Platinum(II) Schiff Base Complexes as Photocatalysts for Visible-Light-Induced Cross-Dehydrogenative Coupling Reactions

Article abstract of DOI:10.1002/cplu.201500157

Four phosphorescent platinum(II) Schiff base complexes are screened for application in visible-light-induced cross-dehydrogenative coupling (CDC) reactions. Preliminary studies show that, among the four platinum(II) complexes, Pt3 is an efficient catalyst

Full text of DOI:10.1002/cplu.201500157

DOI: 10.1002/cplu.201500157
Full Papers
Platinum(II) Schiff Base Complexes as Photocatalysts for
Visible-Light-Induced Cross-Dehydrogenative Coupling
Reactions
Deepak Prakash Shelar,[a] Ting-Ting Li,[a] Yong Chen,*[a] and Wen-Fu Fu[a, b]
Four phosphorescent platinum(II) Schiff base complexes are
screened for application in visible-light-induced cross-dehydro-
genative coupling (CDC) reactions. Preliminary studies show
that, among the four platinum(II) complexes, Pt3 is an efficient
catalyst for CDC reactions with oxygen as an oxidant. Light ir-
radiation (l>420 nm) on a mixture of the PtII complex, tertiary
amine, and a variety of nucleophiles (nitroalkanes, ketones, or
indoles) under aerobic conditions gives a-functionalized terti-
ary amines in good to excellent yields. The photoluminescence
quenching experiment reveals that the CDC reaction is initiat-
ed by photoinduced electron transfer from N-phenyltetrahy-
droisoquinoline to the PtII complex. Further, electron spin reso-
nance (ESR) measurements clearly indicate the formation of su-
CÀ
peroxide radical anions (O2 ) rather than singlet oxygen (1O2)
during the photocatalytic reaction.
Introduction
The development of CÀC bond-forming reactions[1] is an im-
portant topic in organic chemistry. In particular, the cross-dehy-
drogenative coupling (CDC) reaction has attracted considera-
ble interest among synthetic organic chemists, because it does
not require substrate prefunctionalization, and thus, is atom
economic.[2] Whereas organic peroxides such as tBuOOH are
often used as the oxidant for CDC reactions,[3] molecular
oxygen represents one environmentally friendly oxidant, which
produces hydrogen peroxide and decomposes to form water.[2-
platinum(II) polypyridyl complexes have been applied as sensi-
tizers for photo-oxidation reactions[10] and photocatalytic hy-
drogen evolution,[11] their use in CDC reactions is still in its in-
fancy. Only very recently, Wu et al. reported an example of
using a platinum terpyridyl complex for aerobic oxidative CÀH
bond functionalization.[12]
Platinum(II) Schiff base complexes can be synthesized easily
from commercially available chemicals. They have been found
to display broad visible-light absorption in the 400–550 nm
region, and have a long-lived phosphorescence emission in so-
lution.[13] Moreover, these complexes ligated by a tetradentate
dianionic ligand framework are both thermally and photo
stable. Enlightened by their intriguing photophysical proper-
ties, we envision that the robust platinum(II) Schiff base com-
plexes (Figure 1) could be promising candidates for oxidative
CÀH functionalization. Herein, we screen the use of these com-
plexes in CDC reactions, and find that Pt3 is an efficient photo-
catalyst that is capable of catalyzing light-induced aerobic oxi-
dative CÀH functionalization reactions. ESR experiments reveal
a,c]
These advantages inspired the synthetic community to de-
velop aerobic CDC reactions. Recently, the use of visible light
to initiate a CDC reaction has attracted significant interest.[4]
The groups of Macmillan,[5] Yoon,[6] Stephenson,[7] and others[8]
have published seminal works on visible-light-promoted CÀC
bond-forming reactions catalyzed by ruthenium or iridium
polypyridyl complexes. Specifically, the single electron transfer
(SET) process of visible-light-active metal complexes can allow
redox manipulation of organic molecules without the employ-
ment of stoichiometric quantities of redox reagents or the pro-
duction of excess chemical waste. Platinum(II) complexes are
well known for their long-lived excited states, high lumines-
cence quantum yields, and good chemical stabilities, and thus,
are promising for photochemical reactions.[9] Although some
CÀ
that the superoxide radical anion (O2 ) is responsible for the
facile transformation in the present system.
[a] Dr. D. P. Shelar, T.-T. Li, Prof. Dr. Y. Chen, Prof. Dr. W.-F. Fu
Key Laboratory of Photochemical Conversion and Optoelectronic Materials
Technical Institute of Physics and Chemistry
Chinese Academy of Sciences
Beijing 100190 (P. R. China)
E-mail: chenyong@mail.ipc.ac.cn
[b] Prof. Dr. W.-F. Fu
Figure 1. Molecular structures of platinum(II) Schiff base complexes.
College of Chemistry and Chemical Engineering
Yunnan Normal University
Kunming 650092 (P. R. China)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201500157.
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tries 1–9). The presence of both electron-donating and elec-
tron-accepting groups on the phenyl ring had little influence
on the product yields under the present reaction conditions.
The use of nitroethane and nitropropane as a nucleophile in
the oxidative aza-Henry reaction gave the desired products
3j–o but with decreasing yields (Table 2, entries 10–15), which
may be because of the steric effect of the nucleophiles. With
acyclic 4-N,N-trimethylaniline employed as a substrate, a satis-
factory yield of 72% for the desired product 3p was obtained
(Table 2, entry 16).
Results and Discussion
All of the complexes shown in Figure 1 were synthesized ac-
cording to the previously reported procedure[13,14] and
screened for their use in visible-light-induced CDC reactions.
The results of the CDC reactions of 1a with nitromethane
using Pt1–Pt4 as the visible light photoredox catalyst are sum-
marized in Table 1. Gratifyingly, the desired product 3a was ob-
Table 1. Optimization of CDC reaction of amine with nitromethane.
ESR experiments were performed to gain insight into the Pt-
1
catalyzed CDC reaction mechanism. Whereas O2 was found to
play a key role in the photo-oxidation reactions photosensi-
CÀ
tized by platinum(II) complexes,[10a] O2 was proposed recently
as the active species in the CDC reaction photocatalyzed by
a platinum(II) terpyridyl complex.[12] Thus, for determination of
the actual active species of oxygen in the present system, 5,5-
Entry
Conditions[a]
Conv. [%][b]
Yield [%][c]
1
2
3
4
5
6
7[e]
8
Pt1 (1.5 mol%)
Pt2 (1.5 mol%)
Pt3 (1.5 mol%)
Pt4 (1.5 mol%)
No catalyst
No light, Pt3 (1.5 mol%)
Pt3 (1.5 mol%)
Pt3 (1.5 mol%) in air
[Ru(bpy)3]Cl2
37
46
100
36
9
0
7
76
100
100
29
32
94 (89)[d]
29
8
0
trace
63
98
96
dimethyl-1-pyrroline-N-oxide (DMPO) and 2,2,6,6-tetramethyl-1-
1
CÀ
piperidine (TEMP) were used as O2 and O2 scavengers, re-
spectively, in the ESR measurements. Initial effort was engaged
1
in the detection of O2. As shown in Figure 2a, irradiation of an
air-saturated DMF solution of TEMP and Pt3 by a 100 W mer-
cury lamp (l>420 nm) generated the characteristic signal of
1O2.[15] However, the nitroxide radical TEMPO was hardly detect-
ed upon addition of 1a in the same air-saturated DMF solution
9
10
[Ir(ppy)3]
[a] Reaction conditions: 1a (0.2 mmol), CH3NO2 (10 mL). The reaction was
saturated with O2 before irradiation unless indicated otherwise; reaction
time of 8 h. [b] Conversions were determined by H NMR spectroscopy of
CÀ
(Figure 2b). Instead, the characteristic signal of O2 attributed
1
CÀ
to the DMPOÀO2 adduct was observed upon irradiation of
the crude product using 4,4’-dimethyl-2,2’-bipyridine as an internal stan-
dard based on 1a. [c] Yields based on the amount of 1a as determined
a solution of DMPO, Pt3, and 1a by a 100 W mercury lamp
(l>420 nm) (Figure 2c); the spectrum and the hyperfine cou-
pling constants (aN =12.8 G, abH =9.8 G) were in agreement
1
by H NMR spectroscopy. [d] Yield of isolated product based on recovered
1a. [e] The reaction was deoxygenated.
tained, and Pt3 showed the best catalytic activity among all
the catalysts, with a yield of 94% after 8 h irradiation under an
oxygen atmosphere (Table 1, entries 1–4). Interestingly, the de-
sired product 3a was obtained in 8% yield in the absence of
any catalyst (Table 1, entry 5). The control experiments showed
that the reaction did not take place in the dark, and gave
a trace amount of product 3a in the absence of molecular
oxygen (Table 1, entries 6, 7). Upon replacement of oxygen by
air, the system also worked, but a slightly lower yield was ob-
tained (Table 1, entry 8). For comparison, the well-known ruthe-
nium and iridium polypyridyl complexes were also screened
for CDC reactions under the same conditions, and the desired
aza-Henry product 3a was obtained in 96–98% yields (Table 1,
entries 9 and 10). All the above results suggest that light irradi-
ation and molecular oxygen are essential for the reaction, and
in particular, the platinum complex Pt3 as a photocatalyst facil-
itates the CÀC bond formation. Consequently, the optimal re-
action conditions include irradiation on nitromethane contain-
ing 1.5 mol% Pt3 and 1a under an oxygen atmosphere for
8 h.
Figure 2. a) ESR spectrum of a solution in air-saturated DMF of Pt3
(1.0”10À4 molLÀ1) and TEMP (2.0”10À2 molLÀ1) upon irradiation for 120 s.
b) ESR spectrum of a solution in air-saturated DMF of Pt3 (1.0”10À4 molLÀ1),
1a (1.5”10À3 molLÀ1), and TEMP (2.0”10À2 molLÀ1) upon irradiation for
120 s. c) ESR spectrum of a solution in air-saturated DMF of Pt3
With the optimal conditions in hand, we examined the
scope of this visible-light-induced CDC reaction. In general,
a variety of N-aryltetrahydroisoquinolines 1a–i were subjected
to the oxidative aza-Henry reaction, providing the desired cou-
pling products 3a–i in good to excellent yields (Table 2, en-
(1.0”10À4 molLÀ1), 1a (1.5”10À3 molLÀ1), and DMPO (2.0”10À2 molLÀ1
upon irradiation for 120 s. DMF=N,N-dimethylformamide.
)
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I0=I ¼ 1 þ kq t0½QŠ
ð1Þ
Table 2. CDC reaction of tetrahydroisoquinolines with nitroalkanes using Pt3
as photocatalyst.[a]
Evidently, N-phenyltetrahydroisoquinoline 1a interacted
with platinum(II) complex Pt3 in the excited state. In light
of the low energy of Pt3 in the excited state with respect
to that of 1a, the energy transfer from the excited Pt3 to
1a is thermodynamically impossible. Therefore, photoin-
duced electron transfer should be responsible for the pho-
toluminescence quenching. The free energy change (DG)
of the electron transfer process was estimated by using
the Rehm–Weller equation [Eq. (2)].
Entry Product
Yield Entry Product
[%][b]
Yield
[%][b]
1
2
3
4
5
6
7
89
87
83
82
80
78
84
9
74
78
72
65
69
60
49
DG0 ¼ EoxÀEredÀE00Àe2=ed < ZS > ð2Þ
10
11
12
13
14
15
The e value is high for polar solvents such as DMF, so
the last term is negligible. According to previous reports,
the oxidation potential Eox of 1a and the reduction poten-
tial Ered of Pt3 are 0.82 and À1.10 V, respectively;[14] the E00
value (2.25 eV, Figure S1) of Pt3 can be determined from
the cross point of the absorption and emission spectra at
550 nm. Consequently, the negative DG of À0.33 eV con-
firms that the photoinduced electron transfer from Pt3 to
1a is thermodynamically favorable.
On the basis of the above results and literature re-
ports,[17] the reaction mechanism for this photocatalytic
CDC reaction is proposed, as shown in Scheme 1. We be-
lieve that visible light irradiation of Pt3 generates the ex-
cited species Pt3*, which is reductively quenched by 1a
through a single electron transfer (SET) process to form an
CÀ
aminyl radical cation 4 and radical anion Pt3 . The gener-
CÀ
ated Pt3 is subsequently quenched by molecular oxygen
to furnish O2 with concomitant recovery of the photoca-
CÀ
CÀ
8
78
16
72
talyst Pt3. Hydrogen abstraction of 4 by O2 gives the imi-
nium ion 5, and subsequent deprotonation of the nucleo-
phile, that is, CH3NO2, by the hydroperoxide anion HOOÀ
leads to hydrogen peroxide and the nucleophilic anion.[18]
Finally, the iminium ion 5 undergoes nucleophilic addition
to provide the desired product 3a.
[a] Reaction conditions: 1 (0.2 mmol), Pt3 (0.003 mmol), nitroalkane (10 mL), ir-
radiated at ambient temperature in the presence of oxygen. [b] Yield of isolated
product based on substrate 1.
with the literature reports.[16] These observations imply that
1
CÀ
O2 rather than O2 was formed in the presence of N-phenylte-
trahydroisoquinoline.
Then, the photoluminesence quenching of Pt3 with the ad-
dition of N-phenyltetrahydroisoquinoline 1a was performed to
provide further information on the primary process of the reac-
tion. As shown in Figure 3, upon addition of N-phenyltetrahy-
droisoquinoline 1a to the solution of Pt3 in degassed DMF,
there was a drastic decrease in the emission intensity following
a linear Stern–Volmer plot [Eq. (1)], in which I0 is the emission
intensity in the absence of quencher, I is the emission intensity
in the presence of quencher, kq is the quenching rate constant,
t0 is the emission lifetime of Pt3, and [Q] is the concentration
of the quencher. Analysis of the decay gave a quenching rate
constant of kq =3.07”109 sÀ1 mÀ1, suggesting that the intermo-
lecular quenching was diffusion-controlled.
Figure 3. Luminescence spectra of Pt3 (1.0”10À5 m) as a function of concen-
tration of 1a in degassed DMF with excitation at 450 nm. Inset is the Stern–
Volmer plot of Pt3 by 1a.
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ditions using molecular oxygen as oxidant for 8 h. The desired
product 9a was obtained in moderate yield together with the
formation of a byproduct amide 10 (Table S1, entry 1, Support-
ing Information). Upon performing the same reaction in the
absence of indole 8a, only amide 10 as a sole product was ob-
tained in quantitative yield after 7 h (Table S1, entry 2). It has
been reported that the introduction of FeSO4 into this reaction
system can efficiently prevent the formation of amide.[12]
Indeed, the desired product 9a can be obtained with an im-
proved yield of 89% in the presence of FeSO4 as an additive
(Table S1, entry 3). Considering all these results, we determined
the optimal reaction conditions, which include irradiation of
a DMF solution of N-phenyltetrahydroisoquinoline and indole
with platinum complex Pt3 in the presence of FeSO4 under an
oxygen atmosphere for 8 h. For further investigation of the
scope of this protocol, different N-aryltetrahydroisoquinolines
and indole derivatives were subjected to these optimal reac-
tion conditions and provided the desired indolyl tetrahydroiso-
quinolines in good yields (Table 4).
Scheme 1. Proposed reaction pathways for the aerobic photocatalytic CDC
reaction.
The Mannich reaction is a fundamentally important CÀC
bond-forming reaction in organic synthesis, and is widely uti-
lized in syntheses of nitrogen-containing drugs, natural prod-
ucts, and biologically active compounds.[19] Thus, in this work,
the present photocatalytic CDC method was extended to the
coupling of tetrahydroisoquinolines and acyclic ketones. If Pt3
was used to catalyze the photochemical oxidative reaction of
N-aryltetrahydroisoquinoline with acetone 6a or methyl ethyl
ketone 6b in the presence of a cocatalyst, l-proline,[17b] under
visible light irradiation in an oxygen atmosphere, the enantio-
pure Mannich-type product 7(a–f) was obtained in moderate
yield (Table 3).
Table 4. The CDC reaction of aryltetrahydroisoquinolines with indoles.[a]
Indoles and tetrahydroisoquinolines are naturally occurring
heterocycles that are biologically active important pharmaceut-
icals,[20] and hence, the CDC methodology was also adopted
for the coupling of tetrahydroisoquinolines with indoles. Initial-
ly, a solution of N-phenyltetrahydroisoquinoline 1a and indole
8a in DMF was irradiated with visible light under aerobic con-
Product
Yield [%][b] Product
Yield [%][b]
9a
79
74
9c
68
Table 3. The Mannich reaction of aryltetrahydroisoquinolines with ketone.[a]
9b
9d
76
[a] Reaction conditions:
1
(0.2 mmol), Pt3 (0.003 mmol), indoles
(0.4 mmol), FeSO4 (0.4 mmol) dissolved in DMF (4 mL), irradiated at ambi-
ent temperature in the presence of oxygen. [b] Yield of isolated product
based on substrate 1.
Product
Yield ee
[%][b] [%][c]
Product
Yield ee
[%][b] [%][c]
7a
63
66
64
99
99
99
7d
58
62
60
99
99
99
Conclusion
In summary, we have synthesized four platinum(II) Schiff base
complexes and examined their use in visible-light-induced CDC
reactions. It was found that Pt3 is the most efficient photoca-
talyst of the studied catalysts. Moreover, Pt3 was used as the
photocatalyst for the visible-light oxidative coupling reaction
of tetrahydroisoquinoline with different nucleophiles such as
nitroalkanes, ketones, and indoles. An ESR experiment provid-
7b
7e
7 f
7c
CÀ
ed evidence for the generation of O2 under light irradiation.
Further investigations on oxidative coupling reactions using
platinum(II) complexes under visible light irradiation are under-
way in our laboratory.
[a] Reaction conditions:
1
(0.2 mmol), Pt3 (0.003 mmol), l-proline
(0.04 mmol), ketone (6 mL), CH3OH (4 mL), irradiated at ambient tempera-
ture in the presence of oxygen. [b] Yield of isolated product based on sub-
strate 1. [c] Determined by NMR spectroscopy.
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ture was bubbled with a stream of oxygen for 30 min. The tube
was then sealed and irradiated with a 300 W Xe lamp at ambient
temperature. A glass filter was employed to cut off light of wave-
length below 420 nm. After 8 h irradiation, the solvent was re-
moved under vacuum. Then, diethyl ether (25 mL) and water
(25 mL) were added to the residue. The organic layer was extracted
with diethyl ether (3”25 mL). The combined organic phases were
washed with brine and dried over sodium sulfate. The solvent was
removed by rotary evaporation and purified by column chroma-
tography on silica gel to afford the corresponding products.
Experimental Section
Electrospray Ionization (ESI) mass spectra were recorded on a Finni-
gan LCQ quadrupole ion trap mass spectrometer (samples were
dissolved in HPLC-grade methanol). 1H, 13C and 19F NMR spectra
were recorded with a Bruker Avance DPX 400 MHz instrument. UV/
Vis absorption spectra were recorded on a PerkinElmer Lambda 19
UV/Vis spectrophotometer. Steady-state emission spectra were ob-
tained on a SPEX 1681 Fluorolog-2 Model F111 fluorescence spec-
trophotometer equipped with a Hamamatsu R928 PMT detector.
Melting points were determined with RY-1 Melting Point Appara-
tus. ESR spectra were recorded at room temperature with a Bruker
ESP-300E spectrometer at 9.8 GHz, X-band with 100 Hz field modu-
lation. Samples were injected quantitatively into specially made
quartz capillaries for ESR analysis prior to purging with argon or
oxygen for 30 min in the dark, and were illuminated directly in the
cavity of the ESR spectrometer with a 100 W mercury lamp. Com-
mercially available reagents and solvents were used without fur-
ther purification unless indicated otherwise. The solvents used for
spectral measurements were of HPLC grade. All the N-aryltetrahy-
droisoquinolines 1 needed for CDC reactions were prepared by fol-
lowing the reported procedure[21] and purified through column
chromatography.
Acknowledgements
This study was supported by the 973 Program (2013CB834800
and 2013CB632403), the Ministry of Science and Technology of
China (2012DFH40090) and the NSFC (21371175). We thank Bei-
jing Natural Science Foundation (2142033) and CAS–Croucher
Funding Scheme for Joint Laboratories. D.P.S. and Y.C. acknowl-
edge the support of the Chinese Academy of Sciences Visiting Fel-
lowship
for
Researchers
from
Developing
Countries
(2013FFGB0009) and 100 Talents Program, respectively.
Keywords: aerobic reaction
transfer · photochemistry · platinum
·
CÀC coupling
·
electron
General procedure for the CDC reaction of nitroalkanes with
tetrahydroisoquinolines
A
mixture of 2-phenyl-1,2,3,4-tetrahydroisoquinoline (42 mg,
[1] E. J. Corey, X. M. Cheng, The Logic of Chemical Synthesis, John Wiley &
Sons, New York, 1989.
0.2 mmol), and Pt3 (1.6 mg, 0.003 mmol) was dissolved in nitrome-
thane (10 mL) in a 15 mL Pyrex tube equipped with a rubber
septum and magnetic stirrer bar. The mixture was bubbled with
a stream of oxygen for 30 min. The tube was then sealed and irra-
diated with a 300 W Xe lamp at ambient temperature. A glass filter
was employed to cut off light of wavelength below 420 nm. The
progress of the reaction was monitored at regular intervals by
thin-layer chromatography. After 8 h irradiation, the solvent was re-
moved under vacuum, and the residue was purified by column
chromatography on silica gel to afford the corresponding prod-
ucts.
[2] Selected reviews on CDC reactions: a) C.-J. Li, Acc. Chem. Res. 2009, 42,
335; b) Z. Li, D. S. Bohle, C.-J. Li, Proc. Natl. Acad. Sci. USA 2006, 103,
8928; c) S. A. Girard, T. Knauber, C.-J. Li, Angew. Chem. Int. Ed. 2014, 53,
74; Angew. Chem. 2014, 126, 76; d) C. S. Yeung, V. M. Dong, Chem. Rev.
2011, 111, 1215; e) C. J. Scheuermann, Chem. Asian J. 2010, 5, 436; f) S.-
I. Murahashi, D. Zhang, Chem. Soc. Rev. 2008, 37, 1490.
[3] a) Z. Li, C.-J. Li, J. Am. Chem. Soc. 2005, 127, 3672; b) Z. Li, C.-J. Li, Eur. J.
Org. Chem. 2005, 3173; c) L. Zhao, C.-J. Li, Angew. Chem. Int. Ed. 2008,
47, 7075; Angew. Chem. 2008, 120, 7183; d) Z. Li, C.-J. Li, J. Am. Chem.
Soc. 2005, 127, 6968; e) Y. Shen, M. Li, S. Wang, T. Zhan, Z. Tan, C.-C.
Guo, Chem. Commun. 2009, 953; f) A. Sud, D. Sureshkumar, M. Kluss-
mann, Chem. Commun. 2009, 3169.
[4] Visible-light-induced CDC reactions: a) M. Fagnoni, D. Dondi, D. Ravelli,
A. Albini, Chem. Rev. 2007, 107, 2725; b) N. Hoffmann, Chem. Rev. 2008,
108, 1052; c) K. Zeitler, Angew. Chem. Int. Ed. 2009, 48, 9785; Angew.
Chem. 2009, 121, 9969; d) T. P. Yoon, M. A. Ischay, J. Du, Nat. Chem.
2010, 2, 527; e) J. M. R. Narayanam, C. R. J. Stephenson, Chem. Soc. Rev.
2011, 40, 102; f) J. Xuan, W.-J. Xiao, Angew. Chem. Int. Ed. 2012, 51,
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MacMillan, Chem. Rev. 2013, 113, 5322; h) D. M. Schultz, T. P. Yoon, Sci-
ence 2014, 343, 1239176.
[5] a) P. V. Pham, D. A. Nagib, D. W. C. MacMillan, Angew. Chem. Int. Ed.
2011, 50, 6119; Angew. Chem. 2011, 123, 6243; b) H.-W. Shih, M. N. V.
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General procedure for the Mannich reaction of acetone with
tetrahydroisoquinolines
A
mixture of 2-phenyl-1,2,3,4-tetrahydroisoquinoline (42 mg,
0.2 mmol), Pt3 (1.6 mg, 0.003 mmol), and l-proline (4.6 mg,
0.04 mmol) was dissolved in a mixture of acetone (6 mL) and
CH3OH (4 mL) in a 15 mL Pyrex tube equipped with a rubber
septum and magnetic stirrer bar. The mixture was bubbled with
a stream of oxygen for 30 min. The tube was then sealed and irra-
diated with a 300 W Xe lamp at ambient temperature. A glass filter
was employed to cut off light of wavelength below 420 nm. After
8 h irradiation, the solvent was removed under vacuum, and the
residue was purified by column chromatography on silica gel to
afford the corresponding products.
[7] a) L. Furst, J. M. R. Narayanam, C. R. J. Stephenson, Angew. Chem. Int. Ed.
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133, 4160; c) J. M. R. Narayanam, J. W. Tucker, C. R. J. Stephenson, J. Am.
Chem. Soc. 2009, 131, 8756.
[8] a) M.-H. Larraufie, R. Pellet, L. Fensterbank, J.-P. Goddard, E. Lacote, M.
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General procedure for the CDC reaction of indoles with tet-
rahydroisoquinolines
A
mixture of 2-phenyl-1,2,3,4-tetrahydroisoquinoline (42 mg,
0.2 mmol), Pt3 (1.6 mg, 0.003 mmol), indole (0.4 mmol), and FeSO4
(0.4 mmol) was dissolved in DMF (4 mL) in a 15 mL Pyrex tube
equipped with a rubber septum and magnetic stirrer bar. The mix-
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Manuscript received: April 11, 2015
Revised: June 3, 2015
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Final Article published: July 1, 2015
ChemPlusChem 2015, 80, 1541 – 1546
www.chempluschem.org
1546
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim