(Cin = Cinnamyl): A versatile catalyst for C-N and C-C bond formation

Article abstract of DOI:10.1021/om500026s

[Pd(IPr*^OMe)(cin)(Cl)] provides high catalytic activity for Buchwald-Hartwig cross-coupling reactions of sterically demanding aryl chlorides with sterically hindered and deactivated aniline derivatives. This catalyst also proved efficient in Suzuki-Miyaura reactions, thus allowing the preparation of tetra-ortho-substituted biaryls. The Kumada-Corriu coupling has also been investigated using this palladium N-heterocyclic carbene (NHC) catalyst.

Full text of DOI:10.1021/om500026s

Article
pubs.acs.org/Organometallics
[Pd(IPr*OMe)(cin)Cl] (cin = Cinnamyl): A Versatile Catalyst for C−N and
C−C Bond Formation
Gulluzar Bastug and Steven P. Nolan*
EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, U.K.
S
* Supporting Information
ABSTRACT: [Pd(IPr*OMe)(cin)(Cl)] provides high catalytic activity for Buchwald−Hartwig cross-coupling reactions of
sterically demanding aryl chlorides with sterically hindered and deactivated aniline derivatives. This catalyst also proved efficient
in Suzuki−Miyaura reactions, thus allowing the preparation of tetra-ortho-substituted biaryls. The Kumada−Corriu coupling has
also been investigated using this palladium N-heterocyclic carbene (NHC) catalyst.
defined PdII−NHC catalysts are air and moisture stable and
INTRODUCTION
■
each partner (e.g., palladium and ligand) is introduced in the
The presence of various aryl amine and biaryl moieties in many
optimal ratio (1:1).6a,10 As recently described by Glorius,11
natural bioactive compounds has increased the demand for
Organ,12 Dorta13 and Nolan,14 the preparation of tetra-ortho-
developing efficient routes to access these synthetic building
blocks.1 The most often used strategies are metal-catalyzed
substituted biaryls can now be achieved via the use of “bulky yet
flexible” NHC ligands.11,15 The difficulties encountered with
carbon−carbon and carbon−nitrogen bond formation.2 Among
arylamination can also be resolved by meticulous design of the
these cross-coupling reactions, the Buchwald−Hartwig and
NHC moiety and ancillary ligand, as illustrated in the
Suzuki−Miyaura reactions using palladium are highly efficient
literature.10f,14a,16
and have been extensively used for the synthesis of these
valuable products.3
The activity of Pd−NHC catalysts is directly linked to the
properties of the NHCs. Their steric bulk enables stabilization
of a low-valent active intermediate and favors reductive
elimination, while the strong σ-donor character facilitates the
oxidative addition of aryl halides.17 With these factors in mind,
we recently described the synthesis of the bulky and electron-
rich IPr*OMe.HCl.18 Consequently, we present here the use of a
well-defined NHC-based catalyst, namely [Pd(IPr*OMe)(cin)-
Cl)], in the formation of C−N and C−C bonds. As predicted,
this catalyst exhibits excellent catalytic activity.
Palladium-catalyzed aryl amination has become the method
of choice for C−N bond formation, due to recent advances in
catalyst design.1b,4 This reaction offers high functional group
tolerance, selectivity, and mild reaction conditions. Further-
more, this methodology is more general in comparison to other
classical methods, such as electrophilic and nucleophilic
aromatic substitution strategies.5 The main challenge in
Buchwald−Hartwig amination remains the coupling reactions
of cheaper aryl chlorides with deactivated or hindered anilines.6
In recent years, the Suzuki−Miyaura reaction has emerged as
the most practical method for the synthesis of biaryl
compounds.7 The organoboron reagents used in this reaction
are generally moisture and air stable, and a wide range of
functional groups can now be tolerated due to the mild reaction
conditions. Moreover, the boron-containing reagents and
byproducts of this reaction generally exhibit low toxicity.8
However, the Suzuki−Miyaura reaction still faces some difficult
challenges, mainly in the formation of tetra-ortho-substituted
compounds under mild conditions.9
RESULTS AND DISCUSSION
■
The catalyst [Pd(IPr*OMe)(cin)Cl] (3) was successfully
synthesized by the in situ formation of the free carbene,
starting from IPr*OMe.HCl (1) and KOtBu, followed by the
addition of the palladium dimer [Pd(cin)(μ-Cl)]2 (2). The air-
and moisture-stable complex (3) was obtained in good yield
(85%) (Scheme 1).19
NHC ligands have been recognized to be an efficient
alternative to phosphines in palladium catalysis. Moreover, well-
Received: January 12, 2014
Published: February 14, 2014
© 2014 American Chemical Society
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Scheme 1. Synthesis of [Pd(IPr*OMe)(cin)Cl] (3)
low catalyst loadings, although slightly lower yields were
obtained (5f vs 5d and 5g vs 5c). In contrast, the highly active
[Pd(IPent)(PEPPSI)Cl2], previously described in the literature,
afforded compound 5f in a similar yield (65%) at the same
temperature, but with a much higher catalyst loading (4 mol
%).10g Moreover, this was the first time that compound 5g was
synthesized by the Buchwald−Hartwig reaction. In addition,
our system allowed the coupling of highly hindered partners.
Compounds 5h,i were prepared in excellent yields with only 0.1
mol % catalyst loading. These good results can be attributed to
the methoxy group present on the NHC that increases the σ-
donation and could offer a greater stabilization of the Pd0−
NHC intermediate.10h,18,21
Having observed good results in Buchwald−Hartwig
aminations, we then investigated carbon−carbon bond forming
reactions. The first reaction to be studied was the Suzuki−
Miyaura reaction, for the synthesis of tetra-ortho-substituted
biaryls. An optimization study was performed using 2-
bromomesitylene and 2,6-dimethylphenylboronic acid with
various bases and solvents and 0.5 mol % of catalyst (Table
1). The result of this study showed that the optimal base was
Our attention was first focused on carbon−nitrogen bond
formation. According to the literature, electron-rich aryl halides
and electron-deficient anilines are highly disfavored coupling
partners. For that reason, initial optimization studies were
performed using 4-chloroanisole and 4-fluoroaniline, in an
attempt to efficiently access 5d. Different combinations of bases
(KOH, KOtAm, KOtBu, and K2CO3) and solvents (dioxane,
toluene, and isopropyl alcohol) commonly used for this
reaction were explored at a low catalyst loading (0.02 mol %).17
The choice of the base is crucial in order to obtain an optimal
result, as it is involved in several steps of the mechanism.20 In
the case of [Pd(SIPr)(cin)Cl], KOtBu has been described as an
efficient base that readily facilitates the departure of the
cinnamyl ligand and promotes the formation of the Pd(0)
species.14a In the present case, KOtAm was the better choice for
catalyst 3. Very low conversions were observed using other
systems (no more than 10%), while the former showed 40%
conversion. Gratifyingly, complete conversion of the starting
material was obtained with only 0.05 mol % catalyst 3 at 110
°C.
a
Table 1. Optimization Study of Suzuki−Miyaura Reaction
entry
temp (°C)
solvent
base
GC conversion (%)
1
2
3
4
5
6
7
80
80
DME
KOtBu
NaOtBu
KOH
KOtBu
NaOtBu
KOH
10
15
31
24
54
96
12
DME
80
DME
110
110
110
80
dioxane
dioxane
dioxane
iPrOH
The scope of this methodology was then extended to other
anilines and aryl chlorides (Figure 1). 4-Fluoroaniline reacted
efficiently with the hindered 2,6-dimethylchlorobenzene to give
compound 5c. As expected, N-methylaniline reacted in
excellent yields with different aryl chlorides (5a,b), whereas
the coupling reaction of 2-fluoroaniline or 3-(trifluoromethyl)-
aniline required 0.1 mol % of the catalyst (5e−g). Interestingly,
the reaction tolerates a fluorine moiety in the ortho position at
KOH
a
Conditions: aryl halide (0.50 mmol), boronic acid (1 mmol), catalyst
3 (0.5 mol %) in solvent (1 mL), base (1.5 mmol), reflux for 12 h.
potassium hydroxide (entry 3). Potassium and sodium tert-
butoxide led to lower conversions; however, the sodium
Figure 1. Aryl chloride and aryl amine cross−coupling reactions. Conditions: aryl chloride (0.50 mmol), aryl amine (0.55 mmol), catalyst 3 in 1,4-
dioxane (1 mL), KOtAm (0.55 mmol), 110 °C for 12 h. The reaction times have not been optimized. Isolated yields are given after optimal GC
conversion, followed by chromatography on silica gel, as an average of two runs.
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Figure 2. Aryl halide and boronic acid cross-coupling reactions. Conditions: aryl halide (0.50 mmol), boronic acid (1 mmol), catalyst 3 in 1,4-
dioxane (1 mL), KOH (1.50 mmol), 110 °C for 12 h. The reaction times have not been optimized. Isolated yields are given after optimal GC
conversion, followed by chromatography on silica gel, as an average of two runs.
counterion provided better results than the corresponding
potassium alkoxide (entries 1, 2, 4, and 5). Dioxane was the
solvent of choice, affording almost complete conversion at 110
°C, in the presence of KOH (entry 6). This procedure features
some of the mildest reaction conditions described in the
literature at low catalyst loadings.11−14 The significant effect of
the hydroxide base here indicates that the mechanism probably
involves the formation of the trihydroxyborate complex, which
can facilitate the transmetalation step.
and is probably favored by the use of the hydroxide base.
Indeed, the borate salts could be hydrolyzed when the
transmetalation does not occur rapidly. The reaction was
performed under inert conditions, but water could probably be
formed via the equilibrium between boroxines of the boronic
acid and thus stop the reaction.23
After the successful application of our catalyst in the Suzuki−
Miyaura reaction, we then decided to explore its behavior in
Kumada−Corriu coupling.24 Grignard reagents that are
involved in this reaction are particularly attractive because of
their strong reactivity and easy access, principally from the
corresponding halides.5 There are many examples in the
literature related to the coupling of aryl Grignards, but only a
few concerning vinyl Grignard reagents, which made this
strategy more appealing.25 In an attempt to simplify the
reaction conditions, we decided to directly use organo-
magnesium reagents in THF, as they are usually commercially
available in this solvent. Optimization of the reaction conditions
to prepare compound 7a led to full conversion of starting
material at room temperature, with only 0.5 mol % of catalyst.
Under these conditions, isopropenylmagnesium bromide was
successfully coupled to 4-bromoanisole and 4-bromotoluene
(Figure 3; 7a,b). The reaction between the bis-ortho-substituted
aryl bromide and the same vinylmagnesium bromide was also
achieved in a good yield (7c). Unfortunately, this system did
not permit the coupling of substituted vinylmagnesium
bromide in the β and/or β′ positions, where no conversion
of aryl halides was observed.
Several aryl halides and boronic acids were then investigated
to extend the scope of this reaction. Phenyl, naphthyl, and
heteroaryl bromides were easily coupled to phenylboronic acids
in high yields (Figure 2; 6a−o). Hindered arylboronic acids
bearing alkoxy groups in the ortho positions led to the desired
coupling products in good yields (6i,m). However, when the
halide partner also possessed o-methoxy groups, the catalyst,
the amount had to be adjusted, as illustrated by the formation
of product 6h. This reaction required 0.6 mol % of catalyst to
afford an acceptable yield (66%) and could not be improved by
further increasing the catalytic amount of 3. The main issue was
the competitive hydrodeboronation reaction.22 It should be
noted that using 1.5 equiv of the arylboronic acid did not
significantly improve the yield. 1-Bromo-2-methylnaphthalene
was also a poor coupling partner, but the reaction successfully
formed 6c,d when 1 mol % of [Pd(IPr*OMe)(cin)Cl] was used.
The principal limitation of this methodology was the use of aryl
chlorides. The formations of biaryls 6m−o were efficient using
aryl bromides with only 0.5 mol % of catalyst, whereas the yield
was almost halved when using aryl chlorides despite the use of
1 mol % of 3 (Figure 2). The major side products were again
the corresponding protodeboronated products. It seems that
this competitive reaction is faster than the oxidative addition
CONCLUSION
■
In summary we have described the use of [Pd(IPr*OMe)(cin)-
Cl] as an efficient and versatile catalyst. The carbon−nitrogen
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acid (1 mmol). Outside the glovebox, under argon, were added the
aryl halide (0.5 mmol) and a solution of 3 in dioxane (3 mg, 1 mL, 0.5
mol %). The reaction mixture was stirred at 110 °C for 12 h. Then the
solution was cooled, concentrated under reduced pressure, and
quenched with water (2 mL), and the product was extracted with
Et2O (3 × 2 mL). The combined organic layers were dried over
MgSO4, filtered, and concentrated under reduced pressure. The crude
product was finally purified by flash chromatography on silica gel with
ether/pentane as eluent (from 0.1/99.9 to 2/8).
General Procedure for the Kumada−Corriu Reaction. Under
argon, to the aryl halide (0.5 mmol) were added a solution of 3 in
dioxane (3 mg, 0.1 mL, 0.5 mol %) and isopropenylmagnesium
bromide (1.5 mL at 0.5 M in THF, 0.75 mmol). The reaction mixture
was stirred at room temperature for 12 h. Then the solution was
concentrated under reduced pressure and quenched with water (2
mL), and the product was extracted with Et2O (3 × 2 mL). The
combined organic layers were dried over MgSO4, filtered, and
concentrated under reduced pressure. The crude product was finally
purified by flash chromatography on silica gel with ether/pentane as
eluent (from 0.5/99.5 to 2/8).
Figure 3. Kumada−Corriu reaction. Conditions: aryl bromide (0.50
mmol), Grignard reagent (0.75 mmol in THF), catalyst 3 (0.5 mol %)
at room temperature for 12 h. The reaction times have not been
optimized. Isolated yields are given after optimal GC conversion,
followed by chromatography on silica gel, as an average of two runs.
bond formation by the Buchwald−Hartwig reaction was
achieved for challenging substrates. The Suzuki−Miyaura
reaction was successfully applied to the synthesis of tetra-
ortho-substituted biaryls, and this catalyst showed encouraging
results for Kumada−Corriu coupling. Despite the high activity
of our newly designed catalyst, some challenges remain in
cross-coupling reactions, principally concerning the use of aryl
chlorides in the synthesis of tetra-ortho-substituted biaryls and
the coupling reaction of tri- and tetrasubstituted vinyl Grignard
reagents. These issues could probably be solved by a meticulous
study and design of new NHC ligands as well as the ancillary
ligand and are currently under investigation in our laboratory.
4-Methoxy-N-methyl-N-phenylaniline (5a). Yield: 102 mg, 0.48
mmol, 96%; CAS 55251-46-2. 1H NMR (300 MHz, CDCl3): δ 7.25−
7.17 (m, 2H), 7.15−7.06 (m, 2H), 6.95−6.88 (m, 2H), 6.84−6.76 (m,
3H), 3.83 (s, 3H), 3.28 (s, 3H). 13C NMR (101 MHz, CDCl3): δ
156.3, 149.7, 142.2, 128.9, 126.2, 118.3, 115.7, 114.7, 55.5, 40.5.
N,4-Dimethyl-N-phenylaniline (5b). Yield: 98 mg, 0.50 mmol,
99%; CAS 38158-65-5. 1H NMR (400 MHz, CDCl3): δ 7.30−7.21 (m,
2H), 7.13 (t, J = 8.0 Hz, 2H), 7.02 (d, J = 8.4 Hz, 2H), 6.95 (d, J = 7.8
Hz, 2H), 6.89 (t, J = 7.3 Hz, 1H), 3.31 (s, 3H), 2.35 (s, 3H). 13C NMR
(75 MHz, CDCl3): δ 149.3, 146.6, 132.0, 129.9, 129.0, 122.6, 119.8,
118.2, 40.3, 20.7.
N-(4-Fluorophenyl)-2,6-dimethylaniline (5c).16c Yield: 98 mg, 0.46
1
mmol, 91%. H NMR (400 MHz, CDCl3): δ 7.16−7.06 (m, 3H),
EXPERIMENTAL SECTION
■
6.91−6.84 (m, 2H), 6.46 (ddd, J = 8.9, 4.4, 2.0 Hz, 2H), 2.21 (s, 6H).
13C NMR (101 MHz, CDCl3): δ 156.4 (d, J = 235.8 Hz), 142.6, 138.7,
135.6, 128.8, 125.8, 115.8 (d, J = 22.4 Hz), 114.6 (d, J = 7.5 Hz), 18.4.
19F NMR (282 MHz, CDCl3): δ −127.6.
Preparation of [Pd(IPr*OMe)(cin)Cl] (3). In a glovebox, in a 500
mL round-bottomed flask equipped with a magnetic stirring bar were
added IPr*OMe.HCl (1) (2.16 g, 2.2 mmol) and KOtBu (0.28 g, 2.4
mmol) in THF (160 mL). The reaction mixture was stirred at room
temperature for 4 h, and then [Pd(cin)(μ-Cl)]2 (0.512 g, 1 mmol) was
added. The reaction mixture was then stirred overnight at room
temperature. After this time, outside the glovebox, the THF was
evaporated, the crude product was dissolved in CH2Cl2, this solution
was filtered on a pad of silica covered with Celite, and the pad was
eluted with CH2Cl2. After evaporation of the solvents, the complex
was precipitated in pentane, and the supernatant was removed. After
drying under high vacuum, the pure complex was obtained as a beige
powder. Yield: 2.25 g, 1.87 mmol, 85%. 1H NMR (300 MHz,
CD2Cl2): δ 7.54−7.19 (m, 26H), 7.18−7.07 (m, 12H), 3.90−3.79 (m,
8H), 6.58 (s, 4H), 5.93 (s, 2H), 5.82 (s, 2H), 5.21 (s, 2H), 5.17−5.05
(m, 1H), 4.58 (d, J = 13.1, 1H), 3.60 (s, 6H), 2.64 (d, J = 6.5 Hz, 1H),
1.27 (d, J = 9.5 Hz, 1H). 13C NMR (101 MHz, CD2Cl2): δ 183.7,
158.9, 144.3, 144.2, 143.5, 143.3, 143.2, 142.9, 137.9, 131.3, 130.4,
129.1, 128.5, 128.3, 128.1, 127.5, 127.1, 126.5, 126.4, 123.4, 114.7,
114.6, 108.9, 90.9, 55.0, 51.6, 47.0. Anal. Calcd for C78H65ClN2O2Pd:
C, 77.79; H, 5.44; N, 2.33. Found: C, 77.75; H, 5.51; N, 2.38.
General Procedure for the Buchwald−Hartwig Reaction. In a
glovebox, in a vial equipped with a stirring bar and sealed with a screw
cap fitted with a septum, was added KOtAm (0.55 mmol). Outside the
glovebox, under argon, were added the aryl halide (0.5 mmol), the
aniline (0.55 mmol), and finally a solution of 3 in dioxane (0.60 mg, 1
mL, 0.1 mol %). The reaction mixture was stirred at 110 °C for 12 h.
Then the solution was cooled, concentrated under reduced pressure,
and quenched with water (2 mL), and the product was extracted with
Et2O (3 × 2 mL). The combined organic layers were dried over
MgSO4, filtered, and concentrated under reduced pressure. The crude
product was finally purified by flash chromatography on silica gel with
ether/pentane as eluent (from 0.5/99.5 to 3/7).
4-Fluoro-N-(4-methoxyphenyl)aniline (5d). Yield: 102 mg, 0.47
1
mmol, 94%; CAS 1644-00-4. H NMR (300 MHz, CDCl3): δ 7.17−
6.63 (m, 8H), 3.82 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 157.2 (d,
J = 235.3 Hz), 155.0, 141.0, 136.5, 121.2, 117.8 (d, J = 7.5 Hz), 115.8
(d, J = 22.4 Hz), 114.7, 55.6. 19F NMR (376 MHz, CDCl3): δ −124.6.
N-(4-Methoxyphenyl)-3-(trifluoromethyl)aniline (5e). Yield: 80
mg, 0.30 mmol, 60%; CAS 1741-78-2. 1H NMR (300 MHz,
CDCl3): δ 7.37−7.26 (m, 1H), 7.19−6.99 (m, 5H), 6.97−6.89 (m,
2H), 5.66 (br s, 1H), 3.85 (s, 3H). 13C NMR (75 MHz, CDCl3): δ
156.5, 146.4, 134.6, 132.1 (q, J = 31.9 Hz), 130.1, 124.6 (d, J = 272.4
Hz), 123.9, 118.2, 115.9 (dd, J = 7.7, 3.8 Hz), 115.2, 111.6 (q, J = 3.8
Hz), 55.9 (s) 19F NMR (282 MHz, CDCl3): δ −63.4.
2-Fluoro-N-(4-methoxyphenyl)aniline (5f). Yield: 72 mg, 0.33
1
mmol, 65%; CAS 1494-26-4. H NMR (300 MHz, CDCl3): δ 7.23−
6.67 (m, 8H), 3.83 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 155.8,
152.1 (d, J = 239.6 Hz), 134.5, 133.8 (d, J = 10.9 Hz), 124.3 (d, J = 3.4
Hz), 123.1, 118.9 (d, J = 7.0 Hz), 115.1 (d, J = 18.8 Hz), 115.0, 114.7,
55.6. 19F NMR (376 MHz, CDCl3): δ −135.2.
N-(2-Fluorophenyl)-2,6-dimethylaniline (5g).26 Yield: 73 mg, 0.34
mmol, 68%. 1H NMR (300 MHz, CDCl3): δ 7.22−7.11 (m, 3H), 7.07
(ddd, J = 11.8, 8.0, 1.5 Hz, 1H), 6.96−6.79 (m, 1H), 6.76−6.60 (m,
1H), 6.30−6.13 (m, 1H), 5.35 (br s, 1H), 2.24 (s, 6H). 13C NMR (101
MHz, CDCl3): δ 152.5 (d, J = 238.8 Hz), 137.2, 136.3, 134.7 (d, J =
11.2 Hz), 128.6, 126.3, 124.4 (d, J = 3.4 Hz), 117.44 (d, J = 6.9 Hz),
114.70 (d, J = 18.2 Hz), 113.14 (d, J = 3.0 Hz), 18.2. 19F NMR (282
MHz, CDCl3): δ −137.19.0
N-(2,6-Diisopropylphenyl)-4-methoxy-2,6-dimethylaniline (5h).
1
Yield: 136 mg, 0.44 mmol, 87%; CAS 1370356-18-5. H NMR (300
MHz, CDCl3): δ 7.17−6.99 (m, 3H), 6. (s, 2H), 4.65 (br s, 1H), 3.78
(s, 3H), 3.08 (dq, J = 13.7, 6.8 Hz, 2H), 2.02 (s, 6H), 1.13 (d, J = 6.9
Hz, 12H). 13C NMR (101 MHz, CDCl3): δ 154.0, 141.7, 139.8, 136.6,
130.0, 123.5, 123.1, 114.5, 55.6, 28.0, 23.6, 19.7.
General Procedure for the Suzuki−Miyaura Reaction. In a
glovebox, in a vial equipped with a stirring bar and sealed with a screw
cap fitted with a septum, were added KOH (1.5 mmol) and boronic
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N-(2,6-Diisopropylphenyl)-2,6-dimethylaniline (5i).6a Yield: 129
mg, 0.46 mmol, 92%. H NMR (300 MHz, CDCl3): δ 7.20−7.09 (m,
3H), 6.96 (d, J = 7.4 Hz, 2H), 6.74 (t, J = 7.4 Hz, 1H), 3.17 (hept, J =
6.9 Hz, 2H), 2.00 (s, 6H), 1.14 (d, J = 6.9 Hz, 12H). 13C NMR (101
MHz, CDCl3): δ 144.2, 143.1, 138.8, 129.5, 125.6, 124.8, 123.2, 119.6,
28.0, 23.4, 19.3.
(d, J = 8.3 Hz, 2H), 3.73 (s, 6H), 2.01 (s, 6H). 13C NMR (101 MHz,
CDCl3): δ 157.4, 137.1, 134.0, 128.6, 126.8, 117.6, 104.6, 103.9, 55.8,
20.1.
2,2′,4,4′,6,6′-Hexamethyl-1,1′-biphenyl (6n). Yield: 99 mg, 0.42
mmol, 83%; CAS 4482-03-5. 1H NMR (300 MHz, CDCl3): δ 6.95 (s,
4H), 2.35 (s, 6H), 1.88 (s, 12H). 13C NMR (101 MHz, CDCl3): δ
137.0, 136.0, 135.5, 128.2, 21.1, 19.8.
1
1-Mesityl-2-methoxynaphthalene (6a). Yield: 121 mg, 0.44 mmol,
88%; CAS 1021176-79-3. 1H NMR (300 MHz, CDCl3): δ 7.91 (d, J =
9.0 Hz, 1H), 7.87−7.81 (m, 1H), 7.40 (d, J = 9.0 Hz, 1H), 7.37−7.30
(m, 2H), 7.19 (d, J = 7.3 Hz, 1H), 7.03 (s, 2H), 3.87 (s, 3H), 2.41 (s,
3H), 1.87 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 153.6, 137.2,
136.7, 133.1, 132.6, 129.1, 128.8, 128.1, 127.9, 126.4, 124.5, 123.4,
123.3, 113.5, 56.4, 21.3, 20.0.
2,2′,3,4′,5,6,6′-Heptamethyl-1,1′-biphenyl (6o). Yield: 101 mg, 0.4
mmol, 80%; CAS 39502-88-0. 1H NMR (400 MHz, CDCl3): δ 6.98 (s,
1H), 6.95 (d, J = 0.5 Hz, 2H), 2.36 (s, 3H), 2.27 (s, 6H), 1.84 (s, 6H),
1.79 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 140.0, 138.4, 135.9,
135.7, 133.6, 131.5, 130.0, 128.2, 31.1, 21.2, 20.1, 16.0.
1-Methoxy-4-(prop-1-en-2-yl)benzene (7a). Yield: 67 mg, 0.45
2-Methoxy-1-(2,3,5,6-tetramethylphenyl)naphthalene (6b).12a
1
mmol, 90%; CAS 1712-69-2. H NMR (300 MHz, CDCl3): δ 7.47−
1
7.40 (m, 2H), 6.93−6.84 (m, 2H), 5.31 (dd, J = 1.5, 0.7 Hz, 1H), 5.01
(p, J = 1.4 Hz, 1H), 3.84 (s, 3H), 2.15 (dd, J = 1.4, 0.8 Hz, 3H). 13C
NMR (101 MHz, CDCl3): δ 159.2, 142.7, 133.8, 126.7, 113.6, 110.8,
55.4, 22.0.
Yield: 132 mg, 0.46 mmol, 91%. H NMR (400 MHz, CDCl3): δ
7.91 (d, J = 9.0 Hz, 1H), 7.86 (dd, J = 8.3, 1.1 Hz, 1H), 7.41 (d, J = 9.0
Hz, 1H), 7.37−7.29 (m, 2H), 7.17−7.12 (m, 1H), 7.08 (s, 1H), 3.87
(s, 3H), 2.32 (s, 6H), 1.77 (s, 6H). 13C NMR (101 MHz, CDCl3): δ
153.6, 135.5, 133.2, 133.1, 130.8, 129.1, 128.6, 127.8, 126.3, 124.9,
124.6, 123.4, 113.5, 56.4, 20.3, 16.4.
1-Methyl-4-(prop-1-en-2-yl)benzene (7b). Yield: 55 mg, 0.42
1
mmol, 83%; CAS 1195-32-0. H NMR (300 MHz, CDCl3): δ 7.39
1-Mesityl-2-methylnaphthalene (6c).13a Yield: 100 mg, 0.39
(dd, J = 8.4, 1.9 Hz, 2H), 7.16 (d, J = 8.3 Hz, 2H), 5.36 (d, J = 0.7 Hz,
1H), 5.06 (q, J = 1.5 Hz, 1H), 2.37 (s, 3H), 2.16 (dd, J = 1.3, 0.7 Hz,
3H). 13C NMR (75 MHz, CDCl3): δ 143.5, 138.8, 137.6, 129.3, 125.8,
112.0, 22.3, 21.5.
1,3-Dimethoxy-2-(prop-1-en-2-yl)benzene (7c). Yield: 67 mg, 0.38
mmol, 75%; CAS 25108-61-6. 1H NMR (400 MHz, CDCl3): δ 7.21 (t,
J = 8.3 Hz, 1H), 6.60 (d, J = 8.3 Hz, 2H), 5.36 (dd, J = 2.6, 1.0 Hz,
1H), 4.90 (dd, J = 2.1, 0.9 Hz, 1H), 3.83 (s, 6H), 2.05 (d, J = 1.0, 3H).
13C NMR (75 MHz, CDCl3): δ 157.6, 139.7, 128.3, 121.8, 116.1,
104.4, 56.4, 23.8.
1
mmol, 77%. H NMR (300 MHz, CDCl3): δ 7.88 (d, J = 7.9 Hz,
1H), 7.81 (d, J = 8.3 Hz, 1H), 7.49−7.44 (m, 1H), 7.42 (dd, J = 8.1,
1.3 Hz, 1H), 7.33 (ddd, J = 8.0, 6.7, 1.3 Hz, 1H), 7.28−7.22 (m, 1H),
7.05 (s, 2H), 2.43 (s, 3H), 2.16 (s, 3H), 1.83 (s, 6H). 13C NMR (101
MHz, CDCl3): δ 136.6, 136.5, 135.5, 133.1, 132.2, 132.1, 128.7, 128.2,
128.0, 127.9, 126.8, 125.9, 125.1, 124.7, 21.2, 19.9, 19.8.
2-Methyl-1-(2,3,5,6-tetramethylphenyl)naphthalene (6d). Yield:
1
111 mg, 0.41 mmol, 81%; CAS 1380314-22-6. H NMR (300 MHz,
CDCl3): δ 7.87 (d, J = 8.1 Hz, 1H), 7.80 (d, J = 8.4 Hz, 1H), 7.50−
7.37 (m, 2H), 7.35−7.29 (m, 1H), 7.19 (d, J = 8.4 Hz, 1H), 7.08 (s,
1H), 2.32 (s, 7H), 2.10 (s, 3H), 1.71 (s, 6H). 13C NMR (101 MHz,
CDCl3): δ 138.4, 137.9, 133.5, 133.1, 132.3, 132.1, 130.4, 128.6, 127.8,
126.6, 125.8, 125.6, 124.7, 30.9, 20.2, 16.1.
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures giving the 1H and 13C NMR spectra for all compounds
and text giving a general experimental section. This material is
available free of charge via the Internet at http://pubs.acs.org.
2′,4′-Difluoro-2,3,5,6-tetramethyl-1,1′-biphenyl (6e). Yield: 122
1
mg, 0.5 mmol, 99%. H NMR (300 MHz, CDCl3): δ 7.16−7.03 (m,
2H), 7.03−6.86 (m, 2H), 2.30 (s, 6H), 1.93 (s, 6H). 13C NMR (101
MHz, CDCl3): δ 163.4 (d, J = 11.6 Hz), 160.9 (dd, J = 11.7, 5.2 Hz),
158.4 (d, J = 11.8 Hz), 134.4, 133.7, 132.7, 132.2 (dd, J = 9.2, 5.5 Hz),
131.4, 125.3 (dd, J = 18.4, 3.9 Hz), 111.3 (dd, J = 20.9, 3.7 Hz), 104.0
(dd, J = 26.3, 25.5 Hz), 20.2, 16.9. 19F NMR (282 MHz, CDCl3): δ
−110.9 (d, J = 7.2 Hz), −112.6 (d, J = 7.2 Hz). Anal. Calcd for
C16H16F2: C, 78.02; H, 6.55. Found: C, 78.06; H, 6.59.
AUTHOR INFORMATION
Corresponding Author
*E-mail for S.P.N.: snolan@st-andrews.ac.uk.
■
Notes
2′,6′-Dimethoxy-2,4,6-trimethyl-1,1′-biphenyl (6f,i).14c Yield: 117
mg, 0.46 mmol, 91%. 1H NMR (300 MHz, CDCl3): δ 7.33 (t, J = 8.3
Hz, 1H), 6.96 (s, 2H), 6.67 (d, J = 8.3 Hz, 2H), 3.74 (s, 6H), 2.34 (s,
3H), 1.99 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 157.6, 136.9,
136.3, 130.9, 128.4, 127.8, 117.6, 103.9, 55.8, 21.3, 20.0.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Gaetan Le Duc is thanked for helpful discussions, especially
concerning the Buchwald−Hartwig arylamination. We grate-
fully acknowledge Umicore AG for its generous gifts of
materials.
■
̈
2′,6′-Dimethoxy-2,3,5,6-tetramethyl-1,1′-biphenyl (6g).12a Yield:
118 mg, 0.44 mmol, 87%. 1H NMR (300 MHz, CDCl3): δ 7.34 (dd, J
= 11.9, 4.7 Hz, 1H), 7.00 (s, 1H), 6.68 (d, J = 8.3 Hz, 2H), 3.73 (s,
6H), 2.28 (s, 6H), 1.88 (s, 6H). 13C NMR (75 MHz, CDCl3): δ 157.6,
133.7, 132.8, 132.7, 130.9, 128.3, 118.8, 103.8, 55.8, 20.3, 16.4.
2,2′,6,6′-Tetramethoxy-1,1′-biphenyl (6h). Yield: 91 mg, 0.33
mmol, 66%; CAS 19491-10-2. 1H NMR (400 MHz, CDCl3): δ 7.25 (t,
J = 8.3 Hz, 2H), 6.60 (d, J = 8.4 Hz, 4H), 3.92 (s, 12H). 13C NMR
(101 MHz, CDCl3): δ 157.2, 128.2, 104.7, 100.9, 56.4.
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