Sequential Synthesis of Organosilicon-Linked 2-Methoxypyridines by Non-Cryogenic ortho-Metallation Using the nBu2TMPMg·Li Reagent and Hydrosilylation

Article abstract of DOI:10.1002/ejoc.201501570

The non-cryogenic synthesis of 5/6- and/or 3-silyl-functionalised 2-methoxypyridines by a 5-Br/Mg exchange process using nBu₂iPrMg Li and LiCl and involving C-3 metallation using a novel nBu₂TMPMg Li reagent is described. Furthermore, the usefulness of nBu₂TMPMg Li in the functionalisation of 2-methoxypyridine at the 3-position with a wide range of electrophiles was successfully tested. The above achievements have allowed the construction of organosilicon-linked 2-methoxypyridines composed of two, three and four rings by the hydrosilylation of 5- and/or 3-SiH(or alkenyl) derivatives using the hitherto rarely applied [Pt(cod)Me₂] catalyst. Additionally, the synthesis of a one-chain oligomer consisting of eight 2-methoxypyridines obtained by the hydrosilylation/polymerisation approach, followed by protodesilylation of the SiHMe₂ group was also achieved by manipulating the amount of catalyst in the reactions.

Full text of DOI:10.1002/ejoc.201501570

DOI: 10.1002/ejoc.201501570
Full Paper
Si-Functionalised Pyridines
Sequential Synthesis of Organosilicon-Linked
2-Methoxypyridines by Non-Cryogenic ortho-Metallation Using
the nBu2TMPMg·Li Reagent and Hydrosilylation
Łukasz Struk,[a] Jacek G. Sośnicki*[a] Tomasz J. Idzik,[a] and Gabriela Maciejewska[b]
Abstract: The non-cryogenic synthesis of 5/6- and/or 3-silyl- oxypyridines composed of two, three and four rings by the
functionalised 2-methoxypyridines by a 5-Br/Mg exchange hydrosilylation of 5- and/or 3-SiH(or alkenyl) derivatives using
process using nBu2iPrMg Li and LiCl and involving C-3 metalla- the hitherto rarely applied [Pt(cod)Me2] catalyst. Additionally,
tion using a novel nBu2TMPMg Li reagent is described. Further- the synthesis of a one-chain oligomer consisting of eight 2-
more, the usefulness of nBu2TMPMg Li in the functionalisation methoxypyridines obtained by the hydrosilylation/polymerisa-
of 2-methoxypyridine at the 3-position with a wide range of tion approach, followed by protodesilylation of the SiHMe2
electrophiles was successfully tested. The above achievements group was also achieved by manipulating the amount of cata-
have allowed the construction of organosilicon-linked 2-meth- lyst in the reactions.
Introduction
synthetic applications of 2-methoxypyridylsilanes have been
less studied, although the presence of a 2-methoxy group al-
lows many synthetic transformations, for example, into NR and
NH 2-pyridones, 2-chloro-substituted derivatives[24] or cross-
coupled products obtained by the direct replacement of the
2-MeO group by aryl rings.[25]
Previously, 6-,[26] 5-,[27] 4-[28] or 3-functionalised[26b,28b,29] 2-
methoxypyridines equipped with silicon-containing moieties
were obtained by the halogen/lithium exchange method or or-
tho-metallation. In both procedures, organolithium reagents
and cryogenic conditions are usually required.
Organosilicon compounds[1] are of great importance in modern
organic chemistry because of their usefulness in the protection
of functional groups[2] and their broad application in, for exam-
ple, asymmetric synthesis,[3] cross-coupling reactions[4] and nat-
ural product synthesis.[5] This class of compounds and related
siloxanes are the subject of continuously growing interest due
to their ability to form oligomers,[6] dendrimers[7] and poly-
mers[8] and because of their unique properties, which have re-
sulted in certain pivotal developments in the fields of silica-
supported catalysis,[9] biosensors[10] and material[11] and nano
sciences.[12] Moreover, the recognition of the silicon atom as a
bio-isosteric unit[13] and its successful use in bioengineering[14]
also indicate their great value in medicinal applications.[15]
Of numerous substituted pyridines, which form a class of
versatile and most useful heterocycles (because of their utility
in general synthesis,[16] the synthesis of biologically important
compounds and their broad applicability in coordination[17] and
supramolecular[18] chemistry as well as in material sciences),
pyridylsilanes are recognised as a particularly practical combi-
nation. They have been applied, for example, in nicotine[19] and
dihydrosilole[20] synthesis, in a variety of synthetic approaches
based on the strong directing effect of silicon[21] and in the
synthesis of new ligands[22] and materials.[23] The synthesis and
However, recently we reported the synthesis of functional-
ised 2-methoxypyridines by a method based on a halogen/
magnesium exchange process performed under non-cryogenic
conditions (at 0 °C).[30] The starting substrates were 3-iodo-, 5-
bromo- or 6-bromo-substituted 2-methoxypyridine derivatives,
and the halogen/magnesium exchange agent was lithium di-n-
butyl(isopropyl)magnesate (nBu2iPrMg Li + LiCl), which belongs
to the relatively new and useful family of bimetallic “ate” com-
plexes.[31] By applying this method we were able to obtain 3-,
5- or 6-trimethylsilyl-substituted 2-methoxypyridines at around
0 °C.[30]
Continuing our research program aimed at the development
of new synthetic methods that do not require cryogenic condi-
tions, also inspired by the potentially large number of applica-
tions of pyridylsilanes in materials sciences and coordination
chemistry, we propose now a sequential, non-cryogenic synthe-
sis of organosilicon-linked 2-methoxypyridine compounds
(Scheme 1). The essential concept is based on the introduction
of substituents containing alkenylSi and/or HSi groups, first at
C-5 (or C-6) and subsequently at C-3, followed by the connec-
tion of the functionalised pyridine rings by hydrosilylation.[32]
However, although we planned to achieve the initial functional-
[a] West Pomeranian University of Technology, Szczecin, Institute of Chemistry
and Environmental Protection,
Al. Piastów 42, Szczecin 71-065, Poland
http://www.wtiich.zut.edu.pl
[b] Faculty of Chemistry, Wrocław University of Technology,
Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
E-mail: sosnicki@zut.edu.pl
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejoc.201501570.
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isations at C-5 or C-6 (Scheme 1, step 1) by using the previously
described non-cryogenic bromine/magnesium exchange
method,[30] we intended to accomplish the functionalisation at
C-3 by a novel non-cryogenic direct metallation using organo-
magnesium “ate” complexes (Scheme 1, step 2).
Scheme 1. Proposed strategy for the synthesis of organosilicon-linked 2-
methoxypyridines.
Functionalisation at C-3 of 2-methoxypyridines by direct
metallation, which is the original and key achievement of these
studies, could offer a very effective alternative to functionalisa-
tion by the halide/metal exchange process and thus could at-
tract widespread interest. It should be noted that although
magnesates have been used previously for the direct CH metal-
lation of a variety of heterocycles,[33] the ortho-metallation of
2-alkoxypyridine derivatives has been hitherto unreported. Fur-
thermore, apart from this extension, the synthesis of linked 2-
methoxypyridines seemed to be an interesting final synthetic
objective, not only because of the potentially wide-ranging use
of 2-methoxypyridylsilanes in materials and coordination chem-
istry, but also because of their possible further transformation
into linked 2-pyridones, which could also be applied as li-
gands.[34]
Scheme 2. Synthesis of 5-silyl-functionalised 2-methoxypyridines 2a–2e and
4-silyl-functionalised anisoles 3a–3c. [a] Yields estimated by 1H NMR spectro-
scopy using an internal reference are given in the parentheses.
the use of magnesate, nBu2iPr(or nBu3)Mg Li + LiCl, prepared
simply by mixing organolithium and Grignard reagents, gave
no positive results (Table 1, entries 1 and 2). Subsequently we
used 2,2,6,6-tetramethylpiperidine (TMPH) because it had been
successfully employed to prepare bimetallic magnesates with
Results and Discussion
In the first stage of our study, 5- and 6-silyl-functionalised 2- high deprotonative properties.[37] The use of the TMP-ligated
methoxypyridines were obtained according to the method magnesate nBu2TMPMg Li + LiCl (or nBuTMP2Mg Li + LiCl or
mentioned above[30] by using commercially available HSi- or TMP3Mg Li + LiCl), obtained by mixing nBu2iPrMg Li + LiCl and
alkenylSi-functionalised chlorosilanes as electrophiles and in TMPH in a molar ratio of 1:1 (or 1:2 or 1:3, Table 1, entries 4–6)
situ generated magnesate (nBu2iPrMg Li + LiCl) as exchange gave positive results. However, the best results (73 % yield)
reagent (Scheme 2). 2-Methoxypyridine products 2a–2e were were achieved by the use of nBu2TMPMg Li, with no LiCl in the
obtained on a few-gram scale in moderate or good yields and reaction medium, despite an incomplete conversion (ca. 90 %;
were purified mainly by distillation. By using the same protocol, Table 1, entry 7). The latter reaction system was obtained by
anisole derivatives 3a–c were also obtained for comparison by mixing equimolar amounts of nBu2Mg, nBuLi and TMPH. At-
using 4-bromoanisole as substrate. The yields of these reactions tempts to improve the reaction yields by extending the reaction
were higher than those of the corresponding pyridine deriva- time and raising the temperature were unsuccessful (Table 1,
tives 2a–c and comparable to that of 3b and 3c synthesised at entries 8 and 10, respectively). Employment of the nBu3Mg Li +
low temperatures[35,36] (Scheme 2).
2LiBr and nBuTMP2Mg Li + 2LiBr systems (at 22 °C), developed
by Marsais and co-workers[33d], was also found to be less effect-
ive (Table 1, entries 11 and 12), similarly the use of TMPLi
(Table 1, entries 13 and 14).
Next, we investigated the optimal conditions for the intro-
duction of Si-functionalised moieties at C-3 of the 5-functional-
ised 2-methoxypyridines 2a–2e by metallation at C-3 (ortho-
metallation). For our first tests, we used the earlier obtained
The results show that the application of the TMP ligand is
vinyl derivative 2a and (chloro)dimethylsilane, varying the crucial for the success of the synthesis by deprotonation and
amount of deprotonating magnesate used (Table 1) and using that the presence of the LiCl salt in the reaction media had a
a reaction temperature not lower than –5 °C. During the search negative influence on the yield of 4a. It should be noted that
for an efficient method for the ortho-metallation, we found that the negative effect of LiCl on deprotonation contrasts with
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Table 1. Optimisation of the reaction conditions for the synthesis of 4a by direct metallation at C-3 by using various organomagnesate and organolithium
reagents prepared in situ.
Entry[a] R1MgR2 (amount [equiv.]) (x) nBuLi [equiv.] (y)
TMPH [equiv.] (z)
Expected deprotonating agent[b,c] T [°C] Conv. of 2a [%][d] Yield of 4a [%][e]
[f]
1
2
3
4
5
6
7
8
nBuMgCl (1.2) (1)
iPrMgCl (1.2) (1)
nBuMgCl (1.2) (1)
iPrMgCl (1.2) (1)
iPrMgCl (1.2) (1)
iPrMgCl (1.2) (1)
nBuMgnBu (1.2) (1)
nBuMgnBu (1.2) (1)
nBuMgnBu (1.2) (1)
nBuMgnBu (1.2) (1)
MgBr2 (1.1) (1)
MgBr2 (1.1) (1)
–
2.4 (2)
2.4 (2)
2.4 (2)
2.4 (2)
2.4 (2)
2.4 (2)
1.2 (1)
1.2 (1)
1.2 (1)
1.2 (1)
3.3 (3)
3.3 (3)
1.2 (1)
1.2 (1)
–
–
nBu3Mg Li + LiCl
nBu2iPrMg Li + LiCl
nBu2TMPMg Li + LiCl
nBu2TMPMg Li + LiCl
nBuTMP2Mg Li + LiCl
TMP3Mg Li + LiCl
nBu2TMPMg Li
nBu2TMPMg Li
nBuTMP2Mg Li
nBu2TMPMg Li
–5
–5
–5
–5
–5
–5
–5
–5
–5
22
22
22
–55
–5
–
(0)
(0)
(29)
(60)
(58)
(42)
73 (73)
(65)[g]
(25)
[f]
–
–
[f]
1.2 (1)
1.2 (1)
2,4 (2)
3.6 (3)
1.2 (1)
1.2 (1)
2,4 (2)
1.2 (1)
–
79
[f]
–
80
90
96
[f]
9
–
[f]
10
11
12
13
14
–
(53)
[f]
nBu3Mg Li + 2LiBr
nBuTMP2Mg Li + 2LiBr
TMPLi[i]
–
(38)[h]
(53)[h]
(40)
[f]
2.2 (2)
1.1 (0.9)
1.2 (1)
–
70
61
–
TMPLi[j]
(40)
[a] Metallation was conducted over 1 h and 1.5 equiv. of Me2HSiCl was used unless stated otherwise. [b] Proposed composition of deprotonating agent. [c]
TMPH was added to the magnesium “ate” complex unless stated otherwise. [d] Conversions estimated by 1H NMR spectroscopy. [e] Yields estimated by 1H
NMR spectroscopy using an internal reference are given in parentheses. [f] Not assigned. [g] Reaction was prolonged overnight. [h] 3.3 equiv. of Me2HSiCl
was used. [i] TMPLi was prepared at –30 °C. [j] Metallation was conducted over 1.5 h.
its positive influence on the Br/Mg exchange process
Having determined the optimised reaction conditions, we
(Scheme 2).[30] The dual, positive or negative, influence of the next extended 3-silyl functionalisation to the 5-silyl- and 6-silyl-
LiCl salt on the reaction course is an increasingly observed phe- substituted 2-methoxypyridine substrates 2a–2f obtained in
nomenon.[38]
the former step as well as to unsubstituted 2-methoxypyridine
Scheme 3. 3-Silyl-functionalised 2-methoxypyridines obtained by ortho-metallation using the novel nBu2TMPMg Li.
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(Scheme 3) to identify substituent effects, if any. As a result,
Following the excellent structural studies of bimetallic com-
3-functionalised products were obtained in moderate-to-good plexes conducted by Mulvey and Robertson,[39] we proposed a
yields with no significant substituent effect of the 5- or 6-silyl- structure for the intermediate magnesate (nBu[2-MeO-3-pyr-
containing groups observed in comparison with unsubstituted idyl]TMPMg Li) optimised at the semi-empirical PM3 level of
2-methoxypyridine.
theory[40] (Figure 1). Because one THF solvent molecule usually
takes part in the coordination to the lithium atom,[41] we calcu-
lated the proposed structure with one molecule of THF. The
results show relatively short distances between Li and the sur-
rounding atoms in the vicinity of the reactive site.
Our next objective was to determine whether or not other
3-functionalised 2-methoxypyridines equipped with other sub-
stituents could be prepared by using the above optimised con-
ditions for metallation at C-3. Thus, the 3-metallated intermedi-
ates were quenched with electrophiles such as (MeS)2, DMF,
Ph2CO and I2 (Table 2). As a result, 3-SMe (5a–5d), 3-COHPh2
(5e–5h), 3-CHO (5i–5l) and 3-I (5m) substituted products were
obtained, generally in good yields, except for the 3-CHO spe-
cies, which were isolated in modest yields.
Table 2. 3-Functionalised 2-methoxypyridines obtained by ortho-metallation
using the novel nBu2TMPMg Li.
Figure 1. Proposed structure of the intermediate 2-methoxypyridine lithium–
magnesium “ate” complex optimised at the semi-empirical PM3 level of the-
ory with selected distances between Li and the surrounding atoms. Addi-
tional important bond lengths are: C3–Mg 2.37 Å; Mg–N1 1.89 Å (hydrogen
atoms have been omitted for clarity).
The successful introduction of hydrosilyl and alkenylsilyl moi-
eties into the 2-methoxypyridine ring has opened up further
functionalisation possibilities. Numerous examples of modifica-
tions with hydrosilyl[42] and alkenylsilyl[43] groups have been
described in the literature, and their conversions into other
functional groups. Among them, the most important is the abil-
ity to produce covalent Si–C bonds by the insertion of an alkene
into an Si–H bond.
The latter process, called hydrosilylation, is an ideal approach
to the synthesis of a well-defined linkage between organic mol-
ecules.[32,44] Thus, in the next stage of this work we synthesised
organosilicon-linked 2-methoxypyridine chains by hydrosilyl-
ation. Although hydrosilylation reactions can be carried out eas-
ily by using the most popular Karstedt or Speier catalysts due
to their well-recognised high activity, we decided to check the
applicability of [Pt(cod)Me2] (cod = cycloocta-1,5-diene; Fig-
ure 2). This commercially available catalyst has been used previ-
ously in certain cascade reactions,[45] however, to the best of
our knowledge, there is only one article in the literature on its
use in hydrosilylation.[46]
Before synthesising the linked-pyridine, we evaluated the ac-
tivity of [Pt(cod)Me2] in toluene by monitoring by GC–MS the
progress of the reaction between 2a and 2b, varying the
amount of catalyst first at room temperature and then at 60 °C
(see the Supporting Information). The optimisation revealed the
[a] THF, –3 2 °C.
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and turnover frequency: TOF = 76 h–1 (Scheme 4). These results
are similar to the data obtained by using the Karstedt catalyst
under the same conditions, except for the fact that the latter
reaction was faster (it was completed within 4 h, Scheme 4).
TONactual and TOF values of 1798 and 450 h–1, respectively, were
calculated for the reaction with the Karstedt catalyst. It should
be noted that dry and deoxygenated toluene was not required.
Figure 2. Karstedt [Pt0], Speier [PtIV] and [Pt(cod)Me2] [PtII] hydrosilylation
catalysts.
completion of the reaction at 60 °C after 24 h by using
0.0425 mol-% of the catalyst, whereas at room temperature the
reaction was completed after 6.5 days by using 0.125 mol-% of
the catalyst. Repeating the reaction on the 5 mmol scale under
the conditions assumed as optimal (60 °C, 24 h, 0.048 mol-%
catalyst) gave product 7a in an isolated yield of 88 %. These
data allowed the maximum turnovers to be calculated:
TONmax = 2083, actual turnover: TON = TONmax × 0.88 = 1833
Scheme 4. Hydrosilylation of 2a and 2b using [Pt(cod)Me2] and Karstedt cata-
lysts.
Scheme 5. Synthesis of organosilicon-linked 2-methoxypyridines by hydrosilylation using [Pt(cod)Me2] as catalyst.
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The above results and good product yields of the two-ring number of other products of lower molecular weights (not iso-
systems 7b–7h in these reactions with [Pt(cod)Me2] as catalyst lated and assigned), did not contain a terminal SiMe2H group.
showed that the functionalised 2-methoxypyridines and 4-func- The lack of this group was first identified by the absence of a
tionalised anisole derivatives could be easily combined Si–H band in the 2115–2103 cm–1 region of the IR spectra of
(Scheme 5). Furthermore, we found that by using this method, the product 10 and the residue, whereas this band was present
the three-ring system 7i could be obtained by using bifunc- at 2120 cm–1 in the IR spectrum of substrate 4a. Further struc-
tional pyridine 4i. In addition, the successful use of dihydro- tural analysis of 10 based on 1H, 13C, 13C-DEPT-135 and 13C–
siloxane 6 as a linker in the synthesis of 7j indicates high 1H correlation spectroscopy (see the Supporting Information)
prospects for the synthesis of similar linked bis-pyridine com- indicated eight interconnected rings of 2-methoxypyridine with
pounds because a large number or bifunctional SiH or Si(alk- a terminal dimethyl(vinyl)silyl group (located on one terminal
enyl) compounds are commercially available.
2-methoxypyridine ring) and the presence of a 3-H atom in-
stead of a 3-Me2SiH group on the second terminal ring
(Scheme 6). MALDI-TOF analysis of the oligomer (see the Sup-
porting Information) also supports the formation of eight-ring
oligomer 10 as the average peak of the biggest m/z value ap-
pears at around 1933 (for the [M + H]+ ion), which is close to the
molar mass of 10 (1951 Da). It should be noted that repeated
hydrosilylation/polymerisation of 4a in dry and deoxygenated
toluene gave the same result.
Encouraged by the successful synthesis of the three-ring sys-
tem 7i, we performed two additional preliminary experiments
to explore whether it would be possible to obtain compounds
with more than three connected 2-methoxypyridine rings. The
first attempt was to obtain a four-ring system in a sequence of
reactions comprising the introduction of two SiMe2H moieties
by the bis-ortho-metallation of 7a followed by hydrosilylation.
The results presented in Scheme 6 show that this protocol was
successful, however, although the double ortho-functionalisa-
tion led to the product 8 in 46 % yield, the hydrosilylation step
gave a lower yield (26 %), which indicates the need for addi-
tional optimisation of the latter step. In a second attempt, the
hydrosilylation/polymerisation of 4a was performed by using
[Pt(cod)Me2] (Scheme 7). The reaction monitored by TLC
showed that the substrate was very slowly consumed under the
optimal conditions and that an additional portion of the cata-
lyst, 10-fold bigger than that initially applied, was necessary to
be added after 7 days. After an additional day of stirring, the
reaction was complete (TLC indicated that the substrate was
consumed). The results revealed, surprisingly, that the product
10, which was isolated as a thick oil by precipitation from
CH2Cl2 solution initiated by the addition of MeOH, as well as a
Scheme 7. Hydrosilylation/polymerisation of 4a.
Obtaining the oligomerisation product 10 clearly indicates
that apart from hydrosilylation, the [Pt(cod)Me2] complex
causes protodesilylation by cleavage of the C–Si bond between
C-3 and SiMe2H. To shed more light on this reaction, an addi-
tional experiment was performed to study the behaviour of the
3-SiMe2H group in 4a by stirring in toluene in the presence of
0.044 mol-% of the catalyst [Pt(cod)Me2] (which is the optimum
amount used in the hydrosilylation reaction) and then in the
presence of a 10-fold higher amount of the catalyst (0.44 mol-
%). When a small amount of the catalyst was used, we observed
only traces of the protodesilylation product (2-methoxy-5-(tri-
methylsilyl)pyridine, Scheme 8). On increasing the quantity of
catalyst, 51 % yield of the desilylation product was obtained
after 4 days. Almost the same results were observed with the
Karstedt catalyst. These results indicate that protodesilylation as
a side-reaction proceeds very slowly and only sparingly com-
petes with hydrosilylation if a small amount of Pt catalyst is
used, and that the desilylation process could be accelerated by
increasing the quantity of the catalyst. This observation and the
successful synthesis of the eight-ring oligomer 10 indicates that
Scheme 6. Synthesis of organosilicon-linked 2-methoxypyridine 9 composed
of four rings.
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stirred for 1 h at –4 1 °C. Then the electrophile (20.8 mmol) was
added and the mixture was continuously stirred for 1 h at 0 °C.**
A saturated aq. solution of NH4Cl was added, then extracted with
EtOAc (2 × 75 mL) and the aqueous layer was separated. The com-
bined organic layers were dried with MgSO4, filtered, concentrated
in vacuo and purified by distillation or flash column chromatogra-
phy to give the corresponding products 4, 5 and 8. *In the synthesis
of compound 8, 2.07 mmol of substrate 7a was used. **In the syn-
thesis of compound 8, the mixture was also stirred overnight.
manipulating the amount of the [Pt(cod)Me2] catalyst could be
potentially useful in the chain-length-controlled synthesis of
linked poly-2-methoxypyridines by the hydrosilylation/polymer-
isation approach.
3-(Dimethylsilyl)-5-[(ethenyl)dimethylsilyl]-2-methoxypyridine
(4a): Yield 73 %. The crude product purified by distillation gave a
colourless oil. B.p. 71–73 °C (4.0 mbar). 1H NMR (400 MHz, CDCl3,
23 °C): δ = 0.33 (d, J = 3.7 Hz, 6 H, Me2SiH), 0.34 (s, 6 H, Me2Si), 3.95
(s, 3 H, OCH3), 4.36 (sept, J = 3.7 Hz, 1 H, Si-H), 5.75 (dd, J = 20.1,
3.7 Hz, 1 H, =CHH), 6.06 (dd, J = 14.7, 3.7 Hz, 1 H, =CHH), 6.26 (dd,
J = 20.1, 14.6 Hz, 1 H, =CH), 7.77 (d, J = 2.2 Hz, 1 H, 4-H), 8.26 (d,
J = 2.2 Hz, 1 H, 6-H) ppm. 13C NMR (100.6 MHz, CDCl3): δ = –4.31
[Si(CH3)2], –2.87 [Si(CH3)2], 53.19 (OCH3), 118.56 (C-3), 124.08 (C-5),
133.18 (=CH2), 137.49 (=CH), 150.58 (C-4), 153.59 (C-6), 168.40 (C-
Scheme 8. Study of the influence of the quantity of Pt catalysts on the proto-
desilylation reaction.
2) ppm. IR (film): ν = 3052 (w), 3012 (w), 2956 (s), 2904 (w), 2120
˜
(s), 1566 (s), 1548 (s), 1456 (s), 1400 (s), 1360 (m), 1350 (m), 1294
(s), 1248 (s), 1176 (w), 1122 (m), 1098 (m), 1020 (s), 956 (m), 900 (br.
s), 838 (s), 814 (s), 792 (s), 776 (s), 700 (m) cm–1. GC–MS (EI, 70 eV):
m/z (%) = 251 (37) [M]+·, 250 (81), 237 (27), 236 (100), 224 (20), 210
Conclusions
We have extended the known synthesis of 2-methoxy-5-(tri-
methylsilyl)pyridines to other 5-silyl-functionalised derivatives
by a Br/Mg exchange process using the nBu2iPrMg Li + LiCl (34), 206 (20), 192 (29), 177 (38), 162 (16), 89 (20), 59 (51). HRMS
(ESI-TOF): calcd. for C12H22NOSi2 252.1240 [M + H]+; found 252.1240.
reagent and developed a new method for the synthesis of 3-
silyl-functionalised 2-methoxypyridines by a novel C3–H metal-
lation using nBu2TMPMg Li as reagent. Both reactions were per-
formed under non-cryogenic conditions. The successful installa- (SiO2, CH2Cl2) gave a colourless oil. 1H NMR (400 MHz, CDCl3, 23 °C):
3-(Dimethylsilyl)-2-methoxy-5-(trimethylsilyl)pyridine (4b):
Yield 61 %. The crude product purified by column chromatography
δ = 0.26 (s, 9 H, Me3Si), 0.34 (d, J = 3.7 Hz, 6 H, Me2SiH), 3.95 (s, 3
H, OCH3), 4.37 (sept, J = 3.7 Hz, 1 H, Si-H), 7.78 (d, J = 2.1 Hz, 1 H,
4-H), 8.26 (d, J = 2.1 Hz, 1 H, 6-H) ppm. 13C NMR (100.6 MHz, CDCl3):
δ = –4.29 [Si(CH3)2], –1.08 [Si(CH3)3], 53.16 (OCH3), 118.45 (C-3),
125.95 (C-5), 150.17 (C-4), 153.03 (C-6), 168.29 (C-2) ppm. IR (film):
tion of other substituents at the 3-position of 2-methoxy-
pyridine using a wide range of electrophiles was also possible
and indicated that the new nBu2TMPMg Li is a prospective rea-
gent in ortho-metallation reactions. We have also demonstrated
that the successful synthesis of HSi- and/or alkenylSi-functional-
ised 2-methoxypyridines opens up the possibility of synthesis-
ing pyridine-linked derivatives by hydrosilylation. In this field,
the [Pt(cod)Me2] catalyst, rarely used in hydrosilylation, was suc-
cessfully employed in the synthesis of two- and three-ring sys-
ν = 3034 (w), 2956 (s), 2900 (w), 2120 (m), 1566 (s), 1548 (s), 1454
˜
(s), 1398 (s), 1360 (m), 1348 (m), 1296 (s), 1264 (s), 1250 (s), 1176
(w), 1132 (s), 1100 (m), 1022 (s), 892 (s), 834 (s), 792 (s), 754 (m),
724 (w), 694 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 239 (21) [M]+·,
224 (100), 194 (12), 165 (32), 73 (17). HRMS (ESI-TOF): calcd. for
tems. Four-pyridine- and eight-pyridine-ring systems were also C11H22NOSi2 240.1240 [M + H]+; found 240.1237.
constructed by combined double C-3 metallation/hydrosilyl-
3,5-Bis(dimethylsilyl)-2-methoxypyridine (4c): Yield 43 %. The
ation and hydrosilylation/polymerisation, respectively. In the
polymerisation approach, the effect of the amount of catalyst
crude product purified by column chromatography (SiO2, CH2Cl2)
1
gave a colourless oil. H NMR (400 MHz, CDCl3, 23 °C): δ = 0.34 [d,
on the hydrosilylation and protodesilylation of the SiHMe2 J = 3.7 Hz, 12 H, 2 × Si(CH3)2], 3.95 (s, 3 H, OCH3), 4.37 (sept, J =
3.7 Hz, 1 H, SiH), 4.41 (sept, J = 3.7 Hz, 1 H, SiH), 7.80 (d, J = 2.0 Hz,
1 H, 4-H), 8.28 (d, J = 2.2 Hz, 1 H, 6-H) ppm. 13C NMR (100.6 MHz,
CDCl3): δ = –4.32, –3.74 [2 × Si(CH3)2], 53.22 (OCH3), 118.71 (C-3),
123.16 (C-5), 150.74 (C-4), 153.64 (C-6), 168.53 (C-2) ppm. IR (film):
group has potential implications for controlling the chain
length in oligomer synthesis. Further studies in this area are
ongoing.
ν = 3008 (m), 2960 (s), 2904 (m), 2120 (s), 1566 (s), 1548 (s), 1454
˜
(s), 1398 (s), 1360 (m), 1348 (m), 1296 (s), 1248 (s), 1176 (w), 1130
(s), 1098 (m), 1020 (s), 894 (s), 856 (s), 834 (s), 792 (s), 760 (m), 730
(m), 610 (m) cm–1. GC–MS (EI, 70 eV): m/z (%) = 225 (67) [M]+·, 224
(92), 210 (99), 195 (36), 194 (32), 180 (74), 166 (54), 151 (100), 136
(30), 89 (22), 59 (47). HRMS (ESI-TOF): calcd. for C10H20NOSi2
226.1083 [M + H]+; found 226.1090.
Experimental Section
General: See Supporting Information.
General Procedure for the Synthesis of 3-Functionalised 2-
Methoxypyridines 4, 5 and 8 by ortho-Metallation: A 1.6
tion of nBuLi in hexane (3.9 mL, 6.2 mmol) was added by syringe
to a cooled (–4 1 °C) and stirred mixture of 1.0 nBu2Mg in hept-
ane (6.2 mL, 6.2 mmol) and anhydrous THF (40 mL) in a Schlenk
M solu-
M
3-(Dimethylsilyl)-5-[ethenyl(methyl)phenylsilyl]-2-methoxypyr-
idine (4d): Yield 51 %. The crude product purified by column chro-
1
flask under argon. The mixture was stirred for 10 min at –4 1 °C matography (SiO2, CH2Cl2) gave a colourless oil. H NMR (400 MHz,
and anhydrous TMPH (1 mL; 6.2 mmol) was added by syringe and
the mixture stirred for an additional 30 min. Subsequently, a pre-
cooled (–4 1 °C) solution of the appropriate 2-methoxypyridine
(5.2 mmol)* in anhydrous THF (5 mL) was added and the mixture
CDCl3, 23 °C): δ = 0.31 [d, J = 3.7 Hz, 6 H, (CH3)2Si], 0.62 (s, 3 H,
SiMe), 3.95 (s, 3 H, OCH3), 4.34 (sept, J = 3.6 Hz, 1 H, SiH), 5.79 (dd,
J = 20.4, 3.8 Hz, 1 H, =CHH), 6.20 (dd, J = 14.7, 3.8 Hz, 1 H, =CHH),
6.45 (dd, J = 20.4, 14.7 Hz, 1 H, =CH), 7.34–7.40 (m, 3 H, C6H5), 7.50–
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7.53 (m, 2 H, C6H5), 7.79 (d, J = 2.1 Hz, 1 H, 4-H), 8.26 (d, J = 2.1 Hz, 3.7 Hz, 1 H, =CHH), 6.35 (dd, J = 20.5, 14.7 Hz, 1 H, =CH), 7.72 (d,
1 H, 4-H) ppm. 13C NMR (100.6 MHz, CDCl3): δ = –4.52 [Si(CH3)2],
J = 2.1 Hz, 1 H, 4-H), 8.25 (d, J = 2.1 Hz, 1 H, 6-H) ppm. 13C NMR
–4.12 (SiCH3), 53.22 (OCH3), 118.69 (C-3), 122.13 (C-5), 127.93, (100.6 MHz, CDCl3): δ = –3.32 [Si(CH3)2], –1.08 [Si(CH3)3], 53.00
129.47, 134.68 (C6H5), 135.26 (=CH2), 135.34 (=CH), 135.69 (C6H5), (OCH3), 119.28 (C-3), 125.81 (C-5), 132.53 (=CH2), 137.62 (=CH),
151.32 (C-4), 154.67 (C-6), 168.53 (C-2) ppm. IR (film): ν = 3052 (w), 149.67 (C-4), 152.82 (C-6), 168.27 (C-2) ppm. IR (film): ν = 3052 (w),
˜
˜
3012 (w), 2948 (m), 2904 (w), 2124 (m), 1564 (s), 1548 (s), 1454 (s),
3008 (w), 2952 (s), 2900 (w), 1566 (s), 1548 (s), 1454 (s), 1398 (s),
1428 (w), 1398 (s), 1360 (w), 1348 (w), 1296 (s), 1250 (s), 1176 (w), 1348 (m), 1296 (s), 1250 (s), 1176 (w), 1132 (m), 1096 (m), 1022 (s),
1122 (s), 1020 (s), 958 (w), 886 (s), 836 (w), 792 (s), 732 (s), 700 (m),
954 (m), 882 (s), 836 (s), 814 (s), 792 (m), 772 (m), 756 (m), 694
634 (m) cm–1. GC–MS (EI, 70 eV): m/z (%) = 313 (37) [M]+·, 312 (100), (m) cm–1. GC–MS (EI, 70 eV): m/z (%) = 265 (13), 264 (22), 250
298 (46), 286 (13), 254 (13), 239 (12), 121 (25). HRMS (ESI-TOF): calcd. (100), 224 (21), 220 (43), 208 (13), 73 (19). HRMS (ESI-TOF): calcd. for
for C17H24NOSi2 314.1396 [M + H]+; found 314.1398.
C
13H24NOSi2 266.1396 [M + H]+; found 266.1388.
5-[Dimethyl(prop-2-enyl)silyl]-3-(dimethysilyl)-2-methoxypyr- 3,5-Bis[(ethenyl)dimethylsilyl]-2-methoxypyridine (4i): Yield
idine (4e): Yield 53 %. The crude product purified by column chro-
matography (SiO2, CH2Cl2) gave a colourless oil. H NMR (400 MHz,
CDCl3, 23 °C): δ = 0.27 [s, 6 H, Si(CH3)2], 0.34 [d, J = 3.7 Hz, 6 H,
HSi(CH3)2], 1.74 (dt, J = 8.1, 1.2 Hz, 2 H, CH2), 3.95 (s, 3 H, OCH3),
75 %. The crude product purified by column chromatography (SiO2,
hexane/EtOAc, 20:1) gave a colourless oil. 1H NMR (400 MHz, CDCl3,
23 °C): δ = 0.33 [s, 6 H, Si(CH3)2], 0.35 [s, 6 H, Si(CH3)2], 3.94 (s, 3 H,
OCH3), 5.73 (dd, J = 6.5, 3.7 Hz, 1 H, =CHH), 5.78 (dd, J = 6.5, 3.7 Hz,
1
4.37 (sept, J = 3.7 Hz, 1 H, SiH), 4.84–4.90 (m, 2 H, =CH2), 5.71–5.82 1 H, =CHH), 6.03 (t, J = 3.9 Hz, 1 H, =CHH), 6.07 (t, J = 3.9 Hz, 1 H, =
(m, 1 H, =CH), 7.77 (d, J = 2.2 Hz, 1 H, 4-H), 8.26 (d, J = 2.2 Hz, 1 H, CHH), 6.25 (dd, J = 20.2, 14.6 Hz, 1 H, =CH), 6.34 (dd, J = 20.2,
6-H) ppm. 13C NMR (100.6 MHz, CDCl3): δ = –4.31 [Si(CH3)2], –3.40 14.6 Hz, 1 H, =CH), 7.72 (d, J = 2.1 Hz, 1 H, 4-H), 8.25 (d, J = 2.1 Hz,
[Si(CH3)2], 23.64 (CH2), 53.19 (OCH3), 113.73 (=CH2), 118.49 (C-3),
124.28 (C-5), 134.25 (=CH), 150.42 (C-4), 153.33 (C-6), 168.39 (C-
1 H, 6-H) ppm. 13C NMR (100.6 MHz, CDCl3): δ = –3.31 [Si(CH3)2],
–3.9 [Si(CH3)2], 53.03 (OCH3), 119.39 (C-3), 123.93 (C-5), 132.53 (=
CH2), 133.11 (=CH2), 137.56 (=CH), 137.61 (=CH), 150.10 (C-4), 153.41
2) ppm. IR (film): ν = 2960 (m), 2120 (m), 1630 (w), 1564 (m), 1548
˜
(m), 1454 (m), 1400 (m), 1360 (w), 1296 (m), 1248 (m), 1132 (m),
(C-6), 168.41 (C-2) ppm. IR (film): ν = 3052 (w), 3012 (w), 2956 (m),
˜
1020 (w), 890 (s), 824 (m), 792 (m) cm–1. GC–MS (EI, 70 eV): m/z 1564 (s), 1548 (m), 1454 (s), 1396 (s), 1350 (w), 1294 (m), 1250 (s),
(%) = 265 (3) [M]+·, 264 (7), 224 (100). HRMS (ESI-TOF): calcd. for 1176 (w), 1124 (m), 1096 (w), 1022 (m), 954 (m), 878 (s), 838 (s), 810
C13H24NOSi2 266.1396 [M + H]+; found 266.1389.
(s), 774 (m), 694 (m) cm–1. GC–MS (EI, 70 eV): m/z (%) = 277 (16)
[M]+·, 276 (33), 263 (24), 262 (91), 232 (54), 220 (19), 89 (20), 85 (42),
59 (100), 43 (17). HRMS (ESI-TOF): calcd. for C14H24NOSi2 278.1396
[M + H]+; found 278.1399.
3-(Dimethylsilyl)-6-[(ethenyl)dimethylsilyl]-2-methoxypyridine
(4f): Yield 58 %. The crude product purified by column chromatog-
raphy (SiO2, hexane/EtOAc, 20:1) gave a colourless oil. 1H NMR
(400 MHz, CDCl3, 23 °C): δ = 0.32 [d, J = 3.7 Hz, 6 H, HSi(CH3)2], 0.37
[s, 6 H, Si(CH3)2], 3.96 (s, 3 H, OCH3), 4.35 (sept, J = 3.7 Hz, 1 H, SiH),
3-[(Ethenyl)dimethylsilyl]-2-methoxypyridine (4j): Yield 74 %.
The crude product purified by distillation gave a colourless oil. B.p.
1
5.82 (dd, J = 20.3, 3.8 Hz, 1 H, =CHH), 6.06 (dd, J = 14.7, 3.8 Hz, 1 63–64 °C (6.7 mbar). H NMR (400 MHz, CDCl3, 23 °C): δ = 0.34 [s, 6
H, =CHH), 6.33 (dd, J = 20.3, 14.7 Hz, 1 H, =CH), 7.07 (d, J = 6.8 Hz,
H, Si(CH3)2], 3.93 (s, 3 H, OCH3), 5.76 (dd, J = 20.4, 3.7 Hz, 1 H, =
CHH), 6.04 (dd, J = 14.7, 3.7 Hz, 1 H, =CHH), 6.34 (dd, J = 20.4,
1 H, 5-H), 7.60 (d, J = 6.8 Hz, 1 H, 4-H) ppm. 13C NMR (100.6 MHz,
CDCl3): δ = –4.35 [HSi(CH3)2], –3.70 [Si(CH3)2], 52.91 (OCH3), 118.37 14.7 Hz, 1 H, =CH), 6.84 (dd, J = 6.9, 5.1 Hz, 1 H, 5-H), 7.64 (dd, J =
(C-3), 122.83 (C-5), 132.94 (=CH2), 137.40 (=CH), 143.38 (C-4), 164.98
6.9, 2.1 Hz, 1 H, 4-H), 8.16 (dd, J = 5.1, 2.1 Hz, 1 H, 6-H) ppm. 13C
NMR (100.6 MHz, CDCl3): δ = –3.36 [Si(CH3)2], 53.10 (OCH3), 116.69
(C-5), 120.09 (C-3), 132.59 (=CH2), 137.53 (=CH), 144.88 (C-4), 147.95
(C-6), 166.80 (C-2) ppm. IR (film): ν = 3048 (w), 3008 (w), 2960 (m),
˜
2852 (w), 2120 (m), 1564 (s), 1538 (s), 1450 (s), 1404 (m), 1346 (s),
1292 (w), 1248 (s), 1194 (w), 1168 (w), 1066 (w), 1024 (m), 954 (w), (C-6), 167.59 (C-2) ppm. IR (film): ν = 3048 (w), 2948 (m), 1570 (s),
˜
888 (s), 838 (s), 812 (s), 782 (s), 776 (s), 700 (w), 658 (w), 630
1454 (s), 1386 (s), 1296 (m), 1248 (s), 1086 (w), 1022 (s), 954 (m),
(w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 251 (63) [M]+·, 250 (100), 838 (s), 814 (m), 784 (s), 704 (m) cm–1. GC–MS (EI, 70 eV): m/z (%) =
237 (22), 236 (91), 224 (25), 177 (40), 149 (34), 59 (42). HRMS (ESI-
193 (11) [M]+·, 192 (32), 178 (100), 148 (93), 146 (35), 136 (50), 122
(25). HRMS (ESI-TOF): calcd. for C10H16NOSi 194.1001 [M + H]+;
found 194.0991.
TOF): calcd. for C12H22NOSi2 252.1240 [M + H]+; found 252.1243.
3-(Dimethylsilyl)-2-methoxypyridine (4g): Yield 66 %. The crude
product purified by distillation gave a colorless oil; b.p. 85–87 °C
(40.0 mbar). 1H NMR (400 MHz, CDCl3, 23 °C): δ = 0.33 [d, J = 3.7 Hz,
6 H, Si(CH3)2], 3.95 (s, 3 H, OCH3), 4.37 (sept, J = 3.7 Hz, 1 H, SiH),
3-[Dimethyl(prop-2-enyl)silyl]-2-methoxypyridine (4k): Yield
84 %. The crude product purified by distillation gave a colourless
oil. B.p. 53–55 °C (0.01 mbar). H NMR (400 MHz, CDCl3, 23 °C): δ =
1
6.85 (dd, J = 6.9, 5.1 Hz, 1 H, 5-H), 7.70 (dd, J = 6.9, 2.0 Hz, 1 H, 4- 0.26 [s, 6 H, Si(CH3)2], 1.81 (dt, J = 8.1, 1.0 Hz, 2 H, CH2), 3.93 (s, 3
H), 8.18 (dd, J = 5.1, 2.0 Hz, 1 H, 6-H) ppm. 13C NMR (100.6 MHz
H, OCH3), 4.78–4.87 (m, 2 H, =CH2), 5.69–5.80 (m, 1 H, =CH), 6.84
CDCl3): δ = –4.40 [HSi(CH3)2], 53.24 (OCH3), 116.73 (C-5), 119.13 (C- (dd, J = 6.9, 5.0 Hz, 1 H, 5-H), 7.62 (dd, J = 6.9, 2.0 Hz, 1 H, 4-H),
3), 145.20 (C-4), 148.19 (C-6), 167.58 (C-2) ppm. IR (film): ν = 3044 8.16 (dd, J = 5.0, 2.0 Hz, 1 H, 6-H) ppm. 13C NMR (100.6 MHz, CDCl3):
˜
(w), 2956 (s), 2860 (w), 2124 (s), 1570 (s), 1532 (w), 1454 (s), 1386
(s),1296 (s), 1248 (s), 1084 (m), 1022 (s), 892 (s), 840 (m), 786 (s), 760
(w), 720 (w), 694 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 167 (28)
[M+∙], 166 (55), 152 (30), 136 (30), 122 (100), 93 (26), 59 (28), 43
δ = –3.77 [Si(CH3)2], 22.71 (CH2), 53.08 (OCH3), 113.21 (=CH2), 116.67
(C-5), 120.00 (C-3), 134.84 (=CH), 144.75 (C-4), 147.95 (C-6), 167.52
(C-2) ppm. IR (film): ν = 3076 (w), 3044 (w), 2952 (m), 1628 (m),
˜
1570 (s), 1454 (s), 1386 (s), 1294 (m), 1248 (s), 1192 (w), 1156 (m),
(17). HRMS (ESI-TOF): calcd. for C8H14NOSi 168.0845 [M + H]+; found 1084 (m), 1022 (s), 992 (w), 932 (w), 896 (m), 842 (s), 788 (s), 752
168.0841.
(w), 692 (w), 648 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 207 (<1)
[M]+·, 166 (56), 136 (100). HRMS (ESI-TOF): calcd. for C11H18NOSi
208.1158 [M + H]+; found 208.1164.
3-[(Ethenyl)dimethylsilyl]-2-methoxy-5-(trimethylsilyl)pyridine
(4h): Yield 77 %. The crude product purified by column chromatog-
raphy (SiO2, CH2Cl2) gave a colourless oil. 1H NMR (400 MHz, CDCl3, 2-Methoxy-3-(methylsulfanyl)-5-(trimethylsilyl)pyridine (5a):
23 °C): δ = 0.25 [s, 9 H, Si(CH3)3], 0.35 [s, 6 H, Si(CH3)2], 3.94 (s, 3 H,
Yield 71 %. The crude product purified by column chromatography
OCH3), 5.77 (dd, J = 20.3, 3.7 Hz, 1 H, =CHH), 6.05 (dd, J = 14.7, (SiO2, CH2Cl2) gave a colourless oil. 1H NMR (400 MHz, CDCl3, 23 °C):
Eur. J. Org. Chem. 2016, 1292–1304
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δ = 0.28 [s, 9 H, Si(CH3)3], 2.44 (s, 3 H, SMe), 4.02 (s, 3 H, OCH3), 7.45
{2-Methoxy-5-[(ethenyl)dimethylsilyl]-3-pyridyl}diphen-
(d, J = 1.7 Hz, 1 H, 4-H), 8.02 (d, J = 1.7 Hz, 1 H, 6-H) ppm. 13C NMR ylmethanol (5f): Yield 62 %. The crude product purified by column
(100.6 MHz, CDCl3): δ = –1.09 [Si(CH3)3], 14.45 (SCH3), 53.77 (OCH3), chromatography (SiO2, CH2Cl2) gave a colourless solid, m.p. 56–
121.56 (C-3), 127.03 (C-5), 138.81 (C-4), 147.45 (C-6), 161.07 (C- 61 °C (hexane). 1H NMR (400 MHz, CDCl3, 23 °C): δ = 0.18 [s, 6 H,
2) ppm. IR (film): ν = 2952 (m), 1564 (s), 1462 (s), 1410 (s), 1360 (m), Si(CH3)2], 3.85 (s, 3 H, OCH3), 5.00 (s, 1 H, OH), 5.60 (dd, J = 20.0,
˜
1298 (m), 1262 (s), 1176 (w), 1124 (s), 1088 (s), 1018 (m), 882 (m),
3.7 Hz, 1 H, =CHH), 5.95 (dd, J = 14.7, 3.7 Hz, 1 H, =CHH), 6.09 (dd,
J = 20.0, 14.7 Hz, 1 H, =CH), 6.85 (d, J = 1.7 Hz, 1 H, 4-H), 7.18–7.34
834 (s), 766 (m), 694 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 227 (46)
[M]+·, 212 (100). HRMS (ESI-TOF): calcd. for C10H18NOSSi 228.0878 (m, 10 H, 2 × C6H5), 8.18 (d, J = 1.7 Hz, 1 H, 6-H) ppm. 13C NMR
[M + H]+; found 228.0869.
(100.6 MHz, CDCl3): δ = –3.10 [Si(CH3)2], 53.49 (OCH3), 80.97 (C-OH),
124.64 (C-5), 127.29 (C-Ar), 127.62 (C-Ar), 127.81 (C-Ar), 128.66 (C-3),
133.24 (=CH2), 136.93 (=CH), 143.58 (C-4), 145.47 (C-Ar), 151.00 (C-
5-[(Ethenyl)dimethylsilyl]-2-methoxy-3-(methylsulfanyl)pyr-
idine (5b): Yield 77 %. The crude product purified by column chro-
matography (SiO2, CH2Cl2) gave a colourless oil. H NMR (400 MHz,
CDCl3, 23 °C): δ = 0.35 [s, 6 H, Si(CH3)2], 2.43 (s, 3 H, SCH3), 4.02 (s,
3 H, OCH3), 5.76 (dd, J = 20.2, 3.7 Hz, 1 H, =CHH), 6.07 (dd, J = 14.6,
3.7 Hz, 1 H, =CHH), 6.25 (dd, J = 20.2, 14.6 Hz, 1 H, =CH), 7.44 (d,
J = 1.7 Hz, 1 H, 4-H), 8.02 (d, J = 1.7 Hz, 1 H, 6-H) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = –2.87 [Si(CH3)2], 14.36 (SCH3), 53.80 (OCH3),
121.73 (C-3), 125.08 (C-5), 133.44 (=CH2), 137.20 (=CH), 139.05 (C-4),
6), 161.74 (C-2) ppm. IR (film): ν = 3540 (br. m), 3060 (w), 3028 (w),
˜
1
2956 (m), 1582 (s), 1556 (m), 1492 (w), 1466 (s), 1448 (s), 1416 (s),
1364 (s), 1296 (w), 1274 (s), 1248 (w), 1180 (m), 1122 (s), 1014 (s),
964 (m), 916 (w), 838 (s), 812 (s), 776 (s), 758 (s), 702 (s), 664 (w),
646 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 375 (6) [M]+·, 360 (12),
298 (100), 192 (11), 105 (13), 85 (10), 77 (9). HRMS (ESI-TOF): calcd.
for C23H26NO2Si 376.1733 [M + H]+; found 376.1725.
{2-Methoxy-6-[(ethenyl)dimethylsilyl]-3-pyridyl}diphenyl-
methanol (5g): Yield 73 %. The crude product purified by column
chromatography (SiO2, hexane/EtOAc, 20:1) gave a colourless oil. 1H
NMR (400 MHz, CDCl3, 23 °C): δ = 0.36 [s, 6 H, Si(CH3)2], 3.88 (s, 3
H, OCH3), 5.21 (s, 1 H, OH), 5.81 (dd, J = 20.5, 3.8 Hz, 1 H, =CHH),
6.06 (dd, J = 14.7, 3.8 Hz, 1 H, =CHH), 6.32 (dd, J = 20.5, 14.7 Hz, 1
H, =CH), 6.69 (d, J = 7.3 Hz, 1 H, 5-H), 6.91 (d, J = 7.3 Hz, 1 H, 4-H),
7.10–7.27 (m, 10 H, C6H5) ppm. 13C NMR (100.6 MHz, CDCl3): δ =
–3.62 [Si(CH3)2], 53.22 (OCH3), 80.94 (C-OH), 123.04 (C-5), 127.23 (C-
Ar), 127.73 (C-Ar), 127.83 (C-Ar), 128.53 (C-3), 133.10 (=CH2), 136.53
(=CH), 137.23 (C-4), 145.67 (C-Ar), 160.18 (C-6), 162.54 (C-2) ppm. IR
147.93 (C-6), 161.14 (C-2) ppm. IR (film): ν = 3048 (w), 2952 (m),
˜
2924 (w), 2856 (w), 1564 (s), 1462 (s), 1408 (s), 1362 (m), 1300 (m),
1260 (m), 1176 (w), 1124 (s), 1088 (s), 1016 (s), 956 (m), 874 (m),
838 (s), 814 (s), 778 (s), 700 (m) cm–1. GC–MS (EI, 70 eV): m/z (%) =
239 (84) [M]+·, 238 (46), 224 (100), 212 (16), 198 (53). HRMS (ESI-
TOF): calcd. for C11H18NOSSi 240.0878 [M + H]+; found 240.0873.
2-Methoxy-3-(methylsulfanyl)-5-(dimethylsilyl)pyridine (5c):
Yield 74 %. The crude product purified by column chromatography
(SiO2, CH2Cl2) gave a colourless oil. 1H NMR (400 MHz, CDCl3, 23 °C):
δ = 0.35 [d, J = 3.7 Hz, 6 H, Si(CH3)3], 2.44 (s, 3 H, SCH3), 4.02 (s, 3
H, OCH3), 4.43 (sept, J = 3.7 Hz, 1 H, SiH), 7.46 (d, J = 1.7 Hz, 1 H,
4-H), 8.03 (d, J = 1.5 Hz, 1 H, 6-H) ppm. 13C NMR (100.6 MHz, CDCl3):
δ = –3.72 [Si(CH3)3], 14.31 (SCH3), 53.86 (OCH3), 121.98 (C-3), 124.16
(film): ν = 3536 (m), 3060 (w), 2952 (m), 2860 (w), 1690 (m), 1580
˜
(m), 1556 (m), 1490 (w), 1454 (s), 1410 (w), 1364 (m), 1340 (m), 1236
(s), 1168 (w), 1130 (w), 1114 (w), 1016 (s), 954 (w), 866 (w), 834 (m),
812 (s), 778 (m), 760 (s), 702 (s), 664 (w) cm–1. GC–MS (EI, 70 eV):
m/z (%) = 375 (84) [M]+·, 360 (38), 298 (100), 284 (66), 270 (78), 256
(34), 192 (15), 105 (40), 77 (26), 59 (17). HRMS (ESI-TOF): calcd. for
C23H26NO2Si 376.1733 [M + H]+; found 376.1728.
(C-5), 138.91 (C-4), 147.86 (C-6), 161.20 (C-2) ppm. IR (film): ν = 2952
˜
(m), 2920 (m), 2124 (s), 1564 (s), 1466 (s), 1408 (s), 1362 (m), 1298
(m), 1260 (s), 1176 (w), 1124 (s), 1088 (s), 1018 (s), 894 (s), 858 (m),
836 (m), 768 (m), 734 (w), 664 (w) cm–1. GC–MS (EI, 70 eV): m/z
(%) = 213 (86) [M]+·, 212 (20), 198 (100), 168 (13). HRMS (ESI-TOF):
calcd. for C9H16NOSSi 214.0722 [M + H]+; found 214.0716.
(2-Methoxy-3-pyridyl)diphenylmethanol (5h):[48] Yield 49 %. The
crude product purified by column chromatography (SiO2, CH2Cl2)
gave a white solid, m.p. 129–131 °C (hexane). 1H NMR (400 MHz,
CDCl3, 23 °C): δ = 3.86 (s, 3 H, OCH3), 5.10 (s, 1 H, OH), 6.78 (dd, J =
7.3, 4.9 Hz, 1 H, 2 H, 5-H), 6.81 (dd, J = 7.3, 2.2 Hz, 1 H, 4-H), 7.19–
7.33 (m, 10 H, 2 × C6H5), 8.11 (dd, J = 4.9, 2.2 Hz, 1 H, 6-H) ppm.
13C NMR (100.6 MHz, CDCl3): δ = 53.58 (OCH3), 80.86 (C-OH) 116.73
(C-5), 127.32, 127.66, 127.90 (C-Ar), 129.31 (C-3), 138.42 (C-4), 145.53
(C-Ar), 145.83 (C-6), 160.94 (C-2) ppm. GC–MS (EI, 70 eV): m/z (%) =
(13) [M]+·, 214 (100), 186 (13), 136 (33), 105 (21), 77 (21). HRMS (ESI-
TOF): calcd. for C19H18NO2 292.1338 [M + H]+; found 292.1344.
2-Methoxy-3-(methylsulfanyl)pyridine (5d):[47] Yield 70 %. The
crude product purified by column chromatography (SiO2, hexane/
EtOAc, 20:1) gave a colourless solid, m.p. 42–44 °C (hexane). 1H NMR
(400 MHz, CDCl3, 23 °C): δ = 2.42 (s, 3 H, SCH3), 4.02 (s, 3 H, OCH3),
6.88 (dd, J = 7.4, 4.9 Hz, 1 H, 5-H), 7.37 (dd, J = 7.4, 1.7 Hz, 1 H, 4-
H), 7.94 (dd, J = 4.9, 1.7 Hz, 1 H, 6-H) ppm. 13C NMR (100.6 MHz,
CDCl3): δ = 14.18 (SCH3), 53.83 (OCH3), 117.21 (C-5), 122.46 (C-3),
133.39 (C-4), 142.30 (C-6), 160.05 (C-2) ppm.
[2-Methoxy-5-(trimethylsilyl)-3-pyridyl]diphenylmethanol (5e):
Yield 68 %. The crude product purified by column chromatography
(SiO2, CH2Cl2) gave a colourless solid, m.p. 82–85 °C (hexane). 1H
NMR (400 MHz, CDCl3, 23 °C): δ = 0.10 [s, 9 H, Si(CH3)3], 3.85 (s, 3
H, OCH3), 5.01 (s, 1 H, OH), 6.83 (d, J = 1.8 Hz, 1 H, 4-H), 7.19–7.24
(m, 4 H, Ph-H), 7.25–7.34 (m, 6 H, Ph-H), 8.18 (d, J = 1.8 Hz, 1 H, 6-
H) ppm. 13C NMR (100.6 MHz, CDCl3): δ = –1.37 [Si(CH3)3], 53.45
(OCH3), 80.97 (C-OH), 126.56 (C-5), 127.29 (C-Ar), 127.63 (C-Ar),
127.80 (C-Ar), 128.49 (C-3), 143.09 (C-4), 145.50 (C-Ar) 150.42 (C-6),
2-Methoxy-5-(trimethylsilyl)pyridine-3-carbaldehyde (5i): Yield
41 %. The crude product purified by column chromatography (SiO2,
1
CH2Cl2) gave a colourless solid, m.p. 111–113 °C (hexane). H NMR
(400 MHz, CDCl3, 23 °C): δ = 0.30 [s, 9 H, Si(CH3)3], 4.08 (s, 3 H,
OCH3), 8.20 (d, J = 2.0 Hz, 1 H, 4-H), 8.45 (d, J = 2.0 Hz, 1 H, 6-H),
10.39 (s, 1 H, CHO) ppm. 13C NMR (100.6 MHz, CDCl3): δ = –1.22
[Si(CH3)3], 53.80 (OCH3), 118.32 (C-3), 127.51 (C-5), 142.74 (C-4),
157.30 (C-6), 165.04 (C-2), 189.57 (CHO) ppm. IR (KBr pellet): ν =
˜
2956 (m), 1676 (s), 1582 (s), 1556 (m), 1480 (s), 1442 (w), 1420 (w),
1392 (w), 1362 (w), 1324 (w), 1272 (m), 1248 (m), 1176 (w), 1104
161.61 (C-2) ppm. IR (KBr pellet): ν = 3548 (m), 3024 (w), 2952 (m),
˜
1580 (m), 1556 (m), 1460 (s), 1448 (m), 1414 (m), 1364 (m), 1344
(m), 1296 (w), 1268 (s), 1246 (m), 1178 (m), 1120 (m), 1028 (m), 1004
(m), 964 (w), 918 (w), 840 (s), 784 (w), 764 (m), 756 (m), 700 (s), 644
(w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 363 (<1) [M]+·, 347 (6), 287
(w), 1024 (m), 938 (m), 912 (m), 838 (s), 800 (w), 764 (w), 694 (w) cm–1
.
GC–MS (EI, 70 eV): m/z (%) = 209 (14) [M]+·, 194 (100). HRMS (ESI-
TOF): decomposition.
(100), 209 (33), 152 (11), 105 (13), 77 (13). HRMS (ESI-TOF): calcd. for 2-Methoxy-6-[(ethenyl)dimethylsilyl]pyridine-3-carbaldehyde
C22H26NO2Si 364.1733 [M + H]+; found 364.1725.
(5k): Yield 57 %. The crude product purified by column chromatog-
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1
raphy (silica gel, hexane/EtOAc, 20:1) gave a colourless oil. H NMR
2-Methoxy-5-({2-[(6-methoxy-3-pyridyl)dimethylsilyl]-
(400 MHz, CDCl3, 23 °C): δ = 0.40 [s, 6 H, Si(CH3)2], 4.09 (s, 3 H,
ethyl}dimethylsilyl)pyridine (7a): Yield 88 %. The crude product
OCH3), 5.84 (dd, J = 20.3, 3.7 Hz, 1 H, =CHH), 6.10 (dd, J = 14.7, purified by distillation gave a colourless oil. B.p. 141–145 °C
1
3.7 Hz, 1 H, =CHH), 6.31 (dd, J = 20.3, 14.7 Hz, 1 H, =CH), 7.23 (dd,
(0.1 mbar). H NMR (400 MHz, CDCl3, 23 °C): δ = 0.23 [s, 12 H, 2 ×
J = 7.3, 0.7 Hz, 1 H, 4-H), 7.98 (d, J = 7.3 Hz, 1 H, 5-H), 10.37 (d, J = Si(CH3)2], 0.61 [s, 4 H, (CH2)2], 3.94 (s, 6 H, 2 × OCH3), 6.73 (dd, J =
0.7 Hz, 1 H, CHO) ppm. 13C NMR (100.6 MHz, CDCl3): δ = –3.88 8.2, 0.7 Hz, 2 H, 2 × 3-H), 7.60 (dd, J = 8.2, 2.0 Hz, 2 H, 2 × 4-H), 8.20
[Si(CH3)2], 53.51 (OCH3), 117.75 (C-3), 123.09 (C-5), 133.79 (=CH2), (dd, J = 2.0, 0.7 Hz, 2 H, 2 × 6-H) ppm. 13C NMR (100.6 MHz, CDCl3):
135.19 (=CH), 136.30 (C-4), 163.20 (C-6), 173.10 (C-2), 189.92
δ = –3.61 [2 × Si(CH3)2], 7.83 (2 × CH2), 53.22 (2 × OCH3), 110.63
(CHO) ppm. IR (film): ν = 3052 (w), 2952 (m), 2860 (w), 1690 (s), (2 × C-3), 124.95 (2 × C-5), 143.64 (2 × C-4), 151.85 (2 × C-6), 164.72
˜
1580 (s), 1456 (s), 1404 (w), 1388 (m), 1362 (s), 1264 (s), 1216 (w),
1128 (m), 1100 (m), 1018 (s), 956 (m), 814 (s), 782 (s), 706 (m), 676
(2 × C-2) ppm. IR (film): ν = 3020 (w), 3008 (w), 2952 (m), 2924 (w),
2876 (w), 2848 (w), 1582 (s), 1556 (m), 1486 (s), 1462 (m), 1432 (w),
˜
(w), 638 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 221 (44) [M]+·, 220 1408 (w), 1384 (w), 1354 (s), 1336 (m), 1278 (s), 1250 (m), 1180 (w),
(70), 206 (100), 194 (34), 193 (19), 180 (34), 178 (15), 165 (40), 136 1136 (m), 1116 (s), 1076 (w), 1052 (m), 1012 (s), 834 (br. s), 778 (s),
(11), 59 (30). HRMS (ESI-TOF): calcd. for C11H16NO2Si 222.0950 [M + 756 (w), 702 (m), 610 (m) cm–1. GC–MS (EI, 70 eV): m/z (%) = 360
H]+; found 222.0953.
(32) [M]+·, 332 (26), 331 (49), 317 (18), 240 (16), 167 (15), 166 (100).
HRMS (ESI-TOF): calcd. for C18H28N2O2Si2 361.1768 [M + H]+; found
316,1763.
2-Methoxypyridine-3-carbaldehyde (5l): The 1H and 13C NMR
spectroscopic data for this product matched those reported previ-
ously.[30]
2-Methoxy-5-[{2-[(6-methoxy-3-pyridyl)dimethylsilyl]ethyl}-
(methyl)phenylsilyl]pyridine (7b): Yield 98 %. The crude product
purified by column chromatography (SiO2, CH2Cl2) gave a colourless
3-Iodo-2-methoxy-5-(trimethylsilyl)pyridine (5m): Yield 60 %.
The crude product purified by column chromatography (SiO2, hex-
ane/EtOAc, 25:1) gave a colourless oil. 1H NMR (400 MHz, CDCl3,
23 °C): δ = 0.27 [s, 9 H, Si(CH3)3], 3.99 (s, 3 H, OCH3), 8.07 (d, J =
1.6 Hz, 1 H, 4-H), 8.16 (d, J = 1.6 Hz, 1 H, 6-H) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = –1.16 [Si(CH3)3], 54.57 (OCH3), 80.84 (C-3),
129.50 (C-5), 151.06 (C-4), 152.69 (C-6), 162.31 (C-2) ppm. IR (film):
1
oil. H NMR (400 MHz, CDCl3, 23 °C): δ = 0.24 [s, 6 H, Si(CH3)2], 0.52
(s, 3 H, SiCH3), 0.65–0.70 (m, 2 H, CH2), 0.90–0.95 (m, 2 H, CH2), 3.93,
3.94 (2 s, 6 H, 2 × OCH3), 6.72 (dd, J = 8.2, 1.0 Hz, 1 H, 3-H), 6.72
(dd, J = 8.2, 1.0 Hz, 1 H, 3-H), 7.31–7.38 (m, 3 H, C6H5), 7.42–7.46
(m, 2 H, C6H5), 7.57 (dd, J = 8.2, 2.0 Hz, 1 H, 4-H), 7.58 (dd, J = 8.2,
2.0 Hz, 1 H, 4-H), 8.20 (dd, J = 2.0, 1.0 Hz, 1 H, 6-H), 8.22 (dd, J =
2.0, 1.0 Hz, 1 H, 6-H) ppm. 13C NMR (100.6 MHz, CDCl3): δ = –5.11
(SiCH3), –3.62 [Si(CH3)2], 6.27 (CH2), 7.87 (CH2), 53.22, 53.24 (2 ×
OCH3), 110.63, 110.77, (2 × C-3), 123.09, 124.76 (2 × C-5), 127.93,
129.36, 134.35, 136.34 (C6H5), 143.63, 144.37 (2 × C-4), 151.88,
ν = 2952 (m), 1566 (s), 1466 (s), 1412 (s), 1354 (m), 1294 (m), 1260
˜
(m), 1172 (w), 1118 (m), 1052 (m), 1014 (m), 866 (m), 838 (s), 762
(m), 692 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 307 (48) [M]+·, 292
(100). HRMS (ESI-TOF): calcd. for C9H15INOSi 307.9968 [M + H]+;
found 307.9963.
152.71 (2 × C-6), 164.75, 164.88 (2 × C-2) ppm. IR (film): ν = 3080
˜
(w), 2948 (m), 2908 (m), 1586 (s), 1556 (m), 1486 (s), 1462 (m), 1428
(w), 1406 (w), 1354 (s), 1282 (s), 1250 (m), 1176 (w), 1116 (s), 1052
(w), 1026 (s), 830 (s), 788 (s), 736 (m), 702 (m), 606 (m) cm–1. GC–
MS (EI, 70 eV): m/z (%) = 422 (55) [M]+·, 394 (51), 393 (58), 379 (19),
302 (12), 228 (100), 166 (32). HRMS (ESI-TOF): calcd. for
3-(Dimethylsilyl)-5-[(2-{[5-(dimethylsilyl)-6-methoxy-3-pyridyl]-
dimethylsilyl}ethyl)dimethylsilyl]-2-methoxypyridine (8): Yield
46 %. The crude product purified by column chromatography (SiO2,
hexane/EtOAc, 20:1) gave a colourless oil. 1H NMR (400 MHz, CDCl3,
23 °C): δ = 0.23 [s, 12 H, Si(CH3)2], 0.33 [d, J = 3.7 Hz, 12 H, SiH(CH3)2],
0.63 [s, 4 H, (CH2)2], 3.94 (s, 6 H, OCH3), 4.36 (sept, J = 3.7 Hz, 2 H,
SiH), 7.73 (d, J = 2.1 Hz, 2 H, 2 × 4-H), 8.22 (d, J = 2.1 Hz, 2 H, 2 ×
6-H) ppm. 13C NMR (100.6 MHz, CDCl3): δ = –4.28 [2 × Si(CH3)2],
–3.54 [2 × SiH(CH3)2], 7.88 (2 × CH2), 53.16 (2 × OCH3), 118.52 (2 ×
C-3), 124.75 (2 × C-5), 150.39 (2 × C-4), 153.32 (2 × C-6), 168.33 (2 ×
C
23H31N2O2Si2 423.1942 [M + H]+; found 423.1907.
2-Methoxy-5-[(2-{[6-methoxy-5-(methylsulfanyl)-3-pyridyl]-
dimethylsilyl}ethyl)dimethylsilyl]-3-(methylsulfanyl)pyridine
(7c): Yield 91 %. The crude product purified by column chromatog-
1
raphy (SiO2, CH2Cl2) gave a white solid, m.p. 82–84 °C (hexane). H
C-2) ppm. IR (film): ν = 3004 (w), 2952 (s), 2904 (m), 2124 (s), 1566
NMR (400 MHz, CDCl3, 23 °C): δ = 0.25 [s, 12 H, 2 × Si(CH3)2], 0.62
(s, 4 H, 2 × CH2), 2.41 (s, 6 H, 2 × SCH3), 4.02 (s, 6 H, 2 × OCH3), 7.39
(d, J = 1.5 Hz, 2 × 4-H), 7.98 (d, J = 1.5 Hz, 2 H, 2 × 6-H) ppm. 13C
NMR (100.6 MHz, CDCl3): δ = –3.55 [2 × Si(CH3)2], 7.91 (2 × CH2),
14.43 (2 × SCH3), 53.80 (2 × OCH3), 121.71 (2 × C-3), 125.69 (2 × C-
5), 138.69 (2 × C-4), 147.69 (2 × C-6), 161.10 (2 × C-2) ppm. IR (film):
˜
(s), 1548 (s), 1454 (s), 1400 (s), 1360 (m), 1296 (s), 1250 (s), 1176 (m),
1132 (s), 1096 (m), 1020 (s), 896 (br. s), 834 (s), 808 (s), 790 (s), 724
(w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 475 (4) [M]+·, 463 (24), 462
(47), 418 (16), 417 (43), 225 (20), 224 (91), 150 (17), 89 (17), 73 (15),
59 (26). HRMS (ESI-TOF): calcd. for C22H41N2O2Si4 477.2245 [M + H]+;
found 477.2248.
ν = 3036 (w), 3008 (w), 2992 (w), 2952 (m), 2908 (w), 1560 (s), 1468
˜
(m), 1454 (s), 1408 (s), 1364 (m), 1316 (w), 1296 (m), 1252 (m), 1246
(m), 1176 (w), 1120 (s), 1086 (m), 1052 (w), 1016 (m), 966 (w), 872
(m), 836 (m), 808 (s), 780 (m), 760 (w), 708 (w) cm–1. GC–MS (EI,
70 eV): m/z (%) = 452 (46) [M]+·, 437(27), 409 (19), 405 (31), 286
(17), 212 (100), 169 (18). HRMS (ESI-TOF): calcd. for C20H33N2O2S2Si2
453.1522 [M + H]+; found 453.1508.
General Procedure for the Synthesis of 7 and 9: The [Pt(cod)Me2]
catalyst (0.83 mg, 2.5 μmol) was added to a solution of the HSi
(5.5 mmol)* and alkenylSi derivative (5.2 mmol) in toluene (25 mL),
and the reaction mixture was stirred for 24 h at 60 °C.** After cool-
ing, ethyl acetate (25 mL) was added and the solution was passed
through a pad of Celite. Concentration in vacuo and purification by
distillation or flash column chromatography yielded product 7 or 9. 2-Methoxy-5-({3-[(6-methoxy-3-pyridyl)dimethylsilyl]propyl}-
*In the synthesis of 7i, substrates 2b and 4i were used in a molar
ratio of 2.2:1. In the synthesis of 7j, substrates 2a and 6 were used
in a molar ratio of 2:1. In the synthesis of 9 substrates 2a and 8
were used in a molar ratio of 2:1. **In the synthesis of 7e, after
stirring for 24 h at 60 °C, an additional portion (0.83 mg) of the
[Pt(cod)Me2] catalyst was added and the reaction mixture was
stirred for 24 h at 60 °C.
dimethylsilyl)pyridine (7d): Yield 69 %. The crude product purified
by column chromatography (SiO2, CH2Cl2) gave a colourless oil. H
1
NMR (400 MHz, CDCl3, 23 °C): δ = 0.22 [s, 12 H, 2 × Si(CH3)2], 0.76–
0.82 (m, 4 H, 2 × CH2), 1.32–1.41 (m, 2 H, CH2), 3.94 (s, 6 H, 2 ×
OCH3), 6.72 (dd, J = 8.3, 0.9 Hz, 1 H, 2 × 3-H), 7.59 (dd, J = 8.3,
2.0 Hz, 1 H, 2 × 4-H), 8.19–8.21 (m, 1 H, 2 × 6-H) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = –2.91 [2 × Si(CH3)2], 18.26 (CH2), 20.13 (2 ×
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CH2), 53.20 (2 × OCH3), 110.59 (2 × C-3), 125.34 (2 × C-5), 143.56 less oil. H NMR (400 MHz, CDCl3, 23 °C): δ = 0.21, 0.22 (2 s, 12 H,
(2 × C-4), 151.73 (2 × C-6), 164.69 (2 × C-2) ppm. IR (film): ν = 2952 2 × SiMe2), 0.53–0.60 (m, 2 H, CH2), 0.67–0.73 (m, 2 H, CH2), 3.81 (s,
˜
(m), 2916 (m), 1586 (s), 1556 (s), 1488 (s), 1462 (m), 1354 (s), 1286
3 H, OCH3), 3.88 (s, 3 H, OCH3), 6.83 (dd, J = 7.0, 5.0 Hz, 1 H, 5-H),
(s), 1250 (m), 1178 (w), 1116 (s), 1026 (m), 904 (m), 830 (s), 772 (m), 6.90 (d, J = 8.5 Hz, 2 H, C6H4), 7.40 (d, J = 8.5 Hz, 2 H, C6H4), 7.58
698 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 374 (28) [M]+·, 345 (62), (dd, J = 7.0, 2.1 Hz, 1 H, 4-H), 8.14 (dd, J = 5.0, 2.1 Hz, 1 H, 6-H) ppm.
166 (100). HRMS (ESI-TOF): calcd. for C19H31N2O2Si2 375.1924 [M + 13C NMR (151.0 MHz, CDCl3): δ = –3.80 [Si(CH3)2], –3.39 [Si(CH3)2],
H]+; found 375.1921.
6.99, 8.06 (2 × CH2), 53.00, 55.02 (2 × OCH3), 113.50 (Ar), 116.67 (C-
5), 120.64 (C-3), 130.26 (Ar), 135.06 (Ar), 144.86 (C-4), 147.72 (C-6),
2-Methoxy-5-({3-[(2-methoxy-3-pyridyl)dimethylsilyl]propyl}-
dimethylsilyl)pyridine (7e): Yield 99 %. The crude product purified
by column chromatography (SiO2, CH2Cl2) gave a colourless oil. H
160.25 (Ar), 167.63 (C-2) ppm. IR (film): ν = 2952 (s), 2928 (m), 2848
˜
(w), 1594 (s), 1570 (s), 1502 (s), 1454 (s), 1384 (s), 1294 (m), 1278 (s),
1246 (s), 1182 (m), 1134 (m), 1112 (s), 1086 (w), 1054 (w), 1022 (m),
834 (s), 786 (s), 710 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 359 (9)
[M]+·, 344 (32), 330 (22), 166 (100) 165 (89), 136 (92). HRMS (ESI-
TOF): calcd. for C19H30NO2Si2 360.1815 [M + H]+; found 360.1807.
1
NMR (400 MHz): δ = 0.21 [s, 12 H, 2 × Si(CH3)2], 0.76–0.87 (m, 4 H,
2 × CH2), 1.31–1.40 (m, 2 H, CH2), 3.90 (s, 3 H, OCH3), 3.94 (s, 3 H,
OCH3), 6.72 (d, J = 8.1 Hz, 1 H, 3′-H), 6.83 (d, J = 6.8, 5.1 Hz, 1 H, 5-
H), 7.57–7.61 (m, 2 H, 4-H, 4′-H), 8.14 (dd, J = 5.1, 2.1 Hz, 1 H, 6-H),
8.20 (d, J = 2.1 Hz, 1 H, 6′-H) ppm. 13C NMR (151.0 MHz, CDCl3): δ =
–3.19 [Si(CH3)2], –2.89 [Si(CH3)2], 18.39, 19.39, 20.08 (3 × CH2), 53.01,
53.19 (2 × OCH3), 110.56 (C-3′), 116.67 (C-5), 120.83 (C-3), 125.51 (C-
5′), 143.57 (C-4′), 144.58 (C-4), 147.73 (C-6), 151.76 (C-6′), 164.69 (C-
2-Methoxy-3,5-bis({2-[(6-methoxy-3-pyridyl)dimethyl-
silyl]ethyl}dimethylsilyl)pyridine (7i): Yield 63 %. The crude prod-
uct purified by column chromatography (SiO2, hexane/EtOAc, 20:1)
gave a colourless oil. 1H NMR (400 MHz, CDCl3, 23 °C): δ = 0.2–0.25
[m, 24 H, 4 × Si(CH3)2], 0.54–0.74 (m, 8 H, 4 × CH2), 3.89 (s, 3 H,
OCH3,A), 3.94 (s, 6 H, 2 × OCH3,B), 6.72 (d, J = 8.2 Hz, 2 H, 2 × 3-HB),
7.60 (dd, J = 8.2, 2.1 Hz, 1 H, 4-HB), 7.61 (dd, J = 8.2, 2.1 Hz, 1 H, 4-
HB), 7.63 (d, J = 2.1 Hz, 1 H, 4-HA), 8.20 (d, J = 2.2 Hz, 1 H, 6-HA),
8.21–8.23 (m, 2 H, 2 × 6-HB) ppm. 13C NMR (100.6 MHz, CDCl3): δ =
–3.83, [3 × Si(CH3)2], –3.11 [Si(CH3)2], 7.01, 7.84, 7.88, 7.93 (4 × CH2),
52.91 (OCH3,A), 53.19 (2 × OCH3,B), 110.55, 110.62 (2 × C-3), 119.71,
124.48, 124.98, 125.21 (C-3, 3 × C-5), 142.61, 143.66 (2 × C-4B),
149.83 (C-4A), 151.86 (2 × C-6B), 152.90 (C-6A), 164.69, 164.72, 168.29
2′), 167.58 (C-2) ppm. IR (film): ν = 3044 (w), 2952 (m), 2916 (m),
˜
1586 (s), 1570 (s), 1556 (m), 1488 (s), 1454 (s), 1384 (s), 1354 (m),
1336 (w), 1286 (s), 1248 (s), 1116 (s), 1086 (w), 1024 (s), 944 (w), 904
(m), 834 (s), 786 (s), 696 (m) cm–1. GC–MS (EI, 70 eV): m/z (%) = 374
(6) [M]+·, 359 (31), 278 (24), 166 (98), 136 (100). HRMS (ESI-TOF):
calcd. for C19H31N2O2Si2 375.1924 [M + H]+; found 375.1909.
2-Methoxy-5-({2-[(4-methoxyphenyl)dimethylsilyl]ethyl}-
dimethylsilyl)pyridine (7f): Yield 77 %. The crude product purified
by column chromatography (SiO2, hexane/EtOAc, 20:1) gave a col-
ourless oil. 1H NMR (400 MHz, CDCl3, 23 °C): δ = 0.21 [s, 6 H,
Si(CH3)2], 0.22 [s, 6 H, Si(CH3)2], 0.61 (s, 4 H, 2 × CH2), 3.81 (s, 3 H,
OCH3), 3.94 (s, 3 H, OCH3), 6.72 (dd, J = 8.2, 0.9 Hz, 1 H, 3-H), 6.90
(dm, J = 8.5 Hz, 2 H, C6H4), 7.39 (dm, J = 8.5 Hz, 2 H, C6H4), 7.59
(dd, J = 8.2, 1.9 Hz, 1 H, 4-H), 8.2–8.22 (m, 1 H, 6-H) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = –3.23 [Si(CH3)2], –3.11 [Si(CH3)2], 8.20 (CH2),
8.32 (CH2), 53.52 (OCH3), 55.34 (OCH3), 110.91 (C-3), 113.85 (Ar),
125.52 (C-5), 130.27 (Ar), 135.37 (Ar), 144.02 (C-4), 152.21 (C-6),
(3 × C-2) ppm. IR (film): ν = 3016 (w), 2952 (s), 2904 (m), 2840 (w),
˜
1586 (s), 1556 (m), 1486 (s), 1462 (m), 1440 (w), 1396 (s), 1354 (s),
1282 (s), 1246 (s), 1182 (w), 1132 (m), 1114 (s), 1052 (m), 1028 (s),
880 (s), 834 (br. s), 778 (s), 710 (m), 610 (m) cm–1. GC–MS (EI, 70 eV):
m/z (%) = 612 (<1) [M]+·, 596 (2), 418 (39), 417 (100), 387 (10), 166
(35). HRMS (ESI-TOF): calcd. for C30H50N3O3Si4 612.2929 [M + H]+;
found 612.2935.
2-Methoxy-5-[10-(6-methoxy-3-pyridyl)-2,5,5,7,7,10-hexa-
methyl-6-oxa-2,5,7,10-tetrasilaundecan-2-yl]pyridine (7j): Yield
58 %. The crude product purified by column chromatography (SiO2,
hexane/EtOAc, 20:1) gave a colourless oil. 1H NMR (400 MHz, CDCl3,
23 °C): δ = –0.04–0.04 [s, 12 H, 2 × Si(CH3)2], 0.22–0.29 [s, 12 H, 2 ×
Si(CH3)2], 0.35–0.41 (m, 4 H, 2 × CH2), 0.59–0.65 (m, 4 H, 2 × CH2),
3.95 (s, 6 H, 2 × OCH3), 6.72–6.76 (m, 2 H, 2 × 5-H), 7.61–7.66 (m, 2
H, 2 × 4-H), 8.21–8.25 (m, 2 H, 2 × 6-H) ppm. 13C NMR (100.6 MHz,
CDCl3): δ = –3.31 [2 × Si(CH3)2], –0.05 [2 × Si(CH3)2], 7.49 (2 × CH2),
10.51 (2 × CH2), 53.41 (2 × OCH3), 110.88 (2 × C-3), 125.45 (2 × C-5),
143.89 (2 × C-4), 152.12 (2 × C-6), 164.98 (2 × C-2) ppm. IR (film):
160.61 (Ar), 165.04 (C-2) ppm. IR (film): ν = 3016 (w), 2952 (s), 2904
˜
(m), 2840 (w), 1586 (s), 1556 (m), 1502 (s), 1486 (s),1462 (m), 1440
(w), 1408 (w), 1354 (s), 1320 (m), 1282 (s), 1246 (s), 1182 (m), 1132
(m), 1114 (s), 1052 (m), 1028 (s), 834 (br. s), 778 (s), 710 (m), 610
(m) cm–1. GC–MS (EI, 70 eV): m/z (%) = 359 (41) [M]+·, 331 (48), 316
(26), 166 (53), 165 (100). HRMS (ESI-TOF): calcd. for C19H30NO2Si2
360.1815 [M + H]+; found 360.1813.
2-Methoxy-5-({3-[(4-methoxyphenyl)dimethylsilyl]propyl}-
dimethylsilyl)pyridine (7g): Yield 63 %. The crude product purified
by column chromatography (SiO2, CH2Cl2) gave a colourless oil. H
1
ν = 2956 (s), 2908 (m), 1586 (s), 1556 (m), 1486 (s), 1462 (w), 1432
NMR (400 MHz, CDCl3, 23 °C): δ = 0.20 [s, 6 H, Si(CH3)2], 0.21 [s, 6
H, Si(CH3)2], 0.74–0.81 (m, 4 H, 2 × CH2), 1.33–1.42 (m, 2 H, CH2),
3.81 (s, 3 H, OCH3), 3.94 (s, 3 H, OCH3), 6.72 (dd, J = 8.2, 0.9 Hz, 1
H, 3-H), 6.88–6.91 (m, 2 H, C6H4), 7.37–7.41 (m, 2 H, C6H4), 7.59 (dd,
J = 8.3, 2.0 Hz, 1 H, 4-H), 8.20–8.21 (m, 1 H, 6-H) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = –2.88, –2.72 [2 × Si(CH3)2], 18.36, 20.12,
20.40 (3 × CH2), 53.20, 55.00 (2 × OCH3), 110.55 (C-3), 113.49 (Ar),
125.50 (C-5) 130.36 (Ar), 134.91 (Ar), 143.60 (C-4), 151.75 (C-6),
˜
(w), 1406 (w), 1384 (w), 1354 (m), 1284 (s), 1252 (s), 1178 (w), 1132
(m), 1116 (s), 1050 (br. s), 828 (br. s) cm–1. GC–MS (EI, 70 eV): m/z
(%) = 520 (4) [M]+·, 505 (25), 354 (11), 328 (16), 327 (33), 326 (100),
167 (22), 166 (90), 73 (17). HRMS (ESI-TOF): calcd. for C42H71N4O4Si6
521.2507 [M + H]+; found 521.2525.
2-Methoxy-5-[(2-{[6-methoxy-5-({2-[(6-methoxy-3-pyrid-
yl)dimethylsilyl]ethyl}dimethylsilyl)-3-pyridyl]dimethyl-
silyl}ethyl)dimethylsilyl]-3-({2-[(6-methoxy-3-pyridyl)di-
methylsilyl]ethyl}dimethylsilyl)pyridine (9): Yield 26 %. The
crude product purified by column chromatography (SiO2, hexane/
160.20 (Ar), 164.66 (C-2) ppm. IR (film): ν = 2952 (m), 2912 (m), 1586
˜
(s), 1564 (w), 1556 (m), 1502 (m), 1486 (m), 1464 (w), 1354 (m), 1282
(s), 1248 (s), 1182 (m), 1138 (w), 1114 (s), 1028 (m), 904 (m), 828 (s),
770 (m), 694 (w) cm–1. GC–MS (EI, 70 eV): m/z (%) = 373 (28) [M]+·,
344 (32), 264 (50), 165 (100). HRMS (ESI-TOF): calcd. for C20H32NO2Si2
374.1972 [M + H]+; found 374.1777.
1
EtOAc, 20:1) gave a colourless oil. H NMR (400 MHz, CDCl3, 23 °C):
δ = 0.14 [s, 24 H, 4 × Si(CH3)2], 0.15 [s, 12 H, 2 × Si(CH3)2], 0.48–0.65
(m, 12 H, 6 × CH2), 3.80 (s, 6 H, 2 × OCH3), 3.84 (s, 6 H, 2 × OCH3),
2-Methoxy-3-({2-[(4-methoxyphenyl)dimethylsilyl]ethyl}di- 6.63 (dd, J = 8.2, 0.7 Hz, 2 H, 2 × 3-H), 7.52 (dd, J = 8.2, 2.0 Hz, 2 H,
methylsilyl)pyridine (7h): Yield 46 %. The crude product was puri- 2 × 4-H), 7.56 (d, J = 2.0 Hz, 2 H, 2 × 4-H), 8.12 (d, J = 2.0 Hz, 2 H,
fied by column chromatography (silica gel, DCM) to give a colour- 2 × 6-H), 8.14 (dd, J = 2.0, 0.7 Hz, 2 H, 2 × 6-H) ppm. 13C NMR
Eur. J. Org. Chem. 2016, 1292–1304
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[4] For selected examples, see: a) S. E. Denmark, R. F. Sweis, Chem. Pharm.
Bull. 2002, 50, 1531–1541; b) S. E. Denmark, J. H.-C. Liu, Angew. Chem.
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(100.6 MHz, CDCl3): δ = –3.49 [2 × Si(CH3)2], –3.23 [4 × Si(CH3)2],
7.33 (2 × CH2), 8.22 (2 × CH2), 8.26 (2 × CH2), 53.23 (2 × OCH3), 53.46
(2 × OCH3), 110.88 (2 × C-3), 119.99 (2 × C-3), 124.82 (2 × C-5),
125.47 (2 × C-5), 143.95 (2 × C-4), 150.15 (2 × C-4) 152.18 (2 × C-6),
153.23 (2 × C-6), 165.00 (2 × C-2), 168.59 (2 × C-2) ppm. IR (film):
ν = 2952 (s), 2904 (m), 1586 (s), 1564 (s), 1548 (w), 1486 (m), 1454
˜
(m), 1396 (s), 1352 (m), 1286 (s), 1248 (s), 1176 (w), 1132 (m), 1116
(s), 1096 (w), 1054 (m), 1024 (m), 880 (s), 830 (br. s), 710 (w) cm–1
.
GC–MS (EI, 70 eV): m/z (%) = 862 (<1) [M]+·, 669 (29), 417 (100), 166
(50), 89 (12). HRMS (ESI-TOF): calcd. for C42H71N4O4Si6 863.4091 [M
+ H]+; found 863.4097.
[7] For recent examples, see: a) D. Y. Son, Chem. Commun. 2013, 49, 10209–
10210; b) K. Hatano, K. Matsuoka, D. Terunuma, Chem. Soc. Rev. 2013,
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Synthesis of Oligomer 10: The [Pt(cod)Me2] catalyst (0.8 mg,
2.4 μmol) was added to a solution of compound 4a (1.333 g,
5.3 mmol) in toluene (5 mL) and the reaction mixture was stirred
at 60 °C for 7 d. After this time an additional portion of the catalyst
(8 mg, 24 μmol) was added and the mixture was continuously
stirred for an additional 24 h at 60 °C. After cooling, ethyl acetate
(75 mL) was added and the solution was passed through a pad of
Celite and washed with ethyl acetate (15 mL). After concentration
in vacuo, 0.259 g (20 % yield) of product 10 was isolated as a thick
oil by precipitation from CH2Cl2 solution initiated by adding MeOH.
[8] N. N. Makarova, T. V. Astapova, A. I. Buzin, A. P. Polishchuk, N. V. Chizhova,
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5-{[2-({5-[(Ethenyl)dimethylsilyl]-2-methoxy-3-pyridyl}-
dimethylsilyl)ethyl]dimethylsilyl}-2-methoxy-3-{[2-({6-
methoxy-5-[(2-{[6-methoxy-5-({2-[(6-methoxy-5-)]2-})6-meth-
oxy-5-]}2-)]6-methoxy-5-})2-]}-6-methoxy-3-pyridyldimeth-
ylsilyl]ethyl}dimethylsilyl)-3-pyridyl]dimethylsilyl}ethyl)-
dimethylsilyl]-3-pyridyl}dimethylsilyl)ethyl]dimethylsilyl}-3-
pyridyl)dimethylsilyl]ethyl}dimethylsilyl-3-pyridyl]dimeth-
ylsilyl}ethyl)dimethylsilyl]-3-pyridyl}dimethylsilyl)ethyl-
dimethylsilylpyridine (10): 1H NMR (400 MHz, CDCl3, 23 °C): δ =
0.22 [s, 84 H, 14 × Si(CH3)2], 0.33 [s, 6 H, vinylSi(CH3)2], 0.54–0.77 (m,
28 H, 14 × CH2Si), 3.88 (s, 21 H, 7 × OCH3), 3.93 (s, 3 H, OCH3), 5.74
(dd, J = 20.1, 3.6 Hz, 1 H, =CHH), 6.05 (dd, J = 14.6, 3.6 Hz, 1 H, =
CHH), 6.25 (dd, J = 20.1, 14.6 Hz, 1 H, =CH), 6.72 (d, J = 8.2 Hz, 1 H,
3-H), 7.57–7.74 (m, 8 H, 8 × 4-H), 8.17–8.29 (m, 8 H, 8 × 6-H) ppm.
13C NMR (100.6 MHz, CDCl3): δ = –3.81 [7 × Si(CH3)2], –3.51 [7 ×
Si(CH3)2], –2.84 [vinylSi(CH3)2], 7.08 (7 × CH2), 7.94 (7 × CH2), 52.94
(7 × OCH3), 53.19 (OCH3,A), 110.55 (C-3A), 119.71, 119.80 (C-3),
123.83, 124.56, 124.77, 125.20 (C-5), 133.11 (=CH2), 137.56 (=CH),
143.66 (C-4A), 149.88, 150.06 (C-4), 151.85 (C-6A), 152.85, 153.14 (C-
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6), 164.68 (C-2A), 168.21, 168.36 (C-2) ppm. IR (film): ν = 2950 (w),
˜
2894 (w), 1584 (w), 1546 (m), 1490 (w), 1450 (m), 1394 (s), 1350 (w),
1244 (s), 1174 (w), 1132 (m), 1116 (m), 1094 (w), 1054 (w), 1020 (m),
876 (s), 800 (s), 772 (s), 704 (m), 620 (m) cm–1
.
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Acknowledgments
Financial support from the Faculty of Chemical Technology and
Engineering, West Pomeranian University of Technology, Szcze-
cin is gratefully acknowledged. The authors give special thanks
to Prof. Grzegorz Schroeder from A. Mickiewicz University in
Poznań for the MALDI-TOF analyses.
[27]
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Keywords: Nitrogen heterocycles · Metalation ·
Hydrosilylation · Silanes · Magnesates
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Received: December 14, 2015
Published Online: February 4, 2016
Eur. J. Org. Chem. 2016, 1292–1304
www.eurjoc.org
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