Iron-mediated cross dehydrogenative coupling (CDC) of terminal alkynes with benzylic ethers and alkanes

Article abstract of DOI:10.1007/s11426-011-4435-3

Iron-mediated sp-sp³ C-C bond formation through the cross dehydrogenative coupling (CDC) of terminal alkynes with benzylic ethers or alkanes has been developed. The inexpensive iron salt is used as the catalyst to make this transformation envir

Full text of DOI:10.1007/s11426-011-4435-3

SCIENCE CHINA
Chemistry
January 2012 Vol.55 No.1: 50–54
doi: 10.1007/s11426-011-4435-3
• ARTICLES •
· SPECIAL TOPIC · The Frontiers of Chemical Biology and Synthesis
Iron-mediated cross dehydrogenative coupling (CDC) of terminal
alkynes with benzylic ethers and alkanes
XIANG Shi-Kai1, ZHANG Bo1, ZHANG Li-He1, CUI YuXin1 & JIAO Ning1,2*
1 State Key Laboratory of Natural and Biomimetic Drugs; School of Pharmaceutical Sciences, Peking University, Beijing 100191, China
2 Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University,
Shanghai 200062, China
Received August 18, 2011; accepted September 11, 2011; published online December 2, 2011
Iron-mediated sp-sp3 C–C bond formation through the cross dehydrogenative coupling (CDC) of terminal alkynes with ben-
zylic ethers or alkanes has been developed. The inexpensive iron salt is used as the catalyst to make this transformation envi-
ronmentally benign.
iron, cross dehydrogenative coupling, terminal alkynes, benzylic ethers
alkynes with benzylic alcohols in the absence of base for the
1 Introduction
sp-sp3 C–C bond formation (Eq. (2)) [9]. When alcohols are
employed as the alkyl electrophile, H2O becomes the sole
byproduct, which makes this transformation atom efficient
and environmentally benign.
For several decades, organic chemists have been trying to
develop new methodologies to introduce the alkyne unit
into organic compounds, because alkynes are widely dis-
tributed in a vast array of natural products, bioactive com-
pounds, and drugs, as well as ubiquitous units in material
science [1]. It is well-known that the palladium and/or
copper catalyzed Sonogashira cross-coupling reactions [2–4]
of terminal alkynes with halides are among the most pow-
erful methods of introducing the alkyne unit into organic
compounds (Eq. (1)). Despite the extensive development in
the field of sp-sp2 C–C bond formation, the sp-sp3 C–C
bond formation via the coupling of terminal alkynes with
alkyl electrophiles has been less widely explored [5]. Re-
cently, Fu’s [6], Buchwald’s [7] and Glorius’s [8] groups
achieved the Sonogashira coupling of primary alkyl halides,
benzyl halides, and secondary alkyl halides, respectively.
However, alkyl halides were required and halide byproducts
were produced in these methods. Recently, we report a
Fe(OTf)3/TfOH cocatalyzed coupling reaction of terminal
During the past years, the cross-dehydrogenative cou-
pling (CDC reaction) was developed by Li and others [10].
Various C–C bonds were directly formed from C–H and
C–H bonds under oxidative conditions. Such reactions pre-
sent the most direct and efficient synthetic strategy of C–C
bond formation [10]. Additionally, iron catalysts [11] have
recently been extensively investigated due to their inexpen-
sive and environmentally benign features. We speculated
about the possibility of constructing sp-sp3 C–C bonds
through the iron-promoted oxidative coupling reaction of
terminal alkynes with benzylic compounds (Eq. (3)) [12].
(1)
(2)
(3)
*Corresponding author (email: jiaoning@bjmu.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2011
chem.scichina.com www.springerlink.com

Xiang SK, et al. Sci China Chem January (2012) Vol.55 No.1
51
Table 2 Iron-catalyzed CDC reaction of different terminal alkynes with
2 Results and discussion
benzylic ethers and alkanes a)
Initially, diphenylmethane was employed to react with
phenylacetylene. It is intriguing that the target product was
formed using Fe(OTf)3 as the catalyst in the presence of
DDQ as the oxidant. However, the reaction yield can not be
further improved even after optimization. It was noted that
isochroman (1a) was much more active than diphenylme-
thane for this transformation with higher yield under the
same condition. Therefore, we chose isochroman (1a) and
phenylacetylene (2a) as the model substrates to optimize the
reaction conditions (Table 1). The reaction of 1a and 2a
using DDQ as the oxidant in the absence of metal salts as
the catalyst could work, but with low yield (23%, Table 1,
entry 1). When the similar reaction was carried out with 5
mol% of Fe(OTf)3, 42% of 3a was obtained (Table 1, entry
2). This reaction was strongly dependent on different sol-
vents (Table 1, entries 2–5). Polar solvents (MeNO2, DMF)
were not suitable for this transformation (Table 1, entries 3
and 4). Although the reaction executed well in DCE and
toluene, PhCl was proved to be the best solvent, leading to
the formation of 3a in 49% yield. After screening different
iron catalysts (Table 1, entries 6–9), we found
Fe(OTf)2·2MeCN was the best (55%, Table 1, entry 9,).
With the extension of the reaction time, 3a was obtained in
60% yield (Table 1, entry 11).
The scope of the Fe(OTf)2 catalyzed cross dehydrogena-
tive coupling was expanded to a variety of terminal aryl
Table 1 Iron-catalyzed CDC reaction of isochroman (1a) with phenyla-
cetylene (2a) a)
Entry
Catalyst (5 mol%)

Solvent
DCE
Time (h) Yield (%) b)
a) All the reactions were carried out in the scale of 0.5 mmol 1, 0.75
mmol 2, 5 mmol% Fe(OTf)2·2MeCN, 0.6 mmol DDQ in 2 mL solvent at
90 °C under N2 for 16 h. b) Isolated yields in parentheses.
1
16
16
16
16
16
16
16
16
16
16
24
24
23
42
2
Fe(OTf)3
DCE
3
Fe(OTf)3
MeNO2
DMF
toluene
PhCl
trace
trace
40
4
Fe(OTf)3
alkynes and benzylic compounds (Table 2). The results in-
dicate that both electron-deficient and electron-rich aryl
acetylenes were compatible with the reaction conditions and
gave the desired products in moderate yields (Table 2, en-
tries 1–9). Moreover, the methyl substituent at ortho- and
meta-positions (3b, 3c) led to higher yields than that at the
para-position (3d) (Table 2, entries 2–4). The bromo sub-
stituent was compatible under the conditions and the result-
ing product could be further functionalized (Table 2, entry
5). Unfortunately, benzyl methyl ether only formed a trace
amount of product 3j (Table 2, entry 10). In addition to
benzylic ethers, benzylic alkanes could also undergo this
transformation in despite of lower yields (Table 2, entries
5
Fe(OTf)3
6
Fe(OTf)3
49
7
FeCl2
PhCl
8
8
FeCl3
PhCl
10
9
Fe(OTf)2·2MeCN
Fe(OTf)2·2MeCN
Fe(OTf)2·2MeCN
Fe(OTf)2·2MeCN
PhCl
55
10 c)
11 d)
12 d, e)
PhCl
51
PhCl
60
PhCl
51
a) All reactions were carried out in the scale of 0.5 mmol 1a, 0.75
mmol 2a, 5 mmol% catalyst, 0.6 mmol DDQ in 2 mL solvent at 90 °C
under N2 for 16 h. b) Isolated yields. c) 0.75 mmol of DDQ was employed.
d) The reaction was stirred for 24 h. e) The reaction was carried out at
110 °C.

52
Xiang SK, et al. Sci China Chem January (2012) Vol.55 No.1
11 and 12). Aliphatic terminal alkynes such as oct-1-yne
were also investigated, however, no obvious product was
detected.
The catalytic mechanism of this transformation was pro-
posed (Scheme 1). Firstly, the benzylic ethers or alkanes 1
could be oxidized to radical intermediates 4, which could be
further oxidized to form the corresponding benzoxy cations
or carbon cations 5. Cation 5 could be attached by terminal
aryl alkynes 2 to form the final products 3.
4.2 Experimental procedures and characterization of
products
1-(2-Phenylethynyl)-3,4-dihydro-1H-isochromene (3a)
Typical Procedure: Fe(OTf)2·2MeCN (11.0 mg, 0.025
mmol), DDQ (136.0 mg, 0.60 mmol), benzylic ether 1a (63
L, 0.50 mmol), phenylacetylene 2a (82 L, 0.75 mmol),
and PhCl (2.0 mL) were added into a dry Schlenck tube
under N2. The reaction mixture was stirred at 90 °C for 24 h
and monitored by TLC. The solution was cooled to room
temperature and the solvent was removed under vacuum.
The crude product was purified by column chromatography
on silica gel (eluent: petroleum ether/dichloromethane = 5:1)
to afford 69.8 mg (60%) of 3a: Light yellow liquid; IR:
1
(KBr) νmax 1727, 1490, 1289, 1093, 748 cm1; H NMR
(400 MHz, CDCl3, ppm)  7.46–7.43 (m, 2H), 7.36–7.33 (m,
1H), 7.30–7.28 (m, 3H), 7.25–7.14 (m, 2H), 7.14–7.12 (m,
1H), 5.77 (s, 1H), 4.34–4.27 (m, 1H), 4.05–3.99 (m, 1H),
2.94–2.88 (m, 2H); 13C NMR (100 MHz, CDCl3, ppm)
 134.9, 132.8, 131.8, 129.0, 128.4, 128.2, 127.2, 126.4,
126.0, 122.5, 88.1, 85.7, 67.3, 62.7, 28.0; MS (70 eV): m/z
(%): 234.2 (100) [M]+. HRMS m/z (ESI): calcd. for C17H15O
[M+H]+ 235.11174, Found: 235.11170.
Scheme 1 Proposed catalytic mechanism for this transformation.
3 Conclusions
1-(2-o-Tolylethynyl)-3,4-dihydro-1H-isochromene (3b)
In summary, we have developed an iron-mediate cross de-
hydrogenative coupling of terminal alkynes with benzylic
ethers and alkanes for the formation of sp-sp3 C–C bonds.
This observation provides an environmentally benign and
practical approach for the synthesis of alkyl substituted al-
kynes.
The reaction of 1a (63 L, 0.50 mmol), 2b (94 L, 0.75
mmol), Fe(OTf)2·2MeCN (11.1 mg, 0.025 mmol), DDQ
(136.5 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
68.7 mg (55%) of 3b: Light yellow liquid; IR: (KBr) νmax
1
1723, 1487, 1289, 1094, 751 cm1; H NMR (400 MHz,
4 Experimental
CDCl3, ppm)  7.42–7.33 (m, 2H), 7.26–7.08 (m, 6H), 5.81
(s, 1H), 4.34–4.28 (m, 1H), 4.06–3.99 (m, 1H), 2.99–2.84
(m, 2H), 2.40 (s, 3H); 13C NMR (100 MHz, CDCl3, ppm)
 140.4, 135.2, 132.8, 132.1, 129.3, 128.9, 128.4, 127.2,
126.3, 126.0, 125.4, 122.4, 92.1, 84.7, 67.4, 62.6, 28.0, 20.7;
HRMS m/z (ESI): calcd. for C18H15O [M–H]+ 247.11174,
Found: 247.11143.
4.1 General
All reactions were carried out under N2 atmosphere.
1HNMR spectra were recorded on a JEOL AL-300 or
Bruker AVIII-400 spectrometer. Chemical shifts (in ppm)
were referenced to tetramethylsilane ( = 0 ppm) in CDCl3
as an internal standard. 13C NMR spectra were obtained by
the same NMR spectrometers and were calibrated with
CDCl3 ( = 77.00 ppm). Mass spectra were recorded by PE
SCLEX QSTAR spectrometer. Unless otherwise noted,
materials obtained from commercial suppliers were used
without further purification. DCE, DMF, MeNO2, toluene,
PhCl were freshly distilled over CaH2. Fe(OTf)3 [13] and
Fe(OTf)2·2MeCN [14] were synthesized according to the
literature methods. Most of products 3 are not stable in
air.
1-(2-m-Tolylethynyl)-3,4-dihydro-1H-isochromene (3c)
The reaction of 1a (63 L, 0.50 mmol), 2c (97 L, 0.75
mmol), Fe(OTf)2·2MeCN (11.0 mg, 0.025 mmol), DDQ
(135.6 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
65.8 mg (53%) of 3c: Light yellow liquid; IR:(KBr) νmax

Xiang SK, et al. Sci China Chem January (2012) Vol.55 No.1
53
1726, 1487, 1291, 1093, 786, 745 cm1; 1H NMR (400 MHz,
CDCl3, ppm)  7.35–7.32 (m, 1H), 7.28–7.09 (m, 7H), 5.76
(s, 1H), 4.33–4.26 (m, 1H), 4.04–3.98 (m, 1H), 2.94–2.84
(m, 2H), 2.30 (s, 3H); 13C NMR (100 MHz, CDCl3, ppm)
 137.8, 135.0, 132.7, 132.4, 129.3, 128.91, 128.86, 128.1,
127.2, 126.3, 126.0, 122.3, 87.7, 85.8, 67.3, 62.6, 28.0, 21.1;
HRMS m/z (ESI): calcd. for C18H17O [M+H]+ 249.12739,
Found: 249.12730.
72.9 mg (58%) of 3f: Light yellow liquid; IR:(KBr) νmax
1
1721, 1683, 1294, 1237, 852, 746 cm1; H -NMR (400
MHz, CDCl3, ppm)  7.44–7.39 (m, 2H), 7.34–7.31 (m, 1H),
7.23–7.20 (m, 2H), 7.14–7.11 (m, 1H), 7.00–6.94 (m, 2H),
5.75 (s, 1H), 4.32–4.25 (m, 1H), 4.04–3.97 (m, 1H), 2.96–2.83
(m, 2H); 13C-NMR (100 MHz, CDCl3, ppm)  162.6 (d, J =
248.8 Hz), 134.8, 133.7 (d, J = 7.6 Hz), 132.8, 129.0, 127.3,
126.4, 125.9, 118.6 (d, J = 3.7 Hz), 115.5 (d, J = 21.8 Hz),
87.8, 84.5, 67.2, 62.7, 28.0; HRMS m/z (ESI): calcd. for
C17H12FO [M–H]+ 251.08667, Found: 251.08656.
1-(2-p-Tolylethynyl)-3,4-dihydro-1H-isochromene (3d)
1-(2-p-Biphenylethynyl)-3,4-dihydro-1H-isochromene (3g)
The reaction of 1a (63 L, 0.50 mmol), 2d (95 L, 0.75
mmol), Fe(OTf)2·2MeCN (11.0 mg, 0.025 mmol), DDQ
(136.6 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
50.9 mg (41%) of 3d: Light yellow liquid; IR: (KBr) νmax
The reaction of 1a (63 L, 0.50 mmol), 2g (132.7 mg, 0.75
mmol), Fe(OTf)2·2MeCN (11.0 mg, 0.025 mmol), DDQ
(136.5 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
64.0 mg (41%) of 3g: Light yellow liquid; IR: (KBr) νmax
1
1089, 1059, 744 cm1; H NMR (400 MHz, CDCl3, ppm)
 7.35–7.32 (m, 3H), 7.25–7.19 (m, 2H), 7.14–7.08 (m,
3H), 5.76 (s, 1H), 4.33–4.27 (m, 1H), 4.04–3.98 (m, 1H),
2.93–2.88 (m, 2H), 2.33 (s, 3H); 13C NMR (100 MHz,
CDCl3, ppm)  138.5, 135.1, 132.8, 131.7, 128.92, 128.90,
127.2, 126.3, 126.0, 119.5, 87.4, 85.8, 67.4, 62.6, 28.0, 21.4;
MS (70 eV): m/z (%): 248.3 (100) [M]+. HRMS m/z (ESI):
calcd. for C18H17O [M+H]+ 249.12739, Found: 249.12695.
1
1487, 1091, 764, 744, 696 cm1; H-NMR (400 MHz,
CDCl3):  7.56–7.50 (m, 6H), 7.43–7.30 (m, 4H), 7.24–7.13
(m, 2H), 7.12–7.10 (m, 1H), 5.78 (s, 1H), 4.34–4.27 (m,
1H), 4.04–3.98 (m, 1H), 2.92–2.84 (m, 2H); 13C NMR (100
MHz, CDCl3):  141.2, 140.3, 134.9, 132.8, 132.3, 128.9,
128.8, 127.6, 127.2, 127.0, 126.9, 126.4, 126.0, 121.4, 88.7,
85.5, 67.3, 62.7, 28.0; MS (70 eV): m/z (%): 310.4 (100)
[M]+.
1-(2-(4-Bromophenyl)ethynyl)-3,4-dihydro-1H-isochromene
(3e)
1-(2-(4-Tert-butylphenyl)ethynyl)-3,4-dihydro-1H-isochromene
(3h)
The reaction of 1a (63 L, 0.50 mmol), 2e (135.2 mg, 0.75
mmol), Fe(OTf)2·2MeCN (11.1 mg, 0.025 mmol), DDQ
(136.0 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
86.2 mg (55%) of 3e: Light yellow liquid; IR:(KBr) νmax
The reaction of 1a (63 L, 0.50 mmol), 2h (135 L, 0.75
mmol), Fe(OTf)2·2MeCN (11.1 mg, 0.025 mmol), DDQ
(136.2 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
60.0 mg (41%) of 3h: Light yellow liquid; IR: (KBr) νmax
1
1486, 1092, 744 cm1; H NMR (400 MHz, CDCl3, ppm)
 7.43–7.40 (m, 2H), 7.34–7.28 (m, 3H), 7.24–7.19 (m, 2H),
7.15–7.11 (m, 1H), 5.75 (s, 1H), 4.31–4.24 (m, 1H), 4.04–
3.98 (m, 1H), 2.97–2.82 (m, 2H); 13C NMR (100 MHz,
CDCl3, ppm)  134.6, 133.2, 132.7, 131.5, 129.0, 127.3,
126.4, 125.9, 122.7, 121.4, 89.3, 84.5, 67.2, 62.7, 27.9; MS
(70 eV): m/z (%):312.2 (100) [M-1]+, 314.2 (95) [M+1]+.
HRMS m/z (ESI): calcd. for C17H12BrO [M–1–H]+
311.00660, Found: 311.00658.
1
1726, 1092, 835, 744 cm1; H-NMR (400 MHz, CDCl3,
ppm)  7.40–7.25 (m, 5H), 7.23–7.20 (m, 2H), 7.15–7.12
(m, 1H), 5.76 (s, 1H), 4.34–4.27 (m, 1H), 4.04–3.98 (m,
1H), 2.93–2.88 (m, 2H), 1.29 (s, 9H); 13C NMR (100 MHz,
CDCl3, ppm)  151.7, 135.1, 132.8, 131.6, 128.9, 127.2,
126.3, 126.1, 125.2, 119.5, 87.4, 85.8, 67.4, 62.7, 34.7, 31.1,
28.1; HRMS m/z (ESI): calcd. for C21H21O [M-H]+
289.15869, Found: 289.15864.
1-(2-(4-Fluorophenyl)ethynyl)-3,4-dihydro-1H-isochromene
(3f)
1-(2-p-ethylphenylethynyl)-3,4-dihydro-1H-isochromene (3i)
The reaction of 1a (63 L, 0.50 mmol), 2f (86 L, 0.75
mmol), Fe(OTf)2·2MeCN (11.0 mg, 0.025 mmol), DDQ
(136.6 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
The reaction of 1a (63 L, 0.50 mmol), 2i (105 L, 0.75
mmol), Fe(OTf)2.2MeCN (11.0 mg, 0.025 mmol), DDQ

54
Xiang SK, et al. Sci China Chem January (2012) Vol.55 No.1
2
Sonogashira K. Development of Pd-Cu catalyzed cross-coupling of
(136.6 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
terminal acetylenes with sp2-carbon halides. J Organomet Chem,
2002, 653: 46–49
39.6 mg (30%) of 3i: Light yellow liquid; IR: (KBr) νmax
1
1509, 1091, 833, 744 cm1; H NMR (400 MHz, CDCl3,
3
4
Metal-Catalyzed Cross-Coupling Reactions. Eds. Diederich F, de
Meijere A. Wiley-VCH, New York, 2004
Uemura M, Yorimitsu H, Oshima K. Cp*Li as a base: Application to
palladium-catalyzed cross-coupling reaction of aryl-X or alkenyl-X
(X = I, Br, OTf, ONf) with terminal acetylenes. Tetrahedron, 2008,
64(8): 1829–1833
Buck M, Chong JM. Alkylation of 1-alkynes in THF. Tetrahedron Lett,
2001, 42(34): 5825–5827
Eckhardt M, Fu GC. The first applications of carbene ligands in
cross-couplings of alkyl electrophiles: sonogashira reactions of unacti-
vated alkyl bromides and iodides. J Am Chem Soc, 2003, 125(45):
13642–13643
ppm)  7–7.33 (m, 3H), 7.23–7.20 (m, 2H), 7.13–7.10
(m, 3H), 5.76 (s, 1H), 4.33–4.27 (m, 1H), 4.04–3.98 (m,
1H), 2.96–2.85 (m, 2H), 2.68–2.59 (m, 2H), 1.21 (t, J = 7.6
Hz, 3H); 13C NMR (100 MHz, CDCl3, ppm)  144.9, 135.1,
132.8, 131.8, 128.9, 127.8, 127.2, 126.3, 126.0, 119.7, 87.3,
85.8, 67.4, 62.7, 28.8, 28.0, 15.3; MS (70 eV): m/z (%):
262.3 (100) [M]+. HRMS m/z (ESI): calcd. for C19H19O
[M+H]+ 263.14304, Found: 263.14291.
5
6
7
8
9
Larsen CH, Anderson KW, Tundel RE, Buchwald SL. Palladium-
catalyzed heck alkynylation of benzyl chlorides. Synlett, 2006,
2941–2946
1,3,3-Triphenyl-1-propyne (3k)
Altenhoff G., Wurtz S, Glorius F. The first palladium-catalyzed So-
nogashira coupling of unactivated secondary alkyl bromides. Tetra-
hedron Lett, 2006, 47(17): 2925–2928
Xiang S-K, Zhang L-H, Jiao N. Sp-sp3 C–C bond formation via
Fe(OTf)3/TfOH cocatalyzed coupling reaction of terminal alkynes
with benzylic alcohols. Chem Commun, 2009. 6487–6489
The reaction of 1b (83 L, 0.50 mmol), 2a (82 L, 0.75
mmol), Fe(OTf)2·2MeCN (10.9 mg, 0.025 mmol), DDQ
(136.4 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
25.3 mg (20%) of 3k: white solid; IR: (KBr) νmax 1948,
10 For some reviews, see: (a) Li C-J. Cross-dehydrogenative coupling
(CDC): exploring C–C bond formations beyond functional group
transformations. Acc Chem Res, 2009, 42(2): 335–344; (b) Li C-J, Yoo
W-J. Cross-dehydrogenative coupling reactions of sp3-hybridized C–H
bonds. Top Curr Chem, 2010, 292: 281–302; (c) Guo X, Li Z, Li C-J.
Cross-dehydrogenative-coupling (CDC) reaction. Prog Chem (in Chi-
nese), 2010, 22(7): 1434–1441; (d) Scheuermann, CJ. Beyond tradi-
tional cross couplings: The scope of the cross dehydrogenative coupling
reaction. Chem Asian J, 2010, 5(3): 436–451; (e) Yeung CS, Dong VM.
Catalytic dehydrogenative cross-coupling: Forming carbon-carbon
bonds by oxidizing two carbon-hydrogen bonds. Chem Rev, 2011,
111(3): 1215–1292
1595, 1489, 756, 697, 559 cm1; H NMR (300 MHz,
1
CDCl3):  7.47–7.43 (m, 6 H), 7.35–23 (m, 9 H), 5.21 (s,
1 H); 13C NMR (75 MHz, CDCl3):  141.8, 131.8, 128.7,
128.3, 128.0, 127.0, 123.5, 90.2, 84.9, 43.7; MS (70 eV):
m/z (%): 268.2 (100) [M]+.
1-Phenyl-3-phenyl-3-(4-phenylphenyl)-1-propyne (3l)
11 For some reviews, see: (a) Bolm C, Legros J, Le Paih J, Zani L.
Iron-catalyzed reactions in organic synthesis. Chem Rev, 2004,
104(12): 6217–6254; (b) Fürstner A, Martin R. Advances in iron cat-
alyzed cross coupling reactions. Chem Lett, 2005, 34(5): 624–629; (c)
Enthaler S, Junge K, Beller M. Sustainable metal catalysis with iron:
From rust to a rising star? Angew Chem Int Ed, 2008, 47(18):
3317–3321; (d) Sherry BD, Fürstner A. The promise and challenge of
iron-catalyzed cross coupling. Acc Chem Res, 2008, 41(11): 1500–
1511; (e) Bauer EB. Recent advances in iron catalysis in organic
synthesis. Curr Org Chem, 2008, 12(16): 1341–1369; (f) Correa A,
Garcia Mancheno O, Bolm C. Iron-catalysed carbon-heteroatom and
heteroatom-heteroatom bond forming processes. Chem Soc Rev, 2008,
37(6): 1108–1117; (g) Iron Catalysis in Organic Chemistry. Ed.
Plietker B. Wiley-VCH, New York, 2008; (h) Sun C-L, Li B-J, Shi
Z-J. Direct C–H transformation via iron catalysis. Chem Rev, 2011,
111(3): 1293–1314
12 Recently, the similar works catalyzed by Ag or Cu salts have been
reported by Li and co-workers, see: (a) Correia CA, Li C-J. Copper-
catalyzed cross-dehydrogenative coupling (CDC) of alkynes and
benzylic C–H bonds. Adv Synth Catal, 2010, 352: 1446–1450; (b)
Correia CA, Li C-J. Silver-catalyzed oxidative coupling of terminal
aromatic alkynes and benzylic ethers. Heterocycles, 2010, 82(1):
555–562
The reaction of 1c (122.8 mg, 0.50 mmol), 2a (82 L, 0.75
mmol), Fe(OTf)2·2MeCN (11.0 mg, 0.025 mmol), DDQ
(136.5 mg, 0.60 mmol) in PhCl (2.0 mL) under N2 afforded
31.3 mg (18%) of 3l: white solid; IR: (KBr) νmax 1598, 1488,
1
757, 694 cm1; H NMR (300 MHz, CDCl3):  7.58–7.21
(m, 19 H), 5.25 (s, 1 H); 13C NMR (75 MHz, CDCl3): 
141.7, 140.92, 140.87, 140.0, 131.8, 128.82, 128.76, 128.4,
128.3, 128.1, 128.0, 127.5, 127.3, 127.14, 127.06, 123.5,
90.1, 85.0, 43.4; MS (70 eV): m/z (%): 344.4 (100) [M]+.
This work was financially supported by Peking University, the National
Natural Science Foundation of China (20872003) and National Basic
Research Program of China (973 program) (2009CB825300).
13 Haynes JS, Sams JR, Thompson RC. Synthesis and structural studies of
iron(II) and iron(III) sulfonates. Can J Chem, 1981, 59: 669–678
14 Hagen KS. Iron(II) triflate salts as convenient substitutes for per-
chlorate salts: Crystal structures of [Fe(H2O)6](CF3SO3)2 and
Fe(MeCN)4(CF3SO3)2. Inorg Chem, 2000, 39: 5867–5869
1
Acetylene Chemistry: Chemistry, Biology, and Materials Science. Eds.
Diederich F, Stang PJ, Tykwinski RR. Wiley-VCH, New York, 2005