Multicomponent Cascade Synthesis of Trifluoroethyl Isoquinolines from Alkynes and Vinyl Azides

Article abstract of DOI:10.1021/acs.joc.5b01995

A multicomponent cascade reaction is described that provides concise access to the trifluoroethyl isoquinolines using a Rh(III)-Cu(II) bimetallic system and readily available Togni's reagent. The system tolerates various vinyl azides and internal alkynes. Experimental results suggest that Togni's reagent might act as a CF₃ radical supplier.

Full text of DOI:10.1021/acs.joc.5b01995

Note
pubs.acs.org/joc
Multicomponent Cascade Synthesis of Trifluoroethyl Isoquinolines
from Alkynes and Vinyl Azides
Kai Liu, Shuang Chen, Xing Guang Li, and Pei Nian Liu*
Shanghai Key Laboratory of Functional Materials Chemistry, Key Lab for Advanced Materials and Institute of Fine Chemicals, East
China University of Science and Technology, Meilong Road 130, Shanghai, 200237, China
*
S Supporting Information
ABSTRACT: A multicomponent cascade reaction is described that provides concise access to the trifluoroethyl isoquinolines
using a Rh(III)−Cu(II) bimetallic system and readily available Togni’s reagent. The system tolerates various vinyl azides and
internal alkynes. Experimental results suggest that Togni’s reagent might act as a CF radical supplier.
3
he trifluoromethyl group stands out among fluorine
functional groups because of its remarkable potential for
as a powerful and promising tool for constructing diverse
10
T
heterocyclic systems in organic synthesis. Therefore, as part
11
modulating a molecule’s chemical, physical, and biochemical
of our continuing studies of heterocycle construction, we
report here a new three-component cascade reaction involving
α-phenyl vinyl azides, internal alkynes, and Togni’s reagent in
the presence of a Rh−Cu bimetallic catalytic system. We
demonstrate that this trifluoromethylation/C−H activation
reaction provides facile access to complex structures of
trifluoroethyl isoquinolines.
1
properties. It has been incorporated into many pharmaceut-
1a
icals and agrochemicals, and diverse trifluoromethylating
2
−7
reagents have been developed.
Togni’s reagent is a
particularly appealing trifluoromethylating reagent because o6f
its easy preparation, versatile reactivity, and shelf stability.
Togni’s reagent has been used to smoothly trifluoromethylate
various compounds, usually in the presence of Cu salts as the
catalysts. These compounds include arenes and heteroarene-
We began investigating this multicomponent reaction using
α-phenyl vinyl azide 2a, Togni’s reagent 3, and diphenylace-
tylene 1a as model substrates in the presence of Rh (5 mol %)
8
a,b
8c,d
8e
8f,g
8h
8i
s,
alkenes,
phosphines.
allenes, alkynes, alcohols, thiols, and
8
j
and Cu(OAc) (1 equiv) at 90 °C under N (Table 1). The
2
2
Apart from direct trifluoromethylation, Togni’s reagent has
also been used in multicomponent reactions, though these have
been limited primarily to alkene difunctionalization. In 2012, Li
et al. reported the trifluoromethylaminoxylation of alkenes in
target product was obtained in 38% yield in N-methyl-2-
pyrrolidone (NMP) (entry 1). Screening numerous solvents
showed that CH CN performed better, generating the desired
3
product in 55% yield (entries 2−4). Other Cu salts, including
9a
CuI and CuBr , also promoted the reaction, albeit with low
the absence of transition metals. In the following year,
Ilchenko et al. and Liang et al. reported Cu-catalyzed
cyanotrifluoromethylation of styrenes in a three-component
2
yields (entries 5 and 6). Decreasing the Cu(OAc) load to 0.2
2
equiv led to a poor yield (entry 7). To our delight, increasing
the load of the Rh catalyst to 9.5 mol % improved the yield to
9
b,c
reaction.
More recently, He et al. described the three-
6
9% and allowed a shorter reaction time of 3 h (entries 8−10).
component Cu-catalyzed intermolecular cyanotrifluoro-
methylation of alkenes and the cyanotrifluoromethylation/
We were able to further improve the yield to 82% by adding 2
9d,e
equiv of 2a and 1.8 equiv of 3a to the system (entries 11 and
azidotrifluoromethylation of 1,6-enynes.
Wang et al. and
1
2). [Cp*Rh(OAc) ] proved to be less efficient than
Liang et al. reported three-component Cu-catalyzed intermo-
2
[
Cp*RhCl ] (entry 13). Changing the temperature resulted
lecular trifluoromethylarylation, trifluoromethylazidation, and
2 2
9
f−h
in lower yields (entries 14 and 15). Eventually, the optimal
conditions were identified as 1a (1 equiv), 2a (2 equiv), 3a (1.8
trifluoromethlithiocyanation of alkenes.
Despite these
advances, we are unaware of reports using Togni’s reagent in
a multicomponent cascade reaction in which trifluoromethyla-
tion is combined with C−H activation catalyzed by
equiv), Cu(OAc) (1 equiv), and [Cp*RhCl ] (9.5 mol %) in
2
2 2
CH CN at 90 °C under N .
3
2
[
Cp*RhCl ] .
2 2
This is an important area to investigate because direct C−H
Received: August 26, 2015
activation/cyclization catalyzed by [Cp*RhCl ] has emerged
2
2
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.5b01995
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
a
Table 1. Screening of Optimal Conditions
Table 2. Reaction of Various Vinyl Azides and Internal
a b
,
Alkynes
time
(h)
yield
b
entry
catalyst/(mol %)
additive
solvent
(%)
1
[Cp*RhCl ] /5
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
CuI
5
5
5
5
5
5
5
5
3
3
3
3
3
3
3
3
NMP
38
11
46
55
10
15
26
40
67
69
72
82
60
80
78
78
2
2
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
[Cp*RhCl ] /5
t-BuOH
DMF
2
2
[Cp*RhCl ] /5
2
2
[Cp*RhCl ] /5
CH CN
2
2
3
[Cp*RhCl ] /5
CH CN
2
2
3
[Cp*RhCl ] /5
CuBr2
CH CN
2
2
3
c
[Cp*RhCl ] /5
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
CH CN
2
2
3
[Cp*RhCl ] /2.5
CH CN
2
2
3
[Cp*RhCl ] /7.5
CH CN
2
2
3
0
1
2
3
4
5
6
[Cp*RhCl ] /9.5
CH CN
2
2
3
d
d
d
d
d
d
[Cp*RhCl ] /9.5
CH CN
2
2
3
,
,
,
,
,
e
e
e
e
e
[Cp*RhCl ] /9.5
CH CN
2
2
3
Cp*Rh(OAc) /9.5
CH CN
2
3
,
,
,
f
[Cp*RhCl ] /9.5
CH CN
2
2
3
g
h
[Cp*RhCl ] /9.5
CH CN
2
2
3
[Cp*RhCl ] /9.5
CH CN
2
2
3
a
Reactions were performed in sealed tubes containing 1a (0.2 mmol),
2
a (0.3 mmol), Togni’s reagent 3 (0.3 mmol), additive, Rh catalyst,
and solvent (1 mL) under N . Determined by 1H NMR using
b
2
c
PhSiMe as internal standard. Cu(OAc) (0.04 mmol) was used.
3
2
d
e
Togni’s reagent 3a (0.36 mmol) was used. Vinyl azide 2a (0.4
f
g
h
mmol) was used. At 80 °C. At 100 °C. Solvent was CH CN (0.75
3
mL).
Using these optimized conditions, we explored the substrate
scope of the multicomponent cascade reaction of vinyl azides
with Togni’s reagent and internal alkynes (Table 2). Various α-
phenyl vinyl azides reacted with diphenylacetylene to give the
corresponding products 4a−4n in moderate to good yields.
Vinyl azides substituted at the para position with electron-
donating substituents (−OMe, −Me, t-Bu, −SMe) reacted
smoothly to afford the desired products 4b−4e in 66−74%
yields. Additionally, the molecular structure of 4b was
unambiguously confirmed by X-ray diffraction analysis (Figure
1
). In contrast, substrates with conjugated phenyl or electron-
withdrawing groups (−Cl, −Br) at the same position slightly
inhibited the reaction, affording products 4f−4h in 62−68%
yields. Interestingly, meta-bromo-substituted vinyl azide reacted
exclusively at the less sterically hindered position on the phenyl
ring, generating 4i in 48% yield. Ortho-methoxy-substituted
vinyl azide provided the desired product 4j in good yield.
Dimethoxy-substituted vinyl azides showed a preference to
react with 1a at the less sterically hindered position to generate
a
Reaction conditions: 1 (0.2 mmol), 2 (0.4 mmol), 3 (0.36 mmol),
Cp*RhCl ] (9.5 mol %), Cu(OAc) (0.2 mmol), CH CN (1 mL),
0 °C, 3 h, under N . Isolated yield.
2
[
9
2
2
2
3
b
Next we examined the substrate scope of various internal
alkynes. Symmetric diarylacetylenes reacted smoothly with
vinyl azide 2a and delivered the desired isoquinolines 4o−4q in
68−72% yields. Dithiophenylacetylene reacted smoothly under
the standard conditions and afforded the target 4r in excellent
82% yield. Interestingly, the nonsymmetrical alkynes reacted
regioselectively to form, respectively, 4s in 70% yield or 4t in
74% yield. Ethyl 3-phenylpropiolate reacted in a similar manner
with 1g giving the regioselective product 4u in 40% yield.
Dialkyl-substituted alkyne also performed well in this system to
afford the product 4v in 63% yield.
4
k in 54% yield, although the 4k′ isomer was also isolated in
2
1% yield (see Supporting Information). Interestingly,
dimethyl-substituted vinyl azide reacted with 1a regioselectively
to afford product 4l in 85% yield, due to the hindrance effect of
methyl group. We attributed the generation of 4k′ to the
stronger electron-donating effect of the methoxy group rather
than the methyl group, which might activate the C−H bond at
the ortho-position of the methoxyl group to generate 4k′. Both
naphthalene-based vinyl azide and thiophene-based vinyl azide
worked in the reaction, affording the desired products in
respective yields of 63% and 45%.
To gain insight into the mechanism of this multicomponent
reaction, we conducted several controlled experiments (Scheme
1). Adding the radical scavenger 2,2,6,6-tetramethyl-1-piper-
B
DOI: 10.1021/acs.joc.5b01995
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
generated in the reaction although the imine intermediate could
not detected due to its instability.
Scheme 2. Plausible Mechanism for the Cascade Reaction
Figure 1. ORTEP diagram of 4b with ellipsoids shown at the 30%
probability level.
Scheme 1. Investigation of the Reaction Mechanism
8g,12
Based on the experimental results and the literature,
the
reaction mechanism was proposed as depicted in Scheme 2.
First, the CF radical may be generated under the reaction
3
conditions from Togni’s reagent in the presence of Cu(II) (step
8g
1
). The CF radical may add to the vinyl azide 2a to form the
3
putative radical intermediate A, which then could be trapped by
12a,b
Cu(II) to give B (step 2).
Intermediate B would react with
Rh(III) via an iminyl rhodium intermediate C to generate
12c
rhodacyclic intermediate D. Insertion of alkyne 1a would
afford intermediate E, which undergoes reductive elimination to
12c
produce 4a, along with the Rh(I) species. A redox reaction
between Rh(I) and Cu(III) regenerates the Rh(III) species
12c
(
step 3).
In summary, we have developed a multicomponent cascade
protocol that provides direct, concise access to trifluoro-
ethylisoquinolines in moderate to good yield with good
chemoselectivity. This protocol combines, for the first time,
traditional Rh-catalyzed C−H activation and Togni’s reagent.
In this way, it provides a novel approach to constructing
complex trifluoromethylated compounds in a single operation.
The convenience of this method suggests that it is likely to find
broad application in drug synthesis, given the frequent use of
fluorine-containing compounds as bioactive agents.
idinyloxyl (TEMPO) to the reaction under standard conditions
led to only trace amounts of the desired product 4a. Instead,
1
9
8g
compound 5 was detected by F NMR (Scheme 1a). Using
TEMPO instead of Togni’s reagent led to compound 6 in 35%
yield (Scheme 1b). These results suggest that a CF radical may
3
be generated in the system and added to the C−C double bond
of the azide. Using compound 7 could not produce product 4a
(Scheme 1c). The result suggested that trifluoromethylation
might occur prior to isoquinoline assembly. Consistent with
this idea, we were able to rule out 2H-azirine 2a′ as a possible
intermediate because it did not give the desired product under
standard conditions (Scheme 1d). In addition, in the control
EXPERIMENTAL SECTION
■
All manipulations were carried out under a nitrogen atmosphere using
standard Schlenk techniques. The solvents were distilled under
nitrogen from sodium-benzophenone (THF, toluene, dioxane) or
calcium hydride (DMF, MeCN, 1,2-DCE) before being used. (1-
experiment of 2a and 3a with Cu(OAc) (2 equiv) but without
2
1
3
14
[
Cp*RhCl ] , compound 8 was detected after addition of
2 2
Azidovinyl)benzene and its derivatives as well as [Cp*RhCl2]2
AcOH (4 equiv) and an additional 2 h of reaction (Scheme 1e).
were prepared according to the literature methods. Chemical shifts (δ,
The result indicated that intermediate B in Scheme 2 might be
ppm) in the 1H NMR spectra were recorded using TMS as the
C
DOI: 10.1021/acs.joc.5b01995
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
internal standard. Chemical shifts in 13C { H} NMR spectra were
1
m), 7.27−7.29 (2H, m), 7.37−7.46 (8H, m), 7.55−7.57 (2H, m),
13
internally referenced to CHCl (δ = 77.16 ppm).
Typical Procedure for the Synthesis of Trifluoroethyl
Isoquinolines (4). To a mixture of [Cp*RhCl ] (11.8 mg, 0.019
7.88−7.91 (2H, m), 8.26 (1H, d, J = 8.6 Hz); C NMR (CDCl , 100
3
3
MHz) δ 40.2 (q, J = 28.8 Hz), 124.3, 125.7, 125.8, 125.9 (q, J = 276.6
Hz), 127.1, 127.4, 127.7, 127.8, 128.3, 128.6, 129.1, 130.4, 131.3,
131.4, 137.1, 137.2, 140.2, 140.5, 142.9, 149.8 (q, J = 3.0 Hz), 150.4
2
2
mmol), Cu(OAc) (36.3 mg, 0.2 mmol), 1,2-diphenylacetylene (35.6
mg, 0.2 mmol), and Togni’s reagent (113.7 mg, 0.36 mmol) in
acetonitrile (1 mL) was added vinyl azide (58.0 mg, 0.4 mmol) under
a N atmosphere. The reaction mixture was stirred at 90 °C for 3 h,
and the progress was monitored using TLC detection. After
completion of the reaction, the solvent was evaporated under reduced
pressure and the residue was purified by flash column chromatography
PE/EA = 100:1) on silica gel to afford the desired products 4.
,4-Diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4a). The prod-
2
Hz; 19F NMR (CDCl , 376 MHz) δ −62.8 (t, J = 10.1 Hz); HRMS
3
+
+
(EI, TOF) calcd for C H F N [M] : 439.1548, found: 439.1542.
29 20 3
2
6-Chloro-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4g).
The product 4g was obtained in 66% yield (52.5 mg) as a pale
yellow solid after column chromatography (PE/EA = 100:1). Mp:
1
148.5−150.5 °C; H NMR (CDCl , 400 MHz) δ 4.21 (2H, q, J = 10.4
3
(
Hz), 7.19−7.23 (5H, m), 7.34−7.40 (5H, m), 7.57 (1H, dd, J = 1.0,
9.0 Hz), 7.67 (1H, d, J = 2.0 Hz), 8.11 (1H, d, J = 9.0 Hz); C NMR
1
3
3
uct 4a was obtained in 78% yield (56.7 mg) as a white solid after
(CDCl , 100 MHz) δ 40.3 (q, J = 28.9 Hz), 124.9, 125.5, 125.8 (q, J =
3
1
column chromatography (PE/EA = 100:1). Mp: 123.4−124.8 °C; H
276.6 Hz), 127.0, 127.6, 127.9, 128.0, 128.4, 128.7, 130.4, 130.5, 131.2,
1
9
NMR (CDCl , 400 MHz) δ 4.25 (2H, q, J = 10.4 Hz), 7.18−7.25 (5H,
136.5, 136.9, 137.9, 140.0, 149.9 (q, J = 3.4 Hz), 151.0; F NMR
3
m), 7.34−7.39 (5H, m), 7.58−7.72 (3H, m), 8.18 (1H, d, J = 8.0 Hz);
(CDCl , 376 MHz) δ −62.9 (t, J = 10.5 Hz); HRMS (EI, TOF) calcd
3
1
3
+
+
C NMR (CDCl , 100 MHz) δ 40.2 (q, J = 28.8 Hz), 125.1, 125.9 (q,
for C H ClF N [M] : 397.0845, found: 397.0843.
3
23 15 3
J = 276.6 Hz), 126.6, 126.7, 127.4, 127.6, 127.8, 128.5, 130.3, 130.4,
31.2, 131.3, 136.8, 137.2, 140.5, 149.8, 149.9 (q, J = 3.4 Hz); 19
NMR (CDCl , 376 MHz) δ −62.8 (t, J = 10.2 Hz); HRMS (EI, TOF)
6-Bromo-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4h).
The product 4h was obtained in 62% yield (54.8 mg) as a pale
1
F
3
yellow solid after column chromatography (PE/EA = 100:1). Mp:
+
+
1
calcd for C H F N [M] : 363.1235, found: 363.1233.
170.0−171.9 °C; H NMR (CDCl , 400 MHz) δ 4.21 (2H, q, J = 10.4
23
16
3
3
6
-Methoxy-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4b).
Hz), 7.20−7.23 (5H, m), 7.33−7.36 (2H, m), 7.38−7.41 (3H, m),
7.72 (1H, dd, J = 1.8, 9.0 Hz), 7.86 (1H, d, J = 1.8 Hz), 8.04 (1H, d, J
The product 4b was obtained in 66% yield (51.9 mg) as a white solid
= 9.0 Hz); 13C NMR (CDCl , 100 MHz) δ 40.2 (q, J = 29.1), 125.1,
after column chromatography (PE/EA = 100:1). Mp: 125.1−127.0
3
1
°
C; H NMR (CDCl , 400 MHz) δ 3.72 (3H, s), 4.18 (2H, q, J = 10.4
125.6, 125.8 (q, J = 276.6 Hz), 126.9, 127.6, 127.6, 127.9, 128.0, 128.7,
3
Hz), 6.93 (1H, d, J = 2.4 Hz), 7.18−7.28 (6H, m), 7.33−7.37 (5H, m),
128.9, 130.3, 130.4, 130.9, 131.2, 136.4, 138.2, 140.1, 150.0 (q, J = 3.2
.08 (1H, d, J = 9.2 Hz); 13C NMR (CDCl , 100 MHz) δ 40.1 (q, J =
19
8
2
1
1
Hz); F NMR (CDCl , 376 MHz) δ −62.9 (t, J = 10.6 Hz); HRMS
3
3
+
+
8.6 Hz), 55.4, 104.6, 119.9, 122.4, 125.9 (q, J = 277.5 Hz), 127.1,
(EI, TOF) calcd for C H BrF N [M] : 441.0340, found: 441.0339.
23 15 3
27.3, 127.6, 127.8, 128.6, 130.3, 130.4, 131.2, 137.5, 139.0, 140.7,
7-Bromo-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4i).
The product 4i was obtained in 48% yield (42.5 mg) as a pale yellow
49.2 (q, J = 3.3 Hz), 150.4, 160.8; 1 F NMR (CDCl , 376 MHz) δ
9
3
+
−
62.9 (t, J = 10.6 Hz); HRMS (EI, TOF) calcd for C H F NO
solid after column chromatography (PE/EA = 100:1). Mp: 150.0−
24
18 3
+
1
[
M] : 393.1340, found: 393.1342.
-Methyl-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4c).
152.0 °C; H NMR (CDCl , 400 MHz) δ 4.19 (2H, q, J = 10.4 Hz),
3
6
7.19−7.22 (5H, m), 7.34−7.39 (5H, m), 7.58 (1H, d, J = 9.0 Hz), 7.67
(1H, q, J = 1.9, 9.1 Hz), 8.3 (1H, d, J = 1.0 Hz); 13C NMR (CDCl ,
The product 4c was obtained in 72% yield (54.3 mg) as a pale
3
yellow solid after column chromatography (PE/EA = 100:1). Mp:
100 MHz) δ 40.1 (q, J = 29.1), 121.6, 125.7 (q, J = 276.5), 127.4,
127.6, 127.7, 127.8, 127.9, 128.6, 128.7, 130.4, 131.1, 131.2, 133.8,
135.5, 136.6, 140.0, 149.8 (q, J = 3.3 Hz), 150.2; 19F NMR (CDCl3,
376 MHz) δ −62.8 (t, J = 10.6 Hz); HRMS (EI, TOF) calcd for
1
1
(
7
01.0−102.3 °C; H NMR (CDCl , 400 MHz) δ 2.43 (3H, s), 4.20
3
2H, q, J = 10.4 Hz), 7.18−7.24 (5H, m), 7.33−7.38 (5H, m), 7.45−
.48 (2H, m), 8.07 (1H, d, J = 8.5 Hz); C NMR (CDCl , 100 MHz)
13
3
+
+
δ 22.3, 40.2 (q, J = 27.9 Hz), 125.0, 125.1, 125.5, 125.9 (q, J = 276.7
C H BrF N [M] : 441.0340, found: 441.0330.
23 15 3
Hz), 127.3, 127.5, 127.8, 128.5, 129.6, 130.4, 130.7, 131.4, 137.1,
8-Methoxy-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4j).
The product 4j was obtained in 64% yield (50.4 mg) as a white
19
1
3
37.4, 140.6, 140.8, 149.6 (q, J = 3.4 Hz), 149.9; F NMR (CDCl3,
76 MHz) δ −62.8 (t, J = 10.1 Hz); HRMS (EI, TOF) calcd for
solid after column chromatography (PE/EA = 100:1). Mp: 124.1−
+
+
1
C H F N [M] : 377.1391, found: 377.1388.
126.0 °C; H NMR (CDCl , 400 MHz) δ 4.05 (3H, s), 4.60 (2H, q, J
24
18
3
3
6
-(tert-Butyl)-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline
= 10.6 Hz), 6.95 (1H, d, J = 7.6 Hz), 7.17−7.24 (6H, m), 7.33−7.39
(
5H, m), 7.47 (1H, t, J = 8.3 Hz); 13C NMR (CDCl , 100 MHz) δ
(
4d). The product 4d was obtained in 67% yield (56.1 mg) as a white
3
solid after column chromatography (PE/EA = 100:1). Mp: 141.0−
4
0.2 (q, J = 27.9 Hz), 55.8, 106.8, 119.1, 119.3, 126.5 (q, J = 276.6
1
1
=
1
42.6 °C; H NMR (CDCl , 400 MHz) δ 1.28 (9H, s), 4.21 (2H, q, J
3
Hz), 127.3, 127.5, 127.7, 128.5, 130.3, 130.4, 131.4, 137.8, 139.4,
1
40.4, 149.0 (q, J = 3.7 Hz), 157.0; 19F NMR (CDCl , 376 MHz) δ
10.4 Hz), 7.16−7.25 (5H, m), 7.34−7.37 (5H, m), 7.65 (1H, d, J =
3
.7 Hz), 7.72 (1H, dd, J = 1.9, 8.9 Hz); 13C NMR (CDCl , 100 MHz)
+
3
−63.0 (t, J = 10.5 Hz); HRMS (EI, TOF) calcd for C H F NO
2
4
18 3
+
δ 30.9, 35.4, 40.1 (q, J = 28.9 Hz), 121.6, 124.9, 125.0, 125.9 (q, J =
[
M] : 393.1340, found: 393.1335.
,7-Dimethoxy-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline
2
1
76.5 Hz), 126.3, 127.2, 127.5, 127.8, 128.4, 130.4, 131.3, 136.9, 137.3,
6
40.7, 149.4 (q, J = 3.1 Hz), 149.9, 153.4; 19F NMR (CDCl , 376
3
(4k) and 5,6-Dimethoxy-3,4-diphenyl-1-(2,2,2-trifluoroethyl)-
isoquinoline (4k′). The two isomers were prepared from 4-(1-
azidovinyl)-1,2-dimethoxybenzene 2k (82.0 mg, 0.4 mmol) following
the typical procedure. The major product 4k was obtained in 54%
yield (45.7 mg) as a pale yellow solid and the isomer 4k′ was obtained
in 21% yield (17.8 mg) as a pale yellow solid after column
chromatography (PE/EA = 200:1). Mp, 1H and C NMR were
MHz) δ −62.8 (t, J = 10.1 Hz); HRMS (EI, TOF) calcd for
+
+
C H F N [M] : 419.1861, found: 419.1863.
27
24 3
6
-(Methylthio)-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline
(
4e). The product 4e was obtained in 74% yield (60.5 mg) as a white
solid after column chromatography (PE/EA = 100:1). Mp: 121.5−
1
13
1
=
1
1
23.0 °C; H NMR (CDCl , 400 MHz) δ 2.36 (3H, s), 4.19 (2H, q, J
3
1
10.4 Hz), 7.18−7.24 (5H, m), 7.34−7.37 (6H, m), 7.48 (1H, dd, J =
described for the major isomer 4k. Mp: 149.0−151.1 °C; H NMR
.9 Hz), 8.04 (1H, d, J = 8.9 Hz); 13C NMR (CDCl , 100 MHz) δ
3
(CDCl , 400 MHz) δ 3.76 (3H, s), 4.07 (3H, s), 4.19 (2H, q, J = 10.4
3
4.9, 40.1 (q, J = 29.0 Hz), 120.4, 124.3, 125.3, 125.8 (q, J = 125.8
Hz), 6.94 (1H, s), 7.16−7.19 (3H, m), 7.22−7.25 (2H, m), 7.32−7.37
(6H, m); 13C NMR (CDCl , 100 MHz) δ 40.4 (q, J = 29.0 Hz), 55.9,
Hz), 126.2, 127.4, 127.7, 128.8, 128.5, 130.0, 130.4, 131.2, 137.1,
3
1
37.3, 140.4, 142.8, 149.6 (q, J = 3.1 Hz); 19F NMR (CDCl , 376
56.2, 103.3, 104.8, 122.9, 126.1 (q, J = 275.9 Hz), 127.1, 127.6, 127.7,
3
MHz) δ −62.9 (t, J = 10.1 Hz); HRMS (EI, TOF) calcd for
128.5, 130.3, 131.1, 133.7, 137.6, 140.6, 147.2 (q, J = 3.2 Hz), 149.1,
+
+
19
C H F NS [M] : 409.1112, found: 409.1116.
150.2, 152.8; F NMR (CDCl , 376 MHz) δ −62.6 (t, J = 10.5 Hz);
24
18
3
3
+
+
3
,4,6-Triphenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4f). The prod-
HRMS (EI, TOF) calcd for C H F NO [M] : 423.1446, found:
25 20 3 2
uct 4f was obtained in 68% yield (59.7 mg) as a pale yellow solid after
423.1447.
1
column chromatography (PE/EA = 100:1). Mp: 149.0−151.0 °C; H
6,7-Dimethyl-3,4-diphenyl-1-(2,2,2-trifluoroethyl)isoquinoline
(4l). The product 4l was obtained in 82% yield (66.5 mg) as a white
NMR (CDCl , 400 MHz) δ 4.27 (2H, q, J = 10.4 Hz), 7.20−7.24 (3H,
3
D
DOI: 10.1021/acs.joc.5b01995
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
solid after column chromatography (PE/EA = 100:1). Mp: 105.0−
6.80 (1H, dd, J = 1.0, 3.8 Hz), 6.91 (1H, dd, J = 3.8, 5.0 Hz), 7.11 (1H,
dd, J = 1.0, 3.4 Hz), 7.29 (1H, dd, J = 3.4, 5.0 Hz), 7.31 (1H, dd, J =
1
1
4
7
4
1
1
3
07.2 °C; H NMR (CDCl , 400 MHz) δ 2.34 (3H, s), 2.49 (3H, m),
3
1
3
.20 (2H, q, J = 10.5 Hz), 7.13−7.23 (5H, m), 7.32−7.38 (5H, m),
1.0, 5.0 Hz), 7,56−7.67 (4H, m), 8.08 (1H, d, J = 7.8 Hz); C NMR
.42 (1H, s), 7.90 (1H, s); 13C NMR (CDCl , 100 MHz) δ 20.7, 20.8,
3
(CDCl , 100 MHz) δ 39,8 (q, J = 29.0 Hz), 120.7, 124.9, 125.7 (q, J =
3
0.0 (q, J = 28.5 Hz), 124.5, 125.7, 125.9, 126.0 (q, J = 276.2 Hz),
27.1, 127.4, 127.7, 128.4, 128.4, 130.4, 130.5, 131.3, 135.7, 137.4,
37.5, 140.7, 140.9, 148.8 (q, J = 3.2 Hz), 149.1; F NMR (CDCl3,
76 MHz) δ −62.8 (t, J = 10.1 Hz); HRMS (EI, TOF) calcd for
275.6 Hz), 126.0, 126.4, 127.3, 127.8, 127.9, 128.0, 128.1, 128.5, 129.5,
1
9
130.8, 137.3, 138.6, 144.4, 144.8, 150.8 (q, J = 3.1 Hz); F NMR
19
(CDCl , 376 MHz) δ −62.7 (t, J = 10.6 Hz); HRMS (EI, TOF) calcd
3
+
+
for C H F NS [M] : 375.0363, found: 375.0367.
1
9
12
3
2
+
+
C H F N [M] : 391.1548, found: 391.1549.
4-Methyl-3-phenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4s). The
product 4v was obtained in 70% yield (42.1 mg) as a white solid after
column chromatography (PE/EA = 100:1). The structure of 4e was
25
20 3
7
-Methoxy-3,4-diphenyl-1-(2,2,2-trifluoroethyl)benzo[g]-
isoquinoline (4m). The product 4m was obtained in 63% yield (55.8
mg) as yellow solid after column chromatography (PE/EA = 100:1).
1
confirmed by NOESY correlation. Mp: 109.2−111.0 °C; H NMR
1
Mp: 165.1−168.0 °C; H NMR (CDCl , 400 MHz) δ 3.89 (3H, s),
3
(CDCl , 400 MHz) δ 2.66 (3H, s), 4.16 (2H, d, J = 10.4 Hz), 7.38−
3
4
.35 (2H, q, J = 10.4 Hz), 7.02 (1H, d, J = 2.2 Hz), 7.18−7.24 (4H,
m), 7.31−7.34 (2H, m), 7.70−7.44 (5H, m), 7.98 (1H, d, J = 9.2 Hz),
.04 (1H, s), 8.67 (1H, s); 13C NMR (CDCl , 100 MHz) δ 40.5 (q, J
7
.43 (1H, m), 7.46−7.50 (2H, m), 7.57−7.60 (2H, m), 7.64−7.68
(1H, m), 7.75−7.80 (1H, m), 8.10 (1H, d, J = 8.5 Hz), 8.15 (1H, d, J =
8
13
3
8.5 Hz); C NMR (CDCl , 100 MHz) δ 15.8, 40.0 (q, J = 28.8 Hz),
3
=
28.8 Hz), 55.5, 103.8, 122.1, 123.4, 123.6, 125.0, 126.0 (q, J = 276.6
1
1
24.5, 124.9, 125.7, 125.9 (q, J = 275.3 Hz), 126.5, 127.1, 127.9, 128.3,
30.1, 130.3, 137.0, 141.1, 148.2 (q, J = 3.2 Hz), 151.2; F NMR
Hz), 127.2, 127.6, 127.8, 128.5, 128.6, 129.7, 130.5, 130.7, 131.5,
19
19
134.1, 135.6, 137.8, 140.6, 147.4,151.4 (q, J = 3.3 Hz), 159.0;
F
(
CDCl , 376 MHz) δ −63.0 (t, J = 10.2 Hz); HRMS (EI, TOF) calcd
3
NMR (CDCl , 376 MHz) δ −62.4 (t, J = 10.6 Hz); HRMS (EI, TOF)
+ +
3
for C H F N [M] : 301.1078, found: 301.1079.
+
+
18 14 3
calcd for C H F NO [M] : 443.1497, found: 443.1499.
28
20 3
4
-Hexyl-3-phenyl-1-(2,2,2-trifluoroethyl)isoquinoline (4t). The
4
,5-Diphenyl-7-(2,2,2-trifluoroethyl)thieno[2,3-c]pyridine (4n).
product 4t was obtained in 74% yield (54.9 mg) as a pale yellow
The product 4n was obtained in 45% yield (33.2 mg) as an off-
solid after column chromatography (PE/EA = 100:1). Mp: 58.1−59.8
white solid after column chromatography (PE/EA = 100:1). Mp:
1
°
1
(
(
C; H NMR (CDCl , 400 MHz) δ 0.85 (3H, t, J = 7.0 Hz), 1.19−
1
3
1
14.1−115.4 °C; H NMR (CDCl , 400 MHz) δ 3.98 (2H, q, J = 10.4
3
.25 (4H, m), 1.30−1.37 (2H, m), 1.60−1.70 (2H, m), 2.97−3.02
Hz), 7.20−7.25 (6H, m), 7.31−7.37 (5H, m), 7.66 (1H, d, J = 5.5
2H, m), 4.15 (2H, q, J = 10.4 Hz), 7.39−7.43 (1H, m), 7.45−7.52
Hz); 13C NMR (CDCl , 100 MHz) δ 42.4 (q, J = 29.4 Hz), 124.3,
3
4H, m), 7.62−7.67 (1H, m), 7.74−7.79 (1H, m), 8.10 (1H, d, J = 8.5
1
1
25.8 (q, J = 275.9 Hz), 127.5, 127.7, 127.9, 128.5, 130.2, 130.4, 130.5,
13
Hz), 8.16 (1H, d, J = 8.5 Hz); C NMR (CDCl , 100 MHz) δ 14.2,
19
3
31.6, 135.7, 137.8, 139.9, 143.9 (q, J = 3.3 Hz), 146.9, 151.4;
F
2
2.7, 28.8, 29.7, 31.3, 31.5, 40.1 (q, J = 29.0 Hz), 124.6, 125.9 (q, J =
NMR (CDCl , 376 MHz) δ −62.9 (t, J = 10.0 Hz); HRMS (EI, TOF)
calcd for C H F NS [M] : 369.0799, found: 369.0789.
3
+
+
276.5 Hz), 126.0, 127.0, 127.8, 128.4, 129.4, 130.0, 130.2, 136.2, 141.4,
21
14
3
19
1
48.1 (q, J = 3.4 Hz), 151.5; F NMR (CDCl , 376 MHz) δ −63.0 (t,
3
3
,4-Bis(4-methoxyphenyl)-1-(2,2,2-trifluoroethyl)isoquinoline
+ +
J = 10.6 Hz); HRMS (EI, TOF) calcd for C H F N [M] :
23
24 3
(
4o). The product 4o was obtained in 72% yield (60.9 mg) as a white
3
71.1861, found: 371.1856.
Ethyl 3-Phenyl-1-(2,2,2-trifluoroethyl)isoquinoline-4-carboxylate
4u). The product 4u was obtained in 40% yield (28.7 mg) as a pale
solid after column chromatography (PE/EA = 100:1). Mp: 146.1−
1
1
4
7
7
4
2
1
3
47.9 °C, H NMR (CDCl , 400 MHz) δ 3.77 (3H, s), 3.85 (3H, s),
3
(
..22 (2H, q, J = 10.4 Hz), 6.74−6.78 (2H, m), 6.91−6.95 (2H, m),
yellow solid after column chromatography (PE/EA = 200:1). The
.13−7.17 (2H, m), 7.32−7.36 (2H, m), 7.56−7.62 (2H, m), 7.69−
13
structure of 4v was confirmed by NOESY correlation. Mp: 108.5−
.73 (1H, m), 8.13−8.16 (1H, m); C NMR (CDCl , 100 MHz) δ
3
1
1
10.0 °C; H NMR (CDCl , 400 MHz) δ 1.06 (3H, t, J = 7.2 Hz),
3
0.1 (q, J = 28.9 Hz), 55.3, 55.4, 113.3, 114.1, 125.1, 125.9 (q, J =
4
.21 (2H, q, J = 10.3 Hz), 4.26 (2H, q, J = 7.2 Hz), 7.42−7.50 (3H,
76.8 Hz), 126.4, 126.6, 127.0, 129.5, 130.1, 130.2, 131.7, 132.4, 133.1,
37.3, 149.5, 149.6 (q, J = 3.4 Hz), 158.9, 159.0; 19F NMR (CDCl3,
m), 7.66−7.81 (4H, m), 8.07 (1H, d, J = 8.4 Hz), 8.17 (1H, d, J = 8.4
Hz); 13C NMR (CDCl , 100 MHz) δ 13.8, 40.2 (q, J = 29.2 Hz), 62.0,
76 MHz) δ −62.8 (t, J = 10.1 Hz); HRMS (EI, TOF) calcd for
C H F NO [M] : 423.1444, found: 423.1446.
3
+
+
123.9, 125.0, 125.5, 125.6 (q, J = 276.7 Hz), 126.1, 128.1, 128.6, 128.8,
25
20
3
2
1
9
1
29.0, 131.6, 134.2, 139.8, 149.8, 152.0 (q, J = 3.1 Hz), 168.7;
F
3
,4-Di-p-tolyl-1-(2,2,2-trifluoroethyl)isoquinoline (4p). The prod-
NMR (CDCl , 376 MHz) δ −62.8 (t, J = 10.1 Hz); HRMS (EI, TOF)
uct 4p was obtained in 76% yield (59.4 mg) as a white solid after
3
+
+
1
calcd for C H F NO [M] : 359.1133, found: 359.1129.
20 16 3 2
column chromatography (PE/EA = 100:1). Mp: 119.3−120.5 °C; H
3
,4-Diethyl-1-(2,2,2-trifluoroethyl)isoquinoline (4v). The product
NMR (CDCl , 400 MHz) δ 2.3 (3H, s), 2.4 (3H, s), 4..22 (2H, q, J =
3
4
v was obtained in 63% yield (33.6 mg) as a pale yellow solid after
10.4 Hz), 7.02 (2H, d, J = 8.0 Hz), 7.12 (2H, d, J = 8.0 Hz), 7,19 (2H,
1
column chromatography (PE/EA = 100:1). Mp: 42.6−44.1 °C; H
d, J = 7.8 Hz), 7.29 (2H, d, J = 8.0 Hz), 7.57−7.62 (2H, m), 7.68−7.71
1H, m), 8.15 (1H, d, J = 7.8 Hz); 1 C NMR (CDCl , 100 MHz) δ
3
NMR (CDCl , 400 MHz) δ 1.29−1.37 (6H, m), 3.00 (2H, q, J = 7.56
(
3
3
Hz), 3.08 (2H, q, J = 7.56 Hz), 4.08 (2H, q, J = 10.5 Hz), 7.56 (1H, q,
J = 7.24 Hz), 7.67−7.72 (1H, m), 8.04 (1H, d, J = 8.6 Hz), 8.07 (1H,
2
1
1
3
1.3, 21.5, 40.1 (q, J = 28.8 Hz), 125.1, 126.0 (q, J = 276.5 Hz), 126.5,
26.7, 127.1, 128.6, 129.3130.1, 130.3, 130.9, 131.1, 134.3, 137.0,
37.1, 137.2, 137.7, 149.6 (q, J = 3.4 Hz), 149.7; 19F NMR (CDCl3,
76 MHz) δ −62.8 (t, J = 10.0 Hz); HRMS (EI, TOF) calcd for
d, J = 8.5 Hz); 13C NMR (CDCl , 100 MHz) δ 14.8, 15.2, 20.9, 28.4,
3
39.9 (q, J = 28.7 Hz), 123.7, 125.9 (q, J = 125.9 Hz), 126.1, 126.5,
+
+
19
C H F N [M] : 391.1548, found: 391.1549.
129.7, 129.9, 135.8, 148.0 (q, J = 3.8 Hz), 153.4; F NMR (CDCl
3
,
25
20 3
3
,4-Bis(4-chlorophenyl)-1-(2,2,2-trifluoroethyl)isoquinoline (4q).
376 MHz) δ −63.2 (t, J = 10.3 Hz); HRMS (EI, TOF) calcd for
+ +
The product 4q was obtained in 68% yield (58.7 mg) as a pale
C
15
H
16
F
3
N [M] : 267.1235, found: 267.1232.
3,4-Diphenyl-1-(((2,2,6,6-tetramethylpiperidin-1-yl)oxy)methyl)-
isoquinoline 6. To a mixture of [Cp*RhCl ] (10.5 mg, 0.017 mmol),
yellow solid after column chromatography (PE/EA = 100:1). Mp:
1
1
26.6−128.4 °C; H NMR (CDCl , 400 MHz) δ 4.23 (2H, d, J = 10.4
2 2
3
Cu(OAc) (36.3 mg, 0.2 mmol), 1,2-diphenylacetylene (35.6 mg, 0.2
Hz), 7.16−7.23 (4H, m), 7.28−7.31 (2H, m), 7.37−7.41 (2H, m),
2
13
7
.64−7.70 (3H, m), 8.18−8.20 (1H, m); C NMR (CDCl , 100
mmol), and TEMPO (62.4 mg, 0.4 mmol) in acetonitrile (1 mL) was
3
MHz) δ 40.1 (q, J = 29.0 Hz), 125.3, 125.8 (q, J = 276.8 Hz), 126.3,
added vinyl azide (52.4 mg, 0.4 mmol) under a N atmosphere. After
2
1
1
3
26.7, 127.8, 128.2, 129.1, 130.0, 130.8, 131.7, 132.6, 133.7, 140.0,
completion of the reaction, the solvent was evaporated under reduced
pressure and the residue was purified by flash column chromatography
19
35.4, 136.6, 138.6, 148.6, 150.5 (q, J = 3.4 Hz); F NMR (CDCl3,
76 MHz) δ −62.8 (t, J = 10.3 Hz); HRMS (EI, TOF) calcd for
(PE/EA = 50:2) on silica gel to afford the desired products 6 in 35%
+
+
1
C H Cl F N [M] : 431.0455, found: 431.0454.
isolated yield. Mp: 137.4−138.9 °C; H NMR (CDCl
3
, 400 MHz) δ
23
14
2 3
3
,4-Di(thiophen-2-yl)-1-(2,2,2-trifluoroethyl)isoquinoline (4r).
1.14 (6H, s), 1.4 (6H, s), 1.51−1.59 (6H, m), 5.51 (2H, s), 7.16−7.26
13
The product 4r was obtained in 82% yield (61.5 mg) as a pale yellow
(6H, m), 7.33−7.39 (5H, m), 7.56−7.68 (3H, m); C NMR (CDCl ,
3
solid after column chromatography (PE/EA = 100:1). Mp: 115.1−
100 MHz) δ 17.3, 20.4, 33.6, 39.9, 60.2, 80.8, 126.1, 126.4, 126.5,
1
1
17.5 °C; H NMR (CDCl , 400 MHz) δ 4.18 (2H, q, J = 10.4 Hz),
126.6, 127.0, 127.3, 127.6, 128.4, 130.0, 130.5, 131.4, 136.7, 137.7,
3
E
DOI: 10.1021/acs.joc.5b01995
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
+
+
1
4
40.9, 149.2, 156.7; HRMS (EI, TOF) calcd for C H N O [M] :
50.2671, found: 450.2676.
Li, L. H.; Yang, Y. F.; Zhou, Z. Z.; Hua, H. L.; Liu, X. Y.; Liang, Y. M.
Org. Lett. 2014, 16, 3896. (f) Wang, F.; Wang, D.; Mu, X.; Chen, P.;
Liu, G. J. Am. Chem. Soc. 2014, 136, 10202. (g) Wang, F.; Qi, X.;
Liang, Z.; Chen, P.; Liu, G. Angew. Chem., Int. Ed. 2014, 53, 1881.
31
34
2
ASSOCIATED CONTENT
■
(
h) Liang, Z.; Wang, F.; Chen, P.; Liu, G. Org. Lett. 2015, 17, 2438.
10) (a) Colby, D. A.; Bergman, R. G.; Ellman, J. A. Chem. Rev. 2010,
10, 624. (b) Wencel-Delord, J.; Droge, T.; Liu, F.; Glorius, F. Chem.
Soc. Rev. 2011, 40, 4740. (c) Song, G.; Wang, F.; Li, X. Chem. Soc. Rev.
* Supporting Information
S
(
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.5b01995.
1
̈
Copies of H, 13C, and 19F NMR spectra for products
1
2
012, 41, 3651. (d) Li, D. Y.; Chen, H. J.; Liu, P. N. Org. Lett. 2014,
1
6, 6176. (e) Li, D. Y.; Mao, X. F.; Chen, H. J.; Chen, G. R.; Liu, P. N.
4
a−4v and 6 (PDF)
Org. Lett. 2014, 16, 3476. (f) Li, X. G.; Liu, K.; Zou, G.; Liu, P. N. Adv.
Synth. Catal. 2014, 356, 1496. (g) Li, X. G.; Sun, M.; Liu, K.; Jin, Q.;
Liu, P. N. Chem. Commun. 2015, 51, 2380.
X-ray crystallographic data for 4b (CIF)
AUTHOR INFORMATION
Corresponding Author
E-mail: liupn@ecust.edu.cn.
(11) (a) Li, D. Y.; Shang, X. S.; Chen, G. R.; Liu, P. N. Org. Lett.
■
*
2
013, 15, 3848. (b) Li, D. Y.; Shi, K. J.; Mao, X. F.; Chen, G. R.; Liu, P.
N. J. Org. Chem. 2014, 79, 4602. (c) Siyang, H. X.; Wu, X. R.; Liu, H.
L.; Wu, X. Y.; Liu, P. N. J. Org. Chem. 2014, 79, 1505. (d) Li, X. G.;
Sun, M.; Liu, K.; Liu, P. N. Adv. Synth. Catal. 2015, 357, 395. (e) Li, D.
Y.; Chen, H. J.; Liu, P. N. Adv. Synth. Catal. 2015, 357, 1193.
Notes
The authors declare no competing financial interest.
(12) (a) Wang, Y. F.; Lonca, G. H.; Le Runigo, M. L.; Chiba, S. Org.
Lett. 2014, 16, 4272. (b) Wang, Y. F.; Lonca, G. H.; Chiba, S. Angew.
Chem., Int. Ed. 2014, 53, 1067. (c) Wang, Y. F.; Toh, K. K.; Lee, J. Y.;
Chiba, S. Angew. Chem., Int. Ed. 2011, 50, 5927. (d) Wang, Y. F.;
Chiba, S. J. Am. Chem. Soc. 2009, 131, 12570. (e) Chiba, S.; Wang, Y.
F.; Lapointe, G.; Narasaka, K. Org. Lett. 2008, 10, 313. (f) Wang, Y. F.;
Toh, K. K.; Chiba, S.; Narasaka, K. Org. Lett. 2008, 10, 5019.
ACKNOWLEDGMENTS
This work was supported by the National Natural Science
Foundation of China (Project Nos. 21421004, 21172069,
1372072 and 21190033), NCET (NCET-13-0798), the Basic
Research Program of the Shanghai Committee of Sci. & Tech.
Project No. 13M1400802), and the Fundamental Research
■
2
(
(13) (a) Hassner, A.; Fowler, F. W. Tetrahedron Lett. 1967, 8, 1545.
(b) Fowler, F. W.; Hassner, A.; Levy, L. A. J. Am. Chem. Soc. 1967, 89,
Funds for the Central Universities.
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077.
(14) White, C.; Yates, A.; Maitlis, P. M. Inorg. Synth. 1992, 29, 228.
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DOI: 10.1021/acs.joc.5b01995
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