Chemoselective Ruthenium-Catalyzed C-O Bond Activation: Orthogonality of Nickel- and Palladium-Catalyzed Reactions for the Synthesis of Polyaryl Fluorenones

Article abstract of DOI:10.1055/s-0036-1590985

Ruthenium-catalyzed C-O bond activation/arylation of methoxy and O -carbamoyl-substituted fluorenones is reported. Established are new reactions of compound 1 (X = H) to aryl (2) and 1,8-diaryl (3) fluorenones. Orthogonal ruthenium-, palladium- and nickel

Full text of DOI:10.1055/s-0036-1590985

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Chemoselective Ruthenium-Catalyzed C–O Bond Activation:
Orthogonality of Nickel- and Palladium-Catalyzed Reactions for
the Synthesis of Polyaryl Fluorenones
Livia C. R. M. da Frotaa,b
Cédric Schneiderc
Mauro B. de Amorimd
Alcides J. M. da Silvaa
Victor Snieckus*b
Ar
Ar
Ar
O
O
H
[Ru]
[Ru]
[Ru]
66–89% yields
3 examples
4
3
[Pd]
50–81% yields
3 examples
R = OMe
X = H
R = H
X = Br
Ar
a Laboratório de Catálise Orgânica, Instituto de Pesquisa de Produtos
Naturais, Centro de Ciências da Saúde, Bl H, Ilha da Cidade Universitária,
Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-590, Brazil
b Department of Chemistry, Queen’s University, Kingston, ON, K7L 3N6,
Canada
snieckus@chem-queensu.ca
c Normandie Univ, INSA Rouen, UNIROUEN, CNRS, COBRA (UMR 6014),
76000 Rouen, France
d Laboratório de Modelagem Molecular e Espectroscopia Computacional,
Instituto de Pesquisa de Produtos Naturais, Centro de Ciências da Saúde,
Bl H, Ilha da Cidade Universitária, Universidade Federal do Rio de Janeiro,
Rio de Janeiro, RJ 21941-590, Brazil
Ar
Ar
O
(Het)Ar
[Ru]
O
O
R
OMe
H
[Ni]
[Ru]
R = X = H
R = OC(O)NEt2
X = Cl
[Pd]
5
2
X
1
38–96% yields
11 examples
Ar
51–83% yields
3 examples
Published as part of the Cluster C–O Activation
Received: 05.10.2017
Accepted after revision: 31.10.2017
Published online: 14.11.2017
Over the past decade, fluoren-9-one derivatives have at-
tracted considerable attention due to their presence in nat-
ural products1 with a range of biological activities (e.g.,
dengibsin,1d,g dengibsinin,1d dendroflorin,1b cauliphin)1j and
in pharmaceutically important agents (anticancer, antioxi-
dant, and anti-HIV).2 Furthermore, fluorenones, arylated
fluorenones, and benzofluorenones have been incorporated
in oligomers and polymers which have been examined for
potential applications of their optical and electrochemical
properties as organic light-emitting devices3 and liquid
crystals4 (Figure 1).
As a result, the synthetic chemistry community has
voiced considerable interest in fluorenones and, in addition
to the traditional routes,5 new routes have been discovered
and generalized based on a Directed ortho Metalation
(DoM)/Suzuki–Miyaura cross-coupling/Directed remote
DOI: 10.1055/s-0036-1590985; Art ID: st-2017-r0772-c
Abstract Ruthenium-catalyzed C–O bond activation/arylation of me-
thoxy and O-carbamoyl-substituted fluorenones is reported. Estab-
lished are new reactions of compound 1 (X = H) to aryl (2) and 1,8-dia-
ryl (3) fluorenones. Orthogonal ruthenium-, palladium- and nickel-
catalyzed reactions with Suzuki–Miyaura reactions to afford 1,4-diaryl
(4) and 1,4,8-triaryl fluorenones (5) are also described. The ready avail-
ability of starting methoxy fluorenones by directed ortho and remote
metalation tactics confers facility to the presented reactions which may
find application in material science areas. DFT calculations have been
performed to rationalize the lack of C–H bond reactivity in the rutheni-
um-catalyzed reaction.
Key words C–O activation, fluorenone, ruthenium catalysis, nickel
catalysis, palladium catalysis, polyarylation, orthogonal cross-coupling
OH
O
HO
O
OMe
Me
O
Me
N
HO
OH
Me
HO
OH
Fluorenone alkaloid Cauliphin1j
antimyocardial ischemia activity
fluostatin B2a
R
inhibitor of dipeptidyl peptidase III
CO2H
CN
O
S
N
O
1
99
PFO-F (1%)
electrophorescent material
HIQF1 (R = C6H17O)
sensitized dyes for solar cells
R
Figure 1 Natural products, pharmaceutical and photoelectronic materials containing the fluorenone framework
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, 2587–2593

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L. C. da Frota et al.
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Metalation (DreM) strategy6–8 which complements, in the
site selectivity of reaction, the classical Friedel–Crafts
method. Recently, new metal-catalyzed strategies have
been reported including radical cyclization,9 direct C–H
coupling,10 decarboxylative coupling,11 and CO insertion12
processes. Specifically, with respect to the synthesis of pol-
yarylated fluorenones, the literature is very limited despite
their current interest in the area of organic electronics due
to their highly rigid π-conjugated systems.3 Indeed, only
Diels–Alder cycloaddition/aromatization,13 [2+2+2]-cy-
cloaddition,14 and radical cycloisomerization15 strategies
have been reported. Recently, Langer and co-workers de-
scribed the first site-selective arylation of the bistriflate of a
5,10-dihydroxybenzo[b]fluorenone to furnish the corre-
sponding diarylated derivative by a Suzuki–Miyaura cross-
coupling reaction.16 While advances in synthesis of 2-, 3-,
and 4-substituted fluorenones are evident over several de-
cades, few methods for the preparation of 1-substituted
fluorenones, and particularly for the 1-arylated fluo-
renones, have been reported.10i,17
In the past decade, C–C bond-forming reactions based
on aryl C–O bond activation/cross-coupling using transi-
tion-metal catalysis have been discovered which consti-
tutes a fundamental and powerful alternative to the aryl
halide/cross-coupling tactic.18–21 Following Wenkert’s semi-
nal observation,20a Ni-catalyzed processes (Kumada–
Corriu,20a,b Suzuki–Miyaura,20f,22 and Negishi20c reactions)
have historically dominated the process for C–O bond cleav-
age of aryl alkyl ethers. In 2004, Kakiuchi, Chatani, and Mu-
rai triggered a new area of synthetic methodology by the
discovery of the Ru-catalyzed cross-coupling reaction of
aryl ethers with boronates by ortho-ketone-assisted chela-
tion.20e Shortly thereafter, Kakiuchi and coworkers over-
came competitive C–O and C–H activation by use of a bulky
ketone group or a fused aromatic ketone to achieve a regio-
selective C–OMe bond-activation reaction.23,24
Inspired by the discoveries of Kakiuchi, Chatani, and
Murai20e and concurrent with our work on the activation of
unreactive C–H, C–O, and C–N bonds mediated by rutheni-
um catalysis25 for the development of new synthetic meth-
odologies competitive or surpassing the DoM–cross-cou-
pling strategies,6,8,26 we proposed to test the Ru-catalyzed
C–O activation/cross-coupling in the reaction of methoxy-
fluorenones with aryl boroneopentylates for the synthesis
of aryl-substituted fluorenones. As an additional incentive,
we envisaged the potential of SEAr orthogonal reactivity
based on the pendant presence of the strong electron-do-
nating OMe group. Herein we disclose an efficient and
straightforward methodology based on conveniently avail-
able starting materials 1 which combines DoM/DreM proto-
cols with Ru-, Ni- and Pd-catalyzed cross-coupling reac-
tions of C–OMe and also C–OCONR2 bonds for the regiose-
lective synthesis of aryl fluorenones 2, isomeric 1,4- (4) and
1,8-diarylated (3), and 1,4,8-triarylated (5) fluorenones of
potential interest in material science areas (Scheme 1).
In view of the successful C–H activation results on 1-
tetralone and related aromatic ketones24 and those of
Kakiuchi showing nonregioselective C–H and C–O activa-
tion,24f we tested commercially available fluorenone to ini-
tiate our study. Subjection of fluorenone (1a) to reaction
with boronic ester 6a in the presence of 10 mol% of
RuH2(CO)(PPh3)3 in pinacolone or dry toluene solution un-
der microwave irradiation at 150 °C led to recovery of start-
ing material even after 12 h reaction time (Scheme 2).27 In
contrast, 1-methoxyfluorenone (1b), readily available by
the combined DoM/Suzuki–Miyaura cross-coupling proce-
dure (see Supporting Information),5b,6,28 afforded 1-phenyl-
fluorenone (2a) in comparable and excellent yields either in
pinacolone (86%) or toluene (88%) solution after 2.5 h reac-
tion at 150 °C refluxing conditions.29 Reducing the amount
of catalyst (from 5 mol% to 2 mol%) proved to be deleterious
to the reaction affording reduced yields of product in both
solvents or recovery of starting material (see Supporting
Information). Furthermore, to our delight, when 1-O-
Ar
Ar
Ar
O
O
H
[Ru]
[Ru]
[Ru]
66–89% yields
3 examples
4
3
[Pd]
50–81% yields
3 examples
R = OMe
X = H
R = H
X = Br
Ar
Ar
Ar
(Het)Ar
[Ru]
O
O
O
R
OMe
H
[Ni]
[Ru]
R = X = H
R = OC(O)NEt2
X = Cl
[Pd]
5
2
X
1
38–96% yields
11 examples
Ar
51–83% yields
3 examples
Scheme 1 Proposed strategies for the arylation of the fluorenone skeleton
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The convenient availability of the 1,8-dimethoxyfluore-
none 1d by ortho and remote metalation–cross-coupling
chemistry5b,28 prompted the study of its C–O activa-
tion/aryl-Bneop coupling behavior and the results are sum-
marized in Scheme 4. Although the reaction failed with
pinacolone as solvent, use of toluene and the standard
quantity of Ru catalyst afforded product 3a in good yield
and products 3b–c in moderate yields. Compounds 3a–c
show normal IR νC=O absorptions at 1708–1701 cm–1 and
13C NMR at δ = 192 ppm, suggesting that no anisotropic ef-
fects are felt by the carbonyl group and there are minimal
resonance effects on the carbonyl due to twisted position-
ing of the 1,8-aryl groups.
O
O
Me
O
O
R
B
6a
Me
RuH2(CO)(PPh3)3 (10 mol%)
pinacolone or toluene
MW, 150 °C
1a, R = H
1b, R = OMe
1c, R = OC(O)NEt2
2a
Scheme 2 Ru-catalyzed phenylation of fluoren-9-ones 1b and 1c
carbamate of fluorenone (1c) was subjected to the Ru-cata-
lyzed conditions in pinacolone solvent, the aryl fluorenone
2a was obtained in 87% yield thus demonstrating the first
selective C–O activation/cross-coupling reaction of aryl O-
carbamates.30
Ar
Ar
O
O
Investigation of the scope of the reaction (Scheme 3) in-
volved the application of commercial (6b, 6d, and 6e) and
readily available31 aryl-Bneop compounds. Using the micro-
wave and pinacolone solvent conditions, aryl-Bneop deriv-
atives bearing para-EDGs afforded the corresponding prod-
ucts 2b and 2c in excellent yields. The ortho-substituted
aryl boronate (6d) was also a suitable substrate, giving
product 2d in 62% yield while, perhaps surprisingly, the me-
ta-substituted aryl-Bneop (6e) led to a decreased yield of
product 2e. Excellent results were also obtained in the con-
version of aryl boronates substituted with para-EWG (6f–h)
to give the corresponding products 2f–h. Furthermore, the
2-methoxynaphthalene-Bneop 6i was successfully em-
ployed leading to the corresponding product 2i in 88% yield
in spite of potential naphthalene ring C8–H peri interac-
tion.32 Two heterocyclic boronates cases, 6j and 6k, were
subjected to the coupling conditions to afford products 2j
and 2k, respectively, in good yields.
OMe
MeO
RuH2(CO)(PPh3)3 (10 mol%)
6a–c (2.5 equiv)
toluene, MW, 150 °C, 6 h
1d
3a–c
OMe
MeO
F
F
O
O
O
3a; 81%
3b; 50%
3c; 50%
Scheme 4 Synthesis of 1,8-diaryl-fluorenones 3a–c
As demonstrated for the ortho-methoxy benzamide and
-naphthamide systems,25a,c we explored the orthogonal reac-
tivity concept in Ru- and Pd-catalyzed processes (Scheme 5).
For this purpose, compound 1b was easily converted into
O
Me
HetAr
HetAr
B
O
O
Me
OMe
O
6b–i
(4 equiv)
RuH2(CO)(PPh3)3 (10 mol%)
pinacolone, 2.5–8 h
MW, 150 °C
1b
2b–k
MeO
OMe
NMe2
Cl
O
O
O
O
O
OMe
2b; 89%a
2c; 95%a
2d; 62%b
2e; 38%b
2f; 96%a
F
CF3
S
N
O
O
O
O
O
OMe
2g; 91%a
2h; 80%b
2i; 88%c
2j; 80%d
2k; 63%d
Scheme 3 Synthesis of 1-aryl fluorenones (2b–k). a 2.5 h reaction time. b 4 h reaction time. c 8 h reaction time. d 5 h reaction time.
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R2
B(OH)2
O
O
O
OMe
OMe
7a; R1 = H
7b; R1 = OMe
RuH2(CO)(PPh3)3 (10 mol%)
toluene, MW, 150 °C, 6 h
R1
Me
PdCl2(dppf)⋅CH2Cl2 (10 mol%)
Na2CO3 aq (2 M)
O
Me
Br
1e
7a,b (1.4 equiv)
DME, 110 °C, 12 h
B
O
2.5 equiv
R2
6a; R2 = OMe
R1
R1
6g; R2 = F
4a; R1 = H; R2 = OMe (66%)
4b; R1 = R2 = OMe (89%)
4c; R1 = OMe; R2 = F (82%)
8a; R1 = H (95%)
8b; R1 = OMe (92%)
Scheme 5 Orthogonal Pd- and Ru-catalyzed cross-coupling reactions to 1,4-diaryl-fluorenones
the 4-bromofluoreone 1e (83% yield using NBS) which,
upon standard Pd-catalyzed Suzuki–Miyaura coupling with
aryl boronic acids 7a and 7b, provided 4-aryl fluorenones
8a and 8b, respectively. Subsequent coupling of these prod-
ucts with aryl-Bneop derivatives 6a and 6g under Ru-cata-
lyzed conditions afforded the 1,4-diaryl-fluorenones 4a–c,
respectively, in high overall yields from 1-methoxyfluore-
none (1b).
To further pursue the orthogonality concept, chloro de-
rivatives 1f and 1g, prepared by the DoM/Suzuki-Miyaura
coupling/DreM strategy, were subjected to Suzuki–Miyaura
coupling under conditions suitable for aryl chlorides33 to
give the 8-methoxy and 8-O-carbamates 9a and 9b, respec-
tively (Scheme 6). Compound 9a underwent Ru-catalyzed
coupling with Ph-Bneop (6a) and 4-methoxy-phenyl-Bneop
(6b) to afford the first cases of 1,4,8-triarylfluorenones 12a
and 12b, respectively. The structure of 12a was established
by X-ray crystallography analysis (see Supporting Informa-
tion). In the case of the O-carbamate 9b, Ni-catalyzed cross-
coupling conditions using the triphenylboroxine partner 10
was selective for the O-carbamate over the methoxy C–O
bond activation to give the new diaryl fluorenone 11. To
complete the triumvirate metal orthogonality reactions,
compound 11 was exposed to our Ru-catalyzed conditions
in the coupling with aryl-Bneop 6a to afford 1,4,8-triaryl-
fluorenone 12c, bearing three different aryl groups. At-
tempts to prepare 1,4,5,8-tetraaryl fluorenones by further
bromination of 1d and independent synthesis of 1,4,5,8-te-
tramethoxy fluorenone have been thwarted to date (see
Supporting Information).
Scheme 6 Combined Pd-, Ru-, and Ni-catalyzed cross-coupling reactions to triaryl fluorenones
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In order to rationalize the lack of reactivity of the ortho-
C–H bond of fluorenone (1a) and its 1-methoxy derivative
1b, we performed calculations at the DFT level (see Sup-
porting Information for details) of the square-planar Ru(0)
complexes of these compounds and those derived from 2-
methoxyacetophenone (13) for comparison (Figure 2). In
addition, for comparison purposes, geometric data result-
ing from calculations reported for 13 by Lin and cowork-
ers34 at a different level of theory (PBE/LanL2DZ, plus f-type
and d-type polarization functions for Ru and P, and 6-31G*
for H, C and O) are also shown in Figure 2. Our results show
a significant difference in Ru···H distance and C–H elonga-
tion in fluorenone complexes (1aa, 1ba) when compared
with that of acetophenone (13a). In 13a, the distance Ru···H
is significantly shorter (ca. 0.5 Å) than in 1aa and 1ba, while
there is a greater degree of C–H elongation in 13a than in
1aa and 1ba (ca. 0.020 Å, 0,003 Å, and 0.003 Å, respectively)
with respect to other C–H bonds. Such differences lead us to
the hypothesis of absence of agnostic activation in the oxi-
dative addition step of C–H bonds in fluorenones.34 On the
other hand, the distance Ru···O(–C) is also significantly
smaller in 1bb (ca. 2.75–2.90 Å) than in 13b (ca. 3.04–
3.21 Å). These features may imply a lower reactivity of the
ortho-C–H bond in the fluorenones to the oxidative addi-
tion of the C–O bond to Ru(0), justifying our experimental
results. Additional studies are being conducted in order to
test these and other hypotheses.
1,4-, 1,4,8-aryl substituted fluorenones. The coupling of O-
carbamate fluorenones 1c and 9b constitute, to the best of
our knowledge, a new site-selective Ru-catalyzed aryl C–O
activation/cross-coupling reaction on substrates which of-
fer alternative C–H bond-coupling possibility.30 In view of
the ready availability of the starting fluorenones by the or-
tho and remote-directed metalation/cross-coupling proto-
col and the convenience of the chemistry, the application of
the methodology, paralleling that established by Kakiuchi
for anthraquinones,24b,c may be anticipated. DFT calcula-
tions suggest that C–O oxidative addition over C–H bond ac-
tivation is the preferred reaction path.
Acknowledgment
NSERC DG is acknowledged for support of our synthetic programs.
A.J.M.S. and L.C.R.M.F. are grateful for the financial support from CNPq
and CAPES. L.C.R.M.F. thanks CAPES for a fellowship.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1590985.
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References and Notes
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25
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(a) Wunderlich, S. H.; Rohbogner, C. J.; Unsinn, A.; Knochel, P.
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(16) This method requires a five-step process for the synthesis of the
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(17) George, S. R. D.; Scott, L. T.; Harper, J. B. Polycyclic Aromat.
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(20) COMe functional group activation – Ni-catalyzed Kumada–
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reaction: (d) Matsubara, R.; Jamison, T. F. J. Am. Chem. Soc. 2010,
132, 6880. Ru-catalyzed Suzuki-Miyaura type reaction:
(e) Kakiuchi, F.; Usui, M.; Ueno, S.; Chatani, N.; Murai, S. J. Am.
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© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, 2587–2593

2593
L. C. da Frota et al.
Cluster
Synlett
Chem. Soc. 2004, 126, 2706. Ni-catalyzed Suzuki-Miyaura type
reaction: (f) Tobisu, M.; Shimasaki, T.; Chatani, N. Angew. Chem.
Int. Ed. 2008, 47, 4866.
(27) Toluene and pinacolone are both solvents of choice for the Ru-
catalyzed C–H and C–O activation reaction. Whereas pinacolone
has been used as a hydrogen acceptor to suppress the reduction
of the aromatic ketone substrate in the C–H activation reaction
(see ref. 24b) such use for the C-O activation has, to the best of
our knowledge, not been reported.
(28) (a) Alessi, M.; Larkin, A. L.; Ogilvie, K. A.; Green, L. A.; Lai, S.;
Lopez, S.; Snieckus, V. J. Org. Chem. 2007, 72, 1588. (b) Tilly, D.;
Fu, J.-M.; Zhao, B.-P.; Alessi, M.; Castanet, A.-S.; Snieckus, V.;
Mortier, J. Org. Lett. 2010, 12, 68. Compound 1d has been previ-
ously prepared by a ten-step route: (c) Kajigaeshi, S.; Kobayashi,
K.; Kurata, S.; Kitajima, A.; Nakahara, F.; Nago, H.; Nishiida, A.;
Fujisaki, S. Nippon Kagaku Kaishi 1989, 12, 2052.
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Miyaura type reaction: (a) Antoft-Finch, A.; Blackburn, T.;
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K. J. Am. Chem. Soc. 2011, 133, 6352. (c) Ramgren, S. D.; Hie, L.;
Ye, Y.; Garg, N. K. Org. Lett. 2013, 15, 3950. Ni-catalyzed
Kumada–Tamao–Corriu-type reaction: (d) Sengupta, S.; Leite,
M.; Raslan, D. S.; Quesnelle, C.; Snieckus, V. J. Org. Chem. 1992,
57, 4066. (e) Jorgensen, K. B.; Rantanen, T.; Dorfler, T.; Snieckus,
V. J. Org. Chem. 2015, 9410. Rh-catalyzed Suzuki–Miyaura-type
reaction: (f) Nakamura, K.; Yasui, K.; Tobisu, M.; Chatani, N. Tet-
rahedron 2015, 71, 4484. C–OCSO2NR2 functional group activa-
(29) General Procedures to the Ru-Catalyzed Arylation of Fluo-
renones
A dried Biotage microwave vial equipped with a magnetic stir-
ring bar and a nitrogen inlet was sequentially charged with
fluorenone (1, 0.5 mmol), boronic ester (6, 0.5–1 mmol), pina-
colone (0.5 mL), and RuH2(CO)(PPh3)3 (10 mol%). The reaction
mixture was heated under MW irradiation at 150 °C for 2.5–8 h.
The reaction mixture was extracted with EtOAc (15 mL),
washed with brine, subjected to filtration, dried (Na2SO4), and
concentrated under reduced pressure. Purification using flash
column chromatography on silica gel (eluting with 1:9 hex-
anes/EtOAc) afforded product 2.
tion
– Ni-catalyzed Kumada–Tamao–Corriu-type reaction:
(g) Macklin, T. K.; Snieckus, V. Org. Lett. 2005, 7, 2519. Ni-cata-
lyzed Suzuki–Miyaura-type reaction: (h) Quashdorf, K. W.;
Riener, M.; Petrova, K. V.; Garg, N. K. J. Am. Chem. Soc. 2009, 131,
17748. (i) C–OTf, C–OMs, and C–OTs functional group activa-
tion: see ref 18f.
(22) (a) Shimasaki, T.; Konno, Y.; Tobisu, M.; Chatani, N. Org. Lett.
2009, 11, 4890. (b) Tobisu, M.; Yasutome, A.; Kinuta, H.;
Nakamura, K.; Chatani, N. Org. Lett. 2014, 16, 5572.
(23) (a) Kakiuchi, F.; Matsuura, Y.; Kan, S.; Chatani, N. J. Am. Chem.
Soc. 2005, 127, 5936. (b) Ueno, S.; Mizushima, E.; Chatani, N.;
Kakiuchi, F. J. Am. Chem. Soc. 2006, 128, 16516. (c) Kondo, H.;
Kochi, T.; Kakiuchi, F. Org. Lett. 2017, 19, 794. (d) Suzuki, Y.;
Yamada, K.; Watanabe, K.; Kochi, T.; Ie, Y.; Aso, Y.; Kakiuchi, F.
Org. Lett. 2017, 19, 3791.
(24) Aryl C–H activation under Ru catalysis – α-tetralones and 1-
benzosuberones: (a) Kakiuchi, F.; Kan, S.; Igi, K.; Chatani, N.;
Murai, S. J. Am. Chem. Soc. 2003, 125, 1698. (b) Kakiuchi, F.;
Matsuura, Y.; Kan, S.; Chatani, N. J. Am. Chem. Soc. 2005, 127,
5936. Anthraquinones: (c) Kitazawa, K.; Kochi, T.; Sato, M.;
Kakiuchi, F. Org. Lett. 2009, 11, 1951. (d) Matsumura, D.;
Kitazawa, K.; Terai, S.; Kochi, T.; Ie, Y.; Nitani, M.; Aso, Y.;
Kakiuchi, F. Org. Lett. 2012, 14, 3882. 1-Indanone derivatives are
reported to be unreactive under Pd catalysis: (e) Sun, C.-L.; Liu,
N.; Li, B.-J.; Yu, D.-G.; Wang, Y.; Shi, Z.-J. Org. Lett. 2010, 12, 184.
Acetophenones: (f) Ueno, S.; Kochi, T.; Chatani, N.; Kakiuchi, F.
Org. Lett. 2009, 11, 855.
1-(4-Fluorophenyl)-9H-fluoren-9-one (2g)
Yellow solid, 91% yield; mp 156–158 °C (hexanes). 1H NMR (400
MHz, CDCl3): δ = 7.59 (d, J = 7.4 Hz, 1 H), 7.55 (d, J = 7.4 Hz, 1 H),
7.53–7.46 (m, 5 H), 7.29 (t, J = 7.2 Hz, 1 H), 7.16 (dd, J = 8.7, 1.2
Hz, 1 H), 7.12 (d, J = 8.7 Hz, 2 H). 13C NMR (101 MHz, CDCl3): δ =
193.1 (C), 162.9 (d, 1JC–F = 247.3 Hz, C), 145.6 (C), 143.5 (C), 141.2
(C), 134.6 (CH), 134.3 (CH), 134.2 (C), 133.3 (d, 4JC–F = 3.2 Hz, C),
131.5 (CH), 130.9 (d, 3JC–F = 8.26 Hz, 2 CH), 129.6 (C), 129.3 (CH),
2
124.2 (CH), 120.1 (CH), 119.3 (CH), 114.87 (d, JC–F = 21.5 Hz, 2
CH). IR (CH2Cl2): 1709, 1159 cm–1. HRMS (ESI): m/z calcd for
(C19H12FO)+: 275.0867; found: 275.0875.
(30) During the preparation of this manuscript Yasui et al. reported a
reductive cleavage of aryl O-carbamate under Rh-catalysis using
isopropanol as a reductant, see: Yasui, K.; Higashino, M.;
Chatani, N.; Tobisu, M. Synlett 28, 2017, in press; DOI:
10.1055/s-0036-1589093.
(31) Zhao, Y.; Snieckus, V. Org. Lett. 2015, 17, 4674.
(32) Balasubramaniyan, V. Chem. Rev. 1966, 66, 567.
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Littke, A. F.; Fu, G. Angew. Chem. Int. Ed. 2002, 41, 4176.
(34) Wang, Z.; Zhou, Y.; Lam, W. H.; Lin, Z. Organometallics 2017, 36,
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(26) For recent cluster of paper in the area of synthetic aromatic
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© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, 2587–2593