nature, great functional
group toleration and better yields.
synthesis starting from cheap commercially available materials [6].
For example, we have demonstrated that arylstannanes could be
synthesized in excellent yields from phenols via the reaction of the
corresponding aryl diethyl phosphate (ArDEP) with organo-
stannides in liquid ammonia [6a,6d]. Taking into account this
background and the importance of finding new ways to synthesize
pyridylstannanes we started our study. We report here on the
significant results obtained as well as important mechanistic
aspects of the reaction of diverse diethyl pyridyl phosphates
towards trimethyltin sodium (Me3SnNa, 1) in liquid ammonia,
which open up a very efficient route to selective mono- and dis-
tannylated pyridine rings, versatile starting materials for the
tailor-made synthesis of more complex functionalized pyridine
structures.
2. Results and discussion
We chose inexpensive and commercially available pyridinols
and we synthesized the corresponding diethyl pyridyl phosphates
(pyDEP) used as starting materials (Chart 1).
* Corresponding authors. Tel.: þ54 291 4595100; fax: þ54 291 4595187.
E-mail addresses: teresa.lockhart@uns.edu.ar (M.T. Lockhart), abchopa@uns.edu.
ar (A.B. Chopa).
1
Member of CIC.
The results obtained are summarized in Table 1
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.08.032

G.F. Silbestri et al. / Journal of Organometallic Chemistry 695 (2010) 2578e2585
2579
concentration, so, we carried out a series of reactions with different
substrate concentrations using an insufficient amount of 1 (1:1
ratio, 30 min). The results obtained showed that even at lower
substrate concentration (3.12 mM) step 1 competes very efficiently
over step 2; thus, in all the experiments, compound 4a was
obtained as the main reaction product (69e74%) together with
minor amounts of 6a (5e9%) and no distannylated product 3a was
detected (entries 7e9). In order to confirm that 4a is an interme-
diate in the generation of 3a we carried out a reaction between 4a
and 1 (1:1 ratio). After 1 h under irradiation, the GC/MS showed
that 3a was the only reaction product.
The presence of 6a in both reactions carried out at short times
(entries 5 and 6) and in the reactions carried out with a defect of 1
(entries 4, 7e9) could be due to the hydrogen abstraction by C5
radical of 6a from ammonia. On the other hand, the presence of 2-
and 3-(trimethylstannyl)pyridine (5a and 5b) in experiment 1 is
probable due to the photostimulated reaction of 6a with 1, and to
the hydrogen abstraction of radical C6 of 5b from ammonia,
respectively. Nevertheless, these competitive reactions could be
considered worthless.
In general, similar results were obtained in the reactions carried
out between 2b and 1. Thus, under irradiation (2b/1, 1:2.2, 120 min)
the reaction rendered 2,6-bis(trimethylstannyl)pyridine (3b) as the
only product (96% of isolated product). While the analysis (GC/MS)
of the dark reaction of 2b with 1 (1:2.2) showed the presence of
diethyl 6-(trimethylstannyl)pyridin-2-yl phosphate (4b, 82%),
a similar reaction was totally inhibited by the addition of p-DNB
(20 mol %) (entries 11 and 12). These results enable us to say that, as
occurs with 2a, there is a spontaneous ET from 1 to 2b. Moreover,
when the irradiated reaction between 2b and 1 was quenched at
shorter times (30 min), a mixture of monostannylated pyridine 4b
and distannylated pyridine 3b was obtained in a 1:2.2 ratio,
demonstrating that 4b is an intermediate in the formation of 3b
(entry 13).
Chart 1.
It should be emphasized that we employed a special reaction
work-up in order to avoid the generation of undesired proto-
destannylation products during this step (see Experimental
Section).
Photostimulated reaction of 1 and 2a (1/2a, 2.2:1) proceeded
smoothly (30 min) rendering 2,5-bis(trimethylstannyl)pyridine
(3a) in 96% yield, together with tiny amounts of 2-(5a) and 3-tri-
methylstannylpyridine (5b)2 (4% and traces, respectively) (entry 1).
When this reaction was carried out in the dark (60 min), we found
that there was a spontaneous reaction between 1 and 2a giving, as
the only product, the monostannylated compound diethyl 5-(tri-
methylstannyl)pyridin-2-yl phosphate (4a) in a 98% yield of pure
compound (entry 2). It should be noted that no starting material
was detected and that this reaction was totally inhibited by the
addition of p-dinitrobenzene (p-DNB) (20 mol %), a well-known
inhibitor of radical anions [7], recovering starting substrate almost
quantitatively (entry 3). Taking into account that 4a could be really
useful as starting material in selective substitution reactions [8],
and with the aim of finding out if its synthesis was possible using
only one equivalent of 1 (in order to minimize waste material) we
carried out a dark reaction with a defect of 1 (4a/1, 1:1). Unfortu-
nately, the reaction rendered, even after 2 h, 4a in 63% yield
together with a considerable amount of remaining unreacted
starting material (21%) (GC/MS) (entry 4).
The fact that the reaction between 1 and 2a is stimulated by
irradiation and that the reaction in the dark is suppressed by p-
DNB, shows the radical-chain character of the substitution process.
Two extra reactions between 2a and 1 (1:2.2 ratio), quenched at
shorter times, showed that the yield of 3a progressively increased
with time at the expense of 4a, being 3a the main product after
30 min (entries 1, 5 and 6).
Upon these results we are able to say that 4a is an intermediate
in the synthesis of 3a, chlorine is the first nucleofuge replaced in
the reaction3 and the reaction occurs by the SRN1 mechanism,
through two propagation cycles, as sketched in Scheme 1. The
positive dark reaction supports a spontaneous electron transfer
(ET) from the anion 1 to the substrate.
In order to analyze the effect of substrate concentration on the
competition between steps 1 and 2, we carried out experiments 14
and 15. The results obtained showed that meanwhile at higher
substrate concentration (12.50 mM) compound 4b was the only
product (100%) (step 1 prevailed effectively over step 2), at general
substrate concentration (6.25 mM) step 2 competes with step 1 and
a mixture of 3b/4b (0.8:1) was obtained.
With the main goal of finding optimal reaction conditions for
the synthesis of 4b using only one equivalent of 1, we also carried
out the dark experiment 16. With pleasure we found that the
reaction rendered 4b in very high yield (94% of isolated product).
The reactions carried out between compound 2c and 1 also
support an SRN1 mechanism with intermediacy of a mono-
substitution product. The presence of a considerable amount of 5b
(11%) in the product mixture obtained in the photostimulated
reaction (entry 17) could be due either to the photostimulated
reaction of 6b with 1, or to the hydrogen abstraction of C5 radical of
5b from ammonia. In order to minimize the formation of
compound 5b, which difficult the purification of 3c diminishing its
isolated yield, we carried out a reaction employing an excess of 1
(2c/1, 1:5) (entry 18). We found that under these reaction condi-
tions the yield of 3c was improved (90%) and the amount of 5b
diminished. These results would be probably due to the fact that an
excess of 1 increased the rate of the bimolecular reaction between
the C5 radical of 6b and/or the C6 radical of 5b with 1 leading at last
to the disubstitution product 3c. It should be mentioned that in the
dark, although there was a slow reaction which was inhibited by
p-DNB, it was not possible to obtain significant amounts of mon-
ostannylated compound 4c, rendering large amounts of 6b (entries
20 and 21). On the other hand, the photostimulated reaction of 2c
The radical anion 4a$ꢀ may go through two competitive reac-
tions: electron transfer to 2a rendering the monosubstituted
product 4a (step 1) or the expulsion of diethyl phosphate anion,
generating the C6 radical of 5b (step 2) which at the end leads to
the distannylated pyridine 3a. As compound 4a is an intermediate,
step 1 must be faster than step 2 under the reaction conditions. In
a second cycle, compound 4a reacts with 1 leading at last to 3a.
Taking into account that step 1 is bimolecular and step 2 is
unimolecular, the products ratio should depend on the substrate
2
Identified by their retention times (GC/MS).
This is in accord with the fact that chlorobenzene is more reactive than diethyl
3
phenyl phosphate towards 1 in liquid ammonia. Unpublished results.
and 1 (1:1 ratio), at higher substrate concentration, led to

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G.F. Silbestri et al. / Journal of Organometallic Chemistry 695 (2010) 2578e2585
Table 1
Reactions of 2aee towards Me3SnNa (1) in liquid ammonia.
Y
Me3Sn
Me3Sn
Me3SnNa(1) / NH3 (l)
X
SnMe3
DEP
SnMe3
DEP
+
+
+
Conditions
N
N
N
N
N
6a (2-DEP)
6b (3-DEP)
2a, X=2-DEP, Y=5-Cl
2b, X=2-DEP, Y=6-Cl
2c, X=3-DEP, Y=5-Cl
2d, X=2-Cl, Y=3-DEP
2e, X=2-DEP, Y=3-DEP
3a-d
4a (2-DEP, 5-SnMe3)
4b (2-DEP, 6-SnMe3)
4c (3-DEP, 5-SnMe3)
4d (2-SnMe3, 3-DEP)
4e (2-DEP, 3-SnMe3)
5a (2-SnMe3)
5b (3-SnMe3)
Entrya
Substrateb
Conditions, time (min)
Products (%)c
(Me3Sn)2py
(Me3Sn)pyDEP
pySnMe3
pyDEP
1
2a
2a
2a
2a
2a
2a
2a
2a
2a
2b
2b
2b
2b
2b
2b
2b
2c
2c
2c
2c
2c
2c
2c
2d
2d
2d
2d
2d
2e
2e
2e
2e
2e
h
n
, 30
3a, 96 (87)
e
e
5a, 4; 5b, traces
e
e
2
Dark, 60
Dark, p-DNB, 60
Dark, 120
4a, 100 (98)
e
e
3d
e
e
e
4e
e
4a, 63
4a, 92
4a, 24
4a, 70
4a, 74
4a, 69
e
6a, 2
6a, traces
6a, 4
6a, 6
6a, 9
6a, 5
5
hn
hn
hn
hn
hn
hn
, 5
e
e
6
, 15
, 30
, 30
, 30
, 120
3a, 72
e
e
7e
e
8e,f
9e,g
10
e
e
e
e
3b, 100 (96)
e
e
e
e
11
Dark, 10
Dark, p-DNB, 10
4b, 82 (74)
e
e
e
12d
13
e
e
e
hn
hn
hn
, 30
, 60
, 60
3b, 31
3b, 45
4b, 69
4b, 55
4b, 100 (94)
4b, 100 (94)
e
e
14e
15e,g
16e
17
e
e
e
e
e
Dark, 10
e
e
e
hn
hn
hn
, 60
, 60
, 10
3c, 79 (69)
3c, 90 (84)
3c, 16
e
e
5b, 11
5b, 7
5b, 5
e
e
18h
19
20
e
e
4c, 72
4c, 34
6b, 6
6b, 44
Dark, 60
Dark, p-DNB, 60
21d
22e
23e,g
24
e
e
e
e
hn
hn
hn
, 60
, 60
, 20
3c, 53
e
4c, 38
4c, 89 (80)
5b, 9
e
6b, traces
6b, 8
3d, 90 (84)
e
e
5a, 3; 5b, traces
e
e
25e
26d
27e
28e,g
29
Dark, 30
Dark, p-DNB, 30
4d, 90 (86)
e
6b, traces
e
e
e
hn
hn
hn
hn
hn
, 30
, 30
, 180
, 15
, 180
3d, 23
e
4d, 62
4d, 94 (89)
5a, 5
e
e
6b, 3
e
3d, 65
e
e
5a, 16; 5b, 10
e
30
4d, traces; 4e, 7
e
6a, 3; 6b, 2
e
31h
32i
33e,g
a
3d, 62
e
5a, 19; 5b, 10
e
Dark, 180
, 180
e
e
hn
3d, 6
4d, 17; 4e, 39
5a, 7; 5b, traces
6a, 18; 6b, 6
All reactions were conducted at molar ratio of substrate/1 [ 1:2.2 unless otherwise stated.
[substrate] ¼ 6.25 mM unless otherwise stated.
b
c
d
e
f
Determined by GC/MS; isolated yields between parentheses as an average of at lest three independent runs.
p-DNB added, 20 mol %. Starting substrate was recovered.
Molar ratio of substrate/1 ¼ 1:1.
[substrate] ¼ 3.12 mM.
g
h
i
[substrate] ¼ 12.50 mM.
Molar ratio of 2c/1 ¼ 1:5.
2e was recovered.
compound 4c (89%) accompanied with an 8% of 6b (entry 23)
confirming, once more, the prevalence of step 1 over step 2 under
these reaction conditions. On the other hand, at lower concentra-
tion, the reaction of 2c and 1 (1:1 ratio) rendered a mixture of 3c/4c
in a 1.4:1 ratio, confirming the competition between steps 1 and 2
(entry 22).
amounts of the secondary products 5a, 5b and 6b. On the other
hand, the photostimulated reaction of 2e with 1 (1:2.2, 180 min)
rendered product 3d in 65% yield, together with significant
amounts of the undesired products 5a (16%) and 5b (10%) (entry
29). The use of an excess of 1 (2e/1, 1:5) did not produced an
increment on 3d yield (entry 31). It should be mentioned that when
the reaction was quenched at shorter reaction time (15 min) there
was detected diethyl 3-(trimethylstannyl)pyridin-2-yl phosphate
(4e) as the main monostannylated product supporting the prefer-
ential expulsion of the DEP anion from position 3 rather than
position 2 (entry 30). These results are sustained by the different
reactivity previously shown by 2-, 3- and 4-pyridinyl phosphates
towards 1 [6d]. Keeping in mind the results obtained in the
The results summarized in experiments 24e33 point out that
the reactions of either 2d or 2e with 1 also go through an SRN
1
mechanism with intermediacy of monosubstitution products.
Nevertheless, there are some divergences. The reactions carried out
between 2d and 1 rendered either distannylated pyridine 3d (entry
24) or monostannylated pyridine 4d (entries 25 and 28) in high
yields (90%, 90% and 94%, respectively), being detected insignificant

G.F. Silbestri et al. / Journal of Organometallic Chemistry 695 (2010) 2578e2585
2581
undesired secondary product 6a is a consequence of the lower
reactivity of the C5 radical of 6a towards anion 1 which can be
attributed to its lower electrophilicity [7].
The evaluation of the products distribution obtained in the dark
reactions of the different substrates could allow us to link the
reactivity of the diverse radicals towards 1 with this distribution
and, in particular, the effect exerted by the DEP substituent at
different positions of the ring. For this purpose we compare those
reactions that generate radicals on C3 or on C2 of the pyridine ring
(Scheme 2).
For example, the results obtained in experiments 2 and 20
(Table 1) show that the C5 radical of 6b has a lower reactivity
towards 1 comparing with that of the C5 radical of 6a, i.e., larger
amounts of 6b were obtained in experiment 20 confirming that the
relative position of the DEP substituent affect the electrophilicity of
these pyridin-3-yl radicals. On the other hand, a comparison of
experiments 16 and 25 (Table 1) shows that there is not an
appreciable difference between the reactivity of both C6 radical of
6a and C2 radical of 6b and the coupling reaction with 1 competes
efficiently with the proton abstraction.
Also, the SRN1 reaction of nucleophiles with substrates sup-
porting two nucleofugal substituents afford either mono-
substitution or disubstitution product depending on the structure
of the substrate, the nature of the nucleofugal group or the nucle-
ophile [7]. Moreover, the product ratio must be controlled by the
rate of fragmentation. Córsico and Rossi have reported the reaction
of 2,5-, 2,6- and 3,5-dichloropyridines towards 1 in liquid ammonia
[10], and they did not mention the existence of monosubstitution
products as intermediates. Therefore, the different reactivity shown
by chloropyridyl phosphates 2a, 2b and 2c with that shown by the
equivalent dichloropyridines is a consequence of the nature of the
nucleofugal groups and may be due to the different rate of frag-
mentation of a CeCl bond comparing with a C-DEP bond. The
intermediate radical anion expels the halide faster than it transfers
an electron to the substrate rendering the disubstitution product
(step 2 is faster than step 1 in Scheme 1).
In previous works we have found that meanwhile the reaction of
Scheme 1. Proposed mechanistic pathways in the SRN1 reaction of 2a towards 1 in
liquid ammonia.
diethyl 2-chlorophenyl phosphate with
1
afforded the
reactions performed at large substrate concentrations and with the
main goal of finding optimal reaction conditions for the synthesis of
4e, we carried out experiment 33. Unfortunately, the expulsion of
the DEP anion from carbon 3 did not compete efficiently with its
expulsion from carbon 2 and we obtained a mixture of isomeric
monosubstituted pyridines 4d and 4e in a 1/2.3 ratio, together with
considerable amounts of 6a (18%) and 6b (6%). It should be
mentioned that, as we expected [9], the dark reaction of substrate
2e with 1 was negative and starting substrate was completely
recovered (entry 32).
A comparison of the results obtained in experiments 24 and 29
suggests that 2d is more reactive than 2e toward 1 under those
reaction conditions. Probably, the different reactivity is due to the
fact that chloride is a better leaving group compared with diethyl
phosphate anion, affecting the rate of formation of the first pyr-
idinyl radical.
It is known that the success of a chain reaction depends on the
competition between the chain propagation steps and the termi-
nation steps. This competition depends on the rates of the different
propagation steps [7].
An analysis of Scheme 1 shows that the C5 radical of 6a, formed
by elimination of the first nucleofuge, may go through two
competitive reactions, that is, hydrogen abstraction from the
solvent, rendering 6a, or coupling reaction with nucleophile 1,
continuing with the propagation cycle. Thus, the generation of
Scheme 2. pyDEP radicals.

2582
G.F. Silbestri et al. / Journal of Organometallic Chemistry 695 (2010) 2578e2585
substrates. In addition, it is important to mention that many
substituents are compatible with the SRN1 mechanism [7], hence,
the range of functionality would be constrained to the availability of
the coupling partners.
We can affirm that all the pyridylstannanes obtained are
potential synthetic intermediates for a vast number of changes
through organotin chemistry.
Scheme 3. Synthetic strategy for aromatic bifunctionalization by sequential SRN1-SEA
reactions.
4. Experimental
corresponding disubstitution product with intermediacy of a mon-
osubstitution product [6c], isomers 1,3- and 1,4-rendered the dis-
ubstitution product without intermediates [6d]. We considered
that the different reactivity was governed by the rate of fragmen-
tation of the intermediate radical anions and that these different
rates of fragmentation were probably due to different spin densities
at the 2-, 3-, and 4-carbon atoms. The results reported now with
analogous pyridine derivatives are an interesting example of the
influence of the nature of the aromatic core. All the reactions go
through two propagation cycles independently of the relative
positions of the nucleofugal groups, indicating the preferential ET
to the substrate rather than the expulsion of the nucleofuge.
4.1. General considerations
All manipulations were performed under nitrogen or argon. The
solvents used were dried and distilled in accordance with standard
procedures. Irradiation was conducted in a reactor made of Pyrex,
equipped with four 250 W UV lamps emitting maximally at 350 nm
(water-refrigerated). Compounds described in the literature were
characterized by comparing their 1H and 13C NMR spectra, and
melting points (mp) to the previously reported data. Unknown
compounds were purified and analyzed from a single run and, then,
were repeated to determine an average yield. They were charac-
terized by 1H NMR, 13C NMR, MS, mp and elemental analysis. Flash
chromatography was performed over silica gel 60, 40e63 mm.
3. Conclusions
Melting points were determined on a ReicherteKofler hot-stage
microscope and are uncorrected. NMR spectra were recorded in
CDCl3 on a 300 MHz spectrometer (300.1 MHz for 1H, 75.5 MHz for
The overall results obtained are important not only from
a mechanistic but also from a synthetic point of view.
119
13C, 121.5 MHz for 31P and 111.9 MHz for Sn) at 23 ꢁC. Chemical
First, experimental results strongly suggest that the reactions go
through an SRN1 mechanism with intermediacy of a mono-
substitution product whatever the relative positions of both
nucleofuges, which is not a common process in SRN1 mechanism.
Moreover, there are fewer reports related to this special mechanism
involved with heteroaromatic systems [7].
Second, we have developed an efficient and simple two-step
approach for the selective synthesis of bistannylated pyridines from
inexpensive and commercially available pyridinols, being this
a practical alternative to the existing methodologies of synthesis:
reaction of 1 with dihalopyridines, in dimethoxyethane without
irradiation [11], or in liquid ammonia under irradiation [10]. It
should be emphasized that the side products formed by reduction
of the radicals were kept at a minimum (with one exception) and,
as a consequence, the yields of isolated distannylpyridines were
increased.4
shifts (
Me4Sn (119Sn) or PPh3
Mass spectra were obtained with a GC/MS instrument (HP5-MS
m) equipped with 5972
d
) are given in ppm downfield relative to TMS (1H and 13C),
(
31P) and coupling constants (J) are in Hz.
capillary column, 30 m ꢂ 0.25 mm ꢂ 0.25
m
mass selective detector operating at 70 eV (EI). Program: 50 ꢁC for
2 min with increase 10 ꢁC/min to 280 ꢁC. Most of the reagents and
catalyst were commercially available. Diethyl pyridinyl phosphates
were prepared by the method of Kenner and Williams [14] and
characterized by IR5 and NMR spectroscopy, and used without
further purification.
To carry out the reactions in dark, the reaction flask was
wrapped with aluminium foil.
4.2. Synthesis of starting diethyl pyridinyl phosphates
4.2.1. Diethyl 5-chloropyridin-2-yl phosphate (2a)
Moreover, the special reactivity shown by the different starting
substrates towards 1 allows us to find optimal reaction conditions
for the chimioselective monostannylation of the pyridine ring.
Thus, we synthesized a series of new isomeric stannylpyridyl
phosphate esters (4aed) in excellent yields (80e98%), which
should prove to be valuable intermediates for the unsymmetrical
substitution of the pyridine ring as is resumed in Scheme 3.
It is known that a heteroaryletin bond is highly reactive towards
diverse electrophiles [12]. For instance, these compounds would be
suitable intermediates for Stille cross-coupling reactions leading to
a broad range of asymmetric functionalized pyridines [13]. The
organic synthetic strategy resumed in Scheme 3 is based on the
successive selective substitution of a leaving group with a trime-
thyltin group followed by a Pd-catalyzed cross-coupling reaction or
a simple electrophilic substitution, avoiding protection and depro-
tection steps [8]. All the reactions involved are chimioselective;
therefore, it would be possible to synthesize tailored bi-, tri- and
polyheteroaryl materials by choosing the appropriate starting
Kenner’s method was employed for the reaction of 5-chlor-
opyridin-2-ol (5.0 mmol, 0.645 g) with diethyl hydrogen phosphite
(5.2 mmol, 0.670 mL) and triethylamine (5.2 mmol, 0.785 mL) in
CCl4 (3 mL) as solvent. The title compound was obtained as a pale
yellow liquid (0.795 g, 3.0 mmol, 60%); 1H NMR:
d 8.20e8.13 (m,
1H); 7.70e7.62 (m, 1H); 6.96 (m, 1H); 4.33e4.17 (m, 4H); 1.38e1.28
(m, 6H). 13C NMR:
d
155.5 (2JCP ¼ 5.9 Hz, C); 145.8 (CH); 139.2 (CH);
127.8 (C); 113.9 (3JCP ¼ 6.4 Hz, CH); 64.3 (2JCP ¼ 5.3 Hz, CH2); 15.5
(3JCP ¼ 6.7 Hz, CH3). 31P NMR:
d 43.23. MS (m/z, relative intensity):
265 (6, Mþ), 237 [2, (M ꢀ 28)þ] 210 (7), 192 (20), 156 (21), 139 (39),
129 (100), 112 (17), 101 (34), 81 (29). Anal. Calcd. for C9H13ClNO4P
(265.63): C 40.69; H 4.93; N 5.27. Found: C 40.80; H 4.95; N 5.25.
4.2.2. Diethyl 6-chloropyridin-2-yl phosphate (2b)
Kenner’s method was employed for the reaction of 6-chlor-
opyridin-2-ol (5.0 mmol, 0.645 g) with diethyl hydrogen phosphite
(5.2 mmol, 0.670 mL) and triethylamine (5.2 mmol, 0.785 mL) in
CCl4 (3 mL) as solvent. The title compound was obtained as a pale
4
The separation of distannylated products (3aed) from monostannylated pyri-
5
dines (5a and 5b) is hard because of their similar chromatographic behavior. This
fact diminishes the yield of purified distannylated pyridines.
The IR spectra of the esters present characteristic absorptions at 1030,
1155e1164, 1183e1214, and 1265e1274 cmꢀ1
.

G.F. Silbestri et al. / Journal of Organometallic Chemistry 695 (2010) 2578e2585
2583
yellow liquid (0.861 g, 3.25 mmol, 65%); 1H NMR:
d
7.77 (dt,
a nitrogen inlet and magnetic stirrer, were condensed 80 mL of Na-
dried ammonia. Me3SnCl (0.220 g, 1.1 mmol) was dissolved and
sodium metal (0.051 g, 2.2 mmol) was added until the blue colour
persisted for at least 5 min. When the blue colour disappeared,
diethyl 5-chloropyridin-2-yl phosphate (2a, 0.5 mmol, 0.132 g) was
added drop wise and the solution was irradiated with stirring for
3JHH ¼ 7.8 Hz, 5JHP ¼ 1.0 Hz,1H); 7.23 (dd, 3JHH ¼ 7.8 Hz, 4JHP ¼ 1.8 Hz,
3
4
1H); 7.05 (dd, JHH ¼ 8.0 Hz, JHP ¼ 1.5 Hz, 1H); 4.46e4.34 (m, 4H);
1.45 (dt, JHH ¼ 7.0 Hz, JHP ¼ 1.0 Hz, 6H). 13C NMR:
d 156.4
3
4
(2JCP ¼ 5.9 Hz, C); 148.6 (C); 141.8 (CH); 120.7 (CH); 111.3
(3JCP ¼ 5.9 Hz, CH); 64.8 (2JCP ¼ 5.9 Hz, CH2); 15.7 (3JCP ¼ 6.4 Hz,
CH3). 31P NMR:
d
43.23. MS (m/z, relative intensity): 265 (5, Mþ), 237
30 min. The reaction was quenched with IMe (32 mL, 1.1 mmol);
[2, (M ꢀ 28)þ], 210 (6), 192 (19), 156 (20), 139 (49), 129 (100), 101
(34), 81 (28). Anal. Calcd. for C9H13ClNO4P (265.63): C 40.69; H 4.93;
N 5.27. Found: C 40.59; H 4.94; N 5.29.
10 mL of Et2O was added and then liquid ammonia was allowed to
evaporate.6 The resultant solution was treated with water and
extracted with Et2O (3 ꢂ10 mL). The organic phase was succes-
sively washed with water and brine, dried over MgSO4, filtered,
and concentrated in vacuo. Purification by crystallization7 from
EtOH gave 2,5-bis(trimethylstannyl)pyridine (3a) as a white solid
(0.177 g, 0.43 mmol, 87%); mp: 112e113 ꢁC (Lit [11]: 115e116 ꢁC);
4.2.3. Diethyl 5-chloropyridin-3-yl phosphate (2c)
Kenner’s method was employed for the reaction of 5-chloropyr-
idin-3-ol (5.0 mmol, 0.645 g) with diethyl hydrogen phosphite
(5.2 mmol, 0.670 mL) and triethylamine (5.2 mmol, 0.785 mL) in CCl4
(3 mL) as solvent. The title compound was obtained as a brown liquid
3
3
1H NMR:
d
8.54 (s, JHSn ¼ 23.6 Hz, 1H); 7.38 (d, JHH ¼ 7.2 Hz, 1H);
7.17 (d, 3JHH ¼ 7.2 Hz, 1H); 0.11 (s, 2JHSn ¼ 55.5/53.2 Hz, 18H, SnCH3);
(0.928 g, 3.5 mmol, 70%); 1H NMR:
d
8.63e8.58 (m, 1H); 7.83 (dt,
0.09 (s, JHSn ¼ 56.1/53.6 Hz, 3H, SnCH3). 13C NMR:
d 172.7 (C);
2
4JHH ¼ 2.3 Hz, 4JHP ¼ 1.0 Hz, 1H); 7.49 (s, 1H); 4.48e4.36 (m, 4H); 1.54
156.2 (2JCSn ¼ 61.4/38.1 Hz, CH); 141.1 (2JCSn ¼ 32.3/25.8 Hz, CH);
135.4 (C); 131.9 (2JCSn ¼ 84.8/27.2 Hz, CH); ꢀ9.6 (1JCSn ¼ 346.4/
331.8 Hz, SnCH3); ꢀ9.8 (1JCSn ¼ 356.2/339.0 Hz, SnCH3). 119Sn NMR:
3
4
(dt, JHH ¼ 7.1 Hz, JHP ¼ 1.0 Hz, 6H). 13C NMR:
d
147.4 (2JCP ¼ 6.4 Hz,
C); 145.0 (CH); 139.9 (3JCP ¼ 5.9 Hz, CH); 131.4 (C); 127.3
(3JCP ¼ 4.1 Hz, CH); 65.1 (2JCP ¼ 5.9 Hz, CH2); 16.0 (3JCP ¼ 6.4 Hz, CH3).
d
ꢀ25.01; ꢀ48.07. MS (m/z, relative intensity): 407 (7, Mþ), 392 [34,
31P NMR:
d
44.67. MS (m/z, relative intensity): 265 (39, Mþ), 236 [36,
(M ꢀ 15)þ], 377 (2), 362 (22), 328 (13), 309 (7), 257 (32), 238 (29),
(M ꢀ 29)þ], 209 (34), 157 (23), 139 (45), 129 (100), 109 (22), 81 (68).
Anal. Calcd. for C9H13ClNO4P (265.63): C 40.69; H 4.93; N 5.27. Found:
C 40.55; H 4.95; N 5.26.
212 (27), 165 (87), 135 (100), 116 (30).
4.3.2. 2,6-Bis(trimethylstannyl)pyridine (3b)
The representative procedure was followed using Me3SnCl
(1.1 mmol, 0.220 g), sodium metal (2.2 mmol, 0.051 g) and diethyl
6-chloropyridin-2-yl phosphate (2b, 0.5 mmol, 0.132 g) as starting
material. The mixture was irradiated under stirring for 120 min.
Purification by distillation (Kügelrohr) gave 3b as a colorless liquid
(0.195 g, 0.48 mmol, 96%); b.p.: 100 ꢁC/5 Torr (Lit [11]: 132e134 ꢁC/
4.2.4. Diethyl 2-chloropyridin-3-yl phosphate (2d)
Kenner’s method was employed for the reaction of 2-chlor-
opyridin-3-ol (5.0 mmol, 0.645 g) with diethyl hydrogen phosphite
(5.2 mmol, 0.670 mL) and triethylamine (5.2 mmol, 0.785 mL) in
CCl4 (3 mL) as solvent. The title compound was obtained as a pale
yellow liquid (0.835 g, 3.15 mmol, 63%); 1H NMR:
d
8.34 (dd,
10 Torr); 1H NMR:
d
7.35e6.90 (m, 3H); 0.13 (s, 2JHSn ¼ 55.5/53.2 Hz,
3JHH ¼ 4.6 Hz, 4JHH ¼ 0.8 Hz,1 H); 7.95 (dd, 3JHH ¼ 8.0 Hz, 4JHP ¼ 1.1 Hz,
18H, SnCH3). 13C NMR:
d
174.0 (C); 133.5 (3JCSn ¼ 41.1 Hz, CH); 131.1
3
3
1H); 7.39 (dd, JHH ¼ 8.1 Hz, JHH ¼ 4.7 Hz, 1H); 4.48e4.36 (m, 4H);
(2JCSn ¼ 92.1 Hz, CH); ꢀ9.40 (1JCSn ¼ 346.9/331.0 Hz, SnCH3). 119Sn
1.52 (dt, 3JHH ¼ 7.0 Hz, 4JHP ¼ 1.0 Hz, 6H).13C NMR:
d
145.0 (CH); 143.8
NMR:
d
ꢀ50.46. MS (m/z, relative intensity): 407 (1, Mþ), 392 [99,
(3JCP ¼ 5.9 Hz, C); 142.7 (2JCP ¼ 8.2 Hz, C); 129.0 (3JCP ¼ 2.3 Hz, CH);
(M ꢀ 15)þ], 377 (3), 362 (30), 345 (6), 328 (20), 242 (23), 212 (42),
123.1 (CH); 65.1 (2JCP ¼ 6.4 Hz, CH2); 15.8 (3JCP ¼ 7.0 Hz, CH3). 31P
165 (59), 150 (22), 135 (100), 120 (26).
NMR:
d
44.23. MS (m/z, relative intensity): 265 (1, Mþ), 230 [30,
(M ꢀ 35)þ], 202 (21), 174 (100), 156 (2), 129 (11), 109 (21), 81 (33).
Anal. Calcd. for C9H13ClNO4P (265.63): C 40.69; H 4.93; N 5.27. Found:
C 40.77; H 4.95; N 5.29.
4.3.3. 3,5-Bis(trimethylstannyl)pyridine (3c)
The representative procedure was followed using Me3SnCl
(1.1 mmol, 0.220 g), sodium metal (2.2 mmol, 0.051 g) and diethyl
5-chloropyridin-3-yl phosphate (2c, 0.5 mmol, 0.132 g) as starting
material. The mixture was irradiated under stirring for 60 min.
Purification by crystallization from EtOH gave 3c as a white solid8
4.2.5. 2,3-Bis[(diethoxyphosphoryl)oxy]pyridine (2e)
Kenner’s method was employed for the reaction of pyridine-2,3-
diol (5.0 mmol, 0.555 g) with diethyl hydrogen phosphite
(10.4 mmol, 1.340 mL) and triethylamine (10.4 mmol, 1.570 mL) in
CCl4 (3 mL) as solvent. The title compound was obtained as a pale
(0. 138 g, 0.34 mmol, 69%); mp: 107e109 ꢁC (Lit [11]: 118e119 ꢁC/
3
3.5 Torr); 1H NMR:
d
8.42 (s, JHSn ¼ 22.5 Hz, 2H); 7.69 (s,
3JHSn ¼ 40.2 Hz, 1H); 0.22 (s, JHSn ¼ 55.3/53.0 Hz, 18 H, SnCH3). 13
C
2
yellow liquid (0.670 g, 1.75 mmol, 35%); 1H NMR:
d
8.09 (d,
NMR:
d
155.1 (2JCSn ¼ 42.3 Hz, CH); 150.8 (2JCSn ¼ 24.6 Hz, CH);
3JHH ¼ 4.4 Hz, 1H); 7.79 (dd, 3JHH ¼ 8.0 Hz, 4JHP ¼ 1.1 Hz, 1H); 7.2 (dd,
137.2 (C); ꢀ9.6 (1JCSn ¼ 356.2/340.9 Hz, SnCH3). 119Sn NMR:
3JHH ¼ 8.0 Hz, 3JHH ¼ 4.8 Hz, 1H); 4.43e4.34 (m, 4H); 4.33e4.21 (m,
d
ꢀ25.18. MS (m/z, relative intensity): 407 (11, Mþ), 392 [100,
4H); 1.44e1.36 (m, 6H). 13C NMR:
d
149.0 (t, 2JCP ¼ 6.4 Hz, C); 142.7
(M ꢀ 15)þ], 377 (1), 362 (21), 345 (6), 330 (13), 315 (15), 165 (22),
2
3
(CH); 135.9 (dd, JCP ¼ 7.8 Hz, JCP ¼ 6.8 Hz, C); 130.0 (3JCP ¼ 2.3 Hz,
150 (12), 135 (28), 120 (9).
CH); 121.0 (CH); 64.7 (2JCP ¼ 6.2 Hz, CH2); 64.5 (2JCP ¼ 6.0 Hz, CH2);
15.6 (3JCP ¼ 6.8 Hz, CH3). 31P NMR:
d
44.67; 43.43. MS (m/z, relative
4.3.4. 2,3-Bis(trimethylstannyl)pyridine (3d)
intensity): 383 (3, Mþ), 355 [1, (M ꢀ 28)þ], 310 (3), 275 (8), 248 (9),
229 (88), 201 (92), 174 (100), 111 (91), 81 (78). Anal. Calcd. for
C13H23NO8P2 (383.27): C 40.74; H 6.05; N 3.65. Found: C 40.62; H
6.07; N 3.66.
The representative procedure was followed using Me3SnCl
(1.1 mmol, 0.220 g), sodium metal (2.2 mmol, 0.051 g) and diethyl 2-
chloropyridin-3-yl phosphate (2d, 0.5 mmol, 0.132 g). The mixture
6
4.3. Reactions in liquid ammonia
We observed that the usual work-up procedure for reactions with organo-
stannides, i.e., NH4Cl as quencher and evaporation of liquid ammonia to dryness,
prompted proto-destannylation process.
4.3.1. Synthesis of 2,5-bis(trimethylstannyl)pyridine (3a).
Representative procedure
In a 100 mL two-necked round-bottomed flask, equipped with
a cold finger condenser charged with acetone-liquid nitrogen,
7
Proto-destannylation products were formed by purification on silica gel column
chromatography.
8
Spectroscopic data of 3c are in accord with those reported in reference [11].
Nevertheless, we found a divergence in physical characteristics.

2584
G.F. Silbestri et al. / Journal of Organometallic Chemistry 695 (2010) 2578e2585
was irradiated under stirring for 20 min. Purification by distillation
(Kügelrohr) gave 3d as a pale orange liquid (171 g, 0.42 mmol, 84%);
b.p.: 139e141 ꢁC/5 Torr (Lit [11]: 125e127 ꢁC/3 Torr); 1H NMR:
intensity): 395 (15, Mþ), 380 [100, (M ꢀ 15)þ], 365 (2), 350 (25), 322
(5), 304 (4), 290 (4), 265 (5), 243 (5), 217 (10), 165 (9), 135 (8), 120
(5). Anal. Calcd. for C12H22NO4PSn (393.99): C 36.58; H 5.63; N 3.56.
Found: C 36.68; H 5.61; N 3.54.
d
8.60e8.43 (m, 1H); 7.55 (dd, JHH ¼ 1.9 Hz, JHH ¼ 7.3 Hz, 1H);
7.03e6.90 (m,1H); 0.27 (s, 2JHSn ¼ 53.0 Hz,18H).13C NMR:
d 181.6 (C);
150.0 (3JCSn ¼ 41.6 Hz, CH); 148.1 (C); 141.8 (2JCSn ¼ 59.2 Hz, CH); 121.6
(3JCSn ¼ 42.4 Hz, CH); ꢀ7.1 (1JCSn ¼ 346.2/332.9 Hz, SnCH3); ꢀ7.5
(1JCSn ¼ 345.4/330.9 Hz, SnCH3). MS (m/z, relative intensity): 407 (7,
Mþ), 390 [40, (M ꢀ 15)þ], 360 (13), 330 (8), 313 (5), 256 (32), 242 (37),
212 (63), 186 (16), 165 (100), 135 (69), 120 (25).
4.3.8. Diethyl 2-(trimethylstannyl)pyridin-3-yl phosphate (4d)
The representative procedure was followed using 40 mL of
sodium-dried ammonia as solvent and Me3SnCl (0.5 mmol, 0.100 g),
sodium metal (1.1 mmol, 0.025 g) and diethyl 2-chloropyridin-3-yl
phosphate (2d, 0.5 mmol, 0.132 g) as starting material. The mixture
was irradiated under stirring for 30 min. Purification by column
chromatography on silica gel (hexane:EtOAc ¼ 60:40) gave 4d as
4.3.5. Diethyl 5-(trimethylstannyl)pyridin-2-yl phosphate (4a)
The representative procedure was followed using Me3SnCl
(1.1 mmol, 0.220 g), sodium metal (2.2 mmol, 0.051 g) and diethyl
5-chloropyridin-3-yl phosphate (2c, 0.5 mmol, 0.132 g) as starting
material. The flask was wrapped with aluminium foil and the
mixture was stirred for 60 min. Elimination of the solvent rendered
a beige syrup (0.176 g, 0.45 mmol, 89%); 1H NMR:
d 8.56 (d,
3JHH ¼ 4.5 Hz,1H); 7.77e7.58 (m,1H); 7.15 (m,1H); 4.27e4.15 (m, 4H);
3
2
1.35 (t, JHH ¼ 7.0 Hz, 6H); 0.39 (s, JHSn ¼ 55.7 Hz, 9H, SnCH3). 13C
NMR:
d
164.8 (C); 153.7 (2JCP ¼ 6.0 Hz, C); 147.1 (CH); 123.5 (CH);
122.4 (3JCP ¼ 7.8, CH); 64.6 (2JCP ¼ 5.9 Hz, CH2); 15.9 (3JCP ¼ 7.6 Hz,
4a as a pale yellow liquid (0.387 g, 0.98 mmol, 98%); 1H NMR:
d
7.33
CH3); ꢀ8.9 (1JCSn ¼ 342.7/326.2 Hz, SnCH3). 31P NMR:
d
44.59. 119Sn
(dt, 4JHP ¼ 0.9 Hz, 3JHH ¼ 7.0 Hz, 1H); 7.04 (d, 3JHH ¼ 7.0 Hz, 1H); 6.63
NMR:
d
ꢀ50.41. MS (m/z, relative intensity): 395 (3, M$þ), 380 [100,
3
3
(d, JHH ¼ 8.2 Hz, 1H); 4.14e4.04 (m, 4H); 1.14 (dt, JHH ¼ 7.0 Hz,
(M ꢀ 15)þ], 352 (20), 324 (78), 308 (25), 292 (48), 276 (18), 259 (3),
244 (15), 229 (21), 214 (33), 199 (21), 183 (21), 165 (39), 150 (9), 135
(58),120 (12),107 (10), 81 (32), 65 (10). Anal. Calcd. for C12H22NO4PSn
(393.99): C 36.58; H 5.63; N 3.56. Found: C 36.48; H 5.65; N 3.57.
4JHP ¼ 0.9 Hz, 6H); 0.09 (s, JHSn ¼ 56.1/53.8 Hz, 9H, SnCH3). 13C
2
NMR:
d
172.0 (C); 157.4 (2JCP ¼ 5.9 Hz, C); 137.4 (2JCSn ¼ 37.6 Hz, CH);
128.9 (2JCSn ¼ 82.7/79.8 Hz, CH); 111.9 (3JCP ¼ 7.0 Hz, CH); 64.3
(2JCP ¼ 5.9 Hz, CH2); 15.9 (3JCP ¼ 7.0 Hz, CH3); ꢀ9.5 (1JCSn ¼ 354.5/
338.6 Hz, SnCH3). 31P NMR:
d
43.75. 119Sn NMR:
d
ꢀ25.16. MS (m/z,
4.3.9. Diethyl 3-(trimethylstannyl)pyridin-2-yl phosphate (4e)
The representative procedure was followed using Me3SnCl
(0.5 mmol, 0.100 g), sodium metal (1.1 mmol, 0.025 g) and 2,3-bis
[(diethoxyphosphoryl)oxy]pyridine (2e, 0.5 mmol, 0.191 g) as
starting material. The mixture was irradiated under stirring for
180 min. We were not able to isolate compound 4e from the reac-
tion mixture. MS (m/z, relative intensity): 380 [54, (M ꢀ 15)þ], 350
(6), 324 (7), 294 (7), 244 (100), 214 (42), 183 (14), 165 (8), 135 (20),
120 (10), 81 (30), 65 (4).
relative intensity): 395 (1, Mþ), 380 [10, (M ꢀ 15)þ], 365 (1), 350
(20), 322 (69), 304 (21), 290 (19), 275 (26), 258 (7), 244 (100), 228
(28), 214 (41),199 (10),183 (23),165 (62),150 (17),135 (66),123 (17),
109 (45), 94 (26), 81 (74), 65 (14). Anal. Calcd. for C12H22NO4PSn
(393.99): C 36.58; H 5.63; N 3.56. Found: C 36.72; H 5.62; N 3.57.
4.3.6. Diethyl 6-(trimethylstannyl)pyridin-2-yl phosphate (4b)
The representative procedure was followed using Me3SnCl
(0.5 mmol, 0.100 g), sodium metal (1.1 mmol, 0.025 g) and diethyl
6-chloropyridin-2-yl phosphate (2b, 0.5 mmol, 0.132 g) as starting
material. The flask was wrapped with aluminium foil and the
mixture was stirred for 10 min. Purification by column chroma-
tography on silica gel (hexane:EtOAc ¼ 60:40) gave 4b as a beige
Acknowledgments
This work was partially supported by CONICET, CIC, ANPCYT and
the Universidad Nacional del Sur, Bahía Blanca, Argentina. CONICET
is thanked for a research fellowship to MJL F.
syrup (0.186 g, 0.47 mmol, 94%); 1H NMR:
d 7.59e7.23 (m, 1H); 6.79
(d, 3JHH ¼ 8.2 Hz, 1H); 6.32 (d, 3JHH ¼ 8.6 Hz, 1H); 3.95 (m, 4H); 1.15
(t, 3JHH ¼ 7.0 Hz, 6H); 0.33 (s, 2JHSn ¼ 59.9 Hz, 9H, SnCH3). 13C NMR:
Appendix A. Supplementary data
d
165.3 (C); 155.9 (2JCP ¼ 5.7 Hz, C); 142.8 (CH); 128.4 (CH); 114.3
(3JCP ¼ 7.0 Hz, CH); 64.9 (2JCP ¼ 6.4 Hz, CH2); 15.9 (3JCP ¼ 6.7 Hz,
Copies of 1H, 13C and 31P NMR spectra of compounds 4aed.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2010.08.032.
CH3); ꢀ9.6 (1JCSn ¼ 363.3/346.4 Hz, SnCH3). 31P NMR:
d
43.70. 119Sn
NMR:
d
ꢀ50.44. MS (m/z, relative intensity): 395 (13, Mþ), 380 [100,
(M ꢀ 15)þ], 365 (4), 350 (3), 322 (15), 244 (41), 228 (11), 214 (25),
165 (20), 150 (11), 135 (32), 109 (15), 81 (43), 65 (7). Anal. Calcd. for
C12H22NO4PSn (393.99): C 36.58; H 5.63; N 3.56. Found: C 36.68; H
5.61; N 3.55.
References
[1] M. Balabrubramanian, J.G. Keay, in: A.R. Katrizky, C.W. Rees, E.V.F. Scriven
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4.3.7. Diethyl 5-(trimethylstannyl)pyridin-3-yl phosphate (4c)
The representative procedure was followed using 40 mL of
sodium-dried ammonia as solvent and Me3SnCl (0.5 mmol,
0.100 g), sodium metal (1.1 mmol, 0.025 g) and diethyl 5-chlor-
opyridin-3-yl phosphate (2c, 0.5 mmol, 0.132 g) as starting mate-
rial. The mixture was irradiated under stirring for 60 min.
Purification by column chromatography on silica gel
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hedron 65 (2009) 5413;
0.40 mmol, 80%); 1H NMR:
d 8.38e8.29 (s, 2H); 7.60e7.58 (m, 1H);
4.23e4.11 (m, 4H); 1.30 (dt, 3JHH ¼ 7.0 Hz, 4JHP ¼ 1.1 Hz, 6H); 0.28 (s,
(b) C. Corinne Gosmini, C. Bassene-Ernst, M. Durandetti, Tetrahedron 65
(2009) 6141;
(c) H. S-Kim, R.D. Rieke, Tetrahedron Lett. 50 (2009) 5329;
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Tetrahedron 64 (2008) 778;
(e) S.J. Teague, J. Org. Chem. 73 (2008) 9765;
(f) Y. Liu, Q. Ding, X. Wu, J. Org. Chem. 73 (2008) 6025;
(g) S. Diring, P. Retailleau, R.J. Ziessel, Org. Chem. 72 (2007) 10181;
2JHSn ¼ 56.4/54.2 Hz, 9H, SnCH3). 13C NMR:
d
151.7 (2JCSn ¼ 36.4,
CH); 147.8 (2JCP ¼ 7.0 Hz, C); 141.5 (3JCP ¼ 5.3 Hz, CH); 138.4 (C);
2
134.2 (3JCP ¼ 4.1 Hz, JCSn ¼ 34.6/25.8 Hz CH); 64.8 (2JCP ¼ 5.9 Hz,
CH2); 16.1 (3JCP ¼ 6.4 Hz, CH3); ꢀ9.5 (1JCSn ¼ 362.7/346.2 Hz,
SnCH3). 31P NMR:
d
44.65. 119Sn NMR:
d
ꢀ25.20. MS (m/z, relative

G.F. Silbestri et al. / Journal of Organometallic Chemistry 695 (2010) 2578e2585
2585
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[7] For reviews see: (a) R.A. Rossi, R.H. de Rossi, Aromatic substitution by the SRN
1
mechanism, , In: ACS Monograph 178. American Chemical Society, Washington,
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