Dual Photoredox/Gold Catalysis Arylative Cyclization of o-Alkynylphenols with Aryldiazonium Salts: A Flexible Synthesis of Benzofurans

Article abstract of DOI:10.1021/acs.joc.6b01060

A new method for the arylative cyclization of o-alkynylphenols with aryldiazonium salts via dual photoredox/gold catalysis is described. The reaction proceeds smoothly at room temperature in the absence of base and/or additives and offers an efficient app

Full text of DOI:10.1021/acs.joc.6b01060

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Article
Dual Photoredox/Gold Catalysis Arylative Cyclization of ortho-alkynylphenols
with Aryl Diazonium Salts: A Flexible Synthesis of Benzofurans
Zhonghua Xia, Omar Khaled, Virginie Mouriès-Mansuy, Cyril Ollivier, and Louis Fensterbank
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b01060 • Publication Date (Web): 30 Jun 2016
Downloaded from http://pubs.acs.org on July 1, 2016
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Dual Photoredox/Gold Catalysis Arylative Cyclization of
ortho-alkynylphenols with Aryl Diazonium Salts: A Flexible
Synthesis of Benzofurans
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Zhonghua Xia, Omar Khaled, Virginie MourièsꢀMansuy, Cyril Ollivier* and Louis
Fensterbank*
Sorbonne Universités UPMC Univ Paris 06, CNRS, UMR 8232, Institut Parisien de Chimie Moléculaire, 4 place
Jussieu, C.229, Fꢀ75005 Paris, France
Fax: (+33) 1ꢀ4427ꢀ7360; cyril.ollivier@upmc.fr, louis.fensterbank@upmc.fr
Abstract: A new method for the arylative cyclization of orthoꢀalkynylphenols with aryldiazonium salts via dual
photoredox/gold catalysis is described. The reaction proceeds smoothly at room temperature in the absence of base
and/or additives, and offers an efficient approach to benzofuran derivatives. The scope of the transformation is wide
and the limitations are discussed. The reaction is proposed to proceed through a photoredoxꢀpromoted generation of a
vinylgold(III) intermediate that undergoes reductive elimination to provide the heterocyclic coupling adduct.
INTRODUCTION
Homogeneous gold catalysis has received great attention over the last decade. The majority
of reports rely on the πꢀacidity of either gold(I) or gold(III) complexes to activate multiple
bonds present on substrates such as alkenes, allenes, and, especially, alkynes towards
nucleophilic attack.1,2
The selective activation of the carbonꢀcarbon multiple bond by the gold complex generally
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constitutes the preliminary triggering event of the catalytic cycle.3 Whereas a wide range of
different intraꢀ and intermolecular nucleophiles may be employed in these processes, in the
vast majority of cases, the organogold species generated upon nucleophilic attack undergoes
protoꢀdemetalation4 leading to hydrofunctionalized products (Scheme 1a).
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In some instances, the vinylꢀ or arylgold intermediate instead of undergoing
protodemetallation can be advantageously trapped by an external electrophile such as a
halide5 or carbon dioxide.6 Alternatively, cross coupling reaction with a nucleophilic partner
in the presence of an external oxidant has been developed.7 More recently, the groups of
Glorius and Toste8 reported a redox neutral approach, avoiding the use of strong external
oxidants, by merging gold and visibleꢀlight photoredox catalysis9 in a dual catalytic event.10
In these transformations, the protoꢀdemetalation step can be rerouted in favor of an arylation
step thanks to the presence of photoredoxꢀgenerated aryl radicals. Presumably, Au(I) is
oxidized in a stepwise fashion by the photoꢀgenerated aryl radical and the photocatalyst
leading to a cationic Au(III) species, which already bears the aryl coupling partner.
Coordination of the πꢀsystem and nucleophilic attack then lead selectively to the cross
coupling product. This mechanism proposal has been recently supported by DFT
calculations 11 and the isolation of arylgold(III) complexes in related experimental
conditions.12 Extensions of this process to alkynylꢀ13 and vinyl gold14 intermediates have
also been explored (Scheme 1b).
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Scheme 1. GoldꢀCatalyzed Addition to C≡C Multiple Bonds
Because of our interest in gold catalysis15 and photoredox/organometallic dual catalysis
reactions,16 we herein report the successful development of a dual Au and photoredox
catalytic system applicable to the intramolecular oxyarylation of alkynes with aryldiazonium
salts (Scheme 1c). This process involves the formation of new C−Nu and C=C bonds across
the alkyne and occurs at room temperature upon irradiation with a simple household light
bulb. During the course of our investigations into these new dual catalytic events, two reports
of alkyne difunctionalization by dual photoredox/gold catalysis appeared in the literature. The
groups of Hashmi showed that under blue LED irradiation but in the absence of any
photosensitizer, a goldꢀcatalyzed intermolecular difunctionalization of alkynes with aryl
diazonium salts delivering αꢀarylketones takes place smoothly.14c The group of Glorius
focused on propargylic alcohols to develop an arylative version of the MeyerꢀSchuster
rearrangement.14d
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RESULTS and DISCUSSIONS
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In this report, a single example of intramolecular reaction was given from
orthoꢀalkynylphenol substrate 1a and phenyl diazonium 2f coincidentally corresponding to
one of our findings (benzofuran 3af).17,18,19Full scope and limitations are now given on this
transformation.
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Table 1. Optimization of the Reaction Conditionsa
Entry
1
Au cat.
Photocat.
Solvent
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
Yield of 3aab (%)
< 5; (3a, 60)
9; (3a, 35)
Ph3PAuNTf2
IPrAuCl
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
none
2
3
Ph3PAuCld
Ph3PAuCl
Ph3PAuCl
Ph3PAuCl
Ph3PAuCl
ꢀ
45; (3a, 40)
75 (73)c
4
5e
< 5; (3a, 30)
< 5; (3a, 20)
8; (3a, 60)
6e
Ru(bpy)3(PF6)2
Eosin Ye
7
8
Cu(dpp)2PF6.2H2Od
Cu(dpp)2PF6.2H2Od
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
< 5; 3a not detected
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9
Ph3PAuCl
Ph3PAuCl
Ph3PAuCl
Ph3PAuCl
Ph3PAuCl
Ph3PAuCl
10
11
12
13f
14g
MeOH:MeCN(3:1) 60
MeOH:MeCN(4:1) 61
MeOH:MeCN(9:1) 66
MeOH
MeOH
48
39
a General conditions: 1a (0.2 mmol), [Au] catalyst (10 mol%), photocatalyst (2.5 mol%), 2a
b
(0.8 mmol), degassed solvent (2 mL), rt, 16 h, 23 W fluorescent light bulb. Determined by
c
d
e
1H NMR using butadiene sulfone as an internal standard. Isolated yield. 5 mol% used.
Reaction performed in the dark.
f
g
3 equiv of 2a.
2 equiv of 2a. IPr =
1,3ꢀbis(2,6ꢀdiisopropylphenyl)imidazolꢀ2ꢀylidene. dpp = 2,9ꢀdiphenylꢀ1,10ꢀphenanthroline.
Initial studies on the screening of various gold(I) catalysts revealed that the reaction of
2ꢀ(phenylethynyl)phenol 1a with pꢀtolyldiazonium salt 2a (4 equiv) in the presence of
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Ph3PAuCl (10 mol %), Ru(bpy)3(PF6)2 (5 mol %) and visible light in degassed MeOH (0.1 M)
gave the best yield (73%) of product 3aa (Table 1, entry 4). The cationic gold salt
PPh3AuNTf2 or IPrAuCl did not give satisfactory results and the product of classical
cycloisomerisation 3a was obtained instead (Table 1, entries 1ꢀ2).20 Interestingly also, the
presence of a photocatalyst or light proved to be necessary14c since the reaction with
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PPh3AuCl alone afforded only traces of arylative cyclization (entries 5ꢀ6). Based on the
21
involved redox potentials, the use of Eosin Y (E*ox = −1.6 V vs SCE)
and
Cu(dpp)2PF6ꢁ2H2O (E*ox = −1.11 V vs SCE)22 (5 mol %) with or without PPh3AuCl (entries
7ꢀ9) was tested but it could not improve the yield. The use of mixed solvents was not helpful
either (entries 10ꢀ12) and decreasing the equivalents of diazonium salt led to lower yields
(entries 13ꢀ14).
Next, the scope of aryl diazonium salts was studied in reactions with 2ꢀ(phenylethynyl)phenol
1a under the optimal reaction conditions as described in entry 3, Table 1.
3ꢀ(4ꢀNitrophenyl)ꢀ2ꢀphenylbenzofuran 3ab was obtained for 86% yield using paraꢀnitro
aryldiazonium salt as an arylation agent (Table 2). Aryldiazonium salts bearing other
electronꢀwithdrawing CF3 (2c), CN (2d), and Br (2e) groups on the para position reacted
smoothly with 1a, delivering respectively the corresponding arylated benzofurans 3ac, 3ad
and 3ae in good to excellent yields (entries 3ꢀ5). A good yield (65%) of
2,3ꢀdiphenylbenzofuran 3af17 (entry 6) could be obtained when phenyldiazonium salt was
subjected to the reaction. But an electronꢀdonating OCH3 group led to a lower yield of
coupling product 3ag (23%). An aryldiazonium salt containing an ester group at the meta
position was also well tolerated (3ah). However, a substituent at the ortho position of the aryl
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diazonium salt had a dramatic effect on this arylative cyclization reaction and resulted in a
5
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7
much lower yield (compare 3ad, entry 4 vs 3ai, entry 9).
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Table 2. Scope of Aryl Diazonium Salts
O
Ph3PAuCl (10 mol %)
Ru(bpy)3(PF6)2 (2.5 mol %)
OH
R1
+
N2BF4
degassed MeOH
23 W fluorescent bulb
16 h, rt
R1
1a
2
3
3, yield(%)
3aa, 73%
3ab, 86%
entry
2
2a
1
2
N2BF4
O2N
F3C
NC
2b
N2BF4
2c
2d
3ac, 76%
3ad, 81%
3
4
N2BF4
N2BF4
Br
2e
2f
3ae, 61%
5
6
N2BF4
3af
, 65%
N2BF4
H3CO
2g
2h
2i
3ag
, 23%
7
N2BF4
N2BF4
3ah, 62%
3ai, 37%
8
9
O
O
N2BF4
CN
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Reaction conditions: 1a (0.2 mmol) and 2 (4 equiv), Ph3PAuCl (10 mol %), Ru(bpy)3(PF6)2
(2.5 mol %), degassed methanol (2 mL) under Ar, rt, 16 h , 23 W fluorescent light bulb;
isolated yields of 3.
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Substitution effect on both aromatic rings of orthoꢀalkynylphenols 1 was then investigated in
reactions with aryl diazonium salts (Table 3). orthoꢀAlkynylphenol 1j bearing an
electronꢀdonating methoxy group in para position to the alkyne gave a sluggish reaction. The
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expected coupling product 3jd was isolated in only 6%. The major isolated product was the
23
known
ester 4 (21%) resulting presumably from a preferential goldꢀcatalyzed
hydromethoxylation of the alkyne moiety (involving intermediate E, scheme 4) followed by a
goldꢀcatalyzed oxidative cleavage of the generated enol ether.24 In sharp contrast, precursors
with an electronꢀwithdrawing ester group at the para or meta position when reacted with
4ꢀcyanophenyl diazonium salt, delivered the corresponding arylated benzofurans in good
yields (3kd and 3ld).
Table 3. Influence of a substituent on the phenol moiety of orthoꢀalkynylphenols
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Orthoꢀalkynylphenol bearing a paraꢀtolyl group attached to the alkyne reacted efficiently with
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pꢀnitrophenyl
diazonium
tetrafluoroborate
and
afforded
the
corresponding
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3ꢀ(4ꢀnitrophenyl)ꢀ2ꢀ(pꢀtolyl) benzofuran 3mb in 85% yield (Scheme 2). Here also, the
expected reaction was diverted when an electronꢀdonor (OMe) was present as on
2ꢀ((4ꢀmethoxyphenyl)ethynyl)phenol 1n. In that case, the unarylated 2ꢀphenylbenzofuran 3n
was isolated in 96% yield, suggesting that the vinylgold intermediate undergoes competitive
protoꢀdeauration. Similarly, with the pꢀcyano aryl diazonium, 3n was formed in 48% yield
accompanied with 11% yield of arylative cyclization product 3nd.
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Scheme 2. Influence of an electronꢀdonating substituent on the acetylene moiety of
orthoꢀalkynylphenols
The use of the CF3ꢀalkynyl phenol 1o provided another series of contrasted results (Scheme 3).
Arylation took place with phenyl diazonium 2f but there was no formation of the benzofuran
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moiety. Instead, an α,α’ꢀbisꢀarylated ketone bearing a phenol moiety was isolated in good
yield (77%). Based on the fact that no cyclization of the phenol took place but that the
vinylgold intermediate got presumably trapped by methanol in βꢀposition to gold,14c,d we
proposed the regioisomeric ketone structure 5of (originating from the hydrolysis of the
enolether intermediate). Same type of reactivity was observed with 4ꢀnitrophenyl diazonium
salt 2b giving in that case the E/Z mixture of the more stable arylated enolethers 6ob (76%).
All these findings suggest important electronic effects influencing the regioselectivity of the
arylation step that we rationalize below. Finally, we also examined the reactivity of
butylꢀsubstituted and terminal orthoꢀalkynylphenols under the same dual catalysis conditions.
Unfortunately, complex reaction mixtures were obtained in both cases when using
aryldiazonium 2d as radical source.25
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Scheme 3. Influence of an electronꢀwithdrawing substituent on the acetylene moiety of
orthoꢀalkynylphenols
Based on previous studies on dual Au/photoredox catalysis, a mechanism involving a
photoredox induced homogeneous Au(I)/Au(III) redox cycle was proposed (Scheme 4). Upon
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2+
irradiation with visible light, the reaction of ArN2BF4 2 with photoexcited Ru(bpy)3
*
5
6
3+
generates Ru(bpy)3 and an aryl radical that reacts with the gold(I) catalyst to initially
generate gold(II)−aryl complex A. This gold(II) intermediate is further oxidized by RuIII,
giving gold(III)−aryl B and regenerating the photocatalyst. The 5ꢀendoꢀdig cyclization by
intramolecular nucleophilic attack on complex C furnishes alkyneꢀderived heteroaryl −
vinylgold(III) intermediates D, which undergo reductive elimination to give the desired
product 3 and regenerate the gold(I) catalyst. When R2 is electron donor (methoxy in para
position), the basicity of the corresponding vinyl gold intermediate D would significantly
increase4b rendering the protodeauration highly competitive. This would divert the catalytic
cycle to the simple cyloisomerization process to give products 3a and 3n. In the case R2 bears
an electron withdrawing moiety (4ꢀCF3 phenyl group), slippage of gold metal26 would yield
to vinylgold complex E as preferred intermediate. The latter cannot be intramolecularly
intercepted by the phenol moiety so methanol adds intermolecularly to give a mixture of enol
ethers that would be isolated (6ob, E:Z, 1:1) or hydrolyzed (ketone 5of). Reductive
elimination would still take place to give arylation and propagate the catalytic cycle.
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Scheme 4. Proposed Reaction Mechanisms
In summary, we have developed a novel photoredox/gold dual catalysis process which
could be applied to the preparation of various benzofuran derivatives by arylative cyclization
of orthoꢀalkynylphenols with aryl diazonium salts. The reaction takes place smoothly at room
temperature in the absence of additives providing good to excellent yields of heterocyclic
scaffolds. It presumably involves a vinylgold(III) intermediate that is generated through two
concurrent catalytic cycles. The electronic demand of the aryl substituent exerts an important
influence in the efficiency and regioselectivity of the arylation step.
This work constitutes one more example of a successful dual catalytic approach relying
in part on an efficient photoredox catalyzed event and augurs well for further exciting
developments in this domain.
Experimental section
General Experimental Details. All reactions involving air sensitive reagents or
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intermediates were carried out in preꢀheated glassware under an atmosphere of dry argon
using standard Schlenk techniques. Reagents and chemicals were purchased from commercial
sources and used as received. Methanol and acetonitrile were purified by mean of distillation
under dry Argon atmosphere on calcium hydride. The reactions were irradiated by a standard
household lamp with a 23 W fluorescent light bulb. Aryl diazonium tetrafluoroborates 2aꢀ2i
were synthesized following the procedure of Hanson.27 Photocatalysts [Ru(bpy)3]2(PF6)2 (bpy
= 2,2′ꢀbipyridine) and Cu(dpp)2PF6.2H2O (dpp = 2,9ꢀdiphenylꢀ1,10ꢀphenanthroline) were
prepared according to the procedure of Yoon28 and Meyer29 respectively. The gold(I)
complexes Ph3PAuNTf2 and IPrAuCl (IPr = 1,3ꢀbis(2,6ꢀdiisopropylphenyl)imidazolꢀ2ꢀylidene)
were purchased from commercial suppliers. Chromatographic purification was performed
over silica gel (LC60A) SI 60 Å (40ꢀ63 ꢂm). Thin layer chromatography (TLC) was
performed with silica gel 60 F254 precoated on aluminum plates and visualized by UV light
and/or staining with KMnO4. Infrared (IR) spectra were recorded on an ATR
spectrophotometer and only the strongest or the structurally most important peaks were listed.
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1
19
Melting points were determined in open capillary tubes and are uncorrected. H, F, and 13C
NMR spectra were recorded at room temperature at 400, 377, and 100 MHz, respectively, or
at 300, 282, and 75 MHz, respectively. Chemical shifts (δ) are reported in parts per million
(ppm) and coupling constants (J) are given in Hertz (Hz). Abbreviations used for peak
multiplicity are s (singlet); d (doublet); t (triplet); q (quartet); quat (quaternary); quint
(quintet); sept (septet); m (multiplet); br (broad). Referenced relative to residual CDCl3
13
protons signals at δ 7.26 ppm, δ 77.16 for C NMR and reference relative to residual CFCl3
at δ 0.00 ppm for 19F. High resolution mass spectrometries were performed on a LTQ Orbitrap
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General Procedure 1 (GP1). Synthesis of 2ꢀ(phenylethynyl)phenol 1a.30 MOMCl (1.1 g, 13.6
mmol, 1.5 equiv.) was added to a mixture of 2ꢀiodo phenol (2 g, 9.1 mmol, 1 equiv.) and
K2CO3 (5.0 g, 36.36 mmol, 4 equiv.) in DMF (8 mL). The mixture was stirred at room
temperature 2h. The completion of the reaction was monitored by TLC (Pent/Et2O: 9/1). The
solution was diluted with diethyl ether (100 mL) and 60 mL of water were added. The layers
were separated and the aqueous phase was extracted with diethyl ether (3 × 30 mL). The
combined organic layers were washed with brine, dried over MgSO4, filtered and
concentrated under reduced pressure to afford the MOM iodide (2.4 g, quant). The latter was
engaged without purification in the Sonogashira process. To a solution of phenylacetylene
(1.0 g, 10.0 mmol, 1.1 equiv.) and the MOM iodide (2.4 g, 9.1 mmol, 1.0 equiv.) in
triethylamine (90 mL), PdCl2(PPh3)2 (126.3 mg, 0.18 mmol, 2 mol%) and CuI (34.3 mg, 0.18
mmol, 2 mol%) were added. The mixture was stirred at 65°C until complete consumption of
MOM iodide was observed by TLC (Pent/Et2O: 9/1). The reaction mixture was warmed to
room temperature, diethyl ether was added (50 mL) and the mixture was filtrated through a
plug of cotton wool. After removal of the solvent, the residue was purified by silica gel
chromatography (Pent/Et2O: 9/1) to afford the MOM 2ꢀ(phenylethynyl)phenol (1.95 g, 91%).
The deprotection of MOM was conducted by added HCl (0.85 mL, 9.0 mmol, 6N) to a
solution of the previous compound (1.95 g, 8.2 mmol) in MeOH (15 mL). The reaction
mixture was stirred until the deprotection was completed. The mixture was diluted with water
(50 mL) and diethyl ether (30 mL). The layers were separated and the aqueous phase was
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extracted with diethyl ether (3 × 30 mL). The combined organic layers were washed with
brine, dried over Na2SO4, filtered and concentrated under reduced pressure to afford
2ꢀ(phenylethynyl)phenol as a yellow solid (1.3 g, 82%) after purification by flash
chromatography (Pent/Et2O: 9/1).
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General Procedure 2 (GP2). Arylative Cyclization of OrthoꢀAlkynylphenols with Aryl
Diazonium Salts. The photocatalyst [Ru(bpy)3](PF6)2 (4.3 mg, 0.005 mmol, 2.5 mol%), the
gold(I) complex Ph3PAuCl (9.9 mg, 0.02 mmol, 10 mol%), the appropriates diazonium salt 2
(0.8 mmol) and orthoꢀalkynylphenol derivative 1 (0.2 mmol) were introduced in a schlenk
tube equipped with a magnetic stirring bar in which MeOH (2 mL) was added. The mixture
was degassed using three freeze pumpꢀthaw cycles then was irradiated with a 23 W
fluorescent light bulb (~10 cm away from the glassware. If necessary, the air flowing can be
used to cool down the schlenk tube) for 16 h (unless mentioned). The reaction was quenched
with water (2 mL) and a saturated aqueous K2CO3 solution (1 mL) and the solution was
extracted Et2O (4 × 5 mL). The combined organic layer was dried over Na2SO4, filtered and
concentrated under reduced pressure to give the crude product. The residue was purified by
FC on silica gel to afford the desired product.
A. Synthesis of orthoꢀalkynylphenol derivatives as substrates. All orthoꢀalkynylphenol
substrates were prepared according to the procedure reported by Hashmi et al.30 and based on
the synthesis of 2ꢀ(phenylethynyl)phenol 1a, as summarized before part 2, General
Procedure 1 (GP1).
2ꢀ(Phenylethynyl)phenol (1a). Following general procedure GP1 with 2ꢀiodophenol (2 g, 9.1
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mmol) and phenylacetylene (1.0 g, 9.1 mmol) to afford 1a (1.3 g, 74% over three steps).
The spectroscopic data match those previously reported in the literature.30 1H NMR (300 MHz,
CDCl3) δ 7.60ꢀ7.56 (m, 2H), 7.46 (dd, J = 7.8, 1.8 Hz, 1H), 7.43ꢀ7.39 (m, 3H), 7.33ꢀ7.27 (m,
1H), 7.02 (dd, J = 8.1, 0.9 Hz, 1H), 6.94 (td, J = 7.5, 1.2 Hz, 1H), 5.87 (s, 1H).
5ꢀMethoxyꢀ2ꢀ(phenylethynyl)phenol (1j). Following general procedure reported by A. J.
Frontier et al.31 with 2ꢀiodoꢀ5ꢀmethoxyphenol and phenylacetylene. The spectroscopic data
match those previously reported in the literature.32 1H NMR (300 MHz, CDCl3) 7.54ꢀ7.51 (m,
2H), 7.32ꢀ7.27 (m, 4H), 6.56 (d, J = 2.4 Hz, 1H), 6.50 (dd, J = 6.3, 2.4 Hz, 1H), 5.87 (bs, 1H),
3.81 (s, 3H).
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Methyl 4ꢀhydroxyꢀ3ꢀ(phenylethynyl)benzoate (1k). Following general procedure GP1 with
methyl 4ꢀhydroxyꢀ3ꢀiodobenzoate (556 mg, 2 mmol) and phenylacetylene (224.7 mg, 2.2
mmol) to afford 1k (413.7 mg, 82% over three steps). The spectroscopic data match those
previously reported in the literature.33 1H NMR (300 MHz, CDCl3) δ 8.15 (d, J = 2.1 Hz, 1H),
7.96 (dd, J = 8.7, 2.1 Hz, 1H), 7.57ꢀ7.53 (m, 2H), 7.41ꢀ7.38 (m, 3H), 7.02 (d, J = 8.7 Hz, 1H),
6.26 (s, 1H), 3.90 (s, 3H).
Methyl 3ꢀhydroxyꢀ4ꢀ(phenylethynyl)benzoate (1l). Following general procedure GP1 with
methyl 3ꢀhydroxyꢀ4ꢀiodobenzoate (556 mg, 2 mmol) and phenylacetylene (224.7 mg, 2.2
1
mmol) to afford 1l (454 mg, 90% over three steps). Mp 204ꢀ206 °C. H NMR (300 MHz,
CDCl3) δ 7.65 (d, J = 1.5 Hz, 1H), 7.61ꢀ7.54 (m, 3H), 7.43 (d, J = 8.1 Hz, 1H), 7.40ꢀ7.38 (m,
3H), 5.95 (s, 1H), 3.92 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 166.3, 156.3, 131.7, 131.7,
131.6, 129.3, 128.6, 121.9, 121.5, 115.8, 114.3, 98.7, 82.5, 52.3. IR (neat): 3407, 2961, 2922,
2853, 1711, 1607, 1573, 1428, 1292, 1244, 1201, 1094, 986, 915, 881, 799, 755, 692, 590
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cmꢀ1. HRMS calc. for [C16H12NaO3]+ 275.0684; found 275.0679.
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2ꢀ(pꢀTolylethynyl)phenol (1m). Following general procedure GP1 with 2ꢀiodophenol (440 mg,
2 mmol) and 4ꢀethynyltoluene (255 mg, 2.2 mmol) to afford 1m (292 mg, 70% over three
steps). The spectroscopic data match those previously reported in the literature.34 1H NMR
(300 MHz, CDCl3) δ 7.46ꢀ7.40 (m, 3H), 7.30ꢀ7.24 (m, 1H), 7.20ꢀ7.17 (m, 2H), 6.99 (bdd, J =
8.4, 1.2 Hz, 1H), 6.91 (td, J = 7.5, 1.2 Hz, 1H), 5.85 (s, 1H), 2.39 (s, 3H).
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2ꢀ((4ꢀMethoxyphenyl)ethynyl)phenol (1n). Following general procedure GP1 with
2ꢀiodophenol (440 mg, 2 mmol) and 4ꢀethynylanisole (291 mg, 2.2 mmol) to afford 1n (292
mg, 65% over three steps). The spectroscopic data match those previously reported in the
literature.35 1H NMR (300 MHz, CDCl3) δ 7.82ꢀ7.79 (m, 2H), 7.58ꢀ7.50 (m, 2H), 7.26ꢀ7.20
(m, 2H), 7.00ꢀ6.97 (m, 2H), 6.89 (s, 1H), 3.87 (s, 3H).
2ꢀ((4ꢀ(Trifluoromethyl)phenyl)ethynyl)phenol (1o). Following general procedure GP1 with
2ꢀiodophenol (440 mg, 2 mmol) and 4ꢀ(trifluoromethyl)phenylacetylene (374 mg, 2.2 mmol)
to afford 1o (424 mg, 81% over three steps). The spectroscopic data match those previously
reported in the literature.36 1H NMR (300 MHz, CDCl3) δ 1H NMR (300 MHz, CDCl3) δ 7.64
(m, 4H), 7.44 (dd, J = 7.8, 1.5 Hz, 1H), 7.31 (bs, 1H), 7.00 (bd, J = 8.1 Hz, 1H), 6.94 (bt, J =
7.5 Hz, 1H), 5.76 (s, 1H).
B. Products of arylative cyclization of orthoꢀalkynylphenols
2ꢀPhenylbenzofuran (3a). The spectroscopic data match those previously reported in the
literature.37 1H NMR (300 MHz, CDCl3) δ (300 MHz, CDCl3) δ 7.88 (dd, J = 8.4, 1.5 Hz,
2H), 7.59 (dd, J = 7.8, 1.8 Hz, 1H), 7.54 (d, J = 8.4 Hz, 1H), 7.46 (t, J = 7.5 Hz, 2H),
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2ꢀPhenylꢀ3ꢀ(pꢀtolyl)benzofuran (3aa). Following general procedure GP2 with
orthoꢀalkynylphenol 1a (38.8 mg, 0.2 mmol) and aryldiazonium 2a (165 mg, 0.8 mmol). The
crude product was purified by flash column chromatography (Pent/Et2O, 100:1) to afford 3aa
as a yellow solid (42 mg, 73%). The spectroscopic data match those previously reported in the
literature.38 1H NMR (300 MHz, CDCl3) δ 7.68ꢀ7.65 (m, 2H), 7.55ꢀ47 (m, 2H), 7.36 (dd, J =
6.0, 1.8 Hz, 2H), 7.34ꢀ 7.19 (m, 7H), 2.43 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 154.0,
150.3, 137.3, 130.8, 130.4, 129.7, 129.7, 129.6, 128.4, 128.2, 127.0, 124.6, 122.8, 120.1,
117.5, 111.1, 21.4.
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3ꢀ(4ꢀNitrophenyl)ꢀ2ꢀphenylbenzofuran (3ab). Following general procedure GP2 with
orthoꢀalkynylphenol 1a (38.8 mg, 0.2 mmol) and aryldiazonium 2b (190 mg, 0.8 mmol). The
crude product was purified by flash column chromatography (Pent/Et2O, 100:1) to afford 3ab
as a yellow solid (54 mg, 86%). The spectroscopic data match those previously reported in the
literature.38 1H NMR (300 MHz, CDCl3) δ 8.26 (d, J = 8.7 Hz, 2H), 7.70 (d, J = 8.7 Hz, 2H),
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7.63ꢀ7.59 (m, 3H), 7.53ꢀ7.50 (m, 1H), 7.47ꢀ7.36 (m, 4H), 7.33ꢀ7.27 (m, 1H). C NMR (75
MHz, CDCl3) δ 154.1, 151,9, 147.1, 140.2, 130.4, 129.8, 129.1, 128.9, 128.7, 127.4, 125.2,
124.2, 123.4, 119.4, 115.4, 111.4.
2ꢀPhenylꢀ3ꢀ(4ꢀ(trifluoromethyl)phenyl)benzofuran (3ac). Following general procedure GP2
with orthoꢀalkynylphenol 1a (38.8 mg, 0.2 mmol) and aryldiazonium 2c (208 mg, 0.8 mmol).
The crude product was purified by flash column chromatography (Pent/Et2O, 100:0) to afford
3ac as a white solid (51 mg, 76%). The spectroscopic data match those previously reported in
the literature.39 1H NMR (300 MHz, CDCl3) δ 7.78ꢀ7.72 (m, 2H), 7.65ꢀ7.57 (m, 4H), 7.49 (d,
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J = 7.5 Hz, 1H), 7.39ꢀ7.26 (m, 6H). 13C NMR (101 MHz, CDCl3) δ 154.1, 151.3, 136.9, 130.2,
130.1, 129.6, 128.8, 128.7, 128.6, 128.5, 127.2, 125.9 (q, JCꢀF = 4.0 Hz), 125.0, 124.9, 124.2
(q, JCF3 = 270.7 Hz), 123.3, 122.9, 120.9, 119.7, 116.1, 111.3; 19F NMR (282 MHz, CDCl3) δ
ꢀ62.43.
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4ꢀ(2ꢀPhenylbenzofuranꢀ3ꢀyl)benzonitrile (3ad). Following general procedure GP2 with
orthoꢀalkynylphenol 1a (38.8 mg, 0.2 mmol) and aryldiazonium 2d (174 mg, 0.8 mmol). The
crude product was purified by flash column chromatography (Pent/Et2O, 100:1) to afford 3ad
as a colourless solid (48 mg, 81%). The spectroscopic data match those previously reported in
the literature.40 1H NMR (300 MHz, CDCl3) δ 7.77 (d, J = 8.1 Hz, 2H), 7.75ꢀ7.57 (m, 4H),
7.50 (dt, J = 7.5, 1.2, 0.6 Hz, 1H), 7.41ꢀ7.34 (m, 4H), 7.31ꢀ7.26 (m, 1H). 13C NMR (75 MHz,
CDCl3) δ 154.2, 151.7, 138.2, 132.8, 130.4, 129.9, 129.1, 128.7, 127.4, 125.2, 123.4, 119.5,
118.8, 115.8, 111.4, 111.3.
3ꢀ(4ꢀBromophenyl)ꢀ2ꢀphenylbenzofuran (3ae). Following general procedure GP2 with
orthoꢀalkynylphenol 1a (38.8 mg, 0.2 mmol) and aryldiazonium 2e (217 mg, 0.8 mmol). The
crude product was purified by flash column chromatography (Pent/Et2O, 100:0) to afford 3ae
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as a white solid (43 mg, 61%). Mp 120ꢀ122 °C. H NMR (300 MHz, CDCl3) δ 7.67ꢀ7.55 (m,
13
5H), 7.48 (dd, J = 7.5, 1.2 Hz, 1H), 7.41ꢀ7.23 (m, 7H). C NMR (75 MHz, CDCl3) δ 154.0,
150.8, 132.2, 131.9, 131.4, 130.4, 129.8, 128.6, 128.5, 127.1, 124.9, 123.1, 121.7, 119.7,
116.3, 111.2. IR (neat): 2363, 2328, 1487, 1445, 1380, 1256, 1206, 1064, 1001, 956, 839, 804,
741, 681, 606 cmꢀ1. MS (EI, 70 eV) m/z 350 (3ae (81Br)), 348 (3ae (79Br)), 270 (3ae − Br +
H).
2,3ꢀDiphenylbenzofuran (3af). Following general procedure GP2 with orthoꢀalkynylphenol
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1a (38.8 mg, 0.2 mmol) and aryldiazonium 2f (154 mg, 0.8 mmol). The crude product was
purified by flash column chromatography (Pent/Et2O, 100:0) to afford 3af as a colourless oil
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(35 mg, 65%). The spectroscopic data match those previously reported in the literature.39 1
H
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NMR (300 MHz, CDCl3) δ 7.68 (dd, J = 7.2, 2.7 Hz, 2H), 7.57 (d, J = 7.8 Hz, 1H), 7.51ꢀ7.42
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(m, 6H), 7.35ꢀ7.22 (m, 5H). C NMR (75 MHz, CDCl3) δ 154.0, 150.5, 132.9, 130.7, 130.3,
129.8, 129.0, 128.4, 128.3, 127.6, 127.0, 124.7, 122.9, 120.0, 117.5, 111.1.
3ꢀ(4ꢀMethoxyphenyl)ꢀ2ꢀphenylbenzofuran (3ag). Following general procedure GP2 with
orthoꢀalkynylphenol 1a (38.8 mg, 0.2 mmol) and aryldiazonium 2g (178 mg, 0.8 mmol). The
crude product was purified by flash column chromatography (Pent/Et2O, 100:0) to afford 3ag
as a white solid (14 mg, 23%). The spectroscopic data match those previously reported in the
literature.38 1H NMR (300 MHz, CDCl3) δ 7.68 (dd, J = 8.1, 2.1 Hz, 2H), 7.56 (d, J = 8.1 Hz,
1H), 7.51ꢀ7.48 (m, 1H), 7.44 (d, J = 8.7 Hz, 2H), 7.33ꢀ7.24 (m, 5H), 7.02 (d, J = 8.4 Hz, 2H),
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3.89 (s, 3H). C NMR (75 MHz, CDCl3) δ 159.1, 154.0, 150.8, 130.9, 130.8, 130.5, 128.4,
128.2, 126.9, 124.9, 124.6, 122.8, 120.0, 117.1, 114.5, 111.1, 55.3.
3ꢀ(2ꢀPhenylbenzofuranꢀ3ꢀyl)benzoate (3ah). Following general procedure GP2 with
orthoꢀalkynylphenol 1a (38.8 mg, 0.2 mmol) and aryldiazonium 2h (200 mg, 0.8 mmol). The
crude product was purified by flash column chromatography (Pent/Et2O, 100:1) to afford 3ah
as a colourless oil (41 mg, 62%). 1H NMR (300 MHz, CDCl3) δ 8.23ꢀ8.22 (m, 1H), 8.11ꢀ8.08
(m, 1H), 7.69ꢀ7.46 (m, 6H), 7.38ꢀ7.28 (m, 4H), 7.26ꢀ7.23 (m, 1H), 3.93 (s, 3H). 13C NMR (75
MHz, CDCl3) δ 166.8, 154.0, 150.9, 134.4, 133.3, 131.0, 130.8, 130.3, 129.9, 129.1, 128.8,
128.6, 128.5, 127.0, 124.9, 123.1, 119.8, 116.5, 111.2, 52.2. IR (neat): 2963, 2923, 2854, 1726,
1453, 1376, 1295, 1261, 1195, 1112, 1073, 750, 634 cmꢀ1. HRMS calc. for [C22H16NaO3]+
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2ꢀ(2ꢀPhenylbenzofuranꢀ3ꢀyl)benzonitrile (3ai). Following general procedure GP2 with
orthoꢀalkynylphenol 1a (38.8 mg, 0.2 mmol) and aryldiazonium 2i (174 mg, 0.8 mmol). The
crude product was purified by flash column chromatography (Pent/Et2O, 100:1) to afford 3ai
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as a yellow oil (22 mg, 37%). H NMR (300 MHz, CDCl3) δ 7.83 (dd, J = 7.2, 1.5 Hz, 1H),
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7.72 (td, J = 7.5, 1.5 Hz, 1H), 7.63ꢀ7.52 (m, 4H), 7.40ꢀ7.24 (m, 7H). C NMR (101 MHz,
CDCl3) δ 154.0, 152.2, 137.0, 133.9, 133.2, 131.6, 130.1, 129.5, 128.9, 128.7, 128.4, 126.8,
125.1, 125.1, 123.3, 119.6, 117.6, 113.8, 111.4. IR (neat): 2963, 2922, 2854, 1455, 1374, 1258,
1204, 1108, 754, 692, cmꢀ1. HRMS calc. for [C21H13NNaO]+ 318.0895; found 318.0889.
6ꢀMethoxyꢀ3ꢀ(4ꢀmethylphenyl)ꢀ2ꢀphenylꢀ benzofuran (3jd). Following general procedure GP2
with orthoꢀalkynylphenol 1j (37.6 mg, 0.17 mmol) and aryldiazonium 2d (173 mg, 0.8 mmol).
A mixture of products 4 and 3jd were obtained and purified by flash column chromatography
(Pent/Et2O, 100:6) to afford 4 as a colourless oil (6.4 mg, 21%) and 3jd as a colourless oil in
the presence of a trace of 4 (3 mg, 6%). Compound 4 is commercial available and the
spectroscopic data match those previously reported in the literature. Compound 4: 1H NMR
(400 MHz, CDCl3) δ 11.0 Hz (s, 1H), 7.73 (dd, J = 8.0, 0.4 Hz, 1H), 6.45ꢀ6.42 (m, 2H), 3.91
(s, 3H), 3.82 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 170.4, 165.6, 163.8, 131.2, 107.6, 105.4,
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100.7, 55.5, 51.9. Compound 3jd: H NMR (400 MHz, CDCl3) δ 7.74 (d, J = 8.8 Hz, 2H),
7.62 (d, J = 8.4 Hz, 2H), 7.57ꢀ7.54 (m, 2H), 7.36ꢀ7.33 (m, 4H), 7.11 (d, J = 2.0 Hz, 1H), 6.91
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(dd, J = 8.4, 2.0 Hz, 1H), 3.90 (s, 3H). C NMR (101 MHz, CDCl3) δ 158.7, 155.2, 150.7,
138.3, 132.7, 130.3, 130.1, 128.7, 128.7, 127.0, 122.5, 119.7, 118.8, 115.7, 112.4, 111.2, 95.9,
55.8. IR (neat): 3735, 3629, 2916, 2843, 2364, 2328, 2227, 1669, 1617, 1494, 1440, 1347,
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1271, 1196, 1153, 1114, 1068, 1026, 971, 877, 833, 769, 695, 640, 586 cmꢀ1. HRMS calc. for
[C22H15NNaO2]+ 348.0995; found 348.0983.
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Methyl 3ꢀ(4ꢀcyanophenyl)ꢀ2ꢀphenylbenzofuranꢀ5ꢀcarboxylate (3kd). Following general
procedure GP2 with orthoꢀalkynylphenol 1k (50 mg, 0.2 mmol) and aryldiazonium 2d (174
mg, 0.8 mmol). The crude product was purified by flash column chromatography (Pent/Et2O,
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100:4) to afford 3kd as a white solid (60 mg, 85%). Mp 215ꢀ217 °C. H NMR (300 MHz,
CDCl3) δ 8.19 (dd, J = 1.8, 0.6 Hz, 1H), 8.10 (dd, J = 8.4, 1.5 Hz, 1H), 7.79ꢀ7.76 (m, 2H),
7.64ꢀ 7.58 (m, 5H), 7.38ꢀ7.36 (m, 3H), 3.93 (s, 3H). 13C NMR (75 MHz, CDCl3) δ 166.9,
156.6, 153.0, 137.3, 132.9, 130.4, 129.5, 129.3, 129.2, 128.8, 127.4, 126.9, 125.8, 121.9,
118.6, 116.0, 111.7, 111.3, 52.2. IR (neat): 2923, 2853, 2228, 1718, 1606, 1437, 1372, 1293,
1242, 1200, 1098, 991, 918, 848, 763, 692 cmꢀ1. HRMS calc. for [C23H15NNaO3]+ 376.0950;
found 376.0944.
Methyl 3ꢀ(4ꢀcyanophenyl)ꢀ2ꢀphenylbenzofuranꢀ6ꢀcarboxylate (3ld). Following general
procedure GP2 with orthoꢀalkynylphenol 1l (50 mg, 0.2 mmol) and aryldiazonium 2d (174
mg, 0.8 mmol). The crude product was purified by flash column chromatography (Pent/Et2O,
1
100:4) to afford 3ld as a white solid (46 mg, 65%). Mp 148ꢀ150 °C. H NMR (300 MHz,
CDCl3) δ 8.26 (dd, J = 1.2, 0.6 Hz, 1H), 7.99 (dd, J = 6.9, 1.5 Hz, 1H), 7.78ꢀ7.75 (m, 2H),
7.63ꢀ7.58 (m, 4H), 7.50 (dd, J = 8.1, 0.6 Hz, 1H), 7.39ꢀ7.36 (m, 3H), 3.97 (s, 3H). 13C NMR
(75 MHz, CDCl3) δ 166.9, 154.5, 153.5, 137.4, 133.2, 132.9, 130.4, 129.7, 129.3, 128.8,
127.5, 127.0, 124.8, 119.0, 118.6, 115.8, 113.0, 111.7, 52.3. IR (neat): 2952, 2366, 2228, 1705,
1613, 1496, 1428, 1367, 1287, 1222, 1192, 1072, 974, 909, 869, 833, 760, 731, 686, 626 cmꢀ1.
HRMS calc. for [C23H15NNaO3]+ 376.0950; found 376.0944.
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3ꢀ(4ꢀNitrophenyl)ꢀ2ꢀ(pꢀtolyl)benzofuran (3mb). Following general procedure GP2 with
orthoꢀalkynylphenol 1m (42 mg, 0.2 mmol) and aryldiazonium 2b (189 mg, 0.8 mmol). The
crude product was purified by flash column chromatography (Pent/Et2O, 100:1) to afford 3mb
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as a yellow oil (56 mg, 85%). H NMR (300 MHz, CDCl3) δ 8.31 (d, J = 8.7 Hz, 2H)，7.69
(dd, J = 6.9, 1.8 Hz, 2H), 7.58 (d, J = 8.1 Hz, 1H), 7.52ꢀ7.48 (m, 3H), 7.39ꢀ7.34 (m, 1H),
7.31ꢀ7.26 (m, 1H), 7.17 (d, J = 8.1 Hz, 2H), 2.38 (s, 3H). 13C NMR (75 MHz, CDCl3) δ 154.1,
152.3, 147.0, 140.4, 139.4, 130.4, 129.4, 129.0, 127.4, 126.9, 125.0, 124.2, 123.4, 119.3,
114.8, 111.4, 21.4. IR (neat): 2364, 2329, 1603, 1515, 1456, 1347, 1257, 1071, 859, 822, 750,
654, 610 cmꢀ1. HRMS calc. for [C21H15NNaO3]+ 352.0944; found 352.0945.
2ꢀ(4ꢀMethoxyphenyl)benzofuran (3n). Following general procedure GP2 with
orthoꢀalkynylphenol 1n (45 mg, 0.2 mmol) and aryldiazonium 2b (189 mg, 0.8 mmol). The
crude product was purified by flash column chromatography (Pent/Et2O, 100:6) to afford 3n
as a white solid (43 mg, 96%). The spectroscopic data match those previously reported in the
literature.41 1H NMR (300 MHz, CDCl3) δ 7.83ꢀ7.78 (m, 2H), 7.58ꢀ7.49 (m, 2H), 7.29ꢀ7.20
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(m, 2H), 7.01ꢀ6.96 (m, 2H), 6.89 (s, 1H), 3.87 (s, 3H); C NMR (75 MHz, CDCl3) δ 160.0,
156.1, 154.7, 129.5, 126.4, 123.7, 123.4, 122.8, 120.6, 114.3, 111.0, 99.7, 76.6, 55.4.
4ꢀ(2ꢀ(4ꢀMethoxyphenyl)benzofuranꢀ3ꢀyl)benzonitrile (3nd). Following general procedure GP2
with orthoꢀalkynylphenol 1n (45 mg, 0.2 mmol) and aryldiazonium 2d (173 mg, 0.8 mmol).
The crude product was purified by flash column chromatography (Pent/Et2O, 100:6) to afford
3nd as a colourless oil (7 mg, 11%) and 3n as a white solid (21 mg, 48%). 1H NMR 3nd (400
MHz, CDCl3) δ 7.75ꢀ7.73 (m, 2H), 7.64ꢀ7.62 (m, 2H), 7.57ꢀ7.52 (m, 3H), 7.49ꢀ7.47 (m, 1H),
7.37ꢀ7.32 (m, 1H), 7.29ꢀ7.25 (m, 1H), 6.89 (dd, J = 6.8, 2.0 Hz, 2H), 3.84 (s, 3H); 13C NMR
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3nd (101 MHz, CDCl3) δ 191.6, 160.3, 154.0, 151.9, 138.5, 132.7, 130.4, 129.2, 128.9, 124.8,
123.3, 122.4, 119.2, 118.9, 114.2, 111.3, 111.0, 55.3. IR (neat): 3053, 2965, 2923, 2848, 2226,
1608, 1507, 1452, 1373, 1302, 1253, 1175, 1111, 1071, 1027, 963, 838, 747, 599 cmꢀ1. HRMS
calc. for [C22H15NNaO2]+ 348.0995; found 348.0982.
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Compound (5of). Following general procedure GP2 with orthoꢀalkynylphenol 1o (52 mg, 0.2
mmol) and aryldiazonium 2f (154 mg, 0.8 mmol). The crude product was purified by flash
column chromatography (Pent/Et2O, 100:1) to afford the ketone 5of (present in the enol form)
as a colourless oil (55 mg, 77%). 1H NMR (300 MHz, CDCl3) δ 12.15 (s, 1H), 7.81ꢀ7.78 (dd,
J = 8.1, 1.8 Hz, 1H), 7.62ꢀ7.59 (d, J = 8.1 Hz, 1H), 7.49ꢀ7.27 (m, 9H), 7.02ꢀ6.99 (dd, J = 8.4,
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1.2 Hz, 1H), 6.86ꢀ6.81 (td, J = 7.2, 1.2 Hz, 1H), 6.13 (s, 1H). C NMR (75 MHz, CDCl3) δ
203.6, 163.4, 142.6, 137.8, 136.8, 130.5, 129.6, 129.2, 128.9, 127.8, 125.6 (q, JCꢀF = 3.7 Hz),
119.2, 118.9, 118.8, 58.6. Two carbons are missing. 19F NMR (282 MHz, CDCl3) δ ꢀ62.57. IR
(neat): 2924, 1710, 1640, 1576, 1487, 1447, 1414, 1361, 1321, 1226, 1162, 1119, 1066, 1007,
797, 746, 698, 637 cmꢀ1. HRMS calc. for [C21H15F3NaO2]+ 379.0916; found 379.0926.
Compound (6ob). Following general procedure GP2 with orthoꢀalkynylphenol 1o (52 mg, 0.2
mmol) and aryldiazonium 2b (189 mg, 0.8 mmol). The crude product was purified by flash
column chromatography (Pent/Et2O, 100:3) to afford the enol ether 6ob as a yellow oil (62.7
mg, 76%). 1H NMR (300 MHz, CDCl3) δ11.98 (s, 0.05H), 8.22ꢀ8.19 (m, 1.06H), 7.96 (dd, J =
6.9, 1.5 Hz, 0.96H), 7.64ꢀ7.61 (m, 1.16H), 7.46ꢀ7.36 (m, 3.48H), 7.27ꢀ7.22 (m, 1H),
7.11ꢀ7.05 (m, 2H), 6.93ꢀ6.88 (m, 2H), 6.76ꢀ6.70 (m, 1H), 6.03ꢀ5.97 (m, 0.96H), 3.58ꢀ3.57 (m,
3H). 13C NMR (75 MHz, CDCl3) δ 154.5, 154.4, 152.7, 146.9, 146.3, 142.9, 131.8, 131.8,
131.6, 130.8 (q, JCꢀF = 34.1 Hz), 125.3 (q, JCꢀF = 3.7 Hz), 125.1 (q, JCꢀF = 4.0 Hz), 124.1,
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123.4, 123.3, 120.8, 120.7, 118.9, 118.8, 116.5, 116.4, 57.9, 57.8. 19F NMR (282 MHz, CDCl3)
δ ꢀ62.59, ꢀ62.62. IR (neat): 2935, 2844, 1703, 1586, 1513, 1449, 1406, 1322, 1163, 1114,
1069, 1009, 843, 753, 701, 639 cmꢀ1. HRMS calc. for [C22H16F3NNaO4]+ 438.0924; found
438.0940.
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Supporting Information
1H, 13C and 19F NMR Spectra and GC/MS for compounds (PDF)
Acknowledgements
We are very grateful to CNRS, UPMC, IUF, China Scholarship Council (PhD grant to ZX) for
their support. COST Action CM1201 is gratefully acknowledged. We warmly thank PSM of
the ICMG (FR 2607) of Université Grenoble Alpes for GC/MS.
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Experimental conditions by Glorius mention the use of 3 equiv of KH2PO4. We obtained a
better yield of 3af (65% vs 53%) without this additive.
18
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As deduced from the result of entry 1, the cationic catalyst PPh3AuNTf2 triggers the
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cycloisomerization process at the expense of the dual catalytic pathway. In the case of
IPrꢀAuCl complex, the stability of this complex in the reaction conditions can be questioned.
Maybe, it suffers from radical addition on the IPr ligand as a side reactivity and which results
in poor yield.
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CAS 5446ꢀ02ꢀ6
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Only two main products (containing minor impurities) were isolated from the reaction of
butylꢀsubstituted orthoꢀalkynylphenol and aryldiazonium 2d. They could be identified as the
expected arylative cyclization product (4ꢀ(2ꢀbutylbenzofuranꢀ3ꢀyl)benzonitrile, < 15%) and
4ꢀpentanoylbenzonitrile which formation remains unclear (< 16%). It may originate from a
sequential addition of the aryl radical to the alkyne moiety and a subsequent goldꢀcatalyzed
oxidative cleavage of the generated double bond (see ref. 24).
26
(a) Jones, A. C. in Homogeneous Gold Catalysis, Topics in Current Chemistry 2015, 357,
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