Synthesis of substituted indenes through iron-catalyzed annulation of benzylic alcohols with alkynes

Article abstract of DOI:10.1002/adsc.201100065

A convenient and efficient method for the synthesis of polysubstituted indenes has been developed by the iron(III) trichloride-catalyzed tandem mono- and dibenzylation/cyclization reactions of benzylic alcohols with alkynes. This method is featured with the easily available starting materials, cheap catalyst, simple manipulation and mild conditions. Copyright

Full text of DOI:10.1002/adsc.201100065

FULL PAPERS
DOI: 10.1002/adsc.201100065
Synthesis of Substituted Indenes through Iron-Catalyzed
Annulation of Benzylic Alcohols with Alkynes
Xiuli Bu,a Jianquan Hong,a and Xigeng Zhoua,b,*
a
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University,
Shanghai 200433, Peopleꢀs Republic of China
Fax : (+86)-21-6564-1740; phone: (+86)-21-6564-3769; e-mail: xgzhou@fudan.edu.cn
State Key Laboratory of Organometallic Chemistry, Shanghai 200032, Peopleꢀs Republic of China
b
Received: January 26, 2011; Revised: April 21, 2011; Published online: July 14, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adcs.201100065.
Abstract: A convenient and efficient method for the cheap catalyst, simple manipulation and mild condi-
synthesis of polysubstituted indenes has been devel- tions.
oped by the ironACTHNUTRGNEUNG(III) trichloride-catalyzed tandem
mono- and dibenzylation/cyclization reactions of
benzylic alcohols with alkynes. This method is fea- Keywords: alkynes; annulation; benzylic alcohols;
tured with the easily available starting materials, iron trichloride; polysubstituted indenes
Introduction
ates, reports on the utilization of these substrates as
carbon proelectrophiles in difunctionalization of al-
The development of tandem reactions based on readi- kenes and alkynes are very scarce.[7c,8]
ly available starting materials using inexpensive cata-
Many biologically active natural products and phar-
lysts for the efficient construction of heterocyclic or maceutically important compounds contain the
carbocyclic rings is an important goal of organic syn- indene skeleton.[9] Meanwhile, indenes are also exten-
thesis from the viewpoints of operational simplicity, sively used as ligands in organometallics[10a–c] and as
economy and assembly efficiency.[1] Hydroxy and al- functional materials.[10d] Thus, the development of
kynyl units are ubiquitous functional groups in natural new indene-based structures and new methods for
and synthetic organic compounds, thus the develop- their construction has attracted much attention from
ment of synthetic methods for converting simple al- organic chemists.[11] As an extension of our continuing
kynes and alcohols into cyclic compounds is highly effort toward the development of new methods for
desirable. The selective hydroxy substitution of alco- the one-pot synthesis of biologically important heter-
hols represents a fundamentally important synthetic ocyclic and carbocyclic compounds from allylic[6g] and
transformation. Recently, much attention has been di- propargylic alcohol[6d–f] precursors, we became inter-
rected towards Lewis acid-catalyzed direct hydroxy ested in developing the intermolecular cyclizations of
substitution of benzylic, allylic and propargylic alco- simpler and cheaper benzylic alcohols with nucleo-
hols with a variety of nucleophiles as a powerful philes. Herein, we describe the first example of iron-
method for the construction of carbon-carbon and catalyzed sequential benzylation/cyclization of benzyl-
carbon-heteroatom bonds.[2–5] Despite significant ad- ic alcohols with alkynes, which affords a straightfor-
vances in this area, few existing methods allow for the ward way for the convenient synthesis of a diverse va-
construction of the ring nucleus.[6,7] And all the previ- riety of indene derivatives in good to excellent yields.
ously reported annulations are limited to functional-
ized benzylic alcohols.
The Lewis acid-promoted addition of a carbocation Results and Discussion
to unsaturated carbon-carbon functionalities repre-
sents a well-established strategy for carbon-carbon The reaction of diphenylmethanol (1a) and diphenyl-
bond formation. Although it has been well document-
ACHTUNGTRENaNUNG cetylene (2a) was chosen as a model system. When
ed for hydroxy substitutions of benzylic, allylic and the reactants were subjected to FeCl3 (5 mol%) in
propargylic alcohols to involve carbocation intermedi- 1,2-dichloroethane (DCE) at room temperature, small
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Xiuli Bu et al.
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Table 1. Optimization of the reaction conditions.[a]
Entry
Cat. (5%)
Solvent
T [8C]
Time [h]
Yield [%][b]
3aa
4aa
1
2
3
4
5
6
7
8
FeCl3
FeCl3
FeCl3
FeCl3
FeCl3
FeCl3
FeCl3
FeCl3·6H2O
FeCl3·6H2O
TiCl4
DCE
DCE
CH3NO2
Tol
CH3CN
THF
1,4-dioxane
DCE
DCE
DCE
DCE
r.t.
80
80
rt
80
80
80
rt
24
15
12
24
14
12
12
20
6
12
48
20
12
15
43
19
0
11
0
0
60
0
14
37
7
0
0
0
0
34
90
0
9[c]
10
11
12
13
rt
80
80
r.t.
rt
23
29
0
Yb
N
9
0
0
ZnCl2
TsOH·H2O
DCE
DCE
0
[a]
Reaction conditions: 0.17 mmol 1a, 1.0 equiv. 2a, 5 mol% catalyst, 5 mL solvent.
Isolated yield.
2.2 equiv. of 1a were used.
[b]
[c]
amounts of 3aa and 4aa were observed along with the
recovery of unreacted alkyne (Table 1, entry 1). Ele-
vating the reaction temperature did increase the
yields (Table 1, entry 2). We found that coordinating
solvents, such as THF and 1,4-dioxane, tended to shut
down the reacting system, whereas DCE seemed to
be ideal (Table 1, entries 1–7). Using DCE as the sol-
vent, we next set out to find an ideal catalyst system.
It was found that the use of FeCl3·6H2O in place of
FeCl3 provided significantly improved yield and selec-
tivity. Compound 4aa was selectively obtained in 90%
yield when 2.2 equivalents of 1a were used (Table 1,
entry 9), while 3aa was obtained as the main product
if one equivalent of 1a was used (Table 1, entry 8).
The structure of 3aa was confirmed by X-ray diffrac-
tion analysis (Figure 1).[12] In screening several cata-
lysts, we found that a selective procedure for the
preparation of 3aa could be developed by replacing
iron trichloride with TiCl4, but the yield was low
(entry 10). ZnCl2 and TsOH·H2O proved to be inef-
fective (Table 1, entries 12 and 13).
Having demonstrated the viability of the tandem
mono- and dibenzylation/cyclization processes, we set
out to achieve the selective coupling/cyclization of
benzylic alcohols with alkynes. We were pleased to
Figure 1. ORTEP diagram of the single-crystal X-ray struc-
ture of 3aa.
find that the properties of the substrates, except for thus facilitating the dibenzylation/cyclization process.
the stoichiometric ratio of alcohols and alkynes, had a For example, reaction of 2f with 1 equivalent of 1a af-
large impact on the selectivity (Table 2, entries 1 and forded 4af as the main product (Table 2, entry 7). The
2). The electron-deficient alkynes should increase the electron-rich alcohols would also favor the second
rate of a second benzylation relative to cyclization, benzylation, and the reaction of benzylic alcohols 1b–
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Synthesis of Substituted Indenes through Iron-Catalyzed Annulation of Benzylic Alcohols
Table 2. FeCl3-catalyzed regioselective synthesis of indene
Table 2. (Continued)
derivatives from benzylic alcohols and alkynes.[a]
Entry
Product
Yield [%][b]
64
9[d,e]
4bc
4bd
4ca
4da
10[d,e]
11[d,e]
12[d,e]
83
81
60
13[d,e]
4dd
68
Entry
1[c]
Product
Yield [%][b]
90
14
15
16
3ea
3ec
3fa
56
74
73
4aa
3aa
3ab
3ac
3ad
3ae
4af
2
60
71
71
72
63
95
70
3[c]
17
18
3ga
93
4
3ge
4ag
99
68
5
19[d]
6
[a]
Reaction conditions: 0.17–0.20 mmol alkyne, 1.0 equiv.
benzylic alcohol, 5 mol% of FeCl3·6H2O, 5 mL of DCE
at room temperature for 5–14 h.
7[d]
[b]
[c]
[d]
[e]
Isolated yield.
With a trace amount of regioisomer.
2.2 equiv. of 1 was used at 808C for 9–12 h.
As nearly 1:1 mixture of diastereoisomers.
8[d,e]
4ba
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symmetrical alkynes examined smoothly cyclized to
the corresponding indenes with 1a in good yields with
perfect regioselectivity. For example, for alkylarylace-
tylenes the electrophilic attack of the benzyl carbocat-
ion took place at the carbon atom bearing the alkyl
substituent regioselectively, giving only one isomeric
product (Table 2, entries 3–5). These results indicate
that the selectivity would favor the alkenyl cation
which is most stabilized. 1-(Naphthalen-1-yl)ethanol
1e could also be applied in this reaction (Table 2, en-
tries 14 and 15). The results described above clearly
demonstrated that, in the present catalytic system, the
different types and numbers of substituents on the
indene skeleton could be controlled by applying ben-
zylic alcohols and alkynes bearing the desired types
and numbers of substituents.
In contrast to the previously reported stoichiomet-
ric reaction of FeCl3 with benzylic alcohols and aro-
matic alkynes, wherein only alkenyl chlorides were
obtained with high regioselectivity,[8] under the pres-
ent conditions the same internal alkyne 2c preferen-
Figure 2. ORTEP diagram of the single-crystal X-ray struc-
ture of 4af.
1d with 0.5 equivalent of alkynes 2 afforded the corre- tially underwent the tandem benzylation/Friedel–
sponding indene diastereoisomers with acceptable Crafts reaction rather than carbochlorination
yields (Table 2, entries 8–13). The presence of elec- (Table 2, entry 4). This difference in the selectivity
tron-withdrawing substituents such as chloride in the might be attributed to the stronger nucleophilicity of
benzylic alcohols should prevent the second benzyla- chloride compared with aryl, demonstrating the syn-
tion (Table 2, entries 16–18). The structure of 4af was thetic potential and versatility of the reaction between
confirmed by X-ray diffraction analysis (Figure 2).[12]
benzylic alcohols and alkynes.
Aliphatic alkynes, such as dipropylacetylene 2g,
In order to investigate the mechanism for the for-
could also undergo the tandem benzylation and Frie- mation of 4, 3aa was subjected to this catalytic
del–Crafts reaction to afford the desired product 4ag system. When 1a was used, 4aa could be separated in
in 68% yield (Table 2, entry 19). Significantly, the un- 83% yield, indicating that 3aa can undergo authenti-
cally the Friedel–Crafts reaction with 1a (Scheme 1).
With the aim of excluding the possibility that the
second benzylation takes place prior to the cyclization
in the formation of 4aa, the reaction of alone 1a with
FeCl3·6H2O was studied (Scheme 2), but only diben-
zyl ether 5a was obtained without the formation of
the Friedel–Crafts product. In addition, we found that
5a did not react with 2a under the present conditions.
Furthermore, it could not be isomerized to the Frie-
del–Crafts reaction product too.
Although the functionalization of indene rings has
been extensively studied, the successful reactions
occur generally in the five-membered unit. To the
Scheme 1.
Scheme 2.
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Adv. Synth. Catal. 2011, 353, 2111 – 2118

Synthesis of Substituted Indenes through Iron-Catalyzed Annulation of Benzylic Alcohols
Conclusions
In summary, controllable tandem reactions of benzylic
alcohols with alkynes catalyzed by FeCl3·6H2O have
been established, which reveal the potential of benzyl-
ic alcohols as convenient alkylation reagents for for-
À
mation of C C bonds and provide an efficient
method for the synthesis of polysubstituted indenes.
The simplicity, economy, high efficiency and use of
environmentally benign reagents render this method
useful and competitive to the conventional ap-
proaches.
Scheme 3. Cross-dibenzylation/cyclization reaction of al-
kynes with different benzylic alcohols.
best of our knowledge, no regioselective Friedel–
Crafts reaction of the phenyl ring of indenes has been
reported so far. To obtain further insight into the ver-
satility of this class of reactions and developing their
utility in organic synthesis, we further examined the
cross-dibenzylation/cyclization reaction. Significantly,
treatment of 3aa with 1c and 1f in the presence of
FeCl3·6H2O gave the expected Friedel–Crafts reac-
Experimental Section
General Procedure for the Cyclization of Benzylic
Alcohols and Alkynes
To a mixture of alkyne (0.25 mmol) and benzylic alcohol
(0.25 or 0.55 mmol) in DCE (5 mL) was added 5 mol%
FeCl3·6H2O. The reaction mixture was stirred at room tem-
tion products 5ac and 5af, respectively, in good yields perature or 808C until the alkyne was consumed by TLC.
Then the solvent was evaporated. The residue was subjected
to silica gel column chromatography (petroleum ether/ethyl
acetate) to afford the corresponding substituted indene.
(Scheme 3).
Based on the above results, a plausible mechanism
for the formation of 3 and 4 is proposed in Scheme 4.
6-Benzhydryl-1,2,3-triphenyl-1H-indene
(4aa):
White
À
The C O activation by FeCl3·6H2O leads to the for-
1
solid; mp 153.9–155.08C. H NMR (CDCl3, 400 MHz): d=
7.49–7.39 (m, 5H), 7.32–7.28 (m, 5H), 7.24–7.21 (m, 3H),
7.18–7.08 (m, 14H), 7.04 (d, J=8.0 Hz, 1H), 5.59 (s, 1H),
5.13 (s, 1H); 13C NMR (CDCl3, 100 MHz): d=148.53,
145.72, 144.31, 144.18, 143.55, 141.79, 140.55, 139.89, 135.71,
135.68, 129.60, 129.54, 129.40, 128.78, 128.68, 128.37, 128.33,
mation of benzylic cations.[4f] Then regioselective
attack of the carbocation on internal alkyne results in
the formation of vinylic carbocation,[13] which under-
goes an IFC reaction to give polysubstituted indenes
3, which further reacts with second benzylic alcohol
to give 4. Clearly, the steric and electronic factors are 128.22, 127.94, 127.55, 126.74, 126.68, 126.32, 125.44, 120.31,
58.01, 56.92; HR-MS (ESI): m/z=511.2409, calcd. for C40H31
favorable to the addition of benzylic cation to unsym-
metric alkyne from the less sterically hindered alkyl
side, and the electrophilic addition of the benzylic
cation to alkyne is rate-determining step.
[M+H]+: 511.2427.
1-Phenyl-2,3-di-p-tolyl-1H-indene (3ae): White crystalline
material; mp 143.8–144.28C. 1H NMR (CDCl3, 400 MHz):
d=7.39 (d, J=8.0 Hz, 2H), 7.33–7.28 (m, 5H), 7.25–7.17 (m,
6H), 7.09 (d, J=8.0 Hz, 2H), 6.93 (d, J=8.0 Hz, 2H), 5.13
(s, 1H), 2.47 (s, 1H), 2.24 (s, 1H); 13C NMR (CDCl3,
100 MHz): d=148.26, 145.39, 140.24, 137.12, 136.38, 132.85,
Scheme 4. Plausible mechanism.
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132.77, 129.53, 129.49, 129.24, 128.74, 128.73, 128.27, 126.93,
126.65, 125.57, 123.94, 120.49, 57.99, 21.50, 21.24; HR-MS
(ESI): m/z=373.1963, calcd. for C29H25 [M+H]+: 373.1957.
6-Benzhydryl-2,3-bis(4-chlorophenyl)-1-phenyl-1H-indene
(4af): White crystalline material; mp 145.3–145.88C.
1H NMR (CDCl3, 400 MHz): d=7.41–7.33 (m, 4H), 7.29–
7.18 (m, 10H), 7.14–7.06 (m, 9H), 7.03–6.99 (m, 3H), 5.55
(s, 1H), 5.03 (s, 1H); 13C NMR (CDCl3, 100 MHz): d=
148.40, 145.07, 144.16, 144.02, 142.82, 142.34, 139.85, 139.24,
133.88, 133.77, 133.66, 132.82, 132.39, 130.92, 130.56, 129.52,
129.26, 128.84, 128.42, 128.38, 128.33, 127.64, 126.98, 126.41,
125.59, 120.22, 58.05, 56.90; HR-MS (ESI): m/z=579.1666,
calcd. for C40H29Cl2 [M+H]+: 579.1647.
45.98, 45.04, 22.38, 22.29, 16.78; HR-MS (ESI): m/z=
387.2108, calcd. for C30H27 [M+H]+: 387.2114.
1-Ethyl-2,3-diphenyl-6-(1-phenylpropyl)-1H-indene (4da):
1
Yellow oil; nearly 1:1 mixture of diastereoisomers. H NMR
(CDCl3, 400 MHz): d=7.44 (s, 1H), 7.39–7.30 (m, 9H),
7.25–7.18 (m, 8H), 4.10 (q, J=4.0 Hz, 1H), 3.92 (t, J=
8.0 Hz, 1H), 2.21–2.14 (m, 2H), 2.10–2.02 (m, 1H), 1.82–
1.73 (m, 1H), 1.00–0.96 (m, 3H), 0.58–0.54 (m, 3H);
13C NMR (CDCl3, 100 MHz): d=146.90, 146.84, 145.85,
145.70, 145.52, 144.15, 142.33, 142.24, 139.60, 136.17, 135.90,
129.68, 129.47, 128.59, 128.47, 128.18, 128.03, 127.20, 126.75,
126.70, 126.27, 126.04, 123.11, 122.66, 120.20, 120.18, 53.48,
53.43, 29.02, 28.96, 23.43, 23.40, 13.04, 8.65, 8.62; HR-MS
(ESI): m/z=415.2423, calcd. for C32H31 [M+H]+: 415.2427.
1,2-Diethyl-3-phenyl-6-(1-phenylpropyl)-1H-indene (4dd):
Pale-yellow oil; nearly 1:1 mixture of diastereoisomers.
1H NMR (CDCl3, 400 MHz): d=7.48–7.45 (m, 2H), 7.40–
7.35 (m, 4H), 7.32–7.29 (m, 4H), 7.21–7.17 (m, 1H), 7.13–
7.10 (m, 2H), 3.90–3.86 (m, 1H), 3.63–3.59 (m, 1H), 2.69–
2.59 (m, 1H), 2.31–2.22 (m, 1H), 2.18–2.11 (m, 3H), 1.94–
1.86 (m, 1H), 1.16–1.12 (m, 3H), 0.98–0.94 (m, 3H), 0.68–
0.64 (m, 3H); 13C NMR (CDCl3, 100 MHz): d=149.10,
146.61, 145.98, 144.24, 141.25, 138.12, 135.97, 129.29, 128.44,
128.01, 127.02, 126.43, 125.96, 125.87, 122.95, 122.39, 119.20,
53.43, 53.38, 49.80, 49.78, 29.02, 28.97, 22.84, 22.82, 20.21,
14.89, 13.03, 8.86, 8.82; HR-MS (ESI): m/z=389.2239, calcd.
for C28H30Na [M+Na]+: 389.2246.
1,5-Dimethyl-2,3-diphenyl-6-(1-p-tolylethyl)-1H-indene
(4ba): Yellow oil; nearly 1:1 mixture of diastereoisomers.
1H NMR (CDCl3, 400 MHz): d=7.40 (s, 1H), 7.39–7.28 (m,
5H), 7.23–7.17 (m, 5H), 7.14–7.02 (m, 5H), 4.36 (q, J=
7.2 Hz, 1H), 4.01 (q, J=7.6 Hz, 1H), 2.30 (s, 3H), 2.25 (s,
3H), 1.66 (d, J=6.8 Hz, 3H), 1.29 (d, J=7.6 Hz, 3H);
13C NMR (CDCl3, 100 MHz): d=147.62, 147.50, 146.51,
146.44, 143.68, 143.60, 143.02, 141.65, 141.46, 138.39, 138.33,
136.09, 136.05, 136.02, 135.34, 134.65, 134.62, 129.70, 129.69,
129.50, 129.17, 129.15, 128.70, 128.68, 128.18, 127.71, 127.69,
127.26, 126.70, 122.34, 122.30, 121.31, 121.29, 45.93, 45.90,
40.86, 40.66, 22.67, 22.57, 21.16, 21.14, 20.25, 20.22, 17.05,
16.96; HR-MS (ESI): m/z=413.2240, calcd. for C32H29
[MÀH]À: 413.2269.
1-Methyl-2,3-diphenyl-1H-cyclopenta[a]naphthalene
2-Ethyl-1,5-dimethyl-3-phenyl-6-(1-p-tolylethyl)-1H-
(3ea): Yellow crystalline material; mp 119.5–120.88C.
1H NMR (CDCl3, 400 MHz): d=8.14 (d, J=8.8 Hz, 1H),
7.93 (d, J=8.4 Hz, 1H), 7.81 (d, J=8.4 Hz, 1H), 7.57 (t, J=
7.6 Hz, 1H), 7.51–7.43 (m, 6H), 7.41–7.37 (m, 1H), 7.30–
7.21 (m, 5H), 4.47 (q, J=7.6 Hz, 1H), 1.50 (d, J=7.6 Hz,
3H); 13C NMR (CDCl3, 100 MHz): d=148.76, 144.14,
142.28, 138.69, 136.00, 135.65, 132.29, 129.77, 129.61, 129.36,
128.83, 128.31, 127.77, 127.43, 126.93, 126.30, 124.65, 123.75,
119.92, 45.63, 18.51; HR-MS (ESI): m/z=333.1639, calcd.
for C26H21 [M+H]+: 333.1644.
indene (4bd): Colorless oil; nearly 1:1 mixture of diastereo-
isomers. H NMR (CDCl3, 400 MHz): d=7.55–7.41 (m, 6H),
1
7.19–7.14 (m, 4H), 7.05 (d, J=3.2 Hz, 1H), 4.46–4.39 (m,
1H), 3.65–3.58 (m, 1H), 2.73–2.63 (m, 1H), 2.49–2.41 (m,
1H), 2.39 (s, 3H), 2.31 (d, J=8.0 Hz, 3H), 1.75–1.72 (m,
3H), 1.47–1.44 (m, 3H), 1.20 (d, J=8.0 Hz, 3H); 13C NMR
(CDCl3, 100 MHz): d=151.45, 151.40, 146.27, 146.24, 143.89,
143.76, 143.14, 140.58, 140.38, 136.71, 136.04, 135.26, 134.28,
134.24, 129.35, 129.14, 128.53, 127.72, 127.07, 121.52, 121.50,
121.14, 121.10, 44.42, 40.77, 40.60, 22.71, 22.56, 21.17, 20.23,
20.20, 20.10, 20.08, 16.19, 16.12, 14.91; HR-MS (ESI): m/z=
367.2410, calcd. for C28H31 [M+H]+: 367.2427.
1,2-Dimethyl-3-phenyl-1H-cyclopenta[a]naphthalene
1
(3ec): Yellow oil. H NMR (CDCl3, 400 MHz): d=8.05 (d,
J=8.4 Hz, 1H), 7.91 (d, J=8.4 Hz, 1H), 7.77 (d, J=8.4 Hz,
1H), 7.55–7.47 (m, 6H), 7.43–7.38 (m, 2H), 3.79 (q, J=
7.2 Hz, 1H), 2.18 (s, 3H), 1.58 (d, J=7.2 Hz, 3H); 13C NMR
(CDCl3, 100 MHz): d=146.61, 143.63, 142.21, 137.51, 135.67,
131.77, 129.52, 129.42, 129.27, 128.56, 127.12, 126.03, 124.09,
123.52, 119.39, 47.19, 17.59, 13.12; HR-MS (ESI): m/z=
271.1482, calcd. for C21H19 [M+H]+: 271.1488.
5-Chloro-1-(4-chlorophenyl)-2,3-di-p-tolyl-1H-indene
(3ge): White solid; mp 100.3–101.48C. 1H NMR (CDCl3,
400 MHz): d=7.34–7.26 (m, 6H), 7.18 (d, J=8.8 Hz, 2H),
7.14–7.13 (m, 1H), 7.08–7.02 (m, 4H), 6.93 (d, J=8.0 Hz,
2H), 5.04 (s, 1H), 2.44 (s, 3H), 2.23 (s, 3H); 13C NMR
(CDCl3, 100 MHz): d=147.21, 146.70, 145.94, 139.88, 139.57,
138.20, 137.64, 137.07, 133.87, 133.34, 132.58, 132.00, 131.91,
129.78, 129.53, 129.32, 129.22, 129.16, 129.14, 129.08, 128.97,
128.93, 128.51, 125.58, 124.85, 120.82, 56.75, 21.52, 21.28;
HR-MS (ESI): m/z=439.1012, calcd. for C29H21Cl2 [MÀH]À:
439.1020.
1,2,5-Trimethyl-3-phenyl-6-(1-p-tolylethyl)-1H-indene
(4bc): Colorless oil; nearly 1:1 mixture of diastereoisomers.
1H NMR (CDCl3, 400 MHz): d=7.53–7.45 (m, 4H), 7.40 (d,
J=8.8 Hz, 2H), 7.18–7.12 (m, 4H), 7.05 (s, 1H), 4.40 (q, J=
7.2 Hz, 1H), 3.40 (q, J=7.2 Hz, 1H), 2.36 (s, 3H), 2.29 (d,
J=8.0 Hz, 3H), 2.09 (s, 3H), 1.70 (d, J=6.8 Hz, 3H), 1.45–
1.41 (m, 3H); 13C NMR (CDCl3, 100 MHz): d=146.23,
146.20, 145.46, 145.39, 143.89, 143.03, 140.41, 140.22, 137.03,
135.92, 135.23, 134.21, 134.19, 129.35, 129.11, 128.48, 127.70,
127.00, 121.29, 121.04, 120.98, 47.43, 40.74, 40.57, 22.69,
22.56, 21.14, 20.22, 20.20, 16.27, 16.18, 13.08, 13.05; HR-MS
(ESI): m/z=353.2263, calcd. for C27H29 [M+H]+: 353.2270.
1-Methyl-2,3-diphenyl-6-(1-phenylethyl)-1H-indene (4ca):
1
Yellow oil; nearly 1:1 mixture of diastereoisomers. H NMR
(CDCl3, 400 MHz): d=7.44–7.32 (m, 10H), 7.28–7.19 (m,
8H), 4.30 (q, J=7.2 Hz, 1H), 4.04 (q, J=7.2 Hz, 1H), 1.75
(d, J=7.2 Hz, 3H), 1.33 (d, J=7.2 Hz, 3H); 13C NMR
(CDCl3, 100 MHz): d=148.90, 148.85, 147.44, 147.00, 146.70,
143.97, 143.66, 143.19, 143.17, 138.32, 135.92, 135.88, 129.65,
129.49, 128.67, 128.52, 128.50, 128.19, 127.78, 127.75, 127.29,
126.76, 126.49, 126.11, 126.05, 122.62, 122.21, 120.31, 46.01,
6-Benzhydryl-1-phenyl-2,3-dipropyl-1H-indene (4ag): Col-
orless oil. 1H NMR (CDCl3, 400 MHz): d=7.29–7.27 (m,
3H), 7.23–7.16 (m, 7H), 7.09 (d, J=7.6 Hz, 4H), 7.00–6.96
(m, 4H), 5.49 (s, 1H), 4.37 (s, 1H), 2.54 (t, J=7.2 Hz, 2H),
2116
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Adv. Synth. Catal. 2011, 353, 2111 – 2118

Synthesis of Substituted Indenes through Iron-Catalyzed Annulation of Benzylic Alcohols
2.42–2.39 (m, 1H), 2.00–1.93 (m, 1H), 1.71–1.62 (m, 2H),
1.55–1.46 (m, 2H), 1.01 (t, J=7.2 Hz, 3H), 0.88 (t, J=
7.2 Hz, 3H). 13C NMR (CDCl3, 100 MHz): d=148.65,
147.22, 144.54, 144.45, 144.35, 140.76, 140.11, 137.43, 129.53,
128.59, 128.42, 128.29, 128.25, 127.69, 126.55, 126.20, 126.17,
125.16, 118.26, 56.91, 56.83, 28.88, 27.56, 23.23, 22.33, 14.44,
14.30; HR-MS (ESI): m/z=443.2737, calcd. for C34H35 [M+
H]+: 443.2740.
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1,2,3-Triphenyl-6-(1-phenylethyl)-1H-indene (5ac): White
solid; nearly 1:1 mixture of diastereoisomers; mp 74.3–
1
75.28C. H NMR (CDCl3, 400 MHz): d=7.43–7.32 (m, 5H),
7.24–7.00 (m, 18H), 5.06 (d, J=6.8 Hz, 1H), 4.16–4.09 (m,
1H), 1.59 (t, J=6.8 Hz, 3H); 13C NMR (CDCl3, 100 MHz):
d=148.59, 148.54, 147.11, 146.45, 145.41, 144.59, 143.96,
143.35, 143.31, 140.62, 140.04, 139.98, 135.80, 135.73, 129.61,
129.41, 128.80, 128.74, 128.47, 128.44, 127.95, 127.75, 127.64,
127.53, 126.96, 126.70, 126.07, 126.03, 125.86, 124.12, 123.08,
120.46, 58.12, 58.05, 44.95, 44.91, 22.28, 22.12; HR-MS
(ESI): m/z=471.2081, calcd. for C35H28Na [M+Na]+:
471.2089.
6-[1-(4-Chlorophenyl)ethyl]-1,2,3-triphenyl-1H-indene
(5af): White crystalline material; nearly 1:1 mixture of dia-
stereoisomers;
mp
89.5–90.28C.
1H NMR
(CDCl3,
400 MHz): d=7.43–7.33 (m, 5H), 7.23–7.10 (m, 11H), 7.08–
7.01 (m, 6H), 5.06 (d, J=5.6 Hz, 1H), 4.12–4.05 (m, 1H),
1.54 (d, J=3.6 Hz, 3H); 13C NMR (CDCl3, 100 MHz): d=
148.68, 148.63, 145.60, 145.56, 143.97, 143.49, 143.33, 140.53,
139.93, 139.87, 135.71, 135.69, 135.63, 131.74, 131.69, 129.57,
129.38, 129.09, 128.98, 128.80, 128.74, 128.53, 128.48, 128.39,
128.37, 127.94, 127.56, 126.74, 125.76, 123.95, 122.98, 120.52,
120.50, 58.09, 58.02, 44.32, 44.29, 22.20, 22.01; HR-MS (ESI):
m/z=505.1680, calcd. for C35H27Cl Na [M+Na]+: 505.1699.
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Acknowledgements
We thank the NNSF of China, 973 Program
(2009CB825300), Shanghai Science and Technology Commit-
tee (No. 08dj1400100), the Research Fund for the Doctoral
Program of Higher Education of China, and Shanghai Lead-
ing Academic Discipline Project (B108) for financial sup-
port.
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2118
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Adv. Synth. Catal. 2011, 353, 2111 – 2118