Nickel-Catalyzed Decarbonylative Coupling of Aryl Esters and Arylboronic Acids

Article abstract of DOI:10.1002/ejoc.201500630

A variety of functionalized biaryls can be accessed by coupling aryl and heteroaryl esters with boronic acids in Suzuki-Miyaura-type decarbonylative cross-coupling catalyzed by an affordable catalyst system composed of Ni(cod)₂ and PCy₃. The methodology is tolerant of a variety of functional groups and presents an attractive alternative to the use of palladium catalysis currently used in industry to acquire such bis(hetero)aryls, but also reveals challenges associated with nickel catalysis of esters in cross-coupling chemistry.

Full text of DOI:10.1002/ejoc.201500630

FULL PAPER
DOI: 10.1002/ejoc.201500630
Nickel-Catalyzed Decarbonylative Coupling of Aryl Esters and Arylboronic
Acids
Nicole A. LaBerge[a] and Jennifer A. Love*[a]
Keywords: Nickel / Biaryls / Esters / Cross-coupling / Decarbonylation
A variety of functionalized biaryls can be accessed by cou-
pling aryl and heteroaryl esters with boronic acids in Suzuki–
Miyaura-type decarbonylative cross-coupling catalyzed by
an affordable catalyst system composed of Ni(cod)2 and
PCy3. The methodology is tolerant of a variety of functional
groups and presents an attractive alternative to the use of
palladium catalysis currently used in industry to acquire such
bis(hetero)aryls, but also reveals challenges associated with
nickel catalysis of esters in cross-coupling chemistry.
and or production of toxic by-products. Additionally, palla-
dium is costly, and specialized ligands are required to cir-
cumvent low reactivity of aryl chlorides.[10] For heteroaryl
compounds, the potential for catalyst poisoning by hetero-
atom binding presents an additional challenge in cross-cou-
pling.
Introduction
Situated just above palladium in the Periodic Table nickel
is increasingly sought as an inexpensive alternative to palla-
dium for use in cross-coupling methodologies. Nickel is able
to access a variety of oxidation states, which allows for a
diverse range of synthetically useful transformations.[1] The
small atomic radius of nickel renders it more adept than
palladium toward the activation of strong bonds, such as
the C–O bonds of carboxylates,[2] carbamates,[3] and
ethers.[4] Although the last decade has witnessed an increase
in reports on nickel catalysis, to date catalysis with nickel
remains much less studied than with palladium. Conse-
quently, there lies great demand in further exploring the
reactivity and catalytic potential of nickel.
Biaryls are considered “privileged structures” because of
their prominence in pharmaceuticals.[5] In many cases, one
or both of the aryl groups contain a heteroatom. Relevant
examples include Gleevec, a tyrosine kinase inhibitor used
to treat various types of cancers, as well as Atazanavir, an
antiretroviral agent used to treat human immunodeficiency
virus (HIV) (Figure 1).[6] Currently, the most common route
to biaryls involves cross-coupling of aryl halides and orga-
nometallic reagents by using a palladium catalyst (Fig-
ure 2).[7,8] It is noteworthy that aryl chlorides, which are
substantially less expensive than aryl bromides and iodides,
tend to exhibit lower reactivity, presumably because of the
stronger C–Cl bond relative to C–Br and C–I bonds. Biaryls
may also be accessed by decarbonylative coupling with ar-
enes.[9] Challenges associated with these methods include
undesired homocoupling, sometimes use of toxic reagents
Figure 1. Examples of notable bis(hetero)aryls.
[a] Department of Chemistry, University of British Columbia,
2036 Main Mall, Vancouver, British Columbia, V6T 1Z1,
Canada
E-mail: jenlove@chem.ubc.ca
http://love.chem.ubc.ca/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201500630.
Figure 2. Cross-coupling routes to biaryls.
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Ni-Catalyzed Decarbonylative Coupling of Aryl Esters and Arylboronic Acids
Since Gooβen’s report of a decarboxylative arylation Table 1. Reaction condition optimizations. To a sealed tube was
process in 2006,[11] aroyl compounds have received inten-
added phenyl nicotinate (0.5 mmol), phenylboronic acid
(0.75 mmol), Ni(cod)2 (0.05 mmol), ligand (0.1 mmol), base
(1 mmol), and solvent (2 mL).
sified interest as attractive cross-coupling partners in place
of aryl halides due to their low cost, commercial availability
and high thermal stability.[12] Several reports of cross-cou-
pling using ethers,[4] aryl sulfonates,[13] phosphates,[14] carb-
amates,[3] and sulfamates have emerged in the last dec-
ade.[15] Notably in 2012, Itami et al. described an example
decarbonylative coupling of aryl esters and azoles catalyzed
by nickel and dcype [1,2-bis(dicyclohexylphosphino)eth-
ane].[9] Although the method provided a route to bis(hetero)-
aryls, the azole scope was limited. Later in 2013, Itami and
colleagues extended this work to the decarbonylative cou-
pling of alkenyl esters and azoles also using nickel and
dcype.[16]
Despite these accounts, the use of esters as the electro-
philic cross-coupling partner remains rare.[2,9,16] Owing to
the ubiquitous nature of esters, their use in cross-coupling
reactions would be highly advantageous for late-stage syn-
thetic manipulation. Thus, given the small number of cross-
coupling accounts using esters and our previous work in the
field of nickel catalysis,[17] we sought to investigate nickel-
catalyzed C–O activation[2–4,18] toward the preparation of
biaryl scaffolds. Herein, we report that use of ArB(OH)2
expands the scope of biaryls accessible by decarbonylative
coupling of aryl esters.
Results and Discussion
Our investigation began by identifying a suitable trans-
metallating reagent that could be coupled with phenyl
[a] GC yield average based upon two runs by using n-dodecane as
an internal standard. [b] Reaction mixture microwaved at 150 °C
nicotinate in the presence of Ni(cod)2 (cod = 1,5-cyclo-
octadiene) and an appropriate phosphine ligand. Among
those considered, including arylboronic acids, arylzinc rea-
gents and amines, arylboronic acids afforded the best re-
(400 W) for 45 min. [c] Reaction performed under a continuous
flow of N2.
sults (details provided in the Supporting Information). ther study and focused our attention on optimizing the sol-
Markedly, arylboronic acids offer many advantages as vent and the reaction temperature. When the reaction was
cross-coupling partners since they are widely available, exhi- performed in toluene at 150 °C, product conversion was
bit air and moisture stability and are affordable. Having es- found to increase slightly to 31% (Table 1, Entry 11).
tablished that nickel was necessary for catalysis (Table 1, Microwaving the reaction mixture at 150 °C for 45 min gave
Entry 1), our next task involved identifying the optimal the same result as conventional heating (Table 1, Entry 12).
combination of ligand, solvent and temperature (Table 1).
A variety of inorganic bases were additionally screened.[19]
A selection of bidentate and monodentate phosphine li- Of those considered, Cs2CO3 gave the best result (28%;
gands were screened in the presence of 10 mol-% Ni(cod)2. Table 1, Entry 10). Given these low yields, we wondered if
Of the bidentate ligands considered, only dcype generated CO poisoning of the Ni catalyst system might be the cause
the desired product, albeit in Ͻ 5% (Table 1, Entry 2). of the low turnover.
Interestingly, Itami et al. found dcype to be essential for
To test this hypothesis, the reaction was performed under
nickel-catalyzed decarbonylative coupling of aryl esters and a continuous flow of N2 (Table 1, Entry 13), which gave a
azoles to proceed,[9,16] The other bidentate phosphine li- 60% GC yield, corresponding to a substantial improve-
gands examined, including DIPHOS [1,2-bis(diphenylphos- ment. Presumably, preforming the reaction under a con-
phino)ethane], dppb [1,2-bis(diphenylphosphino)butane], stant flow of N2 facilitates removal of CO from the flask,
dppm [1,2-bis(diphenylphosphino)methane], and DPEPhos thus mitigating catalyst poisoning. Photolysis using a
[oxybis(2,1-phenylene)bis(diphenylphosphine)], were all in- broadband halogen lamp was also attempted; however, no
effective for the desired transformation (Table 1, Entries 3– improvement in yield was observed. Likewise, the addition
6). The monodentate phosphine ligands PPh3 and PCy3 of 10 mol-% of pyridine failed to provide any reaction en-
provided 3-phenylpyridine in 11% and 23% yield, respec- hancement. In accordance with these optimizations, the re-
tively (Table 2, Entries 7 and 8). We selected PCy3 for fur- action conditions used were 10 mol-% of Ni(cod)2 and
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Table 2. Scope and limitation of boronic acids.
acetal is additionally permitted (Table 2; 2u), offering po-
tential access to diol functionality that can be utilized in
later transformations. A limitation of this methodology was
observed for electron-deficient boronic acids. Boronic acids
possessing fluorine substitution gave low yields (Table 2;
2m, 2q, 2r), while the presence of a cyano, nitro, chloro, or
bromo substituent was also found to be not compatible
with this transformation (Table 2; 2h, 2j, 2k and 2l). These
limitations are consistent with related methodologies, which
do not tolerate electron-poor arylboronic acids.[2d,2g]
Next, the scope of the aryl ester was considered (Table 3).
Substitution of the nitrogen atom on the aryl ring was not
limited to the 3-position. Phenyl 4-pyridinecarboxylate can
also be successfully cross-coupled to phenylboronic acid
Table 3. Scope and limitation of heteroaryl esters.
[a] Yields are reported for isolated products and are an average of
two runs.
20 mol-% of PCy3, Cs2CO3 (2 equiv.) in toluene at reflux
for 24 h under a dynamic flow of N2.
We next considered the scope of the reaction with respect
to boronic acid and aryl ester. A variety of arylboronic
acids possessing different electronic and steric properties
were considered. Electron-rich and -neutral boronic acids
gave the highest yields (Table 2; 2a–f). Naphthyl- and bi-
phenyl-based boronic acids were easily cross-coupled to
phenyl nicotinate allowing for the generation of substituted
polyarenes 2b and 2e in modest yields (Table 2). The reac-
tion may also be performed on a gram scale; 3-phenylpyr-
idine was obtained in 50% isolated yield. Mass balance is
accounted for by unreacted starting material. Addition of a
methyl or tert-butyl group in the para position of the aryl
ring was also accommodated in the cases of 2c and 2d
(Table 2). Aryl methyl ethers were tolerated in the reaction
and were not susceptible to cleavage by nickel (Table 2; 2f
and 2o), indicating a preference for cleavage of the weaker
ester C–O bond. Methyl esters were also tolerated in the
reaction, illustrating chemoselective preference for aryl ester
activation (Table 2; 2i). Use of a boronic acid bearing a bu-
tyldimethylsilyl-protected alcohol was also tolerated in the
reaction, giving 2g providing a site for further functional-
group interconversion (Table 2).
ortho-Substituted arylboronic acids (Table 2; 2o and 2p)
could also be used as nucleophilic partners; however, these
substrates provided low yields, presumably because of a de-
crease in the efficacy of transmetallation due to steric con-
gestion. Benzofuran and benzothiophene were also coupled
[a] Yields are reported for isolated products and are an average of
two runs. [b] Numbers in parentheses represent GC yield averages
to phenyl nicotinate (Table 2; 2s and 2t). Methylenedioxy based upon two runs by using n-dodecane as an internal standard.
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Ni-Catalyzed Decarbonylative Coupling of Aryl Esters and Arylboronic Acids
giving 4-phenylpyridine in 49% isolated yield (Table 3; 2w). PCy3, and phenyl nicotinate was heated to 373 K giving a
Aryl 2-pyridinecarboxylates were unreactive (Table 3; 1b dark-red solution. NMR analysis showed a predominant
and 1d). The presence of nitrogen in this position likely signal at δ = 42 ppm [assignable to tetrameric aggregate A;
shuts down reactivity due to presumed coordination to Equation (1)], which grew in intensity as the reaction pro-
nickel (vide infra). Altering the electronics of the (O–Ar) gressed. A series of transient phosphine-containing inter-
fragment of the aryl ester influenced the reaction outcome. mediates were also observed.[20] In 2010, Ogoshi et al. also
A fluorine atom in the para position resulted in lower prod- encountered aggregate A in a report of nickel-catalyzed
uct yield (Table 3; 1e). The presence of a methoxy substitu- aldehyde coupling, where it was determined to be a catalyti-
ent in the para position, however, gave 51% – a similar yield cally ineffective off-cycle species.[21] We believe that A is
obtained by using phenyl nicotinate (Table 3; 1f). When likewise a decomposition product.
methyl nicotinate (Table 3; 1h) was treated with phenyl-
boronic acid, no desired product was observed. Use of
nicotinoyl chloride (Table 3; 1i) instead of phenyl nicotinate
resulted in only 13% GC yield of 3-phenylpyridine.
It is also possible to cross-couple non-heteroaryl esters,
although a mixture of biaryl and ketone is produced
(Table 4). The ketone product may arise from transmetalla-
tion with the boronic acid before CO has been extruded.
The electronics of both aryl ester and boronic acid were
(1)
considered. Both electron-rich and electron-deficient aryl
Another stoichiometric experiment was performed by
esters were accommodated; however, differences in product using phenyl 2-pyridinecarboxylate (1b) in the hopes of ob-
selectivity were observed. Aryl esters possessing electron- serving the oxidative addition product [Equation (2)]. In-
neutral or -withdrawing substituents showed predominant stead, Ni(CO)2(PCy3)2 (B; Figure 3) was isolated – an ex-
formation for the biaryl product (Table 4, Entries 1 and 5– pected product of ester decarbonylation.[22] The presence of
7). Interestingly, electron-rich aryl esters primarily formed a nitrogen atom ortho to the ester group may play a critical
the undesired ketone product (Table 4, Entries 2 and 3). role in facilitating Ni insertion into this bond. This result is
Consistent with results obtained with heteroaryl esters, elec- consistent with the limitation of phenyl 2-pyridine- and 2-
tron-deficient boronic acids resulted in lower yields than pyrazinecarboxylate substrates (Table 3; 1b and 1d) in the
electron-rich ones (Table 4, Entries 3, 4, 6, and 7). At ra- cross-coupling reaction. Such a species is proposed to be an
tionale for the formation of the ketone product only when off-cycle Ni(CO)-containing complex and lends support to
non-heteroaryl esters are used is not known and warrants the production of intermediate CO-containing species in
further investigation.
Attempts were made to identify relative catalytic species. (CO)2 (B) can be found in the Supporting Information.
The first step may involve oxidative addition of an aryl ester Based on these results and literature reports, a possible
this catalytic cycle. Crystallographic data for Ni(PCy3)2-
CO–OPh bond or Ar–CO bond. Efforts to identify such a mechanism for this methodology is presented in Fig-
species through stoichiometric reactivity were unsuccessful. ure 4,[8,23,24] although it should be noted that a detailed ki-
Over a period of 4 h a [D8]toluene solution of Ni(cod)2, netic and mechanistic investigation has not yet been con-
Table 4. Scope and limitation of aryl esters.[a]
1
[a] Percentages represent H NMR spectroscopy yields by using acetophenone as an internal standard.
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reductive elimination to yield the desired product followed
by CO extrusion to reform the catalyst concludes the cata-
lytic cycle. Notably, nickel can operate under various oxid-
ation states;[1] however, the depiction in Figure 4 is consis-
tent with the observed product distribution.
(2)
Figure 5. Possible bond cleavages for an aryl ester.
Conclusions
We have reported an example of nickel-catalyzed decarb-
onylative Suzuki–Miyaura cross-coupling of aryl esters and
boronic acids in modest yields. The method showcases a
new economical route to biaryls, including heteroaryls, pro-
viding alternatives to commonly employed palladium cata-
lysts and aryl halides. The reaction offers insight into the
difficulties associated in cross-coupling esters by using
nickel as a catalyst. Efforts to further expand the scope of
this transformation and elucidate a better mechanistic un-
derstanding are currently underway in our laboratory.
Figure 3. ORTEP depiction of the molecular structure of Ni(PCy3)2-
(CO)2 (B) in the crystal (displacement ellipsoids are shown at the
50% probability level; hydrogen atoms omitted for clarity). Selected
bond lengths [Å] and angles [°]: Ni(1)–P(1) 2.2503(8), Ni(1)–P(2)
2.2458(9), Ni(1)–C(1) 1.779(2), Ni(1)–C(2) 1.778(2), C(1)–O(1)
1.149(3), C(2)–O(2) 1.154(3); P(1)–Ni(1)–P(2) 120.35(3), P(1)–
Ni(1)–C(1) 105.04(8), P(1)–Ni(1)–C(2) 105.51(8), P(2)–Ni(1)–C(2)
105.99(8).
ducted. The analysis presented is based on C–O cleavage,
although C–C cleavage is also possible and cannot be ex-
cluded at this time (Figure 5). Following oxidative addition
to give I, CO extrusion would give II, whereupon transme-
tallation would occur to give III. Confirmation that the aryl
fragment bonded to the carbonyl group (ArCO–R) is in-
volved in the transmetallation was provided by substrate
ester 1g, because 3-phenylpyridine was not detected
(Table 3). The CO extrusion and transmetallation steps
likely occur at similar rates as evidenced by the products of
reaction with phenyl benzoate (1k) to afford biaryl and
ketone products in a 2:1 ratio (Table 4, Entry 1). Finally,
Experimental Section
General Procedure for the Nickel-Catalyzed Decarbonylative Cou-
pling of Heteroaryl Esters and Boronic Acids: A 50 mL one-necked
round-bottomed flask equipped with a Teflon stir bar was flame-
dried and brought into the glovebox. Into this vessel were placed
Cs2CO3 (325.8 mg, 1 mmol, 2.0 equiv.), phenyl ester derivative
(0.5 mmol, 1 equiv.), boronic acid (0.75 mmol, 1.5 equiv.), Ni(cod)2
(13.5 mg, 0.05 mmol, 10 mol-%), tricyclohexylphosphine (PCy3:
28.0 mg, 0.1 mmol, 20 mol-%) and toluene (4 mL). To the flask was
attached a condenser equipped with an adapter for the attachment
to an N2 line. The apparatus was removed from the glovebox and
heated to reflux under a continuous flow of nitrogen for 24 h. After
cooling of the vessel to room temperature, the crude reaction mix-
ture was filtered through a small Celite plug with ethyl acetate and
then concentrated in vacuo. Column chromatography was per-
formed to afford the desired product. Yields are reported for iso-
lated product and are an average of two runs.
3-Phenylpyridine (2a) [1008-88-4]:[25] Purification by column
chromatography (hexane/EtOAc, 3:1) afforded 2a as a colourless
oil (39 mg, 51%). 1H NMR (CDCl3, 400 MHz, 298 K): δ = 8.89 (s,
1 H), 8.63 (s, 1 H), 7.92 (d, J = 7.9 Hz, 1 H), 7.60 (d, J = 6.8 Hz,
2 H), 7.49 (m, 4 H) ppm. 13C{1H} NMR (CDCl3, 75 MHz, 298 K):
δ = 148.62, 148.49, 138.01, 136.83, 134.51, 129.23, 128.25, 127.32,
123.72 ppm. HRMS (ESI): calcd. for C11H9N [M + H]+ 156.0735,
found 156.0813.
3-(1-Naphthylenyl)pyridine (2b) [189193-21-3]:[26] Purification by
column chromatography (hexane/EtOAc, 3:1) afforded 2b as a
1
white solid (47 mg, 47%). H NMR (CDCl3, 400 MHz, 298 K): δ
= 8.77 (s, 1 H), 8.70 (d, J = 1.5 Hz, 1 H), 7.94–7.91 (t, J = 7.0 Hz,
2 H), 7.84–7.81 (m, 2 H), 7.61–7.42 (m, 5 H) ppm. 13C{1H} NMR
(CDCl3, 150 MHz, 298 K): δ = 150.16, 148.15, 136.95, 135.98,
135.89, 133.37, 131.05, 128.11, 128.06, 126.98, 125.68 (2 C), 124.97,
Figure 4. Possible reaction mechanism.
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Ni-Catalyzed Decarbonylative Coupling of Aryl Esters and Arylboronic Acids
124.87, 122.76 ppm. HRMS (ESI): calcd. for C15H11N [M + H]+
206.0891, found 206.0891.
7.52 (t, J = 6.4 Hz, 2 H), 7.37 (s, 1 H), 7.20–7.14 (t, J = 8.0 Hz, 2
H) ppm. 13C{1H} NMR (CDCl3, 75 MHz, 298 K): δ = 162.95 (d,
JC,F = 266.2 Hz), 148.24, 147.91, 135.75, 134.46, 133.84 (d, JC,F
=
3-(4-Methyl)pyridine (2c) [4423-09-0]:[27] Purification by column
chromatography (hexane/EtOAc, 3:1) afforded 2c as a colourless
oil (33 mg, 39%). 1H NMR (CDCl3, 400 MHz, 298 K): δ = 8.84 (s,
1 H), 8.57 (s, 1 H), 7.87–7.85 (d, J = 8.4 Hz, 1 H), 7.49–7.47 (d, J
= 7.6 Hz, 2 H), 7.35 (s, 1 H), 7.30–7.26 (d, J = 7.6 Hz, 2 H), 2.41
(s, 3 H) ppm. 13C{1H} NMR (CDCl3, 75 MHz, 298 K): δ = 148.04,
138.11, 136.70, 134.87, 134.29, 129.84 (2 C), 127.00, 123.63, 21.18
ppm. HRMS (ESI): calcd. for C12H11N [M + H]+ 170.0891, found
170.0969.
3-[4-(1,1-Dimethylethyl)pyridine] (2d) [1110656-20-6]:[28] Purifica-
tion by column chromatography (hexane/EtOAc, 3:1) afforded 2d
as a yellow oil (41 mg, 41%). 1H NMR (CDCl3, 400 MHz, 298 K):
δ = 8.86 (s, 1 H), 8.57 (s, 1 H), 7.88–7.86 (d, J = 7.4 Hz, 1 H),
7.52–7.50 (m, 4 H), 7.35–7.33 (m, 1 H), 1.37 (s, 9 H) ppm. 13C{1H}
NMR (CDCl3, 150 MHz, 298 K): δ = 151.47, 148.38, 148.33,
136.71, 135.07, 134.43, 127.01, 126.27, 123.76, 34.82, 31.51 ppm.
HRMS (ESI): calcd. for C15H17N [M + H]+ 212.1361, found
212.1439.
5.2 Hz), 128.82, 123.72, 116.24 (d, JC,F = 17.6 Hz) ppm. 19F{1H}
NMR (CDCl3, 282 MHz, 298 K): δ = –114.64 ppm. HRMS (ESI):
calcd. for C11H8FN [M + H]+ 174.0641, found 174.0720.
3-[4-(Trifluoromethyl)phenyl]pyridine (2n) [426823-25-8]:[31] Purifi-
cation by column chromatography (hexane/EtOAc, 3:1) afforded 2n
as a white solid (30 mg, 27%). 1H NMR (CDCl3, 400 MHz,
298 K): δ = 8.88 (s, 1 H), 8.67 (s, 1 H), 7.91–7.89 (d, J = 8.0 Hz, 1
H), 7.76–7.68 (m, 4 H), 7.42 (m, 1 H) ppm. 13C{1H} NMR (CDCl3,
150 MHz, 298 K): δ = 148.88, 147.88, 141.26, 135.32, 133.91,
127.73, 126.32 (d, JC,F = 3.7 Hz), 124.56 (d, JC,F = 4.8 Hz),124.23
(d, JC,F
=
271.2 Hz), 124.18 ppm. 19F{1H} NMR (CDCl3,
282 MHz, 298 K): δ = –62.49 ppm. HRMS (ESI): calcd. for
C12H8F3N [M + H]+ 224.0609, found 224.0687.
3-(2-Methoxyphenyl)pyridine (2o) [5958-01-0]:[32] Purification by
column chromatography (hexane/EtOAc, 3:1) afforded 2o as a
1
white solid (25 mg, 27%). H NMR (CDCl3, 300 MHz, 298 K): δ
= 8.78 (s, 1 H), 8.57 (s, 1 H), 7.87–7.84 (d, J = 8.0 Hz, 1 H), 7.37–
7.31 (m, 3 H), 7.08–7.00 (m, 2 H), 3.82 (s, 3 H) ppm. 13C{1H}
NMR (CDCl3, 75 MHz, 298 K): δ = 156.59, 150.30, 147.95, 136.79,
134.29, 130.68, 129.56, 127.09, 122.93, 121.07, 111.29, 55.54 ppm.
HRMS (ESI): calcd. for C12H11NO [M + H]+186.0841, found
186.0916.
3-(1,1Ј-Biphenyl-4-yl)pyridine (2e) [93324-68-6]:[29] Purification by
column chromatography (hexane/EtOAc, 3:1) afforded 2e as a
1
white solid (38 mg, 33%). H NMR (CDCl3, 400 MHz, 298 K): δ
= 8.92 (s, 1 H), 8.62 (m, 1 H), 7.94–7.92 (d, J = 7.7 Hz, 1 H), 7.75–
7.73 (d, J = 7.7 Hz, 2 H), 7.68–7.64 (m, 4 H), 7.49–7.46 (m, 2 H),
7.40–7.36 (m, 2 H) ppm. 13C{1H} NMR (CDCl3, 150 MHz,
298 K): δ = 148.16, 147.92, 141.42, 140.51, 136.60, 134.91, 129.11,
128.07, 127.85, 127.71, 127.44, 127.29, 123.99 ppm. HRMS (ESI):
calcd. for C17H13N [M + H]+ 232.1048, found 232.1126.
3-(2,6-Dimethylphenyl)pyridine (2p) [157402-43-2]:[33] Purification
by column chromatography (hexane/EtOAc, 3:1) afforded 2p as a
1
colourless oil (10 mg, 10%). H NMR (CDCl3, 600 MHz, 298 K):
δ = 8.63 (s, 1 H), 8.46 (s, 1 H), 7.55–7.54 (d, J = 7.7 Hz, 1 H),
7.45–7.40 (dd, J = 7.7, 4.4 Hz, 1 H), 7.24–7.20 (t, J = 7.3 Hz, 1 H),
7.14–7.13 (d, J = 7.3 Hz, 2 H), 2.04 (s, 6 H) ppm. 13C{1H} NMR
(CDCl3, 150 MHz, 298 K): δ = 149.82, 147.90, 137.83, 137.40,
136.61, 136.49, 128.16, 127.79, 123.81, 21.13 ppm. HRMS (ESI):
calcd. for C13H13N [M + H]+ 184.1048, found 184.1126.
3-(4-Methoxyphenyl)pyridine (2f) [5958-02-1]:[29] Purification by
column chromatography (hexane/EtOAc, 3:1) afforded 2f as a white
1
solid (42 mg, 45%). H NMR (CDCl3, 400 MHz, 298 K): δ = 8.82
(s, 1 H), 8.55 (s, 1 H), 7.84–7.82 (dt, J = 8.4, 2.1 Hz, 1 H), 7.54–
7.50 (d, J = 8.8 Hz, 2 H), 7.35–7.32 (dd, J = 8.0, 4.0 Hz, 1 H),
7.03–7.00 (d, J = 7.9 Hz, 2 H), 3.86 (s, 3 H) ppm. 13C{1H} NMR
(CDCl3, 150 MHz, 298 K): δ = 160.00, 147.91, 147.78, 136.59,
132.76, 130.30, 128.42, 123.82, 114.77, 55.78 ppm. HRMS (ESI):
calcd. for C12H11NO [M + H]+ 186.0841, found 186.0919.
3-(2,5-Difluorophenyl)pyridine (2q) [426823-29-2]: Purification by
column chromatography (hexane/EtOAc, 3:1) afforded 2q as a
1
colourless oil (30 mg, 23%). H NMR (CDCl3, 400 MHz, 298 K):
δ = 8.79 (s, 1 H), 8.65–8.63 (d, J = 3.4 Hz, 1 H), 7.87–7.85 (d, J =
6.0 Hz, 1 H), 7.41–7.37 (dd, J = 8.2, 3.4 Hz, 1 H), 7.20–7.04 (m, 3
H) ppm. 13C{1H} NMR (CDCl3, 150 MHz, 298 K): δ = 158.44
(dd, JC,F = 242.5, 3.3 Hz) 155.38 (dd, JC,F = 243.7, 3.7 Hz), 149.09,
148.88, 135.77 (d, JC,F = 4.1 Hz), 130. 50, 126.49 (dd, JC,F = 16.9,
8.0 Hz), 122.95, 117.04 (dd, JC,F = 19.3, 8.4 Hz), 116.27 (dd, JC,F
= 24.4, 3.9 Hz), 115.83 (dd, JC,F = 19.9, 7.2 Hz) ppm. 19F{1H}
NMR (CDCl3, 282 MHz, 298 K): δ = –118.30, –123.97 ppm.
HRMS (ESI): calcd. for C11H7F2N [M + H]+ 192.0547, found
192.0625.
3-(4-{[(1,1-Dimehtylethyl)dimethylsilyl]oxy}phenyl)pyridine
(2g):
Purification by column chromatography (hexane/EtOAc, 3:1) af-
forded 2g as a yellow solid (44 mg, 31%). 1H NMR (CDCl3,
400 MHz, 298 K): δ = 8.83 (s, 1 H), 8.56 (s, 1 H), 7.86–7.84 (d, J
= 8.0 Hz, 1 H), 7.47–7.45 (d, J = 8.9 Hz, 2 H), 7.35 (s, 1 H), 6.95–
6.93 (d, J = 8.2 Hz, 2 H), 1.01 (s, 9 H), –0.24 (s, 6 H) ppm. 13C{1H}
NMR (CDCl3, 75 MHz, 298 K): δ = 156.10, 147.75, 147.57, 134.09,
130.73, 128.21, 123.70, 120.75, 25.70, 18.27, –4.35 (2 C) ppm.
HRMS (ESI): calcd. for C17H23NOSi [M + H]+ 286.1549, found
286.1627.
3-(Benzo[b]thien-2-yl)pyridine (2s) [936734-97-3]:[34] Purification by
column chromatography (hexane/EtOAc, 3:1) afforded 2s (10.2 mg,
Methyl 4-(3-Pyridinyl)benzoate (2i) [90395-47-4]:[30] Purification by
column chromatography (hexane/EtOAc, 3:1) afforded 2i as a white
1
10%) as a yellow solid. H NMR (CDCl3, 400 MHz, 298 K): δ =
1
9.00 (s, 1 H), 8.59–8.58 (d, J = 3.4 Hz, 1 H), 7.98–7.96 (d, J =
8.0 Hz, 1 H), 7.85–7.81 (d, J = 7.7 Hz, 2 H), 7.61 (s, 1 H), 7.39–
7.34 (m, 3 H) ppm. 13C{1H} NMR (CDCl3, 150 MHz, 298 K): δ =
148.64, 148.60, 146.95, 139.95, 139.71, 139.23 133.47, 128.43,
124.48, 124.40, 123.45, 121.94, 120.36 ppm. HRMS (ESI): calcd.
for C13H9NS [M + H]+ 212.0456, found 212.0534.
solid (25 mg, 22%). H NMR (CDCl3, 600 MHz, 298 K): δ = 8.91
(s, 1 H), 8.66 (s, 1 H), 8.15–8.14 (d, J = 7.3 Hz, 2 H), 7.93–7.92 (d,
J = 7.8 Hz, 1 H), 7.67–7.65 (d, J = 7.8 Hz, 2 H), 7.42 (s, 1 H), 3.95
(s, 3 H) ppm. 13C{1H} NMR (CDCl3, 150 MHz, 298 K): δ =
166.93, 149.26, 148.37, 142.33, 134.89, 130.58, 129.99, 127.32,
124.03 (2 C), 52.48 ppm. HRMS (ESI): calcd. for C13H11NO2 [M
+ H]+ 214.0790, found 214.0868.
3-(4-Fluorophenyl)pyridine (2m) [85589-65-7]:[29] Purification by col-
umn chromatography (hexane/EtOAc, 3:1) afforded 2m as a color-
less oil (20 mg, 23%). 1H NMR (CDCl3, 300 MHz, 298 K): δ =
3-(2-Benzofuranyl)pyridine (2t) [7035-06-5]:[34] Purification by col-
umn chromatography (hexane/EtOAc, 3:1) afforded 2t as a white
solid (8 mg, 8%). 1H NMR (CDCl3, 600 MHz, 298 K): δ = 9.06 (s,
1 H), 8.53 (s, 1 H), 8.10–8.09 (d, J = 7.9 Hz, 1 H), 7.57–7.55 (d, J
8.82 (s, 1 H), 8.60 (s, 1 H), 7.85–7.83 (d, J = 6.8 Hz, 1 H), 7.55– = 6.9 Hz, 1 H), 7.50–7.48 (d, J = 8.4 Hz, 1 H), 7.39 (s, 1 H), 7.29–
Eur. J. Org. Chem. 2015, 5546–5553
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5551

N. A. LaBerge, J. A. Love
FULL PAPER
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7.26 (t, J = 8.4 Hz, 1 H), 7.21–7.17 (m, 1 H), 7.08 (s, 1 H) ppm.
13C{1H} NMR (CDCl3, 150 MHz, 298 K): δ = 154.67, 152.33,
148.55, 145.73, 131.66, 129.24, 128.29, 124.60, 123.30, 122.87,
120.82, 110.91, 102.46 ppm. HRMS (ESI): calcd. for C13H9NO [M
+ H]+ 196.0684, found 196.0762.
3-(1,3-Benzodioxol-5-yl)pyridine (2u) [869985-49-9]:[35] Purification
by column chromatography (hexane/EtOAc, 3:1) afforded 2u as a
[4]
1
white solid (41 mg, 41%). H NMR (CDCl3, 300 MHz, 298 K): δ
= 8.78 (s, 1 H), 8.55 (s, 1 H), 7.83–7.80 (d, J = 5.9 Hz, 1 H), 7.35
(s, 1 H), 7.04 (s, 2 H), 6.93 (d, J = 8.5 Hz, 1 H), 6.02 (s, 2 H) ppm.
13C{1H} NMR (CDCl3, 75 MHz, 298 K): δ = 148.62 (2 C), 147.99
(2 C), 136.67, 134.34, 132.09, 123.73, 121.05, 109.07, 107.70,
101.53 ppm. HRMS (ESI): calcd. for C12H9NO2 [M + H]+
200.0633, found 200.0712.
4-Phenylpyridine (2w) [939-23-1]:[36] Purification by column
chromatography (hexane/EtOAc, 3:1) afforded 2w (37 mg, 49%) as
1
a white solid. H NMR (CDCl3, 600 MHz, 298 K): δ = 8.67 (s, 2
H), 7.65 (m, 2 H), 7.50 (m, 4 H), 7.45 (m, 1 H) ppm. 13C{1H}
NMR (CDCl3, 150 MHz, 298 K): δ = 150.32, 148.68, 138.28,
129.33, 129.31, 127.20, 121.89 ppm. HRMS (ESI): calcd. for
C11H9N [M + H]+ 156.0735, found 156.0813.
[5]
[6]
CCDC-1404055 (for B) contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
We thank the University of British Columbia (UBC), the Natural
Sciences and Engineering Research Council of Canada (NSERC)
Discovery, Research Tools and Instrument (RTI) Grant Program,
and the Collaborative Research and Training Experience Program
(CREATE) programs for the support of this research. Dr. Brian O.
Patrick is thanked for help with collection of X-ray data.
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Received: May 14, 2015
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5553