An indenone synthesis involving a new aminotransfer reaction and its application to dibenzopentalene synthesis

Article abstract of DOI:10.1002/ejoc.201100575

o-(Phenylethynyl)phenyllithiums, generated by treatment of o-(phenylethynyl)bromobenzenes with tBuLi, were quenched with N,N-dimethylcarboamides to afford various 2-phenylindenone derivatives in moderate to good yields upon acidic workup. The choice of lithiation reagents was critical. When n-butyllithium was used the yields were reduced. The N-alkyl groups in the carboamides were also important: quenching with N,N-diethylbenzamides also afforded 2,3-diphenylindenones as the sole isolated products, but quenching with N-benzoylpiperidine led to 2-benzoyltolane in good yield. Control experiments revealed that the reactions proceed through a multi-step reaction sequence involving a novel intramolecular transamination to the α-acetylenic carbon of the alkynyl group. The method was applicable to the synthesis of dibenzopentalene derivatives as well as various indenone derivatives. A mechanism for the reaction is discussed.

Full text of DOI:10.1002/ejoc.201100575

FULL PAPER
DOI: 10.1002/ejoc.201100575
An Indenone Synthesis Involving a New Aminotransfer Reaction and Its
Application to Dibenzopentalene Synthesis
Kenta Katsumoto,[a] Chitoshi Kitamura,[a] and Takeshi Kawase*[a]
Keywords: Cyclization / Alkynes / Fused-ring systems / Aromatic compounds / Reaction mechanisms
o-(Phenylethynyl)phenyllithiums, generated by treatment of
o-(phenylethynyl)bromobenzenes with tBuLi, were
but quenching with N-benzoylpiperidine led to 2-benzoyl-
tolane in good yield. Control experiments revealed that the
reactions proceed through a multi-step reaction sequence in-
volving a novel intramolecular transamination to the α-acet-
ylenic carbon of the alkynyl group. The method was appli-
cable to the synthesis of dibenzopentalene derivatives as
well as various indenone derivatives. A mechanism for the
quenched with N,N-dimethylcarboamides to afford various
2-phenylindenone derivatives in moderate to good yields
upon acidic workup. The choice of lithiation reagents was
critical. When n-butyllithium was used the yields were re-
duced. The N-alkyl groups in the carboamides were also im-
portant: quenching with N,N-diethylbenzamides also af- reaction is discussed.
forded 2,3-diphenylindenones as the sole isolated products,
Introduction
In the last decade the construction of isoquinoline skel-
etons (such as 1, Scheme 1) from ortho-alkynylbenzylamine
derivatives has been extensively explored.[1,2] In these reac-
tions, intramolecular cycloaminations at the β-acetylenic
carbons of the alkynyl groups, assisted by transition metal
cations (CuII, AgI, IrIII, etc) or by Lewis acids, were com-
monly observed (Scheme 1a). Recently, AgOTf- or CuCl2-
mediated cyclizations of ortho-alkynylbenzamides have been
reported by Ma’s and Miyata’s groups, respectively.[3] The
reactions afforded isocoumarin or isobenzofuranone deriv-
atives 2 and 3, respectively, through attack of the carbonyl
oxygen of the amide group at the α- or β-acetylenic carbon
(Scheme 1b). These results revealed that intramolecular cy-
cloaminations at the α-acetylenic carbons of the alkynyl
groups were rare reaction processes.[4] Polycyclic aromatic
compounds containing carbocyclic five-membered rings,
such as fluorene, pentalene, and indacene π-systems, have
received much attention[5] because of their electronic and
photophysical properties. They have permitted the pro-
duction of new materials with high utility in organic elec-
tronic devices.[6]
Scheme 1. General reaction mechanisms of (a) isoquinoline synthe-
We have recently found a new reaction that yields di-
benzopentalene derivatives from readily available o-bromo-
alkynylbenzenes through treatment with commercially
available nickel complexes.[7] The method is applicable to
the construction of π-extended pentalenes with relatively
ses involving intramolecular cycloamination to β-acetylenic car-
bon, (b) construction of isocoumarin or isobenzofuranone skel-
etons from ortho-alkynylbenzamides, assisted by CuII or AgI ions,
and (c) a new indenone synthesis involving intramolecular trans-
amination to α-acetylenic carbon.
high hole mobility for amorphous materials.[8] The results
promoted us to investigate the construction of polycyclic
conjugated systems containing five-membered ring sys-
tem(s). In the course of the study, we have developed a new
synthetic method for the indenone derivatives 4 through re-
[a] Graduate School of Engineering, University of Hyogo,
2167 Shosha, Himeji, Hyogo 671-2280, Japan
Fax: +81-79-267-4889
E-mail: kawase@eng.u-hyogo.ac.jp
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100575.
Eur. J. Org. Chem. 2011, 4885–4891
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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K. Katsumoto, C. Kitamura, T. Kawase
FULL PAPER
actions between o-(phenylethynyl)phenyllithium (2-lithio- Table 1. Reagents and quenchers in Scheme 2.
tolane) and suitable N,N-dimethylcarboamides. Some con-
Entry Compound
Reagent
Quencher
% Yield of 6
trol experiments revealed that the reactions proceed
through a multi-step reaction sequence involving a novel
intramolecular transamination to the α-acetylenic carbon
of the alkynyl group (Scheme 1c). Although various inde-
none syntheses using Pd,[9] Rh,[10] and Mn[11] catalysts have
been reported previously, our method is unique and versa-
tile. The reaction is applicable to the syntheses of, for exam-
ple, dibenzopentalene derivatives and also indenone deriva-
tives bearing several functional groups. Here we present the
indenone synthesis and its reaction mechanism.
1
2
3
4
5
6
7
5
5
5
5
7
8
8
tBuLi
nBuLi
tBuLi
tBuLi
Et2NLi
PhLi
PhCONMe2
PhCONMe2
PhCONEt2
PhCON(CH2)5
none
65
14
45
62 of 7
0[a]
none
none
85
0
PhMgBr
[a] Complex mixture.
sole isolated product (Table 1, Entry 3), but quenching with
N-benzoylpiperidine led to 2-benzoyltolane (7) in 62% yield
(Table 1, Entry 4). Treatment of 2-phenylethynyl-N,N-di-
methylbenzamide (8) with phenyllithium afforded 6 in 85%
yield (Table 1, Entry 6). On the other hand, use of phenyl-
magnesium bromide in the reaction resulted in failure; 8
was recovered unchanged (Table 1, Entry 7).
Results and Discussion
Treatment of 2-lithiotolane, generated from 2-bromotol-
ane (5, Scheme 2) and tert-butyllithium, with N,N-dimethyl-
benzamide afforded 2,3-diphenylindenone (6)[9a] in 65%
yield rather than 2-benzoyltolane (7) upon quenching with
2 m hydrochloric acid (Scheme 2; Table 1, Entry 1). The
choice of lithiation reagents was critical: when n-butyllith-
ium was used the yield was reduced to 14% (Table 1, En-
try 2). We expected that n-butyl bromide, formed by lith-
ium/halogen exchange under the reaction conditions, would
prevent smooth progress of the reaction. The N-alkyl
groups in the benzamides are also important: quenching
with N,N-diethylbenzamide afforded 6 in 45% yield as the
When the reaction mixture prepared by the general pro-
cedure was quenched with aqueous ammonium chloride in
place of hydrochloric acid, a pale yellow product was ob-
tained instead of the reddish 6 on extraction with hexane/
toluene (4:1). Chromatographic purification on silica gel led
to decomposition of the product to afford 6 in low yield
(11%). Finally, it was isolated in pure form and in 46%
yield by crystallization from the extract. Spectral and ana-
lytical data enable us to determine it to be the amino
alcohol 9 (Scheme 3). Hydrolytic deamination of 9 with hy-
drochloric acid (2 m) indeed provided 6 in good yield.
From these results, we proposed a reaction mechanism
as shown in Scheme 3. N,N-Dialkylcarbamides are versatile
synthetic building blocks:[12] treatment of phenyllithium
with N,N-dimethylbenzamide, for example, afforded benzo-
phenone upon acidic hydrolysis without formation of tri-
phenylmethanol as a byproduct. A key point of this reac-
tion is that the N,N-dimethylaminoalkoxide produced as an
Scheme 2. Syntheses of indenone 6 from o-alkynylbenzenes 5, 7,
and 8.
Scheme 3. Proposed reaction mechanism.
4886
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An Indenone Synthesis Involving a New Aminotransfer Reaction
intermediate is stable enough to interrupt further reaction fer reactions thus appear to be governed by the substituent
under the highly basic condition. The reactions between at the aminoalkoxide carbon [-CR1(NR2)(OLi)]. When R1
N,N-dimethylbenzamide and 2-lithiotolane and between 8 is H, the energy becomes higher, probably due both to elec-
and phenyllithium should thus form the corresponding ami- tronic and to steric effects.
noalkoxide 10 as the first reaction intermediate. We believe
The reactions in which N,N-dimethylarylcarbox-
that the amino group of 10 migrates to the α-acetylenic car- amides[12f] were used as quenchers successfully provided the
bon to generate the vinyl anion 11. The vinyl anion should corresponding 3-aryl-2-phenylindenones 17–20 in moderate
be stabilized by conjugation with the neighboring aryl to good yields. Moreover, the naphthalene analogue 21 and
group and immediately attack the carbonyl carbon of 11 1,4-bis(2-indenonyl)benzene (22) were also obtained from
to form the amino alcohol 9. The efficient formation of 2-bromo-3-(phenylethynyl)naphthalene and bis(2-bromo-
indenones suggested that the intramolecular addition to the
alkyne preferentially proceeded in a trans fashion. As
shown in Scheme 1, intramolecular addition of nitrogen or
oxygen atom to an acetylenic bond usually proceeds in such
a trans fashion. The amino transfer should occur in an in-
tramolecular manner; free lithium dialkylamide should not
participate in the reaction, because treatment of 2-benzo-
yltolane (7) with lithium diethylamide in THF afforded a
complex mixture rather than 6 (Table 1, Entry 5). The pro-
posed reaction mechanism would thus appear reasonable.
The scheme shows the amino group migration occurring
without any assistance from transition metal ions or Lewis
acids. In order to investigate assistance from CuII ion as a
contaminant in the reaction vessel, we deliberately added a
catalytic amount of CuCl2 (10 mol-%) to the reaction mix-
ture. The trial experiment resulted in a significant decrease
in the yield (24%), however. On the other hand, these data
do not rigorously exclude the possibility of assistance from
other transition metal ions. Further experimental investiga-
tion would be needed.
We also investigated the scope and limitations of the re-
action. With 1-bromo-2-(2-trimethylsilylethynyl)benzene
(12) the reaction afforded 2-(2-trimethylsilylethynyl)benzo-
phenone (13,[13] 59%), so the presence of an aryl group at
the end of the alkynyl group seems critical for the reaction.
Moreover, 2-lithiotolane was quenched with N,N,N,N-tetra-
Scheme 5. Synthesis of the dibenzopentalenes 25 and 26. Reagents
and conditions: (a) tBuLi (4 equiv.), THF, –78 °C, 30 min, then
methylurea to give 3-dimethylamino-2-phenylindenone (14)
quenching with ArCONMe2; (b) aq. HCl (2 m); (c) TiCl4 (4 equiv.),
[14]
in 51% yield (Scheme 3). On the other hand, treatment Zn (10 equiv.), THF, reflux, 18 h.
with N,N-dimethylformamide (DMF) under the general re-
action conditions led to 2-formyltolane (15;[15] Scheme 4,
88%), whereas when the reaction mixture was heated at re-
flux for 22 hours before acidic workup, 2-phenylindenone
(16)[16] was obtained in 33% yield as the sole isolated prod-
uct (Scheme 4). The activation energies of the aminotrans-
Scheme 4. Reagents and conditions: (a) tBuLi, THF, –78 °C,
30 min, then quenching with DMF; (b) aq. HCl (2 m); (c) heating
at reflux for 22 h, then aq. HCl (2 m).
Figure 1. ORTEP drawing of 24.
Eur. J. Org. Chem. 2011, 4885–4891
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K. Katsumoto, C. Kitamura, T. Kawase
FULL PAPER
bis[(2-bromophenyl)ethynyl]benzene,[20] N,N-dimethyl-2-(phenyl-
ethynyl)benzamide (8),[21] N,N-diethylbenzamide,[22] and N-benzo-
ylpiperidine[22] were prepared by reported procedures. N,N-Di-
phenylethynyl)benzene, respectively. These results indicate
the wide applicability of the reaction.
In particular, the reaction between 2,2Ј-dilithiotolane,
generated from the corresponding dibromide 23 (Scheme 5),
and N,N-dimethylbenzamide led to 2-(2-benzoylphenyl)-3-
phenylindenone (24) in 65% yield. The structure was deter-
methylbenzamide,
N,N-dimethyl-4-methylbenzamide, N,N-di-
methyl-4-cyanobenzamide, N,N-dimethyl-4-(dimethylamino)benz-
amide, and N,N-dimethyl-2-naphthamide were prepared by our
previously reported synthetic method.[12f]
mined by crystallographic analysis (Figure 1).[17]
A
General Procedure for the Preparation of the Indenones 6, 14, 16–20,
and 21: tert-Butyllithium (1.6 m, 2.5 mmol) was added by syringe at
–78 °C under N2 to a solution of the 2-bromo-1-alkynylbenzene
(1 mmol) in THF (20 mL). The reaction mixture was stirred at the
temperature for 30 min, quenched with ArCONMe2 (1 mmol), and
allowed to warm to room temp. After additional stirring for 90 min
the reaction mixture was extracted with toluene. The organic layer
was washed with aq. NaHCO3, water, and brine and dried with
anhydrous Na2SO4. After evaporation of the solvent the reddish
residue was dissolved in acetone (10 mL) and hydrochloric acid
(2 m, 5 mL) and stirred at room temp. for 1 h. The reaction mixture
was extracted with toluene. The organic layer was washed with aq.
NaHCO3, water, and brine and dried with anhydrous Na2SO4. Af-
McMurry reaction of 24 afforded 3,6-diphenyldibenzo-
pentalene (25)[5c] (Ar = Ph) in 58% yield. A similar pro-
cedure provided 26 (Ar = p-Tol) in 35% yield from 23
(Scheme 5).
Conclusions
A new synthesis of indenones from 2-bromotolanes and
N,N-dialkylcarboxamides as starting materials has been de-
veloped. Although these reactions involved a multi-step re-
action sequence, they proceeded efficiently. A new amino-
transfer reaction was first observed in the reaction se- ter evaporation of the solvent, the reddish residue was subjected to
silica gel column chromatography (15 g) to afford the products.
quence. The synthetic procedure should be widely appli-
cable to the synthesis of various indenone derivatives and
π-extended pentalenes with potential for the construction
of new materials with high utilities in organic electronic de-
vices.
2,3-Diphenylindenone (6):[9a] This compound was prepared from 5
and PhCONMe2 as reddish crystals (185 mg, 0.66 mmol, 66%).
Red solid; m.p. 151–153 °C. 1H NMR (500 MHz, CDCl3): δ = 7.59
(m, J = 7.2 Hz, 1 H, 7-H), 7.43–7.36 (m, 6 H), 7.30 (m, 1 H), 7.28–
7.24 (m, 5 H), 7.15 (m, J = 7.2 Hz, 1 H, 4-H) ppm. 13C NMR
(125.8 MHz, CDCl3): δ = 196.56 (C=O), 155.39, 145.27, 133.50,
132.75, 132.43, 130.79, 130.03, 129.36, 129.01, 128.84, 128.55,
Experimental Section
128.13, 127.80, 123.02, 121.33 ppm. IR (KBr): ν = 3049 (w), 1703
˜
General: All reactions involving air- or moisture-sensitive com-
pounds were carried out in dry reaction vessels under positive pres-
sures of nitrogen. Air- and moisture-sensitive liquids and solutions
were transferred by syringe. Analytical thin-layer chromatography
was performed with precoated glass plates (Merck Art. 7730 Kie-
selgel 60 GF-254). Thin-layer chromatography plates were viewed
under ultraviolet light (UV). Organic solutions were concentrated
by rotary evaporation at ca. 15 Torr (diaphragm pump). Column
chromatography was performed with Merck Kieselgel 60.
(s), 1456 (m), 1348 (m), 1178 (m), 1082 (m), 761 (s), 752 (s), 704
(s) cm–1. MS (EI): m/z = (%) 282 (100) [M]+, 281 (81) [M – 1]+, 252
(53), 126 (38).
3-Dimethylamino-2-phenylindenone (14):[14] The general procedure
with 5 (281 mg, 1.09 mmol) and an excess of N,N,N,N-tetrameth-
ylurea (1 mL) afforded 14 as an orange solid (137 mg, 51%). The
compound was purified by column chromatography (silica gel) with
toluene/ethyl acetate (9:1) as eluent. Red solid; m.p. 99–101 °C. 1H
NMR (500 MHz, CDCl3): δ = 7.53–7.52 (m, 1 H, 7-H), 7.47–7.45
(m, 1 H, 4-H), 7.37–7.28 (m, 6 H), 7.24–7.21 (m, 1 H, 5-H), 3.16
(s, 6 H, -NCH3) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 191.88
(C=O), 164.26, 139.60, 135.82, 134.00, 131.18, 130.66, 129.70,
127.71, 126.18, 121.08, 110.27, 43.82 (NCH3) ppm. MS (EI): m/z
(%) = 249 (100) [M]+, 248 (65) [M – 1]+.
2-Phenylinden-1-one (16):[16] The general procedure was carried out
with 5 (290 mg, 1.13 mmol) and DMF (1 mL) as a quencher. The
resulting reaction mixture was heated at reflux under N2 for 22 h.
The product 16 was purified by column chromatography (silica gel)
with toluene as eluent (76 mg, 33%). Orange solid. 1H NMR
(500 MHz, CDCl3): δ = 7.81–7.79 (m, JAB = 7.8 Hz, 2 H, o-H-Ph),
7.66 (s, 1 H, 3-H), 7.48 (m, J6,7 = 6.8 Hz, 1 H, 7-H), 7.41 (m, J =
7.8 Hz, 2 H, m-H-Ph), 7.35 (m, 2 H, p-H-Ph, 5-H), 7.22 (m, 1 H,
6-H), 7.10 (m, J4,5 = 6.8 Hz, 1 H, 4-H) ppm. MS (EI): m/z (%) =
206 (100) [M]+, 178 (5).
All reagents were purchased from Tokyo Kasei Co., Kishida Co.,
Wako Co., and other commercial suppliers and were used as sup-
plied unless otherwise stated. n-Buthyllithium solution in hexane
was purchased from Mitsuwa Pure Chemicals, Inc. and tert-butyl-
lithium was purchased from Kanto Chemicals Co. Anhydrous di-
ethyl ether, 1,2-dimethoxyethane (DME), and toluene were pur-
chased from Kanto Chemical Co. and dried by standard pro-
cedures where necessary. Tetrahydrofuran (THF) was purchased
from Wako Chemical Co. and distilled from lithium aluminum hy-
dride at 760 Torr under nitrogen before use.
Melting points were recorded with a Yanaco MP–S3 apparatus and
are uncorrected. EI mass spectra were measured with a Shimadzu
GC–MS-QP5050A instrument. 1H NMR spectra (tetramethylsil-
ane; 0 ppm as internal standard) and 13C NMR spectra (CDCl3;
77.0 ppm as internal standard) were recorded with Bruker
DRX 500, and JEOL EX 270 instruments. The chemical shifts are
given in ppm. IR spectra were obtained with a Shimadzu FTIR-
8400 spectrometer. Electronic (UV/Vis) spectra were obtained with
a Hitachi U-3010 spectrophotometer. Elemental analyses were ob-
tained with a Yanaco MT5 CHN corder.
3-(4-Dimethylaminophenyl)-2-phenylindenone (18):[23] The general
procedure with 5 (251 mg, 0.976 mmol) and Me2NC6H4CONMe2
(477 mg, 2.48 mmol) afforded 18 as an orange solid (174 mg, 55%).
The compound was purified by column chromatography (silica gel)
with toluene as eluent and recrystallization from hexane solution.
Brown solid; m.p. 135–136 °C. 1H NMR (500 MHz, CDCl3): δ =
7.56 (m, J7,6 = 7.2 Hz, 1 H, 7-H), 7.39–7.22 (m, 10 H), 6.68 (m, 2
H, o-H-Ar), 3.02 (s, 6 H, -NCH3) ppm. 13C NMR (125.8 MHz,
2-Bromo-1-(phenylethynyl)benzene (5),[18] 2-bromo-1-[(2-bromo-
phenyl)ethynyl]benzene (23),[19] 2-bromo-3-(phenylethynyl)naphth-
alene,[8] 2-bromo-1-[2-(trimethylsilyl)ethynyl]benzene (12),[7a] 1,4-
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An Indenone Synthesis Involving a New Aminotransfer Reaction
CDCl3): δ = 196.57 (C=O), 156.02, 151.03, 145.16, 132.90, 243 (13). C36H22O2 (486.57): calcd. C 88.87, H 4.56; found C 88.91,
131.98 ppm. 131.69, 130.38, 130.20, 130.14, 128.73, 128.10, 127.25,
H 4.92.
122.45, 121.53, 119.66, 111.57, 40.13. IR (KBr): ν = 3031 (w), 2799
˜
2-(2-Phenylethynyl)benzophenone (7):[27] The general procedure
(w), 1697 (s, C=O), 1601 (s), 1518 (m), 1346 (s), 1196 (m), 1080
(m), 1069 (m), 818 (m), 760 (m), 698 (m) cm–1. MS (EI): m/z (%)
= 325 (100) [M]+, 281 (31) [M – NMe2]+, 252 (21), 126 (23).
with
5
(270 mg, 1.05 mmol) and PhCONC5H10 (0.559 g,
2.96 mmol) afforded 7 as a colorless liquid (185 mg, 62%). The
compound was purified by column chromatography (silica gel) with
1
toluene/hexane (1:1) as eluent. Colorless solid; m.p. 49–50 °C. H
4-(1-Oxo-2-phenylinden-3-yl)benzonitrile (19):[24] The general pro-
NMR (500 MHz, CDCl3): δ = 7.90–7.88 (m, 2 H, o-H-Ph), 7.63–
7.44 (m, 7 H), 7.26–7.18 (m, 3 H, 6-H, m-Ph), 7.05–7.04 (m, 2
H, o-Ph) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 197.10 (C=O),
141.60, 137.40, 133.26, 132.63, 131.49, 130.43, 130.31, 128.74,
128.52, 128.49, 128.29, 128.18, 122.65, 121.88, 95.23 (CϵC), 87.59
cedure with
5 (267 mg, 1.03 mmol) and NCC6H4CONMe2
(467 mg, 2.68 mmol) afforded 19 as an orange solid (68 mg, 22%).
The compound was purified by column chromatography (silica gel)
with toluene as eluent and recrystallization from hexane. Orange
solid; m.p. 190–191 °C. 1H NMR (500 MHz, CDCl3): δ = 7.49 (m,
JAB = 8.9 Hz, 2 H, AAЈBBЈ, o-H-Ar), 7.63 (m, J7,6 = 7.2 Hz, 1 H,
7-H), 7.50 (m, JBA = 8.9 Hz, 2 H, AAЈBBЈ, m-H-Ar), 7.41 (dt, J =
1.0, 7.6 Hz, 1 H, 5-H), 7.33 (ddd, J4,5 = 0.9, 7.2, 7.6 Hz, 1 H, 6-
H), 7.30–7.28 (m, 3 H, o,p-H-Ph), 7.22–7.20 (m, 2 H, m-H-Ph), 7.07
(m, J = 7.2 Hz, 1 H, 4-H) ppm. 13C NMR (125.8 MHz, CDCl3): δ
= 195.77 (C=O), 152.72, 144.40, 137.70, 133.83, 132.68, 130.29,
129.92, 129.85, 129.43, 129.37, 128.44, 128.40, 123.60, 120.91,
(CϵC) ppm. IR (KBr): ν = 3059 (w), 2218 (w, CϵC), 1666 (s,
˜
C=O), 1597 (m), 1493 (m), 1448 (m), 1288 (s), 930 (m), 756 (s), 691
(s), 637 (m) cm–1. MS (EI): m/z (%) = 282 (97) [M]+, 281 (100) [M –
1]+, 265 (29), 253 (42), 252 (53), 176 (31).
3-Dimethylamino-1,2-diphenylinden-1-ol
(9):
tert-Butyllithium
(1.6 m, 2.0 mL, 3.2 mmol) was added by syringe at –78 °C under
N2 to a solution of 5 (242 mg, 1.54 mmol) in THF (15 mL). The
reaction mixture was stirred at this temperature for 30 min,
quenched with a solution of C6H5CONMe2 (230 mg, 0.924 mmol)
in THF (5 mL), and allowed to warm to room temp. The reaction
mixture was stirred at room temp. for 90 min and extracted with
toluene. The organic layer was washed with saturated aqueous am-
monium chloride, water, and brine and dried with anhydrous
Na2SO4. The solvent was removed and the viscous pale yellow
product was dissolved with hexane/toluene (5:1). Compound 9 so-
lidified as colorless crystals (140 mg, 46%). Colorless solid; m.p.
133–134 °C. 1H NMR (500 MHz, CDCl3): δ = 7.44 (m, 1 H, 7-H),
7.39–7.37 (m, 2 H, o-H-3-Ph), 7.28–7.12 (m, 9 H), 7.02–7.01 (m, 2
H, o-H-2-Ph), 2.80 (s, 6 H, -NCH3), 2.22 (s, 1 H, -OH) ppm. 13C
NMR (125.8 MHz, CDCl3): δ = 150.36 (-CNMe2), 148.17, 142.68,
140.94, 135.39, 129.96, 128.08, 127.99, 127.40, 126.83, 126.65,
126.59, 124.06, 123.05, 120.61, 85.67 (-CPhOH), 42.68 (-NCH3),
118.40, 112.88 ppm. IR (KBr): ν = 3057 (w), 2226 (m, CϵN), 1707
˜
(s, C=O), 1454 (m), 1346 (m), 858 (m), 756 (m), 692 (m), 596
(m) cm–1. MS (EI): m/z (%) = 307 (48) [M]+, 306 (30) [M – 1]+, 207
(10) [M – C6H4CN]+, 114 (100), 112 (90).
3-(2-Naphthyl)-2-phenylindenone (20):[25] The general procedure
with 5 (259 mg, 1.01 mmol) and N,N-dimethyl-(2-naphthalene)-
carbamide (570 mg, 2.86 mmol) afforded 20 as an orange solid
(198 mg, 59%). Orange solid; m.p. 129–130 °C. 1H NMR
(500 MHz, CDCl3): δ = 8.00 (s, 1 H, 1-H-naph), 7.87–7.82 (m, 3
H, m-H-Ph and 3-H-naph), 7.62 (m, 1 H, 7-H), 7.57–7.52 (m, 2
H, 6,7-H-naph), 7.41–7.22 (m, 9 H) ppm. 13C NMR (125.8 MHz,
CDCl3): δ = 196.58 (C=O), 155.21, 145.32, 133.58, 133.51, 133.21,
132.61, 130.89, 130.79, 130.36, 130.11, 129.07, 128.56, 128.46,
128.17, 128.02, 127.94, 127.89, 127.11, 126.62, 126.23, 123.10,
121.38 ppm. IR (KBr): ν = 3053 (w), 1707 (s, C=O), 1456 (w), 966
˜
40.47 ppm. IR (KBr): ν = 3296 (m, -OH), 3013 (w), 2943 (w), 2795
˜
(w), 820 (m), 756 (s), 746 (m), 719 (m) cm–1. MS (EI): m/z (%) =
(w), 1601 (m), 1491 (m), 1454 (s), 1362 (s), 1173 (w), 1011 (s), 932
(w), 905 (w), 750 (s), 698 (s) cm–1. MS (EI): m/z (%) = 327 (41)
[M]+, 310 (30) [M – OH]+, 282 (100) [M – NMe2 – 1]+. C23H21NO
(327.42): calcd. C 84.37, H 6.46, N 4.28; found C 84.60, H 6.61, N
3.94.
2-(2-Trimethylsilylethynyl)benzophenone (13):[13] The general pro-
cedure with 1-bromo-2-(trimethylsilylethynyl)benzene (12, 451 mg,
1.78 mmol) and C6H5CONMe2 (467 mg, 2.68 mmol) afforded 13
as a colorless liquid (294 mg, 59%). The compound was purified
by column chromatography (silica gel) with toluene/hexane (1:1) as
eluent. Colorless solid. 1H NMR (500 MHz, CDCl3): δ = 7.82–7.80
(m, 2 H, o-H-Ph), 7.59–7.30 (m, 2 H, p-H-Ph and 6-H-benzo-
phenone), 7.49–7.21 (m, 5 H), –0.07 (s, 9 H, Si-CH3) ppm. 13C
NMR (125.8 MHz, CDCl3): δ = 197.06 (C=O), 142.26, 137.33,
133.07, 132.69, 130.12, 130.06, 128.53, 128.28, 121.46, 102.42
332 (100) [M]+, 331 (42) [M – 1]+.
2,3-Diphenylcyclopenta[b]naphthalen-1-one (21):[26] The general
procedure with 2-bromo-3-phenylethynylnaphthalene (307 mg,
1 mmol) and PhCONMe2 (194 mg, 1.3 mmol) afforded 21 as an
orange solid (232 mg, 67%). The compound was purified by col-
umn chromatography (silica gel) with toluene as eluent. Orange
1
solid; m.p. 196–198 °C. H NMR (270 MHz, CDCl3): δ = 8.06 (s,
1 H, 2-H-naph), 7.90 (m, 1 H), 7.74–7.72 (m, 1 H), 7.55–7.43 (m,
10 H), 7.33–7.27 (m, 3 H) ppm. IR (KBr): ν = 3057 (w), 3024 (w),
˜
1697 (s, C=O), 1624 (m), 1354 (s), 1150 (m), 901 (m), 802 (m), 789
(m), 731 (s), 696 (s) cm–1. MS (EI): m/z (%) = 332 (100) [M]+, 331
(67) [M – 1]+, 302 (37), 151 (41).
1,4-Bis(3-phenyl-inden-1-one-2-yl)benzene (22): The general pro-
cedure with 1,4-bis(2-bromophenylethynyl)benzene (438 mg,
1.00 mmol) and PhCONMe2 (521 mg, 3.5 mmol) afforded 22 as a
red solid (275 mg, 56%). The compound was purified by column
chromatography (silica gel) with toluene as eluent. Red solid; m.p.
(CϵC), 100.82 (CϵC), –0.53 (Si-CH ) ppm. IR (KBr): ν = 3065
˜
3
(w), 2961 (m), 2897 (w), 2158 (m, CϵC), 1661 (s, C=O), 1582 (m),
1450 (m), 1317 (m), 1292 (s), 1248 (s), 935 (m), 922 (m), 841 (s),
770 (s), 700 (s), 646 (m) cm–1. MS (EI): m/z (%) = 278 (11) [M]+,
263 (100) [M – CH3]+, 204 (93) [M – SiMe3]+.
Ͼ300 °C. 1H NMR (500 MHz, CDCl3): δ = 7.58–7.57 (m, J7,6
=
6.8 Hz, 2 H, 7-H), 7.41–7.35 (m, 12 H, 6-H, Ph-H), 7.30–7.27 (m,
J4,5,6 = 6.8 Hz, 2 H, 5-H), 7.19 (s, 4 H, 1,4-benzyl-H), 7.13–7.11
(m, J4,5 = 6.8 Hz, 2 H, 4-H) ppm. 13C NMR (125.8 MHz, CDCl3):
δ = 196.82 (C=O), 155.50, 145.27, 133.48, 132.71, 131.84, 130.79,
130.13, 129.61, 129.33, 128.99, 128.80, 128.46, 122.98, 121.26 ppm.
General Procedure for the Preparation of the Dibenzopentalenes 25
and 26
2-(2-Benzoylphenyl)-3-phenylindenone (24): tert-Butyllithium (1.6 m,
2.8 mL, 4.4 mmol) was added by syringe at –78 °C under N2 to a
solution of 2-bromo-1-(2-bromophenyl)ethynylbenzene (23,
336 mg, 1 mmol) in THF (15 mL). The reaction mixture was stirred
IR (KBr): ν = 3055 (w), 1705 (s, C=O), 1593 (m), 1456 (m), 1342
˜
(m), 1180 (m), 1074 (m), 926 (m), 858 (m), 792 (m), 772 (m), 752,
723, 698 (m), 542 (m) cm–1. MS (EI): m/z (%) = 486 (100) [M]+, at that temperature for 30 min, quenched with PhCONMe2
Eur. J. Org. Chem. 2011, 4885–4891
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4889

K. Katsumoto, C. Kitamura, T. Kawase
FULL PAPER
(328 mg, 2.2 mmol), and allowed to warm to room temp. The reac-
tion mixture was then stirred at room temp. for 90 min and ex-
tracted with toluene. The organic layer was washed with aq. ammo-
nium chloride, water, and brine and dried with anhydrous Na2SO4.
The solvent was removed and the residue was dissolved with 2 m
hydrochloric acid/acetone (1:1, 10 mL). The reaction mixture was
stirred at room temp. for 1 h and extracted with toluene. The or-
ganic layer was washed with aq. NaHCO3, water, and brine and
dried with anhydrous Na2SO4. After evaporation of the solvent,
the reddish residue was subjected to silica gel column chromatog-
raphy (15 g) with elution with toluene to afford 24 as reddish crys-
tals (250 mg, 65%). Orange solid (recrystallized from toluene); m.p.
[1]
[2]
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165 °C. 1H NMR (270 MHz, CDCl3): δ = 7.77–7.74 (m, Jo,m
=
8.6 Hz, 2 H, o-H-Ph), 7.51–7.13 (m, 16 H) ppm. 13C NMR
(125.8 MHz, CDCl3): δ = 197.17 (C=O), 195.48 (C=O), 155.56,
144.98, 139.66, 137.52, 133.80, 133.30, 132.47, 132.18, 131.71,
131.61, 130.92, 130.71, 130.26, 129.97, 129.43, 128.81, 128.59,
128.23, 128.06, 127.09, 123.17, 121.26 ppm. IR (KBr): ν = 3059
˜
(w), 1713 (s, C=O), 1651 (s, C=O), 1595 (m), 1312 (m), 1269 (m),
930 (m), 762 (m), 698 (s), 640 (m) cm–1. MS (EI): m/z (%) = 386
(100) [M]+, 357 (31), 281 (66) [M – COC6H5]+, 252 (40). C28H18O2
(386.45): calcd. C 87.02, H 4.69; found C 86.85, H 4.96.
[3]
[4]
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5,10-Diphenylindeno[2,1-a]indene (25):[5g] A suspension of zinc dust
(0.654 g, 10 mmol) and TiCl4 (0.45 mL, 4.07 mmol) in THF
(20 mL) was stirred at reflux under N2 for 2 h. The reaction mixture
was cooled by immersion in an ice bath. A solution of 24
(1.0 mmol) with THF (30 mL) was added dropwise to the suspen-
sion from a titration funnel. The reaction mixture was heated at
reflux in an oil bath for 18 h. The dark reddish reaction mixture
was subjected to column chromatography on alumina with toluene
as eluent to remove insoluble materials. The crude product was
purified by column chromatography on silica gel (toluene elution)
to afford 25 as dark reddish crystals (220 mg, 63%). 1H NMR
(500 MHz, CDCl3): δ = 7.67 (m, Jo,m = 8.4 Hz, 4 H, o-H-Ph), 7.54–
7.51 (m, 4 H, m-H-Ph), 7.47–7.44 (m, 2 H, p-H-Ph), 7.22 (m, J1,2
= 6.6 Hz, 2 H, 1-H-H, 5-H), 7.03 (m, J3,4 = 6.9 Hz, 2 H, 4-H, 8-
H), 6.91–6.80 (m, 4 H, 2-H, 3-H, 6-H, 7-H) ppm.
Attack of γ-amino groups on α-acetylenic carbon atoms is
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5,10-Bis(4-methylphenyl)indeno[2,1-a]indene (26): This compound
was prepared from 23 and N,N-dimethyl-4-methylbenzamide by the
general procedure (163 mg, 39%). Black solid; m.p. 232–233 °C. 1H
NMR (270 MHz, CDCl3): δ = 7.58–7.55 (m, JAB = 7.9 Hz, 4 H,
AAЈBBЈ, o-H-pTol), 7.34–7.30 (m, JBA = 7.9 Hz, 4 H, AAЈBBЈ, m-
[6]
[7]
[8]
[9]
H-pTol), 7.21 (m, J1,2 = 6.8 Hz, 2 H, 1-H, 5-H), 7.03 (m, J3,4
=
6.9 Hz, 2 H, 4-H, 8-H), 6.90–6.81 (m, 4 H, 2-H, 3-H, 6-H, 7-H),
2.45 (s, 6 H, CH3) ppm. 13C NMR (125.8 MHz, CDCl3): δ =
149.67, 142.76, 140.53, 138.79, 135.33, 131.00, 129.36, 128.47,
127.60, 127.32, 122.44, 121.85, 21.54 (CH ) ppm. IR (KBr): ν =
˜
3
3038 (w), 1611 (m), 1506 (m), 1431 (s), 1182 (m), 816 (m), 744 (s),
523 (m) cm–1. MS (EI): m/z (%) = 382 (100) [M]+, 289 (5), 191 (12),
181 (10), 176 (17). C30H22 (382.50): calcd. C 94.20, H 5.80; found
C 94.44, H 6.02.
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Supporting Information (see footnote on the first page of this arti-
1
cle): H NMR spectra of new compounds.
Acknowledgments
This work was supported by Grants-in-Aid for Scientific Research
on Innovative Areas from the Ministry of Education, Culture,
Sports, Science and Technology, Japan (No. 21108521 and
23108719, “pi-Space”).
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4890
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 4885–4891

An Indenone Synthesis Involving a New Aminotransfer Reaction
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Hydrogen atoms were refined isotropically and refined with use
of a riding model. All calculations were performed with the
WinGX program package. CCDC-817430 (for 24) contains the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Crystallographic data for 24: C28H18O2; Mw = 386.42, a =
10.572(2) Å, b = 12.740(3) Å, c = 15.231(3) Å, β = 106.201(3)°,
V = 1970.0(7) Å3, monoclinic, space group P21/n (#14), Z = 4,
T = 223 K, Dcalcd. = 1.303 gcm–3, F(000)= 808, R1 [IϾ2σ(I)]
= 0.0466, wR2 (all data) = 0.1376, GOF = 0.955, refl./param.
= 4833/272.
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slow evaporation from n-hexane. X-ray diffraction data were
collected with a Rigaku/Mercury CCD area-detector dif-
fractometer and use of graphite-monochromated Mo-Kα (α =
0.71073 Å) radiation, Φ and ω scans to a maximum 2θ value
of 55.0°. The structures were solved by a direct method by use
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Received: April 25, 2011
Published Online: July 13, 2011
Eur. J. Org. Chem. 2011, 4885–4891
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4891