Samarium triflate-catalyzed dimerization of vinylarenes

Article abstract of DOI:10.24820/ark.5550190.p011.076

We report the preparation of substituted indanes and their dimeric isomers via the samarium triflate-mediated [Sm(OTf)3, 10 mol%] self-dimerization of vinylarenes in MeNO2 at 25 ^oC for 10 h. The diverse products were obtained in moderate to high yields. The synthesis involves a (3+2) annulation via the formation of carbon-carbon bonds. Plausible mechanisms are proposed and discussed. The investigation of various rare metal triflates catalyst loadings, reaction conditions, and substrate scope led to an operationally easy one-pot Friedel-Crafts reaction protocol.

Full text of DOI:10.24820/ark.5550190.p011.076

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Samarium triflate-catalyzed dimerization of vinylarenes
Meng-Yang Chang*a,b and Yu-Lin Tsaia
a Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 807, Taiwan
b Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan
Email: mychang@kmu.edu.tw
Received 09-28-2019
Accepted 11-05-2019
Published on line 11-30-2019
Abstract
We report the preparation of substituted indanes and their dimeric isomers via the samarium triflate-
o
mediated [Sm(OTf)3, 10 mol%] self-dimerization of vinylarenes in MeNO2 at 25 C for 10 h. The diverse
products were obtained in moderate to high yields. The synthesis involves a (3+2) annulation via the formation
of carbon-carbon bonds. Plausible mechanisms are proposed and discussed. The investigation of various rare
metal triflates catalyst loadings, reaction conditions, and substrate scope led to an operationally easy one-pot
Friedel-Crafts reaction protocol.
Keywords: Samarium triflate, vinylarenes, indane, dimerization
DOI: https://doi.org/10.24820/ark.5550190.p011.076
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Introduction
The catalytic self-dimerization reaction of vinyl arenes (e.g. α-methylstyrenes) to derive functionalized indanes
is one of the most straightforward and useful transformations used to construct carbon-carbon (C-C) bonds.
After pioneer work by Bergmann and co-workers,1 various promoter-mediated synthetic routes have been
documented via the intermolecular hydroarylation of vinyl arenes followed by spontaneous intramolecular
ring-closure of the resulting dimeric isomers (Scheme 1). They include different metal-free reagents (I2, TFA,
aminium salt),2-5 transition-metal complexes (In3+, Bi3+, Ru3+-Ru+4, Pd2+/In3+, Eu3+, Au3+, Mo2+, Ce3+),6-13
nanoparticles (MCM-41, Al-SiO2, H3PW12O40/SiO2, Nafion)14-17 or other methods.18-21 On the basis of
observations, attempts to develop new and efficient catalyst systems for the self-dimerization of vinyl arenes
are still in demand. In an ongoing effort to emphasize the synthetic applications of metal triflates,22-28 we
present, herein, a Ln(OTf)3 (lanthanide triflate)-mediated synthesis of substituted indanes.29-30 To the best of
our knowledge, no examples have been reported for Ln(OTf)3-mediated self-dimerizations of this type.
Scheme 1. Self-dimerization of vinyl arenes.
Results and Discussion
After perusing literature on the synthesis of substituted indanes and reviewing our previous studies on metal
triflate (1)-promoted reactions, 10 commercially available Ln(OTf)3 2a-2j (10 mol%) promoted dimerizations of
o
starting α-methylstyrene (3a) were examined in MeNO2 (5 mL) at 25 C for 5 h. However, no obvious yield
changes occurred with the isolation of 4a using 5 mol% of La(OTf)3 (2a), Ce(OTf)3 (2b), Pr(OTf)3 (2c), Nd(OTf)3
(2d), Sm(OTf)3 (2e), Eu(OTf)3 (2f), Gd(OTf)3 (2g), Dy(OTf)3 (2h), Er(OTf)3 (2i) or Yb(OTf)3 (2j). Only Sm(OTf)3 (2e)
and Gd(OTf)3 (2g) provided 4a in better (66% and 47%) yields, respectively. Other catalysts produced 4a in low
yields (trace amounts to 20%). On the basis of the results, Sm(OTf)3 (2e) was controlled as a catalyst to screen
the optimal conditions (Table 1, entry 1). For comparing the advantages of the shown synthetic procedure
with others previously described in the literature (e.g. InBr3,6 BiCl3,7 or TFA18), we found that Sm(OTf)3 was the
first lanthanide catalyst to promote the formation of substituted indanes via self-dimerization of α-
methylstyrene. Nevertheless, Sm(OTf)3 is relatively expensive because samarium is a rare metal resource.
Further variations in the reaction parameters, such as catalyst loading, the solvent system, temperature and
reaction time, were carried out as follows. In entry 2, decreasing the catalytic equivalent of Sm(OTf)3 (10 → 5
mol%) diminished the yield of 4a (66 → 39%). Entry 3 showed that excess amounts (20 mol%) of Sm(OTf)3 did
not increase the catalytic ability to provide a better yield, and a similar yield (64%) was observed. After
o
elevating the temperature (25 → 75 C), 4a was isolated in only a 41% yield (entry 4). Under a refluxing
o
MeNO2 (101 C) condition, 4a was isolated in a low yield (35%), and a very complex mixture was detected, as
shown in entry 5. With longer reaction times (5 → 10, 20 h), 4a was formed in higher yield (83%, 80%) (entries
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6-7). Furthermore, controlling the reaction conditions for the combination of Sm(OTf)3 (10 mol%), 25 C and
10 h, different solvents were examined. After changing the reaction solvent from MeNO2 to PhMe and CH2Cl2,
4a was produced in lower yields (28%, 60%) than MeNO2 (entries 8 & 9). In particular, entry 10 showed that
the use of DMF did not give the desired product 4a. On the basis of TLC monitoring, only the starting material
3a was detected. However, treatment of 3a with diluted MeNO2 afforded 4a in a similar yield (80%) (entry 11).
This meant that the reaction concentration was not a main factor affecting the 4a yield.
Table 1. Optimal conditionsa-b
entry Sm(OTf)3 (mol%) solvent (mL)
temp (oC)
25
25
25
75
101
25
25
25
25
time (h)
5
5
5
5
5
10
20
10
10
10
10
yieldb (%)
66
39
64
41
1
2
3
4
5
6
7
8
9
10
5
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
PhMe
20
10
10
10
10
10
10
10
10
35
83
80
28c
60
CH2Cl2
DMF
MeNO2
10
11
25
25
NDd
80
e
b
c
a Reaction was run on 3a (1.0 mmol), solvent (5 mL). Isolated yields. Complex
reaction mixture (TLC). d No reaction. e Solvent (10 mL).
On the basis of the highest observed yield (entry 6, 83%), the combination of 10 mol% Sm(OTf)3/MeNO2 (5
o
mL)/25 C/10 h was selected as the optimal reaction conditions for the formation of dimer 4a. On the other
hand, Sm(OTf)3 has been reported as a catalyst for different reaction types, including Ferrier rearrangement,31
Friedel-Crafts alkylation,32 aza-Diels−Alder cycloaddition,33 conjugated addition34 and cross-coupling.35
Remarkably, there are few examples of samarium salt-catalyzed reactions having been performed in
comparison with other commercially available samarium complexes.36-40 With the optimal reaction conditions
in hand (Table 1, Entry 6), we then explored the scope of the conversion with other substrates (Table 2).
For the aryl substituent of α-methylvinyl arenes 3a-p, the Ar ring with diversified electron-neutral, electron-
donating or electron-withdrawing groups was examined next, including a Ph, b 4-CF3C6H4, c 4-MeC6H4, d 3-
MeOC6H4, e 4-ClC6H4, f 4-FC6H4, g 3-FC6H4, h 3,4-(MeO)2C6H3, i 3,4-CH2O2C6H3, j 3,4,5-(MeO)3C6H2, k 2,4-
(MeO)2C6H3, l 2-thienyl, m 4-PhC6H4, n 2-naphthyl, o 4-NO2C6H4 and p 3,4-Cl2C6H3. By the Sm(OTf)3-mediated
self-dimerization of 3a-p, two kinds of dimers, cyclized indanes (4a, 4c-n) and acyclic isomers (4b-1, 4e-1, 4f-1,
4g-1, 4o-1, 4p-1), were provided in a range of 56-83% and 8%-65% yields, respectively. In all examples, the
four electron-neutral aryl groups (for 3a, 3c, 3m-n), five electron-donating oxygenated aryl groups (for 3d, 3h-
k) and one heterocyclic group (for 3l) could trigger the ring-closure to produce a benzo-fused indane skeleton.
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However, six electron-withdrawing aryl groups (for 3b, 3e-f, 3g, 3o-p) afforded an acyclic dimer or a mixture of
a cyclic indane and acyclic dimer. One reason for this is the electron-deficient aryl group does not have enough
electron density to promote spontaneous annulation such that sole acyclic dimers would form, especially for
4-trifluoromethylphenyl, 4-nitrophenyl and 3,4-dichlorophenyl groups. However, another three weaker
electron-withdrawing aryl groups (fluoro-, chloro-) obtained a mixture of a cyclic indane and acyclic dimer.
Among these products 4, only 3d (Ar = 3-MeOC6H4) provided the unseparated mixture of products 4d (for 3-
MeO) and 4d’ (for 5-MeO) with a ratio of 80:20. During the ring-closure procedure, the methoxy group at the
C-5 position exhibited a bulkier steric hindrance such that the isolated yield of 4d’ was lower. Under the
o
kinetically controlled conditions (for 25 C), the terminal methylene group of acyclic isomers 4b-1, 4e-1, 4f-1,
4g-1, 4o-1 and 4p-1 could demonstrate that exo-chemoselectivity. The similar phenomenon had described by
Peppe and Nishibayashi groups, respectively.6,8
Table 2. Sm(OTf)3-catalyzed self-dimerization of 3a-b
a The synthesis was run on 1.0 mmol scale with 3a-p, Sm(OTf)3 (60 mg, 10 mol%),
MeNO2 (5 mL), 10 h, 25 oC. b Isolated yield.
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α-Phenylstyrene (3q) was also studied (Table 2). On the basis of the styrene skeleton, changing the α-methyl
group to α-phenyl was tested. Under the above-mentioned conditions, treatment of 3q with Sm(OTf)3
afforded 4q in a 56% yield along with a 25% yield of unknown and unanalyzed products mixture (Scheme 2).
Scheme 2. Synthesis of indane 4q.
Based on experimental results, a possible reaction mechanism with both electron-withdrawing 4-
trifluoromethylphenyl group and electron-donating 3,4-dimethoxyphenyl groups is shown in Scheme 3. How
were two dimers 4b-1 and 4h produced? The event is initiated to form A by complexation of an olefinic moiety
of 3 with Sm(OTf)3. After releasing a triflate anion, B, with a methylene samarium arm, is generated. Then,
participation of another 3 converts the resulting B into C having a tertiary carbocation. On the basis of the
structure on C, path a (green) shows that the 4-CF3 group decreases the electron density of Ar such that the
triflate anion could trap the proton to stabilize carbocation. Following in-situ formed triflic acid-promoted
protodemetalation of D, the removal of Sm(OTf)3 afforded 4b-1. For path b (red), owing to Ar = 3,4-(MeO)2,
the electron-rich arene could attack the carbocation to give E via the five-membered ring closure procedure.
Following the triflate anion-mediated dehydrogenative aromatization of E, and then, triflic acid-promoted
protodemetalation of F, tetramethoxyindane 4h is obtained along with the recovery of Sm(OTf)3. From the
plausible mechanisms, we understand that electron-density on arene is a key factor in affecting the reaction
pathway and product distribution.
Scheme 3. Plausible mechanism.
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In particular, when Ar with a 2,4-dimethoxy group was treated with the above reaction conditions, only 4k
was generated in a 76% yield. The spiro structure of bis-indane 4k was determined by single-crystal X-ray
crystallography.41 We postulated that three equivalents of 3k were involved to generate 4k (Scheme 4).
According to a series of reaction steps in Scheme 3, path b, II is produced from I with an oxygen-chelated
samarium complex conformation. By removal of 1,3-dimethoxybenzene, III should be formed. This is a very
important step for the formation of a bis-indane skeleton because the formed 3-carbon fragment could
construct a spiro ring. Furthermore, intermolecular Friedel-Crafts type coupling of the corresponding III with
another I produces IV. Next, electron-rich arene attacks the carbocation to give V via intramolecular
benzannulation. Following the above-mentioned steps (triflate anion-mediated dehydrogenative
aromatization of V followed by triflic acid-promoted protodemetalation of VI), tetramethoxy spiro-indane 4k is
obtained along with the recovery of Sm(OTf)3. Compared with the formation of oxygenated indanes 4h-k, only
4k was produced as a spiro system under similar reaction conditions. The detailed reasons are still unclear,
however, we believe that the 2-MeO group of 3k plays a role in triggering the removal of 1,3-
dimethoxybenzene more easily than other oxygenated vinylarenes 3h-j during the conversion process from II
to III.
Scheme 4. Plausible Mechanism of 4k.
Conclusions
We have developed a mild synthesis of substituted indanes and dimeric isomers in moderate yields via a 10
mol% Sm(OTf)3-mediated self-dimerization reaction of substituted vinylarenes in MeNO2 at 25 oC for 10 h. The
control of reaction parameters such as the lanthanide triflates catalyst loading, the reaction temperature, the
solvent and the time, had to be finely tuned to explore optimal conditions. Furthermore, the proposed
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mechanisms for the formation of 4b-1, 4h and 4k are discussed. Further investigation regarding synthetic
applications of lanthanide triflates will be conducted and published in due course.
Experimental Section
General. All reagents and solvents were obtained from commercial sources and used without further
purification. Reactions were routinely carried out under an atmosphere of air with magnetic stirring. Products
in organic solvents were dried with anhydrous magnesium sulfate before concentration in vacuo. All reactions
were monitored by TLC on silica gel 60 F254 (Merck) with detection by UV light. Column chromatography was
performed using silica gel (200-300 mesh). Melting points were determined with a SMP3 melting apparatus.
1H and 13C NMR spectra were recorded on a Varian INOVA-400 spectrometer operating at 400 and 100 MHz,
respectively. Chemical shifts (δ) are reported in parts per million (ppm) and the coupling constants (J) are
given in Hertz (Hz). High resolution mass spectra (HRMS) were measured with a mass spectrometer
Finnigan/Thermo Quest MAT 95XL. X-ray crystal structures were obtained with an Enraf-Nonius FR-590
diffractometer (CAD4, Kappa CCD).
General procedure for the preparation of compounds 4a, 4c-n, 4q, 4b-1, 4e-1, 4f-1, 4g-1, 4o-1 and 4p-1.
o
Sm(OTf)3 (60 mg, 0.1 mmol) was added to a solution of 3 (1.0 mmol) in MeNO2 (5 mL) at 25 C. The reaction
o
mixture was stirred at 25 C for 10 h. The solvent of reaction mixture was concentrated and extracted with
CH2Cl2 (3 × 10 mL). The combined organic layers were washed with brine (2 × 10 mL), dried (MgSO4), filtered
and evaporated to afford crude product mixture under reduced pressure. The remaining mixture was
separated by flash column chromatography (silica gel, eluent: hexanes/EtOAc 100:1 → 20:1) affording
compounds 4a, 4c-n, 4q, 4b-1, 4e-1, 4f-1, 4g-1, 4o-1 and 4p-1.
1,1,3-Trimethyl-3-phenylindan (4a).7 Colorless oil (98 mg, 83%); HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C18H21 237.1643, found 237.1644; 1H NMR (400 MHz, CDCl3): δ 7.45-7.25 (m, 9H), 2.58 (d, J 13.2, 1H), 2.35 (d, J
13.2, 1H), 1.84 (s, 3H), 1.50 (s, 3H), 1.19 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 152.1, 151.0, 148.7, 128.0 (2×),
127.2, 126.64 (2×), 126.61, 125.5, 125.0, 122.5, 59.2, 50.8, 42.8, 30.9, 30.7, 30.4.
4-Methyl-2,4-di(4-trifluoromethylphenyl)-1-pentene (4b-1). Colorless oil (108 mg, 58%); HRMS (ESI-TOF)
1
m/z: [M + H]+ calcd for C20H19F6 373.1391, found 373.1396; H NMR (400 MHz, CDCl3): δ 7.38-7.34 (m, 4H),
7.27 (d, J 8.4, 2H), 7.16 (d, J 8.4, 2H), 5.18 (d, J 1.2, 1H), 4.95 (s, 1H), 2.86 (s, 2H), 1.30 (s, 6H); 13C NMR (100
MHz, CDCl3): δ 152.3, 146.3, 145.5, 128.9 (d, J 32.6), 127.9 (d, J 31.9), 126.8 (2×), 126.4 (2×), 124.2 (q, J 269.8),
124.1 (d, J 269.9), 124.8 (q, J 3.8, 2×), 124.6 (d, J 3.8, 2×), 118.8, 50.0, 38.7, 28.6 (2×).
1,1,3,5-Tetramethyl-3-p-tolylindan (4c).16 Colorless oil (96 mg, 73%); HRMS (ESI-TOF) m/z: [M + H]+ calcd for
1
C20H25 265.1956, found 265.1953; H NMR (400 MHz, CDCl3): δ 7.20-7.17 (m, 6H), 7.02 (s, 1H), 2.49 (d, J 13.2,
1H), 2.46 (s, 3H), 2.40 (s, 3H), 2.28 (d, J 13.2, 1H), 1.78 (s, 3H), 1.44 (s, 3H), 1.16 (s, 3H); 13C NMR (100 MHz,
CDCl3): δ 149.3, 149.1, 148.1, 136.1, 134.8, 128.6 (2×), 128.0, 126.6 (2×), 125.4, 122.2, 59.5, 50.3, 42.5, 30.8
(2×), 30.5, 21.4, 20.9.
5-Methoxy-1-(3-methoxyphenyl)-1,3,3-trimethylindan (4d) and 4-methoxy-3-(3-methoxyphenyl)-1,1,3-
trimethylindan (4d’).18 Unseparated binary mixture; ratio 4d/4d’ 80:20; Colorless oil (112 mg, 76%); HRMS
(ESI-TOF) m/z: [M + H]+ calcd for C20H25O2 297.1855, found 297.1856; for major product 4d, 1H NMR (400 MHz,
CDCl3): δ 7.20 (t, J 8.0, 1H), 7.08 (d, J 8.0, 1H), 6.86-6.70 (m, 5H), 3.87 (s, 3H), 3.78 (s, 3H), 2.46 (d, J 12.8, 1H),
2.22 (d, J 13.2, 1H), 1.69 (s, 3H), 1.36 (s, 3H), 1.06 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 159.4, 159.2, 153.7,
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153.1, 140.6, 128.8, 125.6, 119.3, 113.3, 112.5, 109.9, 107.7, 59.4, 55.3, 55.0, 50.1, 42.8, 31.1, 30.4, 30.2; GC-
MS: m/z (%) 297 (65) [M + H+], 282 (45), 267 (12), 236 (10), 158 (24), 144 (23), 91 (10).
o
5-Chloro-3-(4-chlorophenyl)-1,1,3-trimethylindan (4e).7 Colorless solid (102 mg, 67%); mp 81-82 C (from
hexanes and EtOAc); HRMS (ESI-TOF) m/z: [M + H]+ calcd for C18H19Cl2 305.0864, found 305.0866; 1H NMR (400
MHz, CDCl3): δ 7.27-7.20 (m, 3H), 7.13-7.07 (m, 3H), 7.04 (d, J 2.0, 1H), 2.37 (d, J 12.8, 1H), 2.20 (d, J 12.8, 1H),
1.65 (s, 3H), 1.32 (s, 3H), 1.03 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 150.6, 150.3, 148.7, 132.4, 131.5, 128.2
(2×), 128.0 (2×), 127.7, 124.9, 123.9, 59.2, 50.5, 42.6, 30.59, 30.57, 30.3.
2,4-Di(4-chlorophenyl)-4-methyl-1-pentene (4e-1).42 Colorless oil (12 mg, 8%); HRMS (ESI-TOF) m/z: [M +
H]+ calcd for C18H19Cl2 305.0864, found 305.0868; 1H NMR (400 MHz, CDCl3): δ 7.19-7.15 (m, 6H), 7.12-7.08 (m,
2H), 5.12 (d, J 1.6, 1H), 4.08 (d, J 0.4, 1H), 2.77 (s, 2H), 1.22 (s, 6H); 13C NMR (100 MHz, CDCl3): δ 147.3, 145.4,
141.5, 132.7, 131.3, 128.1 (2×), 127.79 (2×), 127.76 (2×), 127.4 (2×), 117.5, 49.7, 38.4, 28.8 (2×).
5-Fluoro-3-(4-fluorophenyl)-1,1,3-trimethylindan (4f).18 Colorless oil (90 mg, 66%); HRMS (ESI-TOF) m/z: [M
1
+ H]+ calcd for C18H19F2 273.1455, found 273.1456; H NMR (400 MHz, CDCl3): δ 7.15-7.11 (m, 3H), 7.00-6.91
(m, 3H), 6.76 (dd, J 2.4, 9.2, 1H), 2.39 (d, J 12.8, 1H), 2.22 (d, J 13.2, 1H), 1.66 (s, 3H), 1.33 (s, 3H), 1.04 (s, 3H);
13C NMR (100 MHz, CDCl3): δ 162.3 (d, J 242.6), 161.0 (d, J 243.3), 150.7 (d, J 6.8), 147.5 (d, J 2.3), 146.1 (d, J
3.0), 128.0 (d, J 7.6, 2×), 123.7 (d, J 8.3), 114.7 (d, J 20.4, 2×), 114.4 (d, J 22.7), 111.4 (d, J 21.2), 59.6, 50.2,
42.4, 30.8, 30.7, 30.4.
2,4-Di(4-fluorophenyl)-4-methyl-1-pentene (4f-1).42 Colorless oil (20 mg, 15%); HRMS (ESI-TOF) m/z: [M +
H]+ calcd for C18H19F2 273.1455, found 273.1458; 1H NMR (400 MHz, CDCl3): δ 6.85-6.76 (m, 4H), 6.56-6.49 (m,
4H), 4.74 (d, J 1.6, 1H), 4.44 (d, J 0.8, 1H), 2.43 (s, 2H), 0.88 (s, 6H); 13C NMR (100 MHz, CDCl3): δ 161.9 (d, J
244.1), 160.8 (d, J 242.6), 145.6, 144.5, 139.1, 128.0 (d, J 7.6, 2×), 127.4 (d, J 7.6, 2×), 116.9, 114.7 (d, J 21.2,
2×), 114.3 (d, J 20.5, 2×), 50.1, 38.5, 29.0 (2×).
5-Fluoro-1-(3-fluorophenyl)-1,3,3-trimethylindan (4g). Colorless oil (83 mg, 61%); HRMS (ESI-TOF) m/z: [M +
H]+ calcd for C18H19F2 273.1455, found 273.1457; 1H NMR (400 MHz, CDCl3): δ 7.23-7.17 (m, 1H), 7.05 (d, J 8.4,
1H), 7.04 (d, J 8.4, 1H), 6.97-6.91 (m, 2H), 6.88-6.82 (m, 2H), 2.41 (d, J 13.2, 1H), 2.22 (d, J 13.2, 1H), 1.65 (s,
3H), 1.33 (s, 3H), 1.02 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 164.0 (d, J 242.6), 162.7 (d, J 243.3), 154.5 (d, J 6.8),
153.6 (d, J 5.3), 143.4 (d, J 3.0), 129.4 (d, J 8.3), 125.9 (d, J 8.4), 122.2 (d, J 3.0), 113.9 (d, J 19.7), 113.7 (d, J
19.0), 112.4 (d, J 20.5), 109.5 (d, J 21.2), 59.3, 50.3, 42.9, 30.9, 30.4, 30.1.
2,4-Di(3-fluorophenyl)-4-methyl-1-pentene (4g-1). Colorless oil (24 mg, 18%); HRMS (ESI-TOF) m/z: [M + H]+
calcd for C18H19F2 273.1455, found 273.1455; 1H NMR (400 MHz, CDCl3): δ 7.18-7.12 (m, 2H), 7.03-7.01 (m, 1H),
6.98-6.96 (m, 1H), 6.94-6.90 (m, 1H), 6.88-6.83 (m, 2H), 6.80-6.75 (m, 1H), 5.16 (d, J 1.6, 1H), 4.84 (s, 1H), 2.78
(s, 2H), 1.24 (s, 6H); 13C NMR (100 MHz, CDCl3): δ 162.6 (d, J 242.6), 162.5 (d, J 242.6), 151.7 (d, J 8.8), 145.4 (d,
J 2.3), 138.9 (d, J 8.2), 129.4 (d, J 8.3), 129.1 (d, J 8.3), 122.1 (d, J 2.3), 121.6 (d, J 2.3), 117.9, 113.6 (d, J 20.5),
113.3 (d, J 22.0), 113.2 (d, J 21.2), 112.3 (d, J 21.2), 49.6, 38.7, 28.6 (2×).
1-(3,4-Dimethoxyphenyl)-5,6-dimethoxy-1,3,3-trimethylindan (4h).19 Colorless oil (134 mg, 75%); HRMS
1
(ESI-TOF) m/z: [M + H]+ calcd for C22H29O4 357.2066, found 357.2067; H NMR (400 MHz, CDCl3): δ 6.74-6.69
(m 4H), 6.60 (s, 1H), 3.92 (s, 3H), 3.84 (s, 3H), 3.83 (s, 3H), 3.78 (s, 3H), 2.34 (d, J 13.2, 1H), 2.17 (d, J 13.2, 1H),
1.66 (s, 3H), 1.32 (s, 3H), 1.05 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 148.7, 148.3, 148.2, 146.7, 143.9, 143.8,
140.1, 118.5, 110.38, 110.36, 107.4, 105.1, 59.7, 56.0, 55.9, 55.7 (2×), 50.3, 42.7, 30.8, 30.7, 30.4.
5-Benzo[1,3]dioxol-5-yl-5,7,7-trimethyl-6,7-dihydro-5H-indeno[5,6-d][1,3]dioxole (4i).20 Colorless oil (126
1
mg, 78%); HRMS (ESI-TOF) m/z: [M + H]+ calcd for C20H21O4 325.1440, found 325.1438; H NMR (400 MHz,
CDCl3): δ 6.71-6.62 (m, 4H), 6.53 (s, 1H), 5.96 (d, J 1.6, 1H), 5.95 (d, J 1.2, 1H), 5.91 (d, J 2.0, 1H), 5.91 (d, J 1.6,
1H), 2.34 (d, J 13.2, 1H), 2.16 (d, J 12.8, 1H), 1.61 (s, 3H), 1.29 (s, 3H), 1.05 (s, 3H); 13C NMR (100 MHz, CDCl3): δ
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147.4, 147.2, 146.7, 145.3, 145.2 (2×), 141.5, 119.4, 107.6, 107.4, 104.9, 102.8, 101.0, 100.8, 59.7, 50.3, 42.6,
30.93, 30.87, 30.4.
4,5,6-Trimethoxy-1,1,3-trimethyl-3-(3,4,5-trimethoxyphenyl)indan (4j).20 Colorless oil (166 mg, 80%);
1
HRMS (ESI-TOF) m/z: [M + H]+ calcd for C24H33O6 417.2277, found 417.2273; H NMR (400 MHz, CDCl3): δ 6.46
(s, 1H), 6.40 (s, 2H), 3.89 (s, 3H), 3.82 (s, 3H), 3.80 (s, 3H), 3.75 (s, 6H), 3.60 (s, 3H), 2.32 (d, J 13.2, 1H), 2.12 (d,
J 12.8, 1H), 1.76 (s, 3H), 1.30 (s, 3H), 1.07 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 153.8, 152.4 (2×), 150.2, 147.7,
146.9, 141.0, 135.7, 132.8, 103.9 (2×), 100.8, 60.8, 60.5, 60.1, 60.0, 56.0, 55.9 (2×), 51.0, 43.4, 31.0, 30.5, 29.1.
4,5',6,7'-Tetramethoxy-3,3,3',3'-tetramethyl-2,2',3,3'-tetrahydro-1,1'-spirobi[indene] (4k). Colorless solid
o
(150 mg, 76%); mp 154-155 C (from hexanes and EtOAc); HRMS (ESI-TOF) m/z: [M + H]+ calcd for C25H33O4
1
397.2379, found 397.2381; H NMR (400 MHz, CDCl3): δ 6.33 (d, J 2.0, 1H), 6.27 (d, J 2.0, 1H), 6.26 (d, J 2.0,
1H), 5.91 (d, J 2.0, 1H), 3.84 (s, 3H), 3.81 (s, 3H), 3.67 (s, 3H), 3.51 (s, 3H), 2.53 (d, J 12.8, 1H), 2.28 (d, J 13.2,
1H), 2.14 (d, J 13.2, 1H), 2.07 (d, J 12.8, 1H), 1.45 (s, 3H), 1.40 (s, 3H), 1.36 (s, 3H), 1.30 (s, 3H); 13C NMR (100
MHz, CDCl3): δ 160.9, 160.2, 156.9, 156.6, 155.2, 154.1, 130.0, 128.0, 98.9, 97.9, 97.6, 96.8, 60.5, 57.1, 56.7,
55.43, 55.37, 55.1, 54.9, 44.1, 43.5, 31.9, 30.0, 29.0, 28.9. Single-crystal X-Ray diagram: crystal of compound 4k
was grown by slow diffusion of EtOAc into a solution of compound 4k in CH2Cl2 to yield colorless prisms. The
compound crystallizes in the triclinic crystal system, space group P -1, a = 9.4024(3) Å, b = 15.5199(5) Å, c =
16.4035(6) Å, V = 2163.91(13) Å3, Z = 2, dcalcd = 1.217 g/cm3, F(000) = 856, 2θ range 1.328~26.411o, R indices
(all data) R1 = 0.0976, wR2 = 0.2137.
4,6,6-Trimethyl-4-thien-2-yl-5,6-dihydro-4H-cyclopenta[b]thiophene (4l). Colorless oil (81 mg, 65%); HRMS
1
(ESI-TOF) m/z: [M + H]+ calcd for C14H17S2 249.0772, found 249.0773; H NMR (400 MHz, CDCl3): δ 7.21 (d, J
4.8, 1H), 7.12 (dd, J 0.8, 4.8, 1H), 6.87 (dd, J 3.6, 4.8, 1H), 6.78 (d, J 4.8, 1H), 6.69 (dd, J 0.8, 3.6, 1H), 2.72 (d, J
12.8, 1H), 2.54 (d, J 13.2, 1H), 1.72 (s, 3H), 1.40 (s, 3H), 1.28 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 152.3, 149.6,
127.9, 126.4, 123.0, 122.5, 121.3, 121.2, 64.0, 46.8, 42.3, 31.8, 31.6, 31.3.
o
4-(1,3,3-Trimethyl-6-phenylindan-1-yl)biphenyl (4m).8 Colorless solid (134 mg, 69%); mp 102-103 C (from
1
hexanes and EtOAc); HRMS (ESI-TOF) m/z: [M + H]+ calcd for C30H29 389.2269, found 389.2271; H NMR (400
MHz, CDCl3): δ 7.66-7.32 (m, 17H), 2.54 (d, J 13.2, 1H), 2.32 (d, J 12.8, 1H), 1.82 (s, 3H), 1.44 (s, 3H), 1.16 (s, 3H)
13C NMR (100 MHz, CDCl3): δ 151.5, 150.0, 149.4, 141.6, 140.9, 140.0, 138.3, 128.7 (4x), 127.2 (2×), 127.1 (2×),
127.0 (2×), 126.9 (2×), 126.7 (2×), 126.5, 123.7, 122.9, 59.4, 50.7, 42.7, 30.9, 30.7, 30.5.
1,3,3-Trimethyl-1-naphthalen-2-yl-2,3-dihydro-1H-cyclopenta[a]naphthalene (4n).21 Colorless solid (118
mg, 70%); mp 117-118 oC (from hexanes and EtOAc); HRMS (ESI-TOF) m/z: [M + H]+ calcd for C26H25 337.1956,
found 337.1952; 1H NMR (400 MHz, CDCl3): δ 7.97-7.84 (m, 5H), 7.74 (d, J 8.8, 1H), 7.56-7.49 (m, 4H), 7.38 (dt,
J 1.2, 8.0, 1H), 7.33 (dd, J 2.0, 8.8, 1H), 7.19 (dt, J 1.2, 8.4, 1H), 2.58 (d, J 13.6, 1H), 2.46 (d, J 13.2, 1H), 2.19 (s,
3H), 1.56 (s, 3H), 1.51 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 149.4, 148.6, 142.7, 133.9, 133.3, 131.7, 129.8,
128.8, 128.7, 128.1, 128.0, 127.4, 126.3, 125.8, 125.6, 125.3, 125.0, 124.5, 123.5, 121.3, 61.4, 52.1, 43.3, 31.4,
31.3, 28.1.
o
4-Methyl-2,4-di(4-nitrophenyl)-1-pentene (4o-1). Colorless solid (104 mg, 64%); mp 124-125 C (from
1
hexanes and EtOAc); HRMS (ESI-TOF) m/z: [M + H]+ calcd for C18H19N2O4 327.1345 found 327.1345; H NMR
(400 MHz, CDCl3): δ 8.08-8.02 (m, 4H), 7.39 (d, J 8.8, 2H), 7.31 (d, J 8.8, 2H), 5.26 (d, J 1.2, 1H), 4.96 (d, J 0.8,
1H), 2.90 (s, 2H), 1.29 (s, 6H); 13C NMR (100 MHz, CDCl3): δ 156.0, 149.4, 146.8, 146.0, 144.3, 127.2 (2×), 127.0
(2×), 123.4 (2×), 123.1 (2×), 120.7, 49.4, 39.4, 28.7 (2×).
4-Methyl-2,4-di(3,4-dichlorophenyl)-1-pentene (4p-1).43 Colorless oil (121 mg, 65%); HRMS (ESI-TOF) m/z:
[M + H]+ calcd for C18H17Cl4 373.0084, found 373.0086; 1H NMR (400 MHz, CDCl3): δ 7.23 (d, J 8.4, 1H), 7.21 (d,
J 8.4, 1H), 7.18 (d, J 2.4, 1H), 7.09 (d, J 2.4, 1H), 7.01 (dd, J 2.6, 8.4, 1H), 6.92 (dd, J 2.0, 8.4, 1H), 5.15 (d, J 1.2,
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1H), 4.91 (d, J 1.2, 1H), 2.72 (s, 2H), 1.25 (s, 6H); 13C NMR (100 MHz, CDCl3): δ 148.5, 144.3, 142.6, 132.0,
131.8, 130.8, 129.7, 129.6, 129.5, 128.5, 128.3, 125.8, 125.6, 118.5, 49.9, 38.3, 28.5 (2×).
1-Methyl-1,3,3-triphenylindan (4q).18 Colorless oil (101 mg, 56%); HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C28H25 361.1956, found 361.1958; 1H NMR (400 MHz, CDCl3): δ 7.31-7.01 (m, 19H), 3.40 (d, J 13.6, 1H), 3.10 (d,
J 13.2, 1H), 1.55 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 150.5, 149.3, 148.8, 148.5, 147.5, 128.8 (2×), 128.7 (2×),
127.9 (2×), 127.8 (2×), 127.6 (2×), 127.4, 127.3, 126.9 (2×), 126.8, 126.0, 125.64, 125.57, 125.0, 61.3, 60.9,
51.2, 31.9.
Acknowledgements
The authors thank the Ministry of Science and Technology of the Republic of China for financial support (MOST
106-2628-M-037-001-MY3).
Supplementary Material
Scanned photocopies of NMR (CDCl3) spectral data were supported.
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