9,10-Dicyanoanthracene Catalyzed Decarboxylative Alkynylation of Carboxylic Acids under Visible-Light Irradiation

Article abstract of DOI:10.1021/acs.joc.6b02385

A metal-free, visible-light-induced photocatalytic procedure for decarboxylative alkynylation of carboxylic acids was reported. With 9,10-dicyanoanthracene as the photoredox catalyst, the reaction covered a broad scope of α-amino acids, α-oxo acids, and α-keto acids with blue LED irradiation at room temperature under an atmosphere of argon, delivering alkynyl products in moderate to excellent yields. Natural sun light also promoted this alkynylation strategy. This work represents the first example of an organophotocatalytic method for decarboxylative alkynylation of carboxylic acids.

Full text of DOI:10.1021/acs.joc.6b02385

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Article
9, 10-Dicyanoanthracene Catalyzed Decarboxylative
Alkynylation of Carboxylic Acids under Visible-Light Irradiation
Chen Yang, Jin-Dong Yang, Yi-He Li, Xin Li, and Jin-Pei Cheng
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b02385 • Publication Date (Web): 29 Nov 2016
Downloaded from http://pubs.acs.org on November 30, 2016
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The Journal of Organic Chemistry
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9, 10-Dicyanoanthracene Catalyzed Decarboxylative Alkynylation of
Carboxylic Acids under Visible-Light Irradiation
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Chen Yang,† JinꢀDong Yang,‡ YiꢀHe Li,† Xin Li,*,‡ and JinꢀPei Cheng*,†,‡
†Department of Chemistry and Biology, College of Science, National University of Defense Technology, Changsha 410073,
China
‡State Key Laboratory of Elementoꢀorganic Chemistry, Collaborative Innovation Center of Chemical Science and Engineerꢀ
ing, Nankai University, Tianjin 300071, China
ABSTRACT: A metalꢀfree, visibleꢀlightꢀinduced photocatalytic procedure for decarboxylative alkynylation of carboxylic acids
was reported. With 9, 10ꢀdicyanoanthracene as the photoredox catalyst, the
reaction covered a broad scope of αꢀamino acids, αꢀoxo acids and αꢀketo
acids with blue LEDs irradiation at room temperature under the atmosphere
of argon, delivering alkynyl products in moderate to excellent yields. Natuꢀ
ral sun light can also promoted this alkynylation strategy. This work repreꢀ
sents the first example of organophotocatalytic method for decarboxylative
alkynylation of carboxylic acids.
INTRODUCTION
Scheme 1. Photocatalytic Decarboxylative Alkynylation
Reactions11
Carboxylic acids, as abundant and inexpensive basic chemiꢀ
cals, have numerous applications in synthetic organic chemisꢀ
try and industry. 1 One of them is the decarboxylative oxidaꢀ
tion of aliphatic carboxylic acids, which has attracted growing
attention in the past years.1a,e In this regard, transitionꢀmetalꢀ
catalyzed decarboxylative procedure is a most conventional
way.2 Since the MacMillan group firstly introduced photoꢀ
chemistry into the realm of asymmetric catalysis in 2008,3
visibleꢀlight photoredox catalysis has been gradually become
as a smart and competitive tool in many aspects of synthetic
chemistry.4ꢀ5 This strategy can be utilized as a versatile tool to
trigger a lot of radical reactions under very mild conditions.
Recently, the visibleꢀlightꢀinduced decarboxylative functionalꢀ
izations of carboxylic acids are developed, and have been
emerged as a novel and powerful tool to construct CꢀC and Cꢀ
ꢀ6
X bonds. 5 As a result, numerous challengeable transforꢀ
mations on basis of carboxylic acids, such as alkylation,6a
amidation,6b arylation,6c anhydride decarboxylation,6d vinylaꢀ
tion,6e decarboxylative reduction,6f halogenation,6g trifluoroꢀ
methylation,6h trifluoromethylthiolation6i and hydroxylation6j
reactions, have been achieved.5, Very recently, the visibleꢀ
6
lightꢀinduced decarboxylative alkynylation reactions have
been explored with hypervalent iodine(III) reagents7 (Scheme
1). The Chen group reported the decarboxylative ynonylation
of αꢀketo acids with ethynylbenziodoxolones and an extra
oxidant by employment of a Ru(bpy)3(PF6)2 photocatalyst
(Scheme 1a).8 Shortly after that, the Xiao9 and Waser10 group
independently developed a direct decarboxylative alkynylation
reaction with Ir[dF(CF3)ppy]2(dtbbpy)PF6, avoiding the need
of external oxidant. Xiao, Lu and coꢀworkers found that variꢀ
carbon monoxide. Waser and coꢀworkers applied this method
ous carboxylic acids, including aliphatic, αꢀketo and αꢀamino
to synthesize a series of silylꢀ, alkylꢀ, and arylꢀ substituted
acids, are compatible in the reaction (Scheme 1b). Notably,
alkynes (Scheme 1c). While the above mentioned strategy of
this methodology can also obtain ynones in the presence of
photoꢀinduced decarboxylative alkynylation is quite remarkaꢀ
ble, it suffers from the use of either expensive metal photoreꢀ
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dox catalysts or external oxidant and the upꢀscaling problem ethers, esters, thioethers and amines, can also be easily conꢀ
1
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3
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7
8
for the cost of noble metal catalysis. Therefore, new approachꢀ
es to realize the visibleꢀlightꢀinduced decarboxylative alkynylꢀ
ation with organic type photoredox catalysts, which can reꢀ
duce the cost of the reaction, now remain as a formidable chalꢀ
lenge and are still highly desirable (Scheme 1d).
verted to the phenylethynylated products 3qꢀ3u in 54ꢀ85%
yields. Moreover, the alkynylation of αꢀoxo acid can also ocꢀ
cur, in which 3v was isolated in 50% yield. However, the effiꢀ
ciency of this catalytic system for aliphatic carboxylic acid is
not as highly as that of αꢀheteroatom acids. Product 3w was
obtained only in 40% yield. To our delight, the reaction also
works well in the case of αꢀketo acids. As a result, the ynonylꢀ
ated products 3x and 3y were isolated 90% and 64% yields,
respectively. To further explore the substrate scope, reactivity
of three other hypervalent iodine reagents was inspected with
1a. Silyl as well as electroꢀpoor phenyl substituted
ethynylbenziodoxolones, proceeded the alkynylation smoothly,
giving 3zꢀ3ab in 60ꢀ91% yields.
Nowadays, cheap organic dyes have been proved as a reliaꢀ
ble option to the replacement of those metal photoredox cataꢀ
lysts in many valuable transformations.4b,f, ,13 Theoretically, if
12
9
its redox window covered the oxidation potential of carboxꢀ
ylate (Eox = +0.95v (tꢀbutoxycarbonyl)prolinate vs. the saturatꢀ
ed calomel electroder),6h an organic dye would be feasible to
play the role of metal photocatalysts. Cyanoarenes, such as 9,
10ꢀdicyanoanthracene (DCA, Ered* = +1.99V), are classic exꢀ
emplars with high singlet excitedꢀstate oxidation potentials.4b
Meanwhile, DCA possesses a longer singlet lifetime and abꢀ
sorbs visible light (λmax = 422nm). Additionally, its price is
much cheaper than corresponding metal photoredox catalysts
(Scheme 1). Although DCA has the capability of powerful
excited oxidation, to the best of our knowledge, there is no
report on the photoꢀoxidation of carboxylic acids by use of
DCA.13 Thus, we saw an opportunity to demonstrate the utility
of DCA to realize the task of decarboxylative alkynylation
(Scheme 1d).14 Herein, we reported the first organophotocataꢀ
lytic method for decarboxylative alkynylation of carboxylic
acids.
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Table 1 Optimization of the Reaction Conditionsa
Ph
O
I
O
2a (1.5 equiv.)
COOH
N
N
Ph
DCA (x mol%), Base (1 equiv.)
solvent 1 mL, blue LEDs, 24h, RT
Cbz
Cbz
1a (1 equiv.)
solvent
DMF
3a
entry
1
base
x mol%
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
5
% yieldb
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12
19
37
52
56
62
33
52
19
70
20
6
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
NaOH
TMG
2
DMSO
THF
3
RESULTS AND DISCUSSION
4
EtOAc
EtOH
Using 10 mol% DCA as photocatalyst and a commercially
available blue LED strip as light source, our investigations
were started with Cbzꢀprotected proline (1a) and phenyl
ethynylbenziodoxolone (2a) (Table 1). The model reaction
was initially performed in 1.0 mL DMF with 1.0 equivalent
cesium carbonate, and the desired alkynylated product 3a was
obtained, albeit the yield was only 11% (entry 1). Encouraged
by this promising result, we then screened a set of solvents
(entries 1ꢀ10). Chloroform was designated as the suitable one
for its delivery of a best result among the examined media
(entry 7). The amount and kind of bases were subsequently
examined (entries 11ꢀ16). Doubling the amount of base further
raised the yield of product to 70% (entry 11). Under two
equivalents of base condition, potassium carbonate was found
to give the best yield of product 3a (93%) among the examꢀ
ined bases (entry 16). Lowering the catalyst loading to 5 mol%
had little influence on the yield (entry 17). However, the yields
decreased sharply as further reduction of the catalyst loading
(entries 18ꢀ19). Control experiments indicated that photocataꢀ
lyst, light source, base and inert atmosphere were necessary to
this catalytic system (entries 20ꢀ23). Collectively, the optimal
conditions were established by performing the reaction with
1a (0.1 mmol), 2a (0.15 mmol), K2CO3 (0.2 mmol) and DCA
(5 mol%) in 1.0 mL chloroform at room temperature under the
atmosphere of argon and the irradiation of a blue LED strip
(entry 17).
5
6
DCM
7
CHCl3
Et2O
8
9
Anisole
Toluene
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
10
11c
12c
13c
14c
15c
16c
17c
18c
19c
20c
21c,d
22c,e
23c,f
Na2CO3
KHCO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
ꢀ
47
43
93
92
60
31
3
1
0
No reaction
No reaction
No reaction
<5%
5
5
5
a
Unless noted, the reaction was carried out with 1a (0.1 mmol),
We then evaluated the substrate scope with the optimal reꢀ
action conditions (Scheme 2). Cyclic αꢀamino acids were first
examined, and corresponding alkynylated products 3aꢀ3e were
obtained with satisfactory yields (70ꢀ92%). Both NꢀFmoc and
NꢀBoc protected amino acids with various aliphatic side chains
were compatible, affording decarboxylative products 3fꢀ3p in
moderate to excellent yields (65ꢀ96%). Notably, amino acids
equipped with functional groups in the side chains, including
2a (0.15 mmol), base (0.1 mmol) and DCA (10 mol%) in 1.0 mL
solvent at room temperature under the atmosphere of argon and
the irradiation of a blue LED strip for 24 h. b Isolated yield. c 0.2
d
e
mmol base was used. In the absence of light source. In the
presence of air. f No base was used.
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Scheme 2. Reaction Scope of Photocatalytic Decarboxylative Alkynylationa,b
3
4
5
6
R2
O
I
DCA
(5 mol%), K2CO3 (2 equiv.)
R1 COOH
R1
R2
+
O
CHCl3 1 mL, blue LEDs, 24h, RT
1
, 0.1 mmol
2
, 1.5 mmol
3
7
8
9
Cbz
N
10
11
12
13
14
15
16
17
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19
20
21
22
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N
N
N
N
Boc
3d
Ph
Ph
Cbz
Cbz
Boc
Ph
, 80%
Ph
Ph
3a
3b
, 92%
, 88%
3c
, 70%
3e
, 86%
Bn
FmocHN
FmocHN
3g, 85%
BocHN
3j, 95%
FmocHN
3h, 93%
BocHN
Ph
Ph
Ph
Ph
Ph
3f
, 87%
3i
, 65%
nBu
BocHN
BocHN
3m
BocHN
BocHN
BocHN
Ph
Ph
Ph
Ph
Ph
, 96%
3n
, 92%
3o
, 72%
3k
3l
, 72%
, 68%
CO2Me
S
OBn
OBn
Bn
BocHN
BocHN
BocHN
BocHN
BocHN
Ph
Ph
Ph
Ph
Ph
3p
3q
3r
3s
3t
, 60%
, 85%
, 85%
, 78%
, 54%
NHBoc
O
O
BocHN
Ph
O
Ph
Ph
Ph
Br
3v
3x
, 90%
3y
, 64%
3u
, 50%
, 70%
3w, 40%
N
N
N
SiPh2tBu
, 60%
SiiPr3
Cbz
Cbz
Cbz
Br
3z, 91%
3aa
3ab
, 70%
a The reaction was carried out with 1 (0.1 mmol), 2 (0.15 mmol), K2CO3 (0.2 mmol) and DCA (5 mol%) in chloroform (1.0 mL) at
room temperature under the atmosphere of argon and the irradiation of a blue LED strip for 24 h. b Isolated yield.
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source, excited DCA would oxidize the deprotonated acid
. This progress would lead to the formation of a reduced
1
2
3
4
5
6
7
8
1
Scheme 3. Synthetic Utility of the Methodology
species and carboxyl radical. Because of a negative bond
dissociation enthalpy of carboxyl radical,17 a carbon radiꢀ
cal intermediate
release of CO2. Addition of
an unstable radical adduct II, which would undergo a βꢀ
elimination to yield the desired product and benziodoxꢀ
I
would be quickly generated through the
I
to substrate would deliver
2
3
olonyl radical III. The redox potential of reduced photoꢀ
catalyst is ꢀ0.91V,4b which is comparable with the wellꢀ
known iridium catalyst (Ered[IrIII/IrII]=ꢀ1.37V)9,10 used in
decarboxylative transformations. Thus, radical III can be
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reduced to 2ꢀiodobenzoate
6 by this species, finishing the
catalytic cycle and regenerating the catalyst. Besides, a
chain propagation pathway cannot be excluded at preꢀ
sent.18 The intermediate III could work as a direct oxidant
for the deprotonated acid
1
to yield another radical interꢀ
mediate
product
I
, which would react with substrate to give the
2
3.
Scheme 4. Proposed Reaction Mechanism
To expand the synthetic applicability of the products, three
experiments were performed. The model reaction was firstly
carried out under natural sun light (Scheme 3a). Through ten
hours, the desired product 3a was obtained in 83% yield. The
satisfactory yield of a gramꢀscale reaction exhibited the conꢀ
venient scaledꢀup ability of this catalytic system (Scheme 3b).
We subsequently converted product 3m to a Nꢀallylated prodꢀ
uct 4, which is the precursor in the preparation of cyclic prodꢀ
uct 5 (Scheme 3c).15
1.25
2.0
1.5
1.0
0.5
0.0
(a)
(b)
Y = 186.7*X + 1.008
R2= 0.996
1.20
1.15
1.10
1.05
1.00
CONCLUSIONS
In conclusion, we have developed an efficient, organophotoꢀ
catalytic method for decarboxylative alkynylation of carboxꢀ
ylic acids for the first time. The reaction can be carried out at
room temperature by using visible light with only 5 mol% of
cheaply organic type photocatalyst DCA. A set of amino acids,
as well as αꢀoxo acids and αꢀketo acids, can be smoothly conꢀ
verted to the corresponding products in moderate to excellent
yields through the current strategy. The feature of this methꢀ
odology, that is metalꢀfree, optionalꢀsolarꢀlightꢀdriven, feasiꢀ
bly scaledꢀup and syntheticꢀutilityꢀofꢀproduct, may make itself
useful in organic synthesis and industry.
0.0000 0.0002 0.0004 0.0006 0.0008 0.0010 0.0012
0.0000 0.0002 0.0004 0.0006 0.0008 0.0010 0.0012 0.0014
[1a_anion] (M)
[2a] (M)
Figure 1. Stern-Volmer Quenching Studies for (a)
1a_anion, (b) 2a
To probe the mechanism, the standard SternꢀVolmer
analysis was conducted (Figure 1).16 Under basic condiꢀ
tion, it was found excited state of *DCA can be quenched
by substrate 1a. However, no obvious change of *DCA
luminescence in the presence of variable concentrations
of 2a was observed. Although comprehensive studies will
be needed to gain a good understanding of the current
strategy, a putative mechanism was proposed to describe
the decarboxylative alkynylation reactions based on the
quenching experiments and previously studied photoreꢀ
dox catalysis (Scheme 4).9,10 Under the irradiation of light
EXPERIMENTAL SECTION
General Information. Commercial reagents were used as received,
unless otherwise stated. The purchased solvents were dried over moꢀ
lecular sieves and degassed by three cycles of freezeꢀpumpꢀthaw
1
before used in the reaction. H and 13C NMR were recorded on a 400
spectrometer. Chemical shifts are reported in ppm from tetrameꢀ
thylsilane with the solvent resonance as the internal standard. The
following abbreviations were used to designate chemical shift
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mutiplicities: s= singlet, d= doublet, t= triplet, q= quartet, h= heptet,
m= multiplet, br= broad. All firstꢀorder splitting patterns were asꢀ
34.1, 33.4, 24.6, 23.9 ppm.
tert-butyl 2-(phenylethynyl)pyrrolidine-1-carboxylate (3b): colorless
1
2
3
4
5
6
1
signed on the basis of the appearance of the multiplet. Splitting patꢀ
terns that could not be easily interpreted are designated as multiplet
(m) or broad (br). Mass spectra were obtained using ESI mode with a
double focusing mass analyzer. The hypervalent iodine(III) reagents
were prepared according to known methods reported by the Waser
group.10
oil; 23.9 mg, 88% yield. H NMR (400 MHz, CDCl3) δ 7.45 – 7.36
(m, 2H), 7.35 – 7.24 (m, 3H), 4.96 – 4.60 (m, 1H), 3.62 – 3.27 (m,
2H), 2.24 – 1.87 (m, 4H), 1.52 (s, 9H) ppm. 13C NMR (101 MHz,
CDCl3) δ 154.3, 131.7, 128.6, 128.1, 123.3, 82.9, 81.6, 79.8, 48.9,
45.7, 28.6, 23.9, 17.5 ppm. HRMS (ESI): calcd. for [C17H21NO2+H]+
272.1651, found 272.1644.
General procedure for the decarboxylative alkynylation reaction.
Carboxylic acids 1 (0.1 mmol), ethynylbenziodoxolones 2 (0.15
mmol), K2CO3 (0.2 mmol), DCA (1.1 mg) and a magnetic stir bas
were added to an ovenꢀdried 10 mL Schlenk tube. The reaction mixꢀ
ture was degassed for three times. 1mL degassed chloroform was then
added to the mixture in the presence of a flow of argon. The solution
was placed at a distance of about 5 cm from a 5W blue LED strip and
irradiated for 24 h. After that, the crude mixture was purified by colꢀ
umn chromatography (eluent: petroleum ether/ethyl acetate 40:1 to
5:1) to give the product 3.
Procedure for the sunlight-driven decarboxylative alkynylation
reaction. 1a (0.1 mmol), 2a (0.15 mmol), K2CO3 (0.2 mmol), DCA
(1.1 mg) and a magnetic stir bas were added to an ovenꢀdried 10 mL
Schlenk tube. The reaction mixture was degassed for three times.
1mL degassed chloroform was then added to the mixture in the presꢀ
ence of a flow of argon. The solution was stirred under solar light for
10h (Location: 39o6′2′′ N, 117o9′51′′ E). After that, the crude mixture
was purified by column chromatography (eluent: petroleum
ether/ethyl acetate 10:1) to give the product 3a in 83% yield as a colꢀ
orless oil.
Procedure for the gram-scale reaction. 1m 0.92g (4 mmol), 2a
2.08g (6 mmol), K2CO3 1.12g (0.2 mmol), DCA (40 mg), 40mL chloꢀ
roform and a magnetic stir bas were added to an ovenꢀdried 100 mL
twoꢀneck flask. The reaction mixture was degassed by using a freezeꢀ
pumpꢀthaw procedure for three times. The solution was placed at a
distance of about 5 cm from a 5W blue LED strip and irradiated for
48 h. After that, the crude mixture was purified by column chromaꢀ
tography (eluent: petroleum ether/ethyl acetate 30:1) to give the prodꢀ
uct 3m (0.94 g) in 82% yield as a yellow oil.
Procedure for the transformation of product 3m. The transforꢀ
mation was performed according to a known method reported by the
Shin group.19 Under atmosphere of argon, 0.2mmol 3m and 0.6mL
anhydrous DMF were added to an ovenꢀdried 10 mL Schlenk tube.
The solution was cooled to 0oC, and 10 mg NaH (60% dispersion in
mineral oil) was then added. When gas evolution ceased, 36.4 mg
allyl bromide was added. The reaction mixture was warmed to room
temperature and stirred for 4 h. When the reaction was completed, 2.8
mL water was added. The resulting aqueous layer was extracted with
Et2O (4mL*3). The combined organic layer was dried with Na2SO4
for 4h. Na2SO4 was removed by filtration, and the solvent was evapoꢀ
rated. The residue was purified by chromatography (petroleum
ether/ethyl acetate, 15:1) to give 4 (55.4 mg, 85%) as a light yellow
oil.
benzyl 2-(phenylethynyl)piperidine-1-carboxylate (3c): light yellow
oil; 25.5 mg, 80% yield. Analytical data matched previously reported
values.20 1H NMR (400 MHz, CDCl3) δ 7.50 – 7.28 (m, 10H), 5.46
(br. s, 1H), 5.30 – 5.20 (m, 2H), 4.14 (d, J = 13.1 Hz, 1H), 3.27 (t, J =
13.0 Hz, 1H), 2.05 – 1.90 (m, 2H), 1.85 – 1.70 (m, 3H), 1.60 – 1.45
(m, 1H) ppm. 13C NMR (101 MHz, CDCl3) δ 155.2, 136.9, 131.9,
128.6, 128.4, 128.3, 128.1, 127.9, 123.0, 87.3, 84.6, 67.4, 45.1, 40.9,
30.9, 25.5, 20.2 ppm.
tert-butyl 2-(phenylethynyl)piperidine-1-carboxylate (3d): colorless
oil; 20.0 mg, 70% yield. Analytical data matched previously reported
values.21 1H NMR (400 MHz, CDCl3) δ7.45 – 7.38 (m, 2H), 7.33 –
7.26 (m, 3H), 5.28 (s, 1H), 3.96 (d, J = 13.5 Hz, 1H), 3.11 (t, J = 12.8
Hz, 1H), 1.93 – 1.78 (m, 2H), 1.77 – 1.61 (m, 3H), 1.49 (s, 9H), 1.49
– 1.40 (m, 1H) ppm. 13C NMR (101 MHz, CDCl3) δ 154.8, 131.9,
128.4, 128.2, 123.3, 87.8, 84.3, 80.1, 44.9, 40.7, 30.9, 25.5, 20.3 ppm.
benzyl 3-(phenylethynyl)-3,4-dihydroisoquinoline-2(1H)-carboxylate
(3e): colorless oil; 31.6 mg, 86% yield. 1H NMR (400 MHz, CDCl3) δ
7.39 – 6.99 (m, 14H), 5.72 – 5.42 (m, 1H), 5.14 (s, 2H), 4.87 (d, J =
16.6 Hz, 1H), 4.52 (d, J = 16.5 Hz, 1H), 3.20 (dd, J = 15.6, 5.2 Hz,
1H), 2.92 (d, J = 15.9 Hz, 1H) ppm. 13C NMR (101 MHz, CDCl3) δ
155.2, 141.6, 136.6, 134.1, 133.2, 131.9, 129.1, 128.7, 128.4, 128.2,
128.1, 126.7, 126.6, 126.2, 122.7, 87.0, 83.5, 67.7, 66.8, 43.3, 34.9,
29.8 ppm. HRMS (ESI): calcd. for [C25H21NO2+H]+ 368.1651, found
368.1645.
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(9H-fluoren-9-yl)methyl
2-methyl-4-phenylbut-3-yn-2-ylcarbamate
o
1
(3f): white solid; mp:144ꢀ149 C; 33.2 mg, 87% yield. H NMR (400
MHz, CDCl3) δ 7.76 (d, J = 7.5 Hz, 2H), 7.62 (d, J = 7.5 Hz, 2H),
7.49 – 7.20 (m, 9H), 5.08 (s, 1H), 4.42 (d, J = 6.7 Hz, 2H), 4.23 (t, J =
7.0 Hz, 1H), 1.69 (s, 6H) ppm. 13C NMR (101 MHz, CDCl3) 13C
NMR (101 MHz, CDCl3) δ 154.5, 144.1, 141.4, 131.9, 128.3, 127.8,
127.2, 125.2, 122.9, 120.1, 92.7, 81.3, 66.4, 48.3, 47.4, 29.5 ppm.
HRMS (ESI): calcd. for [C26H23NO2+H]+ 382.1807, found 382.1808.
(9H-fluoren-9-yl)methyl 1,4-diphenylbut-3-yn-2-ylcarbamate (3g):
white solid; mp: 100ꢀ104 oC; 37.7 mg, 85% yield. 1H NMR (400 MHz,
CDCl3) δ 7.81 (d, J = 7.6 Hz, 2H), 7.62 (d, J = 7.6 Hz, 2H), 7.48 –
7.29 (m, 14H), 5.08 – 4.72 (m, 2H), 4.54 (dd, J = 10.6, 7.0 Hz, 1H),
4.42 (t, J = 8.7 Hz, 1H), 4.26 (t, J = 6.9 Hz, 1H), 3.22 – 2.85 (m, 2H)
ppm. 13C NMR (101 MHz, CDCl3) δ 155.3, 143.9, 141.5, 131.8,
130.2, 128.6, 128.5, 128.4, 127.9, 127.2, 127.1, 125.3, 125.2, 122.5,
120.1, 87.7, 84.8, 67.0, 47.4, 45.1, 42.0 ppm. HRMS (ESI): calcd. for
[C31H25NO2+H]+ 444.1964, found 444.1957.
(9H-fluoren-9-yl)methyl
5-methyl-1-phenylhex-1-yn-3-ylcarbamate
o
(3h): white solid; mp: 93ꢀ98 C; 38.1 mg, 93% yield. Analytical data
matched previously reported values.9 1H NMR (400 MHz, CDCl3) δ
7.78 (d, J = 7.5 Hz, 2H), 7.62 (d, J = 6.9 Hz, 2H), 7.46 – 7.27 (m, 9H),
5.01 (d, J = 9.0 Hz, 1H), 4.76 (q, J = 8.0 Hz, 1H), 4.51 – 4.40 (m, 2H),
4.25 (t, J = 7.0 Hz, 1H), 1.91ꢀ1.82 (m, 1H), 1.66 (t, J = 7.4 Hz, 2H),
1.00 (d, J = 6.6 Hz, 6H) ppm. 13C NMR (101 MHz, CDCl3) δ 155.6,
144.0, 141.4, 131.8, 129.1, 128.4, 128.4, 127.9, 127.8, 127.2, 125.2,
122.8, 120.1, 88.8, 83.3, 66.9, 47.4, 45.6, 42.7, 25.2, 22.8, 22.2 ppm.
tert-butyl 4-phenylbut-3-yn-2-ylcarbamate (3i): white solid; mp: 76ꢀ
Procedure for the luminescence quenching experiments. The exꢀ
periments were carried out on a fluorescence spectrophotometer. All
samples were prepared in MeOH solution. To a glass cuvette, soluꢀ
tions of photocatalyst, quencher and MeOH were added to obtain a
total volume of 5.0 mL. Before determination, the solution was deꢀ
gassed by three freezeꢀpumpꢀthaw cycles and backfilled with Argon.
When 1a was used as the quencher, 1.5 equivalents of NaOH were
added. The concentration of DCA was 1.4*10ꢀ6 M. All samples were
irradiated at 401 nm, and emission was determined at 432 nm.
o
80 C; 15.9 mg, 65% yield. Analytical data matched previously reꢀ
ported values.22,23 1H NMR (400 MHz, CDCl3) δ 7.44 – 7.36 (m, 2H),
7.35 –7.28 (m, 3H), 4.95 – 4.55 (m, 2H), 1.50 – 1.42 (m, 12H) ppm.
13C NMR (101 MHz, CDCl3) δ 154.9, 131.8, 128.4, 122.9, 90.0, 82.2,
80.0, 39.2, 28.5, 23.1 ppm.
benzyl 2-(phenylethynyl)pyrrolidine-1-carboxylate (3a): colorless oil;
28.1 mg, 92% yield. Analytical data matched previously reported
values.10 1H NMR (400 MHz, CDCl3) δ 7.41 – 7.14 (m, 10H), 5.30 –
5.02 (m, 2H), 4.82 – 4.64 (m, 1H), 3.56 – 3.49 (m, 1H), 3.41 – 3.33
(m, 1H), 2.20 – 2.02 (m, 3H), 1.96 – 1.86 (m, 1H) ppm. 13C NMR
(101 MHz, CDCl3) δ 154.7, 137.1, 132.0, 131.8, 128.5, 128.3, 128.2,
128.1, 127.8, 127.7, 123.0, 89.6, 82.4, 66.9, 49.3, 48.8, 46.3, 45.9,
tert-butyl 4-methyl-1-phenylpent-1-yn-3-ylcarbamate (3j): light yelꢀ
low oil; 26.0 mg, 95% yield. Analytical data matched previously reꢀ
ported values.23 1H NMR (400 MHz, CDCl3) δ 7.45 – 7.37 (m, 2H),
7.33 – 7.27 (m, 3H), 4.82 (brs, 1H), 4.54 (brs, 1H), 2.03 – 1.93 (m,
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Page 6 of 8
1H), 1.47 (s, 9H), 1.04 (d, J = 5.1 Hz, 6H) ppm. 13C NMR (101 MHz,
CDCl3) δ 155.2, 131.8, 128.4, 128.3, 123.1, 87.6, 83.9, 79.9, 49.4,
33.6, 28.5, 19.0 ppm.
tert-butyl 1-phenylhept-1-yn-3-ylcarbamate (3k): light yellow oil;
20.7 mg, 72% yield. Analytical data matched previously reported
values.23 1H NMR (400 MHz, CDCl3) δ 7.44 – 7.38 (m, 2H), 7.32 –
7.27 (m, 3H), 4.78 (s, 1H), 4.62 (d, J = 9.5 Hz, 1H), 1.78 – 1.66 (m,
2H), 1.51 – 1.32 (m, 13H), 0.92 (t, J = 7.2 Hz, 3H) ppm. 13C NMR
(101 MHz, CDCl3) δ 154.9, 131.7, 128.3, 128.2, 122.9, 89.1, 82.8,
80.0, 43.6, 36.4, 28.5, 27.9, 22.3, 14.2 ppm.
87.8, 83.9, 80.3, 51.9, 43.1, 31.6, 30.6, 28.5 ppm. HRMS (ESI): calcd.
for [C18H23NO4+H]+ 318.1705, found 318.1700.
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tert-butyl 5-(methylthio)-1-phenylpent-1-yn-3-ylcarbamate (3t): light
yellow oil; 18.3 mg, 60% yield. 1H NMR (400 MHz, CDCl3) δ 7.46 –
7.36 (m, 2H), 7.33 – 7.27 (m, 3H), 4.89 (brs, 1H), 4.78 (brs, 1H), 2.73
– 2.63 (m, 2H), 2.14 (s, 3H), 2.11 – 1.94 (m, 2H), 1.46 (s, 9H) ppm.
13C NMR (101 MHz, CDCl3) δ 154.9, 131.9, 128.6, 128.4, 122.7,
88.0, 83.8, 80.2, 43.0, 36.0, 30.4, 28.5, 15.7 ppm. HRMS (ESI): calcd.
for [C17H23NO2S+H]+ 306.1528, found 306.1525.
tert-butyl 7-phenylhept-6-yne-1,5-diyldicarbamate (3u): colorless oil;
1
tertꢀbutyl 5ꢀmethylꢀ1ꢀphenylhexꢀ1ꢀynꢀ3ꢀylcarbamate (3l): light yellow
28.2 mg, 70% yield. H NMR (400 MHz, CDCl3) δ 7.43 – 7.36 (m,
1
9
oil; 19.5 mg, 68% yield. H NMR (400 MHz, CDCl3) δ 7.45 – 7.35
2H), 7.32 – 7.27 (m, 3H), 4.81 (s, 1H), 4.70 – 4.50 (m, 2H), 3.20 –
3.02 (m, 2H), 1.82 – 1.68 (m, 2H), 1.60 – 1.46 (m, 4H), 1.46 (s, 9H),
1.43 (s, 9H) ppm. 13C NMR (101 MHz, CDCl3) δ 156.2, 155.0, 131.8,
128.4, 122.9, 88.8, 83.2, 80.0, 79.2, 43.5, 40.5, 36.3, 29.7, 28.6, 23.0
ppm. HRMS (ESI): calcd. for [C23H34N2O4+H]+ 403.2597, found
403.2594.
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(m, 2H), 7.33 – 7.28 (m, 3H), 4.82 – 4.60 (m, 2H), 1.81 – 1.94 (m,
1H), 1.67 – 1.54 (m, 2H), 1.47 (s, 9H), 0.97 (d, J = 5.4 Hz, 6H) ppm.
13C NMR (101 MHz, CDCl3) δ 155.0, 131.8, 128.4, 128.3, 123.1,
89.3, 82.9, 79.9, 45.8, 42.2, 28.5, 25.3, 23.0, 22.1 ppm. HRMS (ESI):
calcd. for [C18H25NO2+H]+ 288.1964, found 288.1958.
tert-butyl 4,4-dimethyl-1-phenylpent-1-yn-3-ylcarbamate (3m): yelꢀ
low oil; 27.6 mg, 96% yield. Analytical data matched previously reꢀ
ported values.23 1H NMR (400 MHz, CDCl3) δ 7.45 – 7.38 (m, 2H),
7.31 – 7.27 (m, 3H), 4.78 (d, J = 9.9 Hz, 1H), 4.46 (d, J = 9.9 Hz,
1H), 1.47 (s, 9H), 1.04 (s, 9H) ppm. 13C NMR (101 MHz, CDCl3) δ
155.5, 131.8, 128.4, 128.3, 123.2, 88.2, 83.8, 79.8, 52.9, 36.2, 28.5,
26.1 ppm.
2-(phenylethynyl)tetrahydrofuran (3v): light yellow oil; 8.6 mg, 50%
yield. Analytical data matched previously reported values.9 1H NMR
(400 MHz, CDCl3) δ 7.45 – 7.41 (m, 2H), 7.32 – 7.27 (m, 3H), 4.85 –
4.79 (m, 1H), 4.08 – 3.96 (m, 1H), 3.90 – 3.82 (m, 1H), 2.32 – 1.78
(m, 4H) ppm. 13C NMR (101 MHz, CDCl3) δ 131.9, 128.4, 128.4,
123.0, 89.2, 84.6, 68.8, 68.1, 33.6, 25.6 ppm.
2-(phenylethynyl)-2,3-dihydro-1H-indene (3w): white solid; mp: 48ꢀ
51oC; 8.7 mg, 40% yield. Analytical data matched previously reported
values.9 1H NMR (400 MHz, CDCl3) δ 7.43 – 7.36 (m, 2H), 7.31 –
7.26 (m, 3H), 7.25 – 7.20 (m, 2H), 7.19 – 7.14 (m, 2H), 3.49 – 3.39
(m, 1H), 3.35 – 3.24 (m, 2H), 3.16 – 3.08 (m, 2H) ppm. 13C NMR
(101 MHz, CDCl3) δ 142.1, 131.7, 128.3, 127.8, 126.7, 124.5, 123.9,
93.1, 80.7, 40.5, 30.9 ppm.
tert-butyl 4-methyl-1-phenylhex-1-yn-3-ylcarbamate (3n): colorless
1
oil; 26.4 mg, 92% yield. H NMR (400 MHz, CDCl3) δ 7.41 (dd, J =
6.7, 3.0 Hz, 2H), 7.33 – 7.27 (m, 3H), 4.90 – 4.74 (m, 1H), 4.71 –
4.56 (m, 1H), 1.73 (d, J = 9.6 Hz, 1H), 1.65 – 1.53 (m, 2H), 1.47 (s,
9H), 1.02 (dd, J = 6.7, 3.2 Hz, 3H), 0.99 – 0.93 (m, 3H) ppm. 13C
NMR (101 MHz, CDCl3) δ 155.2, 131.9, 131.8, 128.4, 128.3, 128.3,
123.1, 88.3, 83.6, 79.9, 48.2, 40.4, 29.8, 28.5, 26.4, 25.2, 15.5, 11.8
ppm. HRMS (ESI): calcd. for [C18H25NO2+H]+ 288.1964, found
288.1958.
tert-butyl 1-cyclohexyl-3-phenylprop-2-ynylcarbamate (3o): white
solid; mp: 92ꢀ96 oC; 22.6 mg, 72% yield. 1H NMR (400 MHz, CDCl3)
δ 7.45 – 7.37 (m, 2H), 7.32 – 7.27 (m, 3H), 4.83 (d, J = 9.2 Hz, 1H),
4.52 (dd, J = 9.3, 5.9 Hz, 1H), 1.91 – 1.74 (m, 4H), 1.71 – 1.63 (m,
2H), 1.46 (s, 9H), 1.33 – 1.08 (m, 5H) ppm. 13C NMR (101 MHz,
CDCl3) δ 155.2, 131.8, 128.4, 128.3, 123.1, 88.1, 83.8, 79.9, 48.7,
43.2, 29.4, 28.5, 26.4, 26.1, 26.0 ppm. HRMS (ESI): calcd. for
[C20H27NO2+H]+ 314.2120, found 314.2121.
tert-butyl 1,4-diphenylbut-3-yn-2-ylcarbamate (3p): light yellow solꢀ
id; mp: 85ꢀ90 oC; 27.3 mg, 85% yield. Analytical data matched previꢀ
ously reported values.9 1H NMR (400 MHz, CDCl3) δ 7.41 – 7.28 (m,
10H), 4.93 (m, 1H), 4.83 (m, 1H), 3.14– 3.02 (m, 2H), 1.48 (d, J = 1.9
Hz, 9H) ppm. 13C NMR (101 MHz, CDCl3) δ 154.8, 136.8, 131.7,
130.1, 128.5, 128.4, 127.0, 122.8, 88.3, 84.4, 80.1, 44.7, 42.2, 28.5
ppm.
1,3-diphenylprop-2-yn-1-one (3x): yellow solid; mp: 44ꢀ48oC; 18.6
mg, 90% yield. Analytical data matched previously reported values.9
1H NMR (400 MHz, CDCl3) δ 8.23 (d, J = 7.0 Hz, 2H), 7.73 – 7.66
(m, 2H), 7.69 – 7.59 (m, 1H), 7.57 – 7.45 (m, 3H), 7.48 – 7.38 (m,
2H) ppm. 13C NMR (101 MHz, CDCl3) δ 178.2, 137.0, 134.3, 133.2,
131.0, 129.7, 128.8, 128.8, 120.3, 93.3, 87.0 ppm.
3-(4-bromophenyl)-1-phenylprop-2-yn-1-one (3y): yellow solid; mp:
o
98ꢀ103 C; 18.2 mg, 64% yield. Analytical data matched previously
reported values.24 1H NMR (400 MHz, CDCl3) δ 8.20 (d, J = 7.7 Hz,
2H), 7.64 (t, J = 7.4 Hz, 1H), 7.60 – 7.48 (m, 6H) ppm. 13C NMR
(101 MHz, CDCl3) δ 178.0, 136.9, 134.5, 134.4, 132.3, 129.7, 128.8,
125.8, 119.2, 91.8, 87.8 ppm.
benzyl 2-((triisopropylsilyl)ethynyl)pyrrolidine-1-carboxylate (3z):
colorless oil; 35.1 mg, 91% yield. Analytical data matched previously
reported values.10 1H NMR (400 MHz, CDCl3) δ 7.44 – 7.27 (m, 5H),
5.16 (d, J = 2.9 Hz, 2H), 4.68 – 4.34 (m, 1H), 3.66 – 3.47 (m, 1H),
3.44 – 3.30 (m, 1H), 2.27 – 1.85 (m, 4H), 1.15 – 0.90 (m, 21H) ppm.
13C NMR (101 MHz, CDCl3) δ 153.7, 136.0, 127.5, 126.9, 126.8,
107.0, 81.8, 66.1, 48.0, 45.1, 33.4, 22.8, 17.7, 10.3 ppm.
benzyl 2-((tert-butyldiphenylsilyl)ethynyl)pyrrolidine-1-carboxylate
(3aa): colorless oil; 28.1 mg, 60% yield. Analytical data matched
previously reported values.10 1H NMR (400 MHz, CDCl3) δ 7.84 –
7.66 (m, 4H), 7.46 – 7.12 (m, 11H), 5.32 – 5.02 (m, 2H), 4.82 – 4.64
(m, 1H), 3.72 – 3.36 (m, 2H), 2.34 – 1.87 (m, 4H), 1.04 (s, 9H) ppm.
13C NMR (101 MHz, CDCl3) δ 154.7, 136.8, 135.7, 133.4, 129.6,
128.6, 127.8, 110.3, 82.1, 67.2, 49.1, 46.3, 34.3, 27.1, 24.0, 18.7 ppm.
benzyl 2-((4-bromophenyl)ethynyl)pyrrolidine-1-carboxylate (3ab):
colorless oil; 26.9 mg, 70% yield. Analytical data matched previously
reported values.10 1H NMR (400 MHz, CDCl3) δ 7.45 – 7.27 (m, 8H),
7.16 (d, J = 8.1 Hz, 1H), 5.43 – 4.95 (m, 2H), 4.85 – 4.69 (m, 1H),
3.66 – 3.34 (m, 2H), 2.22 – 1.82 (m, 4H) ppm. 13C NMR (101 MHz,
CDCl3) δ 154.6, 133.4, 133.3, 131.6, 128.6, 128.1, 127.9, 127.8,
122.5, 90.8, 81.4, 67.0, 49.3, 48.8, 46.4, 46.0, 34.0, 33.3, 29.9, 23.9
ppm.
tert-butyl 1-(benzyloxy)-4-phenylbut-3-yn-2-ylcarbamate (3q): colorꢀ
1
less oil; 29.9 mg, 85% yield. H NMR (400 MHz, CDCl3) δ 7.46 –
7.26 (m, 10H), 5.06 (s, 1H), 4.86 (s, 1H), 4.71 – 4.58 (m, 2H), 3.68 (d,
J = 4.8 Hz, 2H), 1.47 (s, 9H) ppm. 13C NMR (101 MHz, CDCl3) δ
155.1, 138.0, 131.9, 128.6, 128.5, 128.4, 127.9, 127.8, 122.8, 87.1,
83.3, 80.2, 73.4, 72.3, 43.6, 28.5 ppm. HRMS (ESI): calcd. for
[C22H25NO3+Na]+ 374.1732, found 374.1730.
tert-butyl 4-(benzyloxy)-1-phenylpent-1-yn-3-ylcarbamate (3r): colorꢀ
1
less oil; 28.5 mg, 78% yield. H NMR (400 MHz, CDCl3) δ 7.55 –
7.22 (m, 10H), 5.18 – 4.98 (m, 1H), 4.82 – 4.53 (m, 3H), 3.84 – 3.72
(m, 1H), 1.46 (m, 9H), 1.36 – 1.25 (m, 3H) ppm. 13C NMR (101
MHz, CDCl3) δ 155.3, 155.0, 138.4, 131.8, 131.7, 128.4, 128.4,
128.3, 128.3, 128.2, 127.8, 127.7, 122.9, 87.6, 86.1, 84.1, 83.3, 79.9,
79.9, 76.6, 75.9, 71.8, 71.0, 47.6, 28.4, 16.6, 16.3 ppm. HRMS (ESI):
calcd. for [C23H27NO3+H]+ 366.2069, found 366.2061.
methyl 4-(tert-butoxycarbonylamino)-6-phenylhex-5-ynoate (3s):
colorless oil; 17.1 mg, 54% yield. 1H NMR (400 MHz, CDCl3) δ 7.49
– 7.35 (m, 2H), 7.34 – 7.27 (m, 3H), 4.86 (s, 1H), 4.69 (s, 1H), 3.68 (s,
3H), 2.60 –2.43 (m, 2H), 2.15 – 2.01 (m, 2H), 1.46 (s, 9H) ppm. 13C
NMR (101 MHz, CDCl3) δ 173.6, 154.9, 131.9, 128.6, 128.4, 122.6,
tert-butyl allyl(4,4-dimethyl-1-phenylpent-1-yn-3-yl)carbamate (4):
1
light yellow oil; 27.8 mg, 85% yield. H NMR (400 MHz, CDCl3) δ
7.47 – 7.33 (m, 2H), 7.36 – 7.28 (m, 3H), 6.06 – 5.82 (m, 1H), 5.29 –
4.86 (m, 3H), 4.18 – 3.79 (m, 2H), 1.46 (s, 9H), 1.06 (s, 9H) ppm. 13C
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The Journal of Organic Chemistry
NMR (101 MHz, CDCl3) δ 155.1, 135.4, 130.7, 127.4, 127.2, 122.3,
114.5, 85.7, 85.1, 79.0, 56.5, 47.7, 36.9, 27.5, 26.0 ppm. HRMS (ESI):
1
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3
4
5
6
7
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W. C. Science 2014, 345, 437. (d) Le, C. C.; MacMillan, D. W. C. J.
Am. Chem. Soc. 2015, 137, 11938. (e) Noble, A.; MacMillan, D. W. C.
J. Am. Chem. Soc. 2014, 136, 11602. (f) Cassani, C.; Bergonzini, G.;
Wallentin, C.ꢀJ. Org. Lett. 2014, 16, 4228. (g) RuedaꢀBecerril, M.;
Mahé, O.; Drouin, M.; Majewski, M. B.; West, J. G.; Wolf, M. O.;
Sammis, G. M.; Paquin, J.ꢀF. J. Am. Chem. Soc. 2014, 136, 2637. (h)
Beatty, J. W.; Douglas, J. J.; Cole, K. P.; Stephenson, C. R. J. Nature
Commun. 2015, 6, 7919. (i) Candish, L.; Pitzer, L.; GómezꢀSuárez, A.;
Glorius, F. Chem. Eur. J. 2016, 22, 4753. (j) Song, H.ꢀT.; Ding, W.;
Zhou, Q.ꢀQ.; Liu, J.; Lu L.ꢀQ.; Xiao, W.ꢀJ. J. Org. Chem. 2016,
81, 7250.
calcd. for [C21H29NO2+Na]+ 350.2096, found 350.2095.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website.
1H and 13C NMR spectral data for compounds 3aꢀ3ab and 4
(PDF)
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) (a) Wang L. J.; Liu, J. Eur. J. Org. Chem. 2016, 1813. (b)
Yoshimura, A.; Zhdankin, V. V. Chem. Rev. 2016, 116, 3328.
) Huang, H.; Zhang G.; Chen, Y. Angew. Chem. Int. Ed. 2015, 54,
7872.
(9) Zhou, Q.ꢀQ.; Guo,W.; Ding, W.; Wu, X.; Chen, X.; Lu, L.ꢀQ.;
AUTHOR INFORMATION
Corresponding Author
(
8
*Eꢀmail: xin_li@nankai.edu.cn (X. Li)
*Eꢀmail: chengjp@most.cn (J.ꢀP. Cheng)
Notes
Xiao, W.ꢀJ. Angew. Chem. Int. Ed. 2015, 54, 11196.
(10) Le Vaillant,F.; Courant, T.; Waser, J. Angew. Chem. Int. Ed.
2015, 54, 11200.
The authors declare no competing financial interest.
(
11) Prices for Ru(bpy)3(PF6)2, Ir[dF(CF3)ppy]2(dtbbpy)PF6 and 9,
10ꢀdicyanoanthracene available at http://www.sigmaaldrich.com.
12) Selected organic photocatalysis, see: (a) Theriot, J. C.; Lim, C.
ACKNOWLEDGMENT
(
We are grateful to the Foundation for SpeciallyꢀAppointed Proꢀ
fessors at National University of Defense Technology and the
National Natural Science Foundation (Grant Nos. 21390400 and
21421062) at Nankai University for financial support. C.Y. also
thanks Dr. HeꢀLue Sun at Nankai University for the help of conꢀ
ducting luminescence quenching experiments.
H.; Yang, H.; Ryan, M. D.; Musgrave, C. B.; Miyake, G. M. Science
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