Ruthenium-catalyzed regioselective cyclization of aromatic ketones with alkynes: An efficient route to indenols and benzofulvenes

Article abstract of DOI:10.1002/ejoc.201101364

The reactions of substituted acetophenones with diphenylacetylene in the presence of [{RuCl₂(p-cymene)}₂] (2 mol-%), AgSbF ₆ (8 mol-%), and Cu(OAc)₂·H₂O (25 mol-%) in 1,2-dichloroethane at 120 °C for

Full text of DOI:10.1002/ejoc.201101364

FULL PAPER
DOI: 10.1002/ejoc.201101364
Ruthenium-Catalyzed Regioselective Cyclization of Aromatic Ketones with
Alkynes: An Efficient Route to Indenols and Benzofulvenes
Ravi Kiran Chinnagolla[a] and Masilamani Jeganmohan*[a]
Keywords: C–H activation / Metalation / Ruthenium / Cyclization / Ketones / Alkynes
The reactions of substituted acetophenones with diphenyl-
acetylene in the presence of [{RuCl2(p-cymene)}2] (2 mol-%),
AgSbF6 (8 mol-%), and Cu(OAc)2·H2O (25 mol-%) in 1,2-
dichloroethane at 120 °C for 10 h provided substituted ind-
enol derivatives in good-to-excellent yields. Under similar re-
action conditions, unsymmetrical alkynes such as 1-phenyl-
1-propyne, 1-phenyl-1-butyne, 1-phenyl-2-(trimethylsilyl)-
acetylene, and a substituted enyne also reacted efficiently
with substituted acetophenones to afford the corresponding
indenol derivatives in a highly regioselective manner. The
amount of silver salt plays a key role in the reaction. When
the amount of silver salt exceeded more than 8 mol-% in the
presence of 2 mol-% [{RuCl2(p-cymene)}2], a different type
of dehydration product, namely a benzofulvene derivative,
started to appear. In the presence of 20 mol-% AgSbF6, sub-
stituted acetophenones readily reacted with alkynes in the
presence of [{RuCl2(p-cymene)}2] (2 mol-%) to give benzo-
fulvene derivatives in excellent yields. A plausible reaction
mechanism is proposed to account for the cyclization reac-
tion.
Ackermann et al. reported a ruthenium-catalyzed oxidative
cyclization of acrylamides with alkynes[11a,11b] as well as the
cyclization of aromatic acids with alkenes.[11c]
Introduction
The transition-metal-catalyzed carbocyclization reaction
is one of the most efficient methods for constructing carbo-
and heterocyclic compounds in one pot.[1] Several ap-
proaches have been reported in the literature for the synthe-
sis of cyclic compounds in the presence of metal catalysts.[1]
Of these approaches, the cyclization of o-haloaromatic car-
bonyls or imines with π components has been established
as a powerful synthetic method.[2] More recently, the cycli-
zation of o-acylphenylboronic acids with π components has
been used to synthesize cyclic compounds.[3] In carbocycli-
zation reactions, a preactivated coupling partner such as a
C–X or C–M reagent is usually required as a starting mate-
rial to construct the carbo- and heterocyclic compounds.
However, if the cyclization could be carried out directly by
C–H bond activation instead of with a preactivated species,
it would be very useful because this would be highly atom
economic as well as an environmentally friendly process.[4–6]
In this regard, transition-metal chelation-assisted cycliza-
tion of the ortho aromatic C–H bond with π components is
a very useful method for the construction of cyclic com-
pounds.[6] In general, mostly rhodium complexes have pre-
viously been used as catalysts in this cyclization reaction[7,8]
and the use of less-expensive ruthenium catalysts in carbo-
cyclization processes is underexplored.[9,10] Very recently,
In this paper we wish to report the cyclization of aro-
matic ketones with alkynes in the presence of a less expens-
ive ruthenium catalyst. This method offers a general
method for the highly regioselective synthesis of indenols
and benzofulvenes in good-to-excellent yields. The reac-
tions of aromatic ketones with alkynes in the presence of
[RuH2(CO)(PPh3)3] have been reported in the litera-
ture,[12a,12b] however, only addition products were observed
(Scheme 1). Similar carbonyl-directed C–H activated alken-
ylation reactions with alkynes have also been studied by
other research groups.[12c–12i] In contrast, in this work, cy-
clic products were exclusively observed for the reaction per-
formed in the presence of [{RuCl2(p-cymene)}2] (Scheme 1).
Scheme 1.
Results and Discussion
[a] Department of Chemistry, Indian Institute of Science
Education and Research,
In the presence of [{RuCl2(p-cymene)}2] (2 mol-%),
AgSbF6 (8 mol-%), and Cu(OAc)2·H2O (25 mol-%), 4-bro-
moacetophenone (1a) reacted with diphenylacetylene (2a)
in 1,2-dichloroethane (DCE) at 120 °C for 10 h to give ind-
Pune 411021, India
Fax: +91-20-25865315
E-mail: mjeganmohan@iiserpune.ac.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201101364.
Eur. J. Org. Chem. 2012, 417–423
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
417

R. K. Chinnagolla, M. Jeganmohan
FULL PAPER
enol derivative 3a in 89% isolated yield (Scheme 2). The variety of sensitive functional groups such as I, Br, OMe,
reaction was completely atom economic. Interestingly, only and NH on the aromatic and heteroaromatic rings of 1
a catalytic amount of oxidant Cu(OAc)2·H2O (25 mol-%) (Scheme 2 and Table 1).
was required, whereas in most rhodium-catalyzed reactions
stoichiometric amounts of oxidant were used.[7,8] Control
Table 1. Ruthenium-catalyzed cyclization reactions of substituted
aromatic ketones 1b–h with diphenylacetylene (2a).[a]
experiments revealed that no reaction occurred at all in the
absence of [{RuCl2(p-cymene)}2], AgSbF6, or Cu(OAc)2·
H2O. Note that substituted indenol derivatives are known
to show important biological properties such as analgesic,
insecticidal, and myorelaxation activity.[13]
Scheme 2. Reaction of 4-bromoacetophenone (1a) with diphenyl-
acetylene (2a) in the presence of ruthenium catalyst.
To optimize this ruthenium-catalyzed cyclization reac-
tion, the reaction of 1a with 2a in the presence of
[{RuCl2(p-cymene)}2] (2 mol-%) was examined with various
solvents, additives (8 mol-%), and Cu(OAc)2·H2O (25 mol-
%). The reaction was first tested in various solvents. Of the
solvents tested, 1,2-dichloromethane (DCE) was the most
effective, affording 3a in 96% yield. The yield of 3a was
1
determined by the H NMR integration method using me-
sitylene as the internal standard. Toluene was also effective,
providing 3a in 55% yield. Other solvents such as THF and
tert-amyl alcohol were less effective, giving 3a in yields of
25 and 15%, respectively. Other solvents such as DMF,
CH3CN, and CH3COOH were totally ineffective. Next, the
effect of the silver salt (8 mol-%) was examined. A variety
of silver salts such as AgSbF6, AgOTf, AgBF4, AgOAc, Ag-
O2CCF3, and Ag2O were tested. Of these, AgSbF6 was very
effective, giving 3a in 96% yield. AgOTf and AgBF4 were
less effective, giving 3a in yields of 40 and 21%, respectively.
AgOAc, AgO2CCF3, and Ag2O were totally ineffective.
This ruthenium-catalyzed cyclization reaction was suc-
[a] All reactions were carried out with substituted aromatic ketones
1 (1.00 mmol), diphenylacetylene (2a) (1.20 mmol), [{RuCl2(p-
cymene)}2] (2 mol-%), AgSbF6 (8 mol-%), Cu(OAc)2·H2O (25 mol-
%), and 1,2-dichloroethane (3.0 mL) at 120 °C for 10 h. [b] Isolated
yields.
cessfully extended to different substituted aromatic ketones
1b–h and substituted alkynes 2b–e (Table 1 and Table 2).
The reaction of acetophenone (1b) with diphenylacetylene
(2a) under the optimized reaction conditions, that is,
[{RuCl2(p-cymene)}2] (2 mol-%), AgSbF6 (8 mol-%), and
Cu(OAc)2·H2O (25 mol-%) in 1,2-dichloroethane afforded
Next we examined the reaction of various substituted un-
product 3b in 83% yield (Table 1, entry 1). Similarly, iso- symmetrical alkynes 2b–e with substituted aromatic ketones
butyrophenone (1c) and benzophenone (1d) reacted with 1a 1 (Table 2). In all these reactions, complete regioselectivity
to give the corresponding cyclization products 3c and 3d in was observed. Thus, 1-phenyl-1-propyne (2b) and 1-phenyl-
yields of 76 and 73%, respectively (entries 2 and 3). Under 1-butyne (2c) underwent cyclization with 4-iodoaceto-
similar conditions, 4-iodoacetophenone (1e) and 4-meth- phenone (1e) or acetophenone (1b) to give products 3i and
oxyacetophenone (1f) reacted well with 2a to afford ind- 3j in yields of 83 and 79%, respectively, in a highly regiose-
enols 3e and 3f in yields of 88 and 85%, respectively (en- lective manner (Table 2, entries 1 and 2). In the indenols 3i
tries 4 and 5). The reaction of 1-naphthophenone (1g) with and 3j, the alkynic phenyl group is placed at the C-2 carbon
2a provided 3g exclusively in 82% yield (entry 6) with the next to the alcohol group and the alkyl group at the C-3
C–H bond activation taking place at the carbon adjacent carbon. The regiochemistry of the reactions was established
to the acetyl group of 1g. This catalytic reaction was also by NOESY experiments (see the Supporting Information).
tested with a heteroaromatic compound: Treatment of ind- Similarly, in the reaction of 1-phenyl-2-(trimethylsilyl)-
ole-3-acetophenone (1h) with 2a gave 3h in 69% yield (en- acetylene (2d) with 1c, the silylated indenol derivative 3k
try 7). It is significant that this catalytic reaction tolerates a was obtained in 76% yield in a highly regioselective manner
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Regioselective Cyclization of Aromatic Ketones with Alkynes
with the Ph group attached to C-2 and the silyl group at- 1,2-dichloroethane at 120 °C for 10 h afforded benzofulvene
tached to C-3 (entry 3). It is significant that most metal- derivative 4a in 93% isolated yield (Table 3, entry 1). Re-
catalyzed chelation-assisted cyclization reactions of the or- cently, Shibata and co-workers reported the synthesis of
tho aromatic C–H bond with 2d provide only desilylated benzofulvene derivatives by the iridium-catalyzed ortho C–
compounds.[7d,14] The catalytic reaction was also tested with H bond alkenylation of aryl ketones with alkynes followed
substituted unsymmetrical enyne 2e, which reacted with 1c by cyclization and dehydration.[8g,9] It is significant that
to give a single regioisomeric product 3l in 71% yield with benzofulvene derivatives find versatile applications in mate-
the Ph group present at the C-2 carbon (entry 4).
rials science, organometallics, and medicinal chemistry.[15]
Table 2. Ruthenium-catalyzed cyclization reactions of substituted
aromatic ketones 1b,c,e with unsymmetrical alkynes 2b–e.[a]
Table 3. Ruthenium-catalyzed synthesis of benzofulvene deriva-
tives.[a]
[a] All reactions were carried out with substituted aromatic ketones
1b,c,e (1.00 mmol), alkynes 2 (1.20 mmol), [{RuCl2(p-cymene)}2]
(2 mol-%), AgSbF6 (8 mol-%), Cu(OAc)2·H2O (25 mol-%), and 1,2-
dichloroethane (3.0 mL) at 120 °C for 10 h. [b] Isolated yields.
In the cyclization reactions, the alkynic carbon atom
bearing the less electron-donating substituent (Ph) connects
to the keto group of 1 and the alkynic carbon atom with
the more electron-donating substituent (Me, Et, and SiMe3)
attaches to the ortho carbon of the aryl ketone moiety. This
regiochemistry exactly matches that observed for the cycli-
zation reactions of o-halophenyl ketones with unsymmetri-
cal alkynes in the presence of cobalt and nickel cata-
lysts.[2a–2d] Although the exact reason for this is not clear,
the Michael-type addition pattern dominates the product
distribution and the trend in regiochemistry is as proposed
by Cheng and co-workers.[2a–2d]
The amount of silver salt plays an important role in the
reaction. When the amount of silver salt exceeded 8 mol-
% in the presence of 2 mol-% of [{RuCl2(p-cymene)}2], a
different type of dehydration product, namely a benzo-
fulvene derivative, started to appear (see below). Thus,
treatment of 4-bromoacetophenone (1a) with diphenylacet-
ylene (2a) in the presence of [{RuCl2(p-cymene)}2] (2 mol-
[a] All reactions were carried out with substituted acetophenones
1 (1.00 mmol), alkyne 2 (1.20 mmol), [{RuCl2(p-cymene)}2] (2 mol-
%), AgSbF6 (20 mol-%), Cu(OAc)2·H2O (25 mol-%), and 1,2-
dichloroethane (3.0 mL) at 120 °C for 10 h. [b] Isolated yields. [c]
%), AgSbF6 (20 mol-%), and Cu(OAc)2·H2O (25 mol-%) in E:Z stereoisomeric ratio: 4h 85:15, 4i 98:2.
Eur. J. Org. Chem. 2012, 417–423
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419

R. K. Chinnagolla, M. Jeganmohan
FULL PAPER
In the presence of an excess amount of silver salt termediate 6. Intramolecular insertion of the C=O group
(20 mol-%), acetophenone (1b), 4-iodoacetophenone (1e), into the Ru–alkenyl bond of 6 affords the five-membered
4-methoxyacetophenone (1f), 4-methylacetophenone (1i), ruthenium alkoxide intermediate 7. Protonation of the in-
and 4-fluoroacetophenone (1j) efficiently reacted with 2a to termediate 7 by means of Cu(OAc)2 provided the final
provide benzofulvene derivatives 4b–f in yields of 86–92% product 3 and regenerated the active ruthenium species for
(Table 3, entries 2–6). Similarly, 1-napthophenone (1g) af- the next catalytic cycle. The exact role of the copper source
forded 4g exclusively in 80% yield (entry 7) with the C–H in the reaction is not clear, but we propose that Cu(OAc)2·
bond activation taking place at the carbon atom adjacent H2O provides the OAc– source to the active ruthenium spe-
to the acetyl group. Likewise, propiophenone (1k) and 2- cies to accelerate the ortho-metalation and also to replace
phenylacetophenone (1l) also reacted efficiently with 2a to the ruthenium species in intermediate 7 by transmetalation
give benzofulvene derivatives 4h and 4i in yields of 85 and in the first catalytic cycle. In subsequent catalytic cycles,
82% with E/Z ratios of 85:15 and 98:2, respectively (en- protonation of the intermediate 7 by AcOH provides the
tries 8 and 9). Interestingly, benzophenone (1d) reacted with final product 3 and regenerates the active ruthenium species
the unsymmetrical 1-phenyl-1-propyne (2b) to give 4b in for the next catalytic cycle.
75% yield (entry 10). In this reaction, one of the hydrogen
In this reaction the amount of silver salt added deter-
atoms of the methyl group of the C-3 carbon of the indenol mines the nature of the product. The role of the silver salt,
moiety (intermediate) was involved in intramolecular de- as stated above, is likely to remove chloride ligands from
hydration [Reaction (1)]. Note that no dehydration product [{RuCl2(p-cymene)}2]. In the reaction, 2 mol-% of
was observed in the reaction of isobutyrophenone (1c) with [{RuCl2(p-cymene)}2] was used and 8 mol-% of Ag salt is
diphenylacetylene (2a), even in the presence of an excess enough to remove all four chloride ligands. When the
amount of the silver salt (20 mol-%).
amount of silver salt exceeded 8 mol-%, the dehydration
product benzofulvene was observed. The formation of this
product can be explained by the coordination of the alcohol
group of indenol 3 to the excess silver salt followed by sub-
sequent dehydration. The proposed silver-catalyzed dehy-
dration pathway is strongly supported by Reaction (2):
Treatment of indenol 3a (1.0 mmol) with AgSbF6 (20 mol-
%) in the presence of DCE at 120 °C for 10 h gave the prod-
uct 4a in 94% yield.
(1)
Based on the above observations and known metal-cata-
lyzed C–H bond activation reactions,[4–10] a plausible reac-
tion mechanism is proposed in Scheme 3. The first step
likely starts with the removal of the chloride ligands from
the [{RuCl2(p-cymene)}2] complex with the aid of the Ag+
salt. Next, coordination of the carbonyl oxygen of 1 to the
active ruthenium cationic species followed by ortho met-
alation provides intermediate 5. Coordinative insertion of
alkyne 2 into the Ru–C bond of intermediate 5 affords in-
(2)
Conclusions
We have developed a highly regioselective ruthenium-cat-
alyzed cyclization of substituted aromatic ketones with
alkynes that occurs by C–H bond activation. This method-
ology offers a simple and mild method for the synthesis of
indenols and benzofulvenes in a highly regioselective man-
ner. The amount of silver salt used determined the nature
of the product: In the presence of 2 mol-% of the ruthenium
catalyst, 8 mol-% of the silver salt favored the formation of
indenols whereas with 20 mol-% of the silver salt benzo-
fulvenes were obtained. Extending the scope of these cycli-
zation reactions to other π components is underway as well
a detailed study of the reaction mechanism.
Experimental Section
General Procedure for the Cyclization of Aromatic Ketones 1 with
Alkynes 2: A 15 mL pressure tube containing [{RuCl2(p-cymene)}2]
(2 mol-%), AgSbF6 (8 mol-%), and Cu(OAc)2·H2O (25 mol-%) was
Scheme 3. Proposed mechanism for the cyclization reaction.
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Regioselective Cyclization of Aromatic Ketones with Alkynes
evacuated and purged with nitrogen gas three times. Freshly dis-
1
(ATR): ν = 3356, 2924, 1591, 1474, 1030 cm–1. H NMR (CDCl ,
˜
3
tilled 1,2-dichloromethane (3.0 mL), aromatic ketones
1
400 MHz): δ = 7.39–7.36 (m, 3 H), 7.27–7.24 (m, 5 H), 7.14–7.13
(m, 3 H), 6.72 (s, 1 H), 6.70 (d, J = 8.0 Hz, 1 H), 3.71 (s, 3 H),
2.04 (br. s, 1 H), 1.50 (s, 3 H) ppm. 13C NMR (CDCl3, 100 MHz):
δ = 160.5, 148.3, 143.9, 141.8, 138.4, 134.9, 134.7, 129.5, 129.4,
128.7, 128.1, 127.7, 127.4, 122.6, 111.1, 107.6, 82.9, 55.7, 24.2 ppm.
HRMS (EI): calcd. for C23H20O2 328.1463; found 328.1460.
(1.00 mmol) and alkynes 2 (1.20 mmol) were sequentially added to
the system and the reaction mixture was stirred at 120 °C for 10 h.
The mixture was filtered through a short Celite and silica gel pad
and washed with dichloromethane several times. The filtrate was
concentrated and the residue was purified on a silica gel column
using hexanes/ethyl acetate as eluent to afford the cyclization prod-
ucts 3. Products 4a–i were also synthesized according to this pro-
cedure, but 20 mol-% of AgSbF6 were required.
1-Methyl-2,3-diphenyl-1H-cyclopenta[a]naphthalen-1-ol (3g): Red
semi-solid; eluent: 10% ethyl acetate in hexanes. IR (ATR): ν =
˜
3417, 2922, 1589, 1127 cm–1. 1H NMR (CDCl3, 400 MHz): δ =
8.29 (d, J = 8.0 Hz, 1 H), 7.77 (d, J = 8.0 Hz, 1 H), 7.67 (d, J =
8.0 Hz, 1 H), 7.43–7.37 (m, 3 H), 7.35–7.31 (m, 3 H), 7.26–7.20 (m,
5 H), 7.14–7.07 (m, 2 H), 2.21 (br. s, 1 H), 1.65 (s, 3 H) ppm. 13C
5-Bromo-1-methyl-2,3-diphenyl-1H-inden-1-ol (3a): Yellow solid;
m.p. 127–129 °C; eluent: 10% ethyl acetate in hexanes. IR (ATR):
ν = 3396, 2923, 1589, 1453, 1264, 1082 cm–1. 1H NMR (CDCl3,
˜
400 MHz): δ = 7.41–7.38 (m, 4 H), 7.34–7.30 (m, 4 H), 7.28–7.21 NMR (CDCl3, 100 MHz): δ = 148.5, 143.2, 139.2, 138.6, 135.1,
(m, 5 H), 2.02 (br. s, 1 H), 1.55 (s, 3 H) ppm. 13C NMR (CDCl3, 134.8, 133.1, 129.7, 129.5, 129.2, 129.1, 128.7, 128.6, 128.1, 127.7,
100 MHz): δ = 148.3, 148.2, 144.3, 137.8, 134.3, 134.0, 129.5, 129.3,
129.2, 128.8, 128.2, 127.9, 127.7, 124.0, 123.3, 122.6, 83.0,
24.0 ppm. GC–MS (70 eV, CI): m/z = 377 [M + H]+, 201, 199, 119,
92. HRMS (EI): calcd. for C22H17OBr 376.0463; found 376.0468.
127.4, 126.6, 125.0, 124.0, 119.6, 85.1, 25.1 ppm. GC–MS (70 eV,
CI): m/z = 349 [M + H]+, 346, 338, 328, 128. HRMS (EI): calcd.
for C26H20O 348.1514; found 348.1509.
1-Methyl-2,3-diphenyl-1,4-dihydrocyclopenta[b]indol-1-ol (3h): Red
1-Methyl-2,3-diphenyl-1H-inden-1-ol (3b): Pale-yellow solid; m.p.
semi-solid; eluent: 35% ethyl acetate in hexanes. IR (ATR): ν =
˜
123–125 °C; eluent: 10% ethyl acetate in hexanes. IR (ATR): ν =
3372 (br., s), 2923, 1611, 1430, 1025 cm–1. 1H NMR (CDCl3,
400 MHz): δ = 8.51 (dd, J = 8.0, 4.0 Hz, 2 H), 7.37–7.28 (m, 6 H),
7.16–7.11 (m, 3 H), 7.05–6.99 (m, 3 H), 1.26 (s, 3 H) ppm. 13C
NMR (CDCl3, 100 MHz): δ = 142.0, 140.3, 135.6, 135.5, 133.1,
132.6, 129.8, 129.7, 117.0, 129.2, 129.1, 129.0, 128.7, 126.5, 123.9,
123.3, 122.9, 111.3, 90.3, 14.3 ppm. HRMS (ESI): calcd. for
˜
3369, 2924, 1596, 1451, 1269 cm–1. 1H NMR (CDCl3, 400 MHz):
δ = 7.52 (d, J = 8.0 Hz, 1 H), 7.44–7.41 (d, J = 8.0 Hz, 2 H), 7.34–
7.29 (m, 5 H), 7.26–7.24 (m, 2 H), 7.23–7.20 (m, 4 H), 2.01 (br. s,
1 H), 1.59 (s, 3 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 149.6,
147.0, 142.3, 138.8, 134.8, 129.5, 129.3, 128.9, 128.6, 127.9, 127.4,
127.2, 127.2, 126.7, 122.0, 120.9, 83.4, 24.0 ppm. GC–MS (70 eV, C24H20NO [M + H]+ 338.1545; found 338.1530.
CI): m/z = 298 [M + H]+, 252, 123. HRMS (ESI): calcd. for
5-Iodo-1,3-dimethyl-2-phenyl-1H-inden-1-ol (3i): Orange oil; eluent:
10% ethyl acetate in hexanes. IR (ATR): ν = 3345, 2923, 1447,
C22H18ONa [M + Na]+ 321.1255; found 321.1263.
˜
1-Isopropyl-2,3-diphenyl-1H-inden-1-ol (3c): Pale-yellow solid; m.p. 1081 cm–1. 1H NMR (CDCl3, 400 MHz): δ = 7.58 (d, J = 8.0,
151–153 °C; eluent: 10% ethyl acetate in hexanes. IR (ATR): ν = 4.0 Hz, 1 H), 7.56 (s, 1 H), 7.52–7.50 (m, 2 H), 7.43–7.40 (m, 2 H),
˜
3439, 2925, 1596, 1456, 1026 cm–1. 1H NMR (CDCl3, 400 MHz):
δ = 7.51 (d, J = 8.0 Hz, 1 H), 7.43 (d, J = 8.0 Hz, 1 H), 7.34–7.29
(m, 3 H), 7.28–7.23 (m, 4 H), 7.22–7.18 (m, 5 H), 2.21–2.16 (m, 1
7.35 (t, J = 8.0 Hz, 1 H), 7.18 (d, J = 8.0 Hz, 1 H), 2.05 (s, 3 H),
1.92 (br. s, 1 H), 1.45 (s, 3 H) ppm. 13C NMR (CDCl3, 100 MHz):
δ = 148.9, 147.8, 145.8, 135.3, 134.9, 133.6, 129.2, 128.8, 128.5,
H), 2.14 (br. s, 1 H), 1.21 (d, J = 8.0 Hz, 3 H), 0.57 (d, J = 8.0 Hz, 127.8, 123.4, 94.2, 83.0, 23.8, 11.7 ppm. HRMS (ESI): calcd. for
3 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 146.6, 146.4, 143.9,
140.4, 135.4, 134.8, 129.6, 129.4, 128.5, 128.4, 128.0, 127.5, 127.3,
126.1, 123.6, 120.7, 89.2, 34.0, 16.9, 16.8 ppm. GC–MS (70 eV, CI):
m/z = 327 [M + H]+, 315, 298, 221. HRMS (ESI): calcd. for
C24H22ONa [M + Na]+ 349.1568; found 349.1568.
C17H16IO [M + H]+ 363.0246; found 363.0242.
3-Ethyl-1-methyl-2-phenyl-1H-inden-1-ol (3j): Orange semi-solid;
eluent: 10% ethyl acetate in hexanes. IR (ATR): ν = 3349, 2969,
˜
1597, 1457, 1363, 1088 cm–1. 1H NMR (CDCl3, 400 MHz): δ =
7.45–7.42 (m, 2 H), 7.41–7.36 (m, 3 H), 7.33–7.28 (m, 2 H), 7.26–
7.18 (m, 2 H), 2.46 (q, J = 8.0 Hz, 2 H), 1.88 (br. s, 1 H), 1.44 (s,
3 H), 1.17 (t, J = 8.0 Hz, 3 H) ppm. 13C NMR (CDCl3, 100 MHz):
δ = 149.6, 146.5, 142.3, 140.1, 135.4, 129.1, 128.5, 128.3, 127.5,
126.3, 121.8, 119.9, 83.1, 23.8, 19.3, 13.6 ppm. HRMS (EI): calcd.
for C18H18O 250.1358; found 250.1363.
1,2,3-Triphenyl-1H-inden-1-ol (3d): Colorless solid; m.p. 206–
208 °C; eluent: 10% ethyl acetate in hexanes. IR (ATR): ν = 3438,
˜
2922, 1591, 1449, 1125 cm–1. 1H NMR (CDCl3, 400 MHz): δ =
7.66 (d, J = 8.0 Hz, 2 H), 7.53 (t, J = 8.0 Hz, 2 H), 7.49–7.45 (m,
3 H), 7.36–7.31 (m, 6 H), 7.27–7.23 (m, 3 H), 7.15–7.12 (m, 3 H),
2.91 (br. s, 1 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 151.2,
147.7, 142.9, 141.9, 140.8, 135.1, 133.9, 129.8, 129.2, 128.7, 128.5,
128.4, 127.8, 127.3, 127.1, 125.3, 123.1, 121.2, 87.2 ppm. GC–MS
(70 eV, CI): m/z = 361 [M + H]+, 294, 176, 142, 134. HRMS (ESI):
calcd. for C27H20ONa [M + Na]+ 383.1412; found 383.1412.
1-Isopropyl-2-phenyl-3-(trimethylsilyl)-1H-inden-1-ol (3k): Orange
oil; eluent: 4% ethyl acetate in hexanes. IR (ATR): ν = 3402, 1580,
˜
1
1128 cm–1. H NMR (CDCl3, 400 MHz): δ = 7.45 (d, J = 8.0 Hz,
1 H), 7.38–7.31 (m, 4 H), 7.29–7.24 (m, 3 H), 7.15 (d, J = 8.0 Hz,
1 H), 2.00–1.97 (m, 1 H), 1.95 (br. s, 1 H), 1.15 (d, J = 8.0 Hz, 3
H), 0.56 (d, J = 8.0 Hz, 3 H), 0.02 (s, 9 H) ppm. 13C NMR (CDCl3,
100 MHz): δ = 146.8, 146.1, 139.8, 137.6, 129.5, 128.5, 128.3, 128.0,
127.8, 125.1, 123.5, 122.6, 89.7, 33.2, 17.1, 16.4, 0.3 ppm. HRMS
(EI): calcd. for C21H26OSi 322.1753; found 322.1758.
5-Iodo-1-methyl-2,3-diphenyl-1H-inden-1-ol (3e): Pale-yellow solid;
m.p. 151–153 °C; eluent: 10% ethyl acetate in hexanes. IR (ATR):
ν = 3367, 2923, 1589, 1449, 1085 cm–1. 1H NMR (CDCl3,
˜
400 MHz): δ = 7.51 (d, J = 8.0 Hz, 1 H), 7.43 (s, 1 H), 7.31 (dd, J
= 8.0, 4.0 Hz, 2 H), 7.26–7.22 (m, 3 H), 7.19–7.16 (m, 2 H), 7.15–
7.12 (m, 4 H), 1.57 (s, 3 H) ppm. 13C NMR (CDCl3, 100 MHz): δ
= 149.1, 148.0, 144.5, 137.9, 135.5, 134.3, 134.1, 129.8, 129.5, 129.2,
128.9, 128.2, 127.9, 127.7, 123.8, 94.2, 83.2, 24.0 ppm. HRMS (EI):
calcd. for C22H17OI 424.0324; found 424.0331.
3-(Cyclohex-1-en-1-yl)-1-isopropyl-2-phenyl-1H-inden-1-ol
(3l):
˜
Orange oil; eluent: 10% ethyl acetate in hexanes. IR (ATR): ν =
3422, 2930, 1591, 1456, 1370, 1267, 1035 cm–1. H NMR (CDCl3,
1
400 MHz): δ = 7.65 (d, J = 8.0 Hz, 1 H), 7.39–7.31 (m, 4 H), 7.29–
7.23 (m, 3 H), 7.10 (t, J = 8.0 Hz, 1 H), 5.77 (t, J = 4.0 Hz, 1 H),
5-Methoxy-1-methyl-2,3-diphenyl-1H-inden-1-ol (3f): Pale-yellow 2.31–2.25 (m, 1 H), 2.18–2.11 (m, 2 H), 2.09–2.01 (m, 1 H), 1.91–
solid; m.p. 142–144 °C; eluent: 15% ethyl acetate in hexanes. IR 1.85 (m, 2 H), 1.79–1.61 (m, 3 H), 1.13 (d, J = 8.0 Hz, 3 H), 0.51
Eur. J. Org. Chem. 2012, 417–423
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
421

R. K. Chinnagolla, M. Jeganmohan
(d, J = 8.0 Hz, 3 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 146.7, 123.6, 119.6, 110.9 ppm. GC–MS (70 eV, CI): m/z
331
FULL PAPER
=
143.7, 136.2, 135.9, 132.3, 129.1, 128.8, 128.2, 127.9, 127.2, 125.7,
123.4, 120.5, 88.9, 34.1, 28.0, 25.5, 22.9, 22.2, 16.9, 16.7 ppm.
HRMS (EI): calcd. for C24H26O 330.1984; found 330.1983.
[M + H]+, 281, 268, 209, 191. HRMS (ESI): calcd. for C26H19 [M
+ H]+ 331.1487; found 331.1487.
(E)- and (Z)-1-Ethylidene-2,3-diphenyl-1H-indene (4h): Pale-yellow
oil; eluent: hexanes. E/Z ratio 85:15. 1H NMR (CDCl3, 400 MHz):
δ = 7.89 (d, J = 8.0 Hz, 1 H) (major isomer), 7.65 (d, J = 8.0 Hz,
1 H) (minor isomer), 7.42 (t, J = 8.0 Hz, 1 H), 7.33–7.22 (m, 10
H), 7.19–7.16 (m, 2 H), 6.90 (q, J = 8.0 Hz, 1 H) (minor isomer),
6.37 (q, J = 8.0 Hz, 1 H) (major isomer), 2.40 (d, J = 8.0 Hz, 3 H)
(major isomer), 1.68 (d, J = 8.0 Hz, 1 H) (minor isomer) ppm. 13C
NMR (CDCl3, 100 MHz): δ = 143.6, 141.7, 139.5, 138.7, 137.8,
135.4, 135.3, 135.0, 132.9, 131.2, 130.4, 129.7, 129.5, 128.2, 128.1,
127.9, 127.3, 127.1, 127.0, 126.9, 125.4, 125.3, 123.9, 120.3, 120.0,
118.4, 15.9, 15.6 ppm. GC–MS (70 eV, CI): m/z = 295 [M + H]+,
278, 217, 145.
5-Bromo-1-methylene-2,3-diphenyl-1H-indene (4a): Pale-yellow
1
semi-solid; eluent: hexanes. H NMR (CDCl3, 400 MHz): δ = 7.56
(d, J = 8.0 Hz, 1 H), 7.46 (s, 1 H), 7.40 (dd, J = 8.0, 4.0 Hz, 1 H),
7.35–7.29 (m, 4 H), 7.28–7.25 (m, 4 H), 7.19–7.17 (m, 2 H), 6.25
(s, 1 H), 5.77 (s, 1 H) ppm.13C NMR (CDCl3, 100 MHz): δ = 146.8,
144.7, 141.1, 138.7, 135.0, 134.2, 133.9, 130.7, 129.4, 128.5, 128.4,
128.2, 127.8, 127.3, 123.3, 122.4, 121.2, 115.4 ppm. GC–MS (70 eV,
CI): m/z = 359 [M + H]+, 338, 294, 272, 196.
1-Methylene-2,3-diphenyl-1H-indene (4b): Pale-yellow oil; eluent:
1
hexanes. H NMR (CDCl3, 400 MHz): δ = 7.71 (d, J = 8.0 Hz, 1
H), 7.34 (t, J = 8.0 Hz, 1 H), 7.30–7.25 (m, 10 H), 7.20–7.18 (m, 2
H), 6.25 (s, 1 H), 5.72 (s, 1 H) ppm. 13C NMR (CDCl3, 100 MHz):
δ = 147.7, 142.8, 140.9, 137.5, 136.3, 134.7, 134.6, 130.8, 129.4,
128.6, 128.3, 128.1, 127.5, 127.0, 125.8, 120.2, 119.9, 114.2 ppm.
GC–MS (70 eV, CI): m/z = 281 [M + H]+, 265, 220.
(E)-1-Benzylidene-2,3-diphenyl-1H-indene (4i): Pale-yellow semi-so-
lid; eluent: hexanes. 1H NMR (CDCl3, 400 MHz): δ = 7.60–7.56
(m, 3 H), 7.45 (t, J = 8.0 Hz, 2 H), 7.39 (t, J = 8.0 Hz, 2 H), 7.35–
7.26 (m, 11 H), 7.20 (s, 1 H), 7.05 (t, J = 8.0 Hz, 1 H) ppm. 13C
NMR (CDCl3, 100 MHz): δ = 144.0, 141.7, 140.7, 139.9, 137.3,
135.3, 134.9, 134.8, 134.7, 131.5, 130.4, 129.9, 129.8, 129.6, 128.7,
128.4, 128.3, 128.2, 127.5, 127.2, 125.5, 123.5, 120.3 ppm. GC–MS
(70 eV, CI): m/z = 357 [M + H]+, 325, 295, 217, 167.
5-Iodo-1-methylene-2,3-diphenyl-1H-indene (4c): Pale-yellow solid;
eluent: hexanes. 1H NMR (CDCl3, 400 MHz): δ = 7.67 (s, 1 H),
7.62 (dd, J = 8.0, 4.0 Hz, 1 H), 7.45 (d, J = 8.0 Hz, 1 H), 7.35–7.30
(m, 4 H), 7.29–7.25 (m, 4 H), 7.20–7.18 (m, 2 H), 6.28 (s, 1 H),
5.78 (s, 1 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 147.0, 144.9,
138.6, 135.8, 134.6, 134.3, 134.1, 130.9, 129.8, 129.6, 129.2, 128.7,
128.3, 127.9, 127.5, 121.7, 115.6, 94.1 ppm. GC–MS (70 eV, CI):
m/z = 407 [M + H]+, 330, 266, 225, 108.
Supporting Information (see footnote on the first page of this arti-
1
cle): H and 13C NMR spectra of all compounds.
Acknowledgments
5-Methoxy-1-methylene-2,3-diphenyl-1H-indene (4d): Orange semi-
solid; eluent: 1% ethyl acetate in hexanes. 1H NMR (CDCl3,
400 MHz): δ = 7.65 (d, J = 8.0 Hz, 1 H), 7.34–7.28 (m, 8 H), 7.25–
7.22 (m, 2 H), 6.96 (s, 1 H), 6.83 (dd, J = 8.0, 4.0 Hz, 1 H), 6.15
(s, 1 H), 5.66 (s, 1 H), 3.84 (s, 3 H) ppm. 13C NMR (CDCl3,
100 MHz): δ = 160.6, 147.2, 144.5, 141.5, 138.9, 134.8, 134.6, 130.8,
129.6, 129.1, 128.4, 128.1, 127.6, 127.1, 120.9, 112.9, 110.8, 106.6,
55.7 ppm. GC–MS (70 eV, CI): m/z = 311 [M + H]+, 179, 167, 119.
We thank the Indian Institute of Science Education and Research,
Pune, India for the support of this research.
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5-Methyl-1-methylene-2,3-diphenyl-1H-indene (4e): Pale-yellow oil;
eluent: hexanes. 1H NMR (CDCl3, 400 MHz): δ = 7.62 (d, J =
8.0 Hz, 1 H), 7.35–7.31 (m, 4 H), 7.30–7.27 (m, 4 H), 7.22–7.20 (m,
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CI): m/z = 295 [M + H]+, 181, 152, 129.
5-Fluoro-1-methylene-2,3-diphenyl-1H-indene (4f): Pale-yellow oil;
eluent: hexanes. 1H NMR (CDCl3, 400 MHz): δ = 7.52 (dd, J =
8.0, 4.0 Hz, 1 H), 7.22–7.15 (m, 8 H), 7.10–7.07 (m, 2 H), 6.95 (dd,
J = 8.0, 4.0 Hz, 1 H), 6.86–6.81 (m, 1 H), 6.08 (s, 1 H), 5.61 (s, 1
H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 164.9 and 162.4 (C-F
coupling), 146.7, 144.9 and 144.8 (C-F coupling), 141.0, 139.2,
134.4, 134.1, 132.0, 130.8, 129.4, 128.5, 128.2, 127.8, 127.3, 121.0
and 120.9 (C-F coupling), 114.6, 112.3 and 112.1 (C-F coupling),
107.8 and 107.6 (C-F coupling) ppm. GC–MS (70 eV, CI): m/z =
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1
(d, J = 8.0 Hz, 1 H), 7.86 (dd, J = 8.0, 4.0 Hz, 1 H), 7.79 (d, J =
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www.eurjoc.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Alfa-Asear, whereas 1 g of [{Cp*RhCl2}2] costs $702 and 1 g
of [Ir(cod)2]BF4 costs $571.
[10] For selected ruthenium-catalyzed addition reactions of aceto-
phenones with alkenes, see: a) S. Murai, F. Kakiuchi, S. Sekine,
Y. Tanaka, A. Kamatani, M. Sonoda, N. Chatani, Nature 1993,
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Received: September 19, 2011
Published Online: November 21, 2011
Eur. J. Org. Chem. 2012, 417–423
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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