New synthesis of dibenzofulvenes by palladium-catalyzed double cross-coupling reactions

Article abstract of DOI:10.1071/CH12060

Palladium-catalyzed double cross-coupling reactions of 1,1-bis(pinacolato) borylalk-1-enes with 2,2′-dibromobiaryls and of 9-stannafluorenes with 1,1-dibromoalk-1-enes have been demonstrated to serve as new synthetic methods for dibenzofulvenes.

Full text of DOI:10.1071/CH12060

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2012, 65, 1277–1284
Full Paper
http://dx.doi.org/10.1071/CH12060
New Synthesis of Dibenzofulvenes by Palladium-Catalyzed
Double Cross-Coupling Reactions
A C
,
A
A
Masaki Shimizu,
Ikuhiro Nagao, Shin-ichi Kiyomoto,
A B
,
and Tamejiro Hiyama
A
Department of Materials Chemistry, Graduate School of Engineering,
Kyoto University Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
Current address: Research & Development Initiative, Chuo University,
1-13-27, Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.
B
C
Corresponding author. Email: m.shimizu@hs2.ecs.kyoto-u.ac.jp
Palladium-catalyzed double cross-coupling reactions of 1,1-bis(pinacolato)borylalk-1-enes with 2,20-dibromobiaryls and
of 9-stannafluorenes with 1,1-dibromoalk-1-enes have been demonstrated to serve as new synthetic methods for
dibenzofulvenes.
Manuscript received: 31 January 2012.
Manuscript accepted: 22 February 2012.
Published online: 13 April 2012.
Introduction
As shown in Scheme 1, the conventional methods of
synthesizing 9-(diorganomethylidene)fluorenes involve
There has been growing interest in cross-conjugated compounds
having a 9-(alkylidene)fluorene framework, as organic func-
tional materials.[1] For example, 9-[bis(4-propoxyphenyl)
methylidene]fluorene (1) shows crystallization-induced emis-
sion enhancement with high solid-state quantum yields
(Fig. 1).[1a–1c] Fused fulvalene 2 acts as an electron acceptor in a
solar cell device with good performances.[1d,1e] Indeno[1,2-b]
fluorene derivative 3 has been developed for use as an air-stable
n-type semiconducting material.[1f–1h] Dibenzofulvene 4 is dem-
onstrated to act as a molecular motor.[1i–1k] Hence, the develop-
ment of a new synthetic approach to the 9-(diorganomethylidene)
fluorene skeleton is important to expand the repertoire of
accessible dibenzofulvenes and thereby to contribute to the
advancement of optoelectronic organic materials.
4
aldehyde/ketone addition of fluorenylmetal reagents, followed
by dehydration[2] and Wittig-type olefination/Knoevenagel con-
densation of fluorenone (routes a and b).[3] These approaches
involve the formation of a carbon–carbon double bond (C1¼C2)
from the tricyclic starting materials. Recently, several types of
palladium-catalyzed syntheses of 4 from acyclic starting com-
pounds have been developed, as shown in routes c–e.[4–7] In
these methods, the molecular skeleton of the fluorene moiety is
constructed by the formation of a bond between benzylic and
aromatic carbons (C2–C6) or the concomitant formation of a
biaryl bond (C4–C5) and a C2–C6 bond. These methods involve
the use of non-tricyclic substrates and afford numerous structur-
ally diverse fluorene moieties and hence are more attractive than
the conventional syntheses. Recently, we demonstrated that
palladium-catalyzed double cross-coupling reactions of orga-
nodiboron compounds and 9-stannafluorenes with organic
dihalides is a versatile method for the synthesis of polycyclic
aromatic hydrocarbons such as fused fluorenes, phenanthrenes,
triphenylenes, and dibenzo[g,p]chrysenes.[8] We then planned
double cross-coupling reactions of 1,1-diborylalk-1-enes 5[9]
with 2,20-dibromobiaryls 6 (route f ) and that of 9-stannafluorene
7 with 1,1-dibromoalk-1-enes 8 (route g), with the aim of
developing a new synthetic route to 4 and increasing the
synthetic utility of the double cross-coupling strategy of dime-
tallic reagents and their equivalents. The proposed reactions
involve the construction of a five-membered ring through
simultaneous C2–C3 and C2–C6 bond formation. We report the
palladium-catalyzed [4 þ 1] type annulations.[10]
PrO
OPr
MeO
OMe
1
2
NC
CN
R
S
S
R
Results and Discussion
NC
CN
3
4
At the outset, we screened the conditions for the double cross-
coupling reaction of 1,1-diborylalk-1-enes with 2,20-dihalobiaryls
Fig. 1. Functional materials containing dibenzofulvene moiety.
Journal compilation Ó CSIRO 2012
www.publish.csiro.au/journals/ajc

1278
M. Shimizu et al.
R1
(b)
(c)
(d)
(e)
ϩ
O
R1
ϩ
Ar
Br
ϩ
C2ϪC6
R2ϪC1
I
Pd cat.
formation
(R2 ϭ Ar)
R1
R2
(a)
C1
C2
M
OMe
(1) R1R2CϭO
(2) dehydration
N
Pd cat.
C3
C4
C6
C5
ϩ
C1ϭC2
formation
C2–C6, C4–C5
R1–C1, R2–C1
formation
4
Ar
I
(R1 ϭ R2 ϭ Ar)
(g): This work
(f): This work
Me2
Sn
R1
R2
Br Br
R1
Br
R2
Br
Pd cat.
Pd cat.
ϩ
C2–C3
C2–C6
formation
C2–C3
C2–C6
formation
B
B
7
8
5
6
B ϭ pinacolatoboryl
Scheme 1.
using 2,2-diphenyl-1,1-bis(pinacolatoboryl)ethene (5a) and
2,20-dibromo- and 2,20-diiodobiaryls (6a and 6a9). The results
are summarized in Table 1. The reaction of 5a (1.0 equiv.) with
6a (1.3 equiv.) in dimethoxyethane (DME) at 808C in the pres-
ence of PdCl2(dppf ) catalyst and 3 M aq. KOH afforded the
expected product 4a in only 13 % gas chromatographic (GC)
yield (entry 1). The use of other bases such as K2CO3, K3PO4,
and Cs2CO3 instead of KOH did not affect the yield of 4a
(entries 2–4). When diiodide 6a9 is used in place of 6a, the yields
of 4a were lower than those obtained using 6a (entries 5–7). In
all cases, the major product was 1,1-diphenylethene, suggesting
that protodeborylation of 5a was much faster than transmeta-
lation to a palladium complex generated from PdCl2(dppf ) in
the presence of 6a or 6a9. We then examined a palladium cat-
alyst using 6a as the dihalide and K3PO4 as the base. As shown in
entries 9 and 10, the yield of 4a largely increased when using
Pd(OAc)2/2-dicyclohexylphosphino-20,60-dimethoxybiphenyl
and Pd(PtBu3)2, although 1,1-diphenylethene was still observed
to be the major by-product. Finally, the best result (77 % GC
yield; 74 % isolated yield) was obtained when the 5a/6a molar
ratio was reversed to 1.3/1.0 and highly concentrated aq. K3PO4
(6 M) was used as the base (entry 11).
Table 1. Screening of reaction conditionsA
Pd cat.
base
X X
ϩ
DME
B
B
80ЊC
6a (X ϭ Br)
6a؅ (X ϭ I)
4a
5a
B ϭ pinacolatoboryl
Entry
6
Catalyst
Base
Yield [%]B
1
6a
6a
6a
6a
6a9
6a9
6a9
6a
6a
6a
6a
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
Pd(PPh3)4
3 M aq. KOH
13
11
13
13
6
2
3 M aq. K2CO3
3 M aq. K3PO4
3 M aq. Cs2CO3
3 M aq. KOH
3
4
5
6
3 M aq. K3PO4
3 M aq. Cs2CO3
3 M aq. K3PO4
3 M aq. K3PO4
3 M aq. K3PO4
6 M aq. K3PO4
5
7
9
8
11
64
67
77 (74)
9C
10
11D
Pd(OAc)2/L
Pd(PtBu3)2
Pd(PtBu3)2
The scope of the annulation of 5 and 6 is shown in Table 2.
Annulation of 5a with substituted dibromobiphenyls 6b and 6c
proceeded under the optimized conditions to give 4b and 4c,
respectively, in moderate yields. Dibromobithiophene 6d and
dibromobinaphthyl 6e could also be used for the annulation,
although the isolated yields of the corresponding products, 4e
and 4d, respectively, were low.[11] Substituted diboryldipheny-
lethenes 5b and 5c reacted with 6a and 6b to give 4f–4i in
A5a (1.0 equiv.), 6 (1.3 equiv.), Pd catalyst (10 mol %), base (6 equiv.),
1,2-dimethoxyethane (DME), 808C.
BGas chromatographic yield. The value in parentheses is isolated yield.
CL: 2-dicyclohexylphosphino-20,60-dimethoxybiphenyl.
D5a (1.3 equiv.), 6 (1.0 equiv.), Pd catalyst (10 mol %), base (6 equiv.),
DME, 808C.

New Synthesis of Dibenzofulvenes
1279
Table 2. Palladium-catalyzed double cross-coupling reaction of 5 with 6A
Entry
1
5
6
4
Yield [%]B
50
5a
5a
6b (R ¼ Me)
4b
4c
2C
6c (R ¼ OMe)
58
3C
5a
6d
4d
37
4
5
5a
6e
4e
4f
30
42
5b (R ¼ Me)
6a (R0 ¼ H)
6C
7
5b (R ¼ Me)
5c (R ¼ F)
6b (R0 ¼ Me)
6a (R0 ¼ H)
4g
4h
48
36
Ј
Ј
Ј
Ј
Ј
Ј
8C
5c (R ¼ F)
6b (R0 ¼ Me)
4i
42
Ј
Ј
9D
5d
6a
4j
57
A5 (1.3 equiv.), 6 (1.0 equiv.), Pd(PtBu3)2 (10 mol %), 6 M aq. K3PO4 (6 equiv.), 1,2-dimethoxyethane (DME), 808C, 6 h.
BIsolated yields.
C5 (1.5 equiv.), 6 (1.0 equiv.), Pd(PtBu3)2 (20 mol %), 6 M aq. K3PO4 (6 equiv.), DME, 808C, 6 h.
D5 (1.5 equiv.), 6 (1.0 equiv.), Pd(PtBu3)2 (20 mol %), 6 M aq. KOH (6 equiv.), DME, 808C, 6 h.
36–48 % yields. In addition, methyl- and phenyl-substituted
1,1-diborylethene 5d underwent annulation to afford 4j in
acceptable yield. The low-to-moderate isolated yields of 4 were
ascribed to the competing protodeborylation of 5 under the
reaction conditions adopted.
We then focussed on the double cross-coupling reaction of
9-stannafluorene 7 with 1,1-dibromoalk-1-enes 8; this reaction
can be regarded as an umpolung variant of the annulation using 5
and 6. The representative results for the screening of the reaction
conditions using 7 and 8a/8b are summarized in Table 3. Under
the optimized conditions (Pd(PtBu3)2, THF, 608C) for the
annulation between 7 and 1,2-dibromoarenes,[8d] the reaction
of 7 with 8a did not proceed at all, and 7 and 8a were
quantitatively recovered (entry 1). However, when CsF
(5 equiv.) was added under the same conditions, the desired
product (4a) was formed in a moderate yield (entry 2). The yield
of 4a largely increased upon heating the reaction mixture to
1308C in 1,4-dioxane (entry 3). When using the less hindered 8b,
annulation proceeded smoothly even at 608C in the presence of
CsF to give 4k in good to high yields (entry 4). As shown in
entry 5, the reaction carried out at 1308C resulted in a slightly
lower yield (75 %).
The scope of application of 8 to the double cross-coupling
reaction of 7 is summarized in Table 4. Dibromostyrene deri-
vatives 8c–8h underwent the annulation smoothly at 608C to
give 4c–4h in good-to-excellent yields (entries 1–6). Thus,
functional groups such as MeO, CF3, CO2Me, CN, Cl, and
F groups/atoms were tolerated under the reaction conditions.
The coupling of (dibromoethenyl)thiophene 8i gave 4r in 96 %
yield (entry 7). Ethyl- and phenyl-substituted dibenzofulvene 4s
was produced in a moderate yield from 8j (entry 8). The
annulation of 2,2-diaryl-1,1-dibromoethenes 8k–8m proceeded

1280
M. Shimizu et al.
Table 3. Screening of reaction conditionsA
(GC-MS) analyses were performed with a JEOL JMS-700
spectrometer by electron ionization (EI) at 70 eV. Elemental
analyses were carried out with a YANAKO MT2 CHN
CORDER machine at Elemental Analysis Center of Kyoto
University. TLC analyses were performed by means of Merck
Kieselgel 60 F254 and column chromatography was carried out
using Merck Kieselgel 60 (230–400 mesh). Preparative HPLC
was carried out with a Japan Analytical Industry Co., Ltd,
LC-908 chromatograph using a JAIGEL-1H and -2H GPC
columns. Tetrahydrofuran was passed through two packed
columns of neutral alumina and copper oxide under a nitrogen
atmosphere before use. All reactions were carried out under an
argon atmosphere.
Me2
Sn
R
Pd(PtBu3)2
R
CsF
Solvent
Temp.
ϩ
Br
Br
7
8a (R ϭ Ph)
8b (R ϭ H)
4
Entry
8
Solvent/temp [8C]
Time [h]
4
Yield [%]B
1C
2
8a
8a
8a
8b
8b
THF/60
48
48
12
24
24
4a
4a
4a
4k
4k
0
THF/60
62
Typical Procedure for Preparation of 1,1-Dibromoalkenes
3
4D
Dioxane/130
Dioxane/60
Dioxane/130
86 (90)
88 (80)
75
To a toluene (100 mL) solution of CBr4 (19.8 g, 60 mmol) and
benzophenone (5.46 g, 30 mmol) was added PPh3 (31.8 g,
120 mmol), and then the resulting mixture was stirred at 1208C
for 100 h. The reaction mixture was filtered though a silica gel
column and concentrated under vacuum. The residue was
purified by silica gel column chromatography (hexane) to give
1,1-dibromo-2,2-diphenylethene as a colourless solid (7.7 g,
76 % yield).
5
A7 (0.05 mmol), 8 (0.05 mmol), Pd(PtBu3)2 (2.5 mmol), CsF (5 equiv.),
solvent (1 mL).
BYield was estimated by 1H NMR spectroscopy using 1,3,5-(MeO)3-C6H3 as
an internal standard. The values in parentheses are isolated yields.
C7 (0.05 mmol), 8a (0.05 mmol), Pd(PtBu3)2 (2.5 mmol), THF (1 mL).
D7 (0.50 mmol), 8b (0.50 mmol), Pd(PtBu3)2 (25 mmol), CsF (2.5 mmol),
1,4-dioxane (10 mL).
1,1-Dibromo-2,2-bis(4-methylphenyl)ethene
Yield: 60 %. Colourless solid. Mp 120.3–121.08C. Rf 0.50
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 2.34 (s, 6H), 7.13
(d, J 8.4, 4H), 7.18 (d, J 8.4, 4H); dC (100 MHz, CDCl3) 21.4,
89.2, 128.6, 128.8, 137.7, 138.5, 147.5. nmax (KBr)/cmꢀ1 2916,
1506, 1445, 1182, 1113, 1022, 955, 833, 814, 754, 739, 577, 534,
486. m/z (FAB) 368 (8 %, [M þ 4]þ), 367 (4, [M þ 3]þ), 366
(16, [M þ 2]þ), 368 (3, [M þ 1]þ) 364 (8, Mþ), 206 (11).
(Found: C 52.58, H 3.96. Anal. Calc. for C16H14Br2: C 52.49,
H 3.85 %.)
upon heating the reaction mixture at 1308C, to afford 4f, 4t, and
4u, respectively, in good yields (entries 9–11). Bifluorenylidene
4v was obtained in an excellent yield from the reaction of 7 with
(dibromomethylene)fluorene 8n (entry 12). Double annulation
of 7 with tetrabromides 8o and 8p was also feasible, and 4w and
4x were obtained in high-to-excellent yields (entries 13 and 14).
Thus, palladium-catalyzed annulation of 9-stannafluorenes with
1,1-dibromoalk-1-enes is a powerful tool for the synthesis of
dibenzofulvenes.
1,1-Dibromo-2,2-bis(4-fluorophenyl)ethene
Conclusion
Yield: 61 %. Colourless solid. Mp 60.3–60.58C. Rf 0.50
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 7.03 (t, J 8.8,
4H), 7.22ꢀ7.29 (m, 4H); dC (100 MHz, CDCl3) 90.8, 115.4
(d, J 22.1), 130.6 (d, J 8.4), 136.9 (d, J 3.0), 145.6, 162.0 (d, J
247.1); dF (282 MHz, CDCl3) ꢀ113.3. nmax (KBr)/cmꢀ1 3043,
1896, 1599, 1501, 1402, 1292, 1217, 1153, 1096, 1017, 955,
833, 750. m/z (FAB) 376 (19 %, [M þ 4]þ), 375 (8, [M þ 3]þ),
374 (38, [M þ 2]þ), 373 (4, [M þ 1]þ), 372 (21, Mþ), 214 (52).
(Found: C 45.06, H 2.36. Anal. Calc. for C14H8Br2F2: C 44.96,
H 2.16 %.)
We have presented palladium-catalyzed double cross-coupling
reactions of 1,1-diborylalk-1-enes with 2,20-dibromobiaryls and
9-stannafluorenes with 1,1-dibromoalk-1-enes as new strategies
for the synthesis of dibenzofulvenes. While the product yields in
the boron-based annulation are largely moderate because of the
competing protodeborylation of diboryl reagents used, the
proposed stannafluorene-based strategy is highly effective for
dibenzofulvene synthesis.
Experimental
1,1-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
2,2-bis(4-methylphenyl)ethene (5b)
Melting points were determined using a Yanagimoto Micro
1
Point Apparatus. H NMR spectra were measured on Varian
Mercury 300 (300 MHz) and 400 (400 MHz) spectrometers. The
Prepared according to the reported procedure.[9] Yield: 34 %.
Colourless solid. Mp 160.0–160.78C. Rf 0.68 (hexane/EtOAc
2 : 1). dH (400 MHz, CDCl3) 1.16 (s, 24H), 2.33 (s, 6H), 7.04
(d, J 7.6, 4H), 7.12 (d, J 7.6, 4H); dC (100 MHz, CDCl3) 21.4, 24.7,
83.1, 128.1, 129.4, 137.3, 141.7, 164.5. nmax (KBr)/cmꢀ1 2980,
1593, 1506, 1465, 1344, 1298, 1269, 1144, 1026, 966, 853, 824.
m/z (FAB) 462 (1 %, [M þ 2]þ), 461 (5, [M þ 1]þ), 460 (8, Mþ),
459 (3, [M ꢀ 1]þ), 458 (1, [M ꢀ 2]þ). (Found: C 73.14, H 8.17.
Anal. Calc. for C28H38B2O4: C 73.07, H 8.32 %.)
1
chemical shifts of H NMR are expressed in parts per million
downfield relative to the internal tetramethylsilane (d 0) or
chloroform (d 7.26). Splitting patterns are indicated as s, singlet;
d, doublet; t, triplet; q, quartet; m, multiplet. 13C NMR spectra
were measured on Varian Mercury 300 (75 MHz) and 400
(100 MHz) spectrometers with tetramethylsilane as an internal
standard (d 0) or chloroform (d 77.0). 19F NMR spectra were
measured on a Varian Mercury 300 (282 MHz) spectrometer
with CFCl3 as an internal standard (d 0). Chemical shift values
are given in parts per million downfield relative to the internal
standard. Infrared spectra were recorded on a Shimadzu FTIR-
8400 spectrometer. Gas chromatography–mass spectrometry
1,1-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
2,2-bis(4-fluorophenyl)ethene (5c)
Prepared according to the reported procedure.[9] Yield: 43 %.
Colourless solid. Mp 158.5–159.48C. Rf 0.65 (hexane/EtOAc

New Synthesis of Dibenzofulvenes
1281
Table 4. Palladium-catalyzed double cross-coupling reaction of 7 with 8A
Entry
8
4
Yield [%]B
1
2
8c (R1 ¼ OMe)
8d (R1 ¼ CF3)
4l (R1 ¼ OMe)
4m (R1 ¼ CF3)
75
81
3
4
5
8e (R1 ¼ CO2Me)
8f (R1 ¼ CN)
4n (R1 ¼ CO2Me)
4o (R1 ¼ CN)
4p (R1 ¼ Cl)
87
96
58
8 g (R1 ¼ Cl)
6
8h
4q
73
7
8
8i
8j
4r
4s
96
55
9C
8k (R1 ¼ R2 ¼ Me)
8l (R1 ¼ R2 ¼ F)
8m (R1 ¼ Ph, R2 ¼ H)
4f (R1 ¼ R2 ¼ Me)
4t (R1 ¼ R2 ¼ F)
4u (R1 ¼ Ph, R2 ¼ H)
69
62
72
10C
11C
12
8n
4v
98
13D
8o
4w
96
14D
8p
4x
87
A7 (0.50 mmol), 8 (0.50 mmol), Pd(PtBu3)2 (25 mmol), CsF (2.5 mmol), 1,4-dioxan, 608C, 12 h.
BIsolated yields.
C7 (1.0 mmol), 8 (1.0 mmol), Pd(PtBu3)2 (50 mmol), CsF (5 mmol), 1,4-dioxan, 1308C, 12 h.
D7 (1.5 mmol), 8 (0.50 mmol), Pd(PtBu3)2 (50 mmol), CsF (50 mmol), 1,4-dioxan, 608C, 12 h.

1282
M. Shimizu et al.
2 : 1). dH (400 MHz, CDCl3) 1.16 (s, 24H), 6.94 (t, J 8.8, 4H),
7.16–7.23 (m, 4H); dC (100 MHz, CDCl3) 24.6, 83.3, 114.4 (d, J
21.3), 131.0 (d, J 9.6), 140.3 (d, J 3.0), 162.1, 162.4 (d, J 245.5);
dF (282 MHz, CDCl3) ꢀ114.8. nmax (KBr)/cmꢀ1 2982, 1599,
1503, 1381, 1350, 1296, 1217, 1144, 856. m/z (FAB) 470 (8 %,
[Mþ 2]þ), 469 (39, [M þ 1]þ), 468 (48, Mþ), 467(21, [M ꢀ 1]þ),
466 (4, [Mꢀ 2]þ). (Found: C 66.70, H 6.80. Anal. Calc. for
C26H32B2F2O4: C 66.70, H 6.89 %.)
(s, 6H), 6.31 (s, 2H), 7.37–7.45 (m, 12H); dC (100 MHz, CDCl3)
20.2, 20.4, 119.9, 126.0, 127.7, 128.5, 129.6, 133.8, 134.3,
136.0, 136.7, 138.7, 142.7, 143.1. nmax (KBr)/cmꢀ1 3076,
1622, 1597, 1489, 1443, 1281, 982, 864, 770, 756, 698, 658.
m/z (EI) 388 (6 %, [M þ 2]þ), 387 (34, [M þ 1]þ), 386
(100, Mþ), 149 (51). m/z (HRMS) Found: 386.2019. Calc. for
C30H26 (Mþ): 386.2035.
9-(Diphenylmethylene)-2,3,6,7-
1,1-Dibromo-2,2-bis(4-methylphenyl)ethene (8k)
tetramethoxy-9H-fluorene (4c)
Yield: 60 %. Colourless solid. Mp 120.3–121.08C. Rf 0.50
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 2.34 (s, 6H), 7.13
(d, J 8.4, 4H), 7.18 (d, J 8.4, 4H); dC (100 MHz, CDCl3) 21.4,
89.2, 128.6, 128.8, 137.7, 138.5, 147.5. nmax (KBr)/cmꢀ1 2916,
1506, 1445, 1182, 1113, 1022, 955, 833, 814, 754, 739, 577, 534,
486. m/z (FAB) 368 (8 %, [M þ 4]þ), 367 (4, [M þ 3]þ), 366 (16,
[M þ 2]þ), 368 (3, [M þ 1]þ) 364 (8, Mþ), 206 (11). (Found:
C 52.58, H 3.96. Anal. Calc. for C16H14Br2: C 52.49, H 3.85 %.)
Yield: 58 %. Yellow solid. Mp 239.6–240.08C. Rf 0.20
(hexane/EtOAc 2 : 1). dH (400 MHz, CDCl3) 3.39 (s, 6H), 3.97
(s, 6H), 6.15 (s, 2H), 7.03 (s, 2H), 7.36–7.48 (m, 10H); dC
(100 MHz, CDCl3) 55.3, 56.1, 101.3, 108.5, 127.8, 128.7, 129.6,
131.1, 134.0, 134.0, 141.5, 142.5, 146.7, 149.1. nmax (KBr)/cmꢀ1
2936, 1601, 1494, 1468, 1439, 1268, 1258, 1217, 1165, 1155,
1080, 866, 833, 756, 704, 561. m/z (EI) 452 (10 , [M þ 2]þ), 451
(47, [M þ 1]þ), 450 (100, Mþ). (Found: C 80.00, H 5.81. Anal.
Calc. for C30H26O4: C 79.98, H 5.82 %.)
4,40-(2,2-Dibromoethene-1,1-diyl)
bis(fluorobenzene) (8l)
7-(Diphenylmethylene)-7H-cyclopenta
[1,2-b:4,3-b0]dithiophene (4d)
Yield: 61 %. Colourless solid. Mp 60.3–60.58C. Rf 0.50
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 7.03 (t, J 8.8,
4H), 7.22–7.29 (m, 4H); dC (100 MHz, CDCl3) 90.8, 115.4 (d,
J 22.1), 130.6 (d, J 8.4), 136.9 (d, J 3.0), 145.6, 162.0 (d,
J 247.1); dF (282 MHz, CDCl3) ꢀ113.3. nmax (KBr)/cmꢀ1 3043,
1896, 1599, 1501, 1402, 1292, 1217, 1153, 1096, 1017, 955,
833, 750. m/z (FAB) 376 (19 %, [M þ 4]þ), 375 (8, [M þ 3]þ),
374 (38, [M þ 2]þ), 373 (4, [M þ 1]þ), 372 (21, Mþ), 214 (52).
(Found: C 45.06, H 2.36. Anal. Calc. for C14H8Br2F2: C 44.96,
H 2.16 %.)
Yield: 37 %. Yellow solid. Mp 194.5–195.08C. Rf 0.40
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 6.98 (d, J 4.8,
2H), 7.06 (d, J 4.8, 2H), 7.39–7.51 (m, 10H); dC (100 MHz,
CDCl3) 117.9, 127.9, 128.6, 128.9, 129.3, 129.6, 138.8, 140.5,
142.0, 143.7. nmax (KBr)/cmꢀ1 2918, 1616, 1505, 1442, 878,
853, 772, 754, 727, 700, 685. m/z (EI) 344 (14 %, [M þ 2]þ), 343
(31, [M þ 1]þ), 342 (100, Mþ), 279 (15). m/z (HRMS) Found:
342.0535. Calc. for C22H14S2 (Mþ): 342.0537.
7-(Diphenylmethylene)-7H-dibenzo[c,g]fluorene (4e)
4-(2,2-Dibromo-1-phenylethenyl)-1,10-biphenyl (8m)
Yield: 30 %. Orange solid. Mp 244.9–245.68C. Rf 0.38
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 6.87 (d, J 8.8,
2H), 7.43–7.53 (m, 16H), 7.82 (d, J 8.0, 2H), 8.55 (d, J 8.0, 2H);
dC (100 MHz, CDCl3) 122.3, 124.6, 125.2, 126.3, 127.1, 128.1,
128.2, 128.5, 128.7, 130.9, 134.0, 135.8, 138.1, 138.4, 142.8,
148.2. nmax (KBr)/cmꢀ1 3045, 1593, 1510, 1443, 820, 781, 696.
m/z (EI) 432 (9 %, [M þ 2]þ), 431 (40, [M þ 1]þ), 430 (100,
Mþ). m/z (HRMS) Found: 430.1718. Calc. for C34H22 (Mþ):
430.1722.
Yield: 43 %. Colourless solid. Rf 0.20 (hexane/EtOAc/
CH2Cl2 50 : 1 : 1). dH (400 MHz, CDCl3) 7.32–7.46 (m, 10H),
7.55–7.60 (m, 4H); dC (100 MHz, CDCl3) 90.2, 126.8, 126.9,
127.4, 127.9, 128.3, 128.66, 128.68, 129.1, 140.0, 140.2, 140.6,
141.3, 147.3. nmax (KBr)/cmꢀ1 1485, 1441, 1400, 1074, 1030,
941, 841, 799, 787, 758, 729, 689, 615, 600. m/z (EI) 418 (1 %,
[M þ 6]þ), 417 (12, [M þ 5]þ), 416 (57, [M þ 4]þ), 415 (24,
[M þ 3]þ), 414 (100, [M þ 2]þ), 413 (12, [M þ 1]þ), 412 (57,
Mþ). m/z (HRMS) Found: 411.9482. Calc. for C20H14Br2 (Mþ):
411.9462.
9-[Bis(4-methylphenyl)methylene]-9H-fluorene (4f)
Yield: 42 %. Pale yellow solid. Mp 145.0–145.58C. Rf 0.43
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 2.45 (s, 6H), 6.76
(d, J 7.6, 2H), 6.96 (d, J 7.6, 2H), 7.20–7.30 (m, 10H), 7.72 (d,
J 7.6, 2H); dC (100 MHz, CDCl3) 21.6, 119.0, 124.6, 126.1,
127.2, 129.3, 129.7, 133.5, 138.0, 138.8, 140.1, 140.1, 145.8.
nmax (KBr)/cmꢀ1 3020, 1605, 1506, 1445, 814, 783, 733, 586.
m/z (EI) 360 (5 %, [M þ 2]þ), 359 (31, [M þ 1]þ), 358 (100,
Mþ), 343 (16). (Found: C 94.07, H 6.28. Anal. Calc. for C28H22:
C 93.81, H 6.19 %.)
Representative Procedure for Pd-Catalyzed Double
Cross-Coupling Reaction of Diborylalkenes 5
and Dibromides 6
To a solution of 5 (56 mg, 0.13 mmol), 6 (31 mg, 0.10 mmol),
and Pd(PtBu3)2 (5.1 mg, 10 mmol) in DME (2 mL) was added
6 M aq. K3PO4 (0.1 mL). The solution was stirred at 808C for 6 h.
The resulting mixture was quenched with sat. aq. NH4Cl (1 mL)
and was diluted with Et2O (3 mL). The organic layer was dried
over anhydrous magnesium sulfate and concentrated under
vacuum. The crude product was purified by preparative TLC
(hexane/EtOAc 10 : 1) and then GPC (CHCl3) to give 4a as a
colourless solid (24 mg, 74 % yield).
9-[Bis(4-methylphenyl)methylene]-2,3,6,7-
tetramethyl-9H-fluorene (4g)
Yield: 48 %. Yellow solid. Mp 109.5–110.08C. Rf 0.55
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 2.01 (s, 6H), 2.28
(s, 6H), 2.43 (s, 6H), 6.42 (s, 2H), 7.19 (d, J 8.0, 4H), 7.24 (d, J
8.0, 4H), 7.40 (s, 2H); dC (100 MHz, CDCl3) 20.2, 20.5, 21.5,
119.8, 125.9, 129.1, 129.8, 130.6, 133.7, 135.7, 136.9, 137.5,
138.5, 140.4, 143.2. nmax (KBr)/cmꢀ1 2916, 1510, 1452, 1325,
9-(Diphenylmethylene)-2,3,6,7-
tetramethyl-9H-fluorene (4b)
Yield: 50 %. Yellow solid. Mp 225.2–225.68C. Rf 0.48
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 2.00 (s, 6H), 2.28

New Synthesis of Dibenzofulvenes
1283
1233, 899, 880, 804, 764, 714, 598. m/z (EI) 416 (20 %,
[M þ 1]þ), 415 (55, [M þ 1]þ), 414 (100, Mþ), 384 (12).
(Found: C 92.47, H 7.56. Anal. Calc. for C32H30: C 92.71,
H 7.29 %.)
(d, J 6.8, 1H); dC (100 MHz, CDCl3) 119.7, 119.9, 120.4, 124.3,
125.0, 125.5 (JC–F 3.9), 126.8, 127.1, 128.7, 129.1, 129.6, 136.1,
137.9, 139.1, 139.4, 140.7, 141.5, 129.5 (JC–F 50), 130.8 (JC–F
160); dF (282 MHz, CDCl3) ꢀ63.10 (s). nmax (KBr)/cmꢀ1 1613,
1449, 1437, 1408, 1325, 1161, 1124, 1105, 1064, 1017, 858,
829, 777, 733. m/z (EI) 324 (7 %, [M þ 2]þ), 323 (25, [M þ 1]þ),
322 (100, Mþ). m/z (HRMS) Found: 322.0962. Calc. for
C21H13F3 (Mþ): 322.0969.
9-[Bis(4-fluorophenyl)methylene]-9H-fluorene (4h)
Yield: 36 %. Pale yellow solid. Mp 194.5–195.08C. Rf 0.44
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 6.68 (d, J 8.0, 2H),
6.98 (t, J 7.6, 2H), 7.13 (t, J 7.6, 4H), 7.27 (t, J 7.6, 2H), 7.34
(t, J 6.4, 4H), 7.71 (d, J 7.6, 2H); dC (100 MHz, CDCl3) 115.8
(d, J 21.4), 119.3, 124.5, 126.4, 127.8, 131.7 (d, J 7.6), 134.7,
138.3, 138.5 (d, J 3.0), 140.4, 142.7, 162.6 (d, J 246.3);
dF (282 MHz, CDCl3) ꢀ113.3. nmax (KBr)/cmꢀ1 2916, 1890,
1601, 1505, 1445, 1236, 1155, 874, 831, 787, 739, 584, 527.
m/z (EI) 368 (7 %, [M þ 2]þ), 367 (43, [M þ 1]þ), 366 (100,
Mþ), 270 (36). (Found: C 85.17, H 4.55. Anal. Calc. for
C26H16F2: C 85.23, H 4.40 %.)
Methyl 4-[(9H-Fluoren-9-ylidene)methyl]benzoate (4n)
Yield: 87 %. Colourless solid. Mp 116.2–117.08C. Rf 0.30
(hexane/EtOAc 10 : 1). dH (400 MHz, CDCl3) 7.06 (dd, J 7.2,
7.2, 1H), 7.31–7.42 (m, 3H), 7.50 (d, J 8.0, 1H), 7.64 (s, 1H),
7.66 (d, J 8.0, 2H), 7.71 (d, J 8.0, 2H), 7.77 (d, J 7.2, 1H),
8.13–8.15 (m, 2H), 3.98 (s, 3H), dC (100 MHz, CDCl3) 52.2,
119.6, 119.8, 120.3, 124.4, 125.6, 126.7, 127.0, 128.6, 128.9,
129.3, 129.4, 129.7, 136.1, 137.6, 139.1, 139.3, 141.1, 141.7,
166.8. nmax (KBr)/cmꢀ1 1703, 1603, 1450, 1437, 1283, 1113,
1103, 772, 727. m/z (EI) 314 (9 %, [M þ 2]þ), 313 (35, [Mþ 1]þ),
312 (100, Mþ). m/z (HRMS) Found: 312.1153. Calc. for
C22H16O2 (Mþ): 312.1150.
9-[Bis(4-fluorophenyl)methylene]-2,3,6,7-
tetramethyl-9H-fluorene (4i)
Yield: 42 %. Pale yellow solid. Mp 211.0–211.38C. Rf 0.50
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 2.03 (s, 6H), 2.29
(s, 6H), 6.37 (s, 2H), 7.29–7.35 (m, 4H), 7.11 (t, J 8.4, 4H), 7.41
(s, 2H); dC (100 MHz, CDCl3) 20.3, 20.5, 115.6 (d, J 21.4),
120.0, 125.7, 131.7 (d, J 7.6), 134.0, 135.0, 136.4, 136.4, 138.8,
138.9 (d, J 3.0), 140.0, 162.5 (d, J 246.3); dF (282 MHz, CDCl3)
ꢀ114.0. nmax (KBr)/cmꢀ1 2920, 1597, 1503, 1452, 1215, 1157,
1091, 876, 835, 592. m/z (EI) 424 (13 %, [M þ 2]þ), 423 (76,
[M þ 1]þ), 422 (100, Mþ), 392 (23). (Found: C 85.00, H 5.96.
Anal. Calc. for C30H24F2: C 85.28, H 5.73 %.)
4-[(9H-Fluoren-9-ylidene)methyl]benzonitrile (4o)
Yield: 96 %. Colourless solid. Mp 140.6–141.48C. Rf 0.22
(hexane/EtOAc 50 : 1). dH (400 MHz, CDCl3) 7.07 (dd, J 7.6,
7.6, 1H), 7.32–7.43 (m, 4H), 7.57 (s, 1H), 7.67–7.77 (m, 6H);
dC (100 MHz, CDCl3) 11.4, 118.8, 119.7, 120.0, 120.5, 124.2,
124.3, 126.9, 127.2, 128.9, 129.3, 130.0, 132.3, 135.8, 138.5,
138.9, 139.4, 141.6, 141.9. nmax (KBr)/cmꢀ1 1602, 1501, 1449,
1437, 866, 831, 777, 731, 565. m/z (EI) 281 (6 %, [M þ 2]þ), 280
(25, [M þ 1]þ), 279 (100, Mþ). m/z (HRMS) Found: 278.0967.
Calc. for C21H13N (Mþ): 279.1048.
9-(1-Phenylethylidene)-9H-fluorene (4j)
Yield: 57 %. Colourless solid. Mp 111.1–111.88C. Rf 0.43
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 2.78 (s, 3H), 6.26
(d, J 8.0, 1H), 6.86 (t, J 7.6, 1H), 7.18 (t, J 7.6, 1H), 7.32–7.52
(m, 7H), 7.69 (d, J 8.0, 1H), 7.78–7.82 (m, 1H), 7.98–8.02
(m, 1H); dC (100 MHz, CDCl3) 26.0, 118.9, 119.4, 124.5, 125.2,
126.3, 126.7, 126.7, 127.1, 127.5, 127.5, 128.9, 132.9, 138.4,
138.8, 139.4, 140.3, 142.7, 145.3. nmax (KBr)/cmꢀ1 3030, 1616,
1593, 1489, 1447, 1341, 1265, 1182, 1072, 1024, 781, 764, 733,
702. m/z (EI) 270 (5 %, [M þ 2]þ), 269 (25, [M þ 1]þ), 268 (100,
Mþ), 253 (86). m/z (HRMS) Found: 268.1254. Calc. for C21H16
(Mþ): 268.1252.
9-(4-Chlorobenzylidene)-9H-fluorene (4p)
Yield: 58 %. Colourless solid. Mp 143.6–144.48C. Rf 0.34
(hexane). dH (400 MHz, CDCl3) 7.08 (t, J 7.6, 1H), 7.33 (t, J 8.0,
2H), 7.39 (t, J 7.6, 1H), 7.43 (d, J 8.4, 2H); dC (100 MHz, CDCl3)
119.6, 119.8, 120.2, 124.3, 125.6, 126.7, 127.0, 128.4, 128.8,
130.6, 132.6, 133.8, 135.3, 136.2, 137.0, 139.19, 139.22, 141.3.
n
max (KBr)/cmꢀ1 1487, 1449, 1437, 1397, 1084, 1015, 862, 824,
779, 731. m/z (EI) 291 (5 %, [M þ 3]þ), 290 (25, [M þ 2]þ), 289
(19, [M þ 1]þ), 288 (70, Mþ), 252 (100). m/z (HRMS) Found:
288.0710. Calc. for C20H13Cl (Mþ): 288.0706.
Representative Procedure for Palladium-Catalyzed
Double Cross-Coupling Reaction of 9-Stannafluorenes
7 with 1,1-Dibromoalk-1-enes 8
9-(1-Phenylpropylidene)-9H-fluorene (4s)
Yield: 55 %. Colourless solid. Mp 132.0–132.78C. Rf 0.33
(hexane/EtOAc2/CH2Cl2 50 : 1 : 1). dH (400 MHz, CDCl3) 1.31
(t, J 7.6, 3H), 3.12 (q, J 7.6, 2H), 6.13 (d, J 6.1, 1H), 6.83 (dd,
J 7.2, 7.2, 1H), 7.31 (dd, J 6.4, 2.0, 2H), 7.35–7.51 (m, 5H), 7.67
(d, J 7.2, 1H), 7.77–7.79 (m, 1H), 7.95–7.97 (m, 1H); dC
(100 MHz, CDCl3) 11.8, 31.3, 118.9, 119.4, 124.6, 124.7,
126.3, 126.7, 126.9, 127.2, 127.5, 127.8, 128.8, 132.2, 138.1,
138.5, 139.5, 140.4, 143.8, 149.1. nmax (KBr)/cmꢀ1 1445, 785,
766, 733, 704, 602. m/z (EI) 284 (4 %, [M þ 2]þ), 283 (33,
[M þ 1]þ), 282 (100, Mþ). m/z (HRMS) Found: 282.1403.
Calc. for C22H18 (Mþ): 282.1409.
A Schlenk tube (80 mL) was charged with 7 (0.30 g, 1.0 mmol),
8a (0.34 g, 1.0 mmol), Pd(PtBu3)2 (26 mg, 50 mmol), CsF
(0.76 g, 5.0 mmol), and 1,4-dioxan (20 mL) in a glove box. The
vial was taken outside from the glove box and heated at 1308C
for 12 h. The reaction mixture was cooled to room temperature,
filtered through a pad of Florisil, and concentrated under
vacuum. The residue was purified by column chromatography
on silica gel (hexane/AcOEt/CH2Cl2 50 : 1 : 1) to give 4a
(0.22 g, 65 % yield) as a yellow solid.
9-[4-(Trifluoromethyl)benzylidene]-9H-fluorene (4m)
9-[Bis(4-fluorophenyl)methylene]-9H-fluorene (4t)
Yield: 81 %. Colourless solid. Mp 88.7–89.58C. Rf 0.38
(hexane/EtOAc2 50 : 1). dH (400 MHz, CDCl3) 7.09 (t, J 7.2,
1H), 7.33–7.47 (m, 5H), 7.63 (s, 1H), 7.71–7.74 (m, 5H), 7.79
Yield: 36 %. Pale yellow solid. Mp 194.5–195.08C. Rf 0.44
(hexane/EtOAc 9 : 1). dH (400 MHz, CDCl3) 6.68 (d, J 8.0, 2H),
6.98 (t, J 7.6, 2H), 7.13 (t, J 7.6, 4H), 7.27 (t, J 7.6, 2H),

1284
M. Shimizu et al.
7.34 (t, J 6.4, 4H), 7.71 (d, J 7.6, 2H); dC (100 MHz, CDCl3)
115.8 (d, J 21.4), 119.3, 124.5, 126.4, 127.8, 131.7 (d, J 7.6),
134.7, 138.3, 138.5 (d, J 3.0), 140.4, 142.7, 162.6 (d, J 246.3);
dF (282 MHz, CDCl3) ꢀ113.3. nmax (KBr)/cmꢀ1 2916, 1890,
1601, 1505, 1445, 1236, 1155, 874, 831, 787, 739, 584, 527. m/z
(EI) 368 (7 %, [M þ 2]þ), 367 (43, [M þ 1]þ), 366 (100, Mþ),
270 (36). (Found: C 85.17, H 4.55. Anal. Calc. for C26H16F2: C
85.23, H 4.40 %.)
(l) T. L. Andrew, J. R. Cox, T. M. Swager, Org. Lett. 2010, 12, 5302.
doi:10.1021/OL102384K
[2] M. L. T. M. B. Franco, B. J. Herold, J. C. Evans, C. C. Rowlands,
J. Chem. Soc., Perkin Trans. 2 1988, 443. doi:10.1039/P29880000443
[3] M. Banerjee, S. J. Emond, S. V. Lindeman, R. Rathore, J. Org. Chem.
2007, 72, 8054. doi:10.1021/JO701474Y
[4] (a) N. Chernyak, V. Gevorgyan, J. Am. Chem. Soc. 2008, 130, 5636.
doi:10.1021/JA8006534
(b) N. Chernyak, V. Gevorgyan, Adv. Synth. Catal. 2009, 351, 1101.
doi:10.1002/ADSC.200800765
Supplementary Material
(c) S. A. Kandil, R. E. Dessy, J. Am. Chem. Soc. 1966, 88, 3027.
doi:10.1021/JA00965A025
[5] (a) Q. Tian, R. C. Larock, Org. Lett. 2000, 2, 3329. doi:10.1021/
OL000220H
1H and 13C NMR spectra of 8m, 4b, 4d, 4e, 4j, 4m, 4n, 4o, 4p,
and 4s are available on the Journal’s website.
(b) R. C. Larock, Q. Tian, J. Org. Chem. 2001, 66, 7372. doi:10.1021/
JO010561O
Acknowledgements
This work was supported by Grants-in-Aid for Creative Scientific Research,
No. 16GS0209 from the Ministry of Education, Culture, Sports, Science and
Technology, Japan, and The Asahi Glass Foundation (M. S.).
(c) See also T. Morishita, H. Yoshida, J. Ohshita, Chem. Commun.
2010, 46, 640. doi:10.1039/B919301D
[6] V. S. Thirunavukkarasu, K. Parthasarathy, C.-H. Cheng, Chem.–Eur.
J. 2010, 16, 1436. doi:10.1002/CHEM.200902726
[7] (a) C. V. Ramana, B. K. Kishore Reddy, C. Nageswara Reddy, R. G.
Gonnade, M. K. Gurjar, Synlett 2007, 127. doi:10.1055/S-2006-
958407
(b) S. Paul, T. Gorai, A. Koley, J. K. Ray, Tetrahedron Lett. 2011, 52,
4051. doi:10.1016/J.TETLET.2011.05.148
[8] (a) M. Shimizu, I. Nagao, Y. Tomioka, T. Hiyama, Angew. Chem. Int.
Ed. 2008, 47, 8096. doi:10.1002/ANIE.200803213
(b) M. Shimizu, Y. Tomioka, I. Nagao, T. Hiyama, Synlett 2009, 3147.
doi:10.1055/S-0029-1218341
References
[1] (a) H. Tong, Y. Dong, M. Ha¨ußler, J. W. Y. Lam, H. H. Y. Sung,
I. D. Williams, J. Sun, B. Z. Tang, Chem. Commun. 2006, 1133.
doi:10.1039/B515798F
(b) H. Tong, Y. Dong, Y. Hong, M. Haussier, J. W. Y. Lam, H. H. Y.
Sung, X. Yu, J. Sun, I. D. Williams, H. S. Kwok, B. Z. Tang, J. Phys.
Chem. C 2007, 111, 2287. doi:10.1021/JP0630828
(c) X. Luo, J. Li, C. Li, L. Heng, Y. Q. Dong, Z. Liu, Z. Bo, B. Z. Tang,
Adv. Mater. 2011, 23, 3261. doi:10.1002/ADMA.201101059
(d) F. G. Brunetti, X. Gong, M. Tong, A. J. Heeger, F. Wudl, Angew.
Chem. Int. Ed. 2010, 49, 532. doi:10.1002/ANIE.200905117
(e) F. G. Brunetti, A. Varotto, N. A. Batara, F. Wudl, Chem.–Eur. J.
2011, 17, 8604. doi:10.1002/CHEM.201100442
(f) H. Usta, A. Facchetti, T. J. Marks, J. Am. Chem. Soc. 2008, 130,
8580. doi:10.1021/JA802266U
(g) H. Usta, A. Facchetti, T. J. Marks, Org. Lett. 2008, 10, 1385.
doi:10.1021/OL8000574
(h) H. Usta, C. Risko, Z. Wang, H. Huang, M. K. Deliomeroglu,
A. Zhukhovitskiy, A. Facchetti, T. J. Marks, J. Am. Chem. Soc. 2009,
131, 5586. doi:10.1021/JA809555C
(i) J. Vicario, M. Walko, A. Meetsma, B. L. Feringa, J. Am. Chem. Soc.
2006, 128, 5127. doi:10.1021/JA058303M
(j) R. Eelkema, B. L. Feringa, Chem. Asian J. 2006, 1, 367.
doi:10.1002/ASIA.200600116
(k) D. Pijper, B. L. Feringa, Angew. Chem. Int. Ed. 2007, 46, 3693.
doi:10.1002/ANIE.200604941
(c) M. Shimizu, I. Nagao, Y. Tomioka, T. Kadowaki, T. Hiyama,
Tetrahedron 2011, 67, 8014. doi:10.1016/J.TET.2011.08.019
(d) I. Nagao, M. Shimizu, T. Hiyama, Angew. Chem. Int. Ed. 2009, 48,
7573. doi:10.1002/ANIE.200903779
[9] (a) T. Hata, H. Kitagawa, H. Masai, T. Kurahashi, M. Shimizu,
T. Hiyama, Angew. Chem. Int. Ed. 2001, 40, 790. doi:10.1002/1521-
3773(20010216)40:4,790::AID-ANIE7900.3.0.CO;2-T
(b) T. Kurahashi, T. Hata, H. Masai, H. Kitagawa, M. Shimizu,
T. Hiyama, Tetrahedron 2002, 58, 6381. doi:10.1016/S0040-4020
(02)00648-8
(c) M. Shimizu, C. Nakamaki, K. Shimono, M. Schelper, T. Kurahashi,
T. Hiyama, J. Am. Chem. Soc. 2005, 127, 1250. doi:10.1021/
JA054484G
[10] In ref. [8d], two examples of the annulation using 7 and 1,1-
dibromoalk-1-enes were preliminarily reported.
[11] To the best of our knowledge, this is the first synthesis of dinaphtho-
fulvenes of type 4e.