Intermolecular Three-Component Synthesis of Fluorene Derivatives by a Rhodium-Catalyzed Stitching Reaction/Remote Nucleophilic Substitution Sequence

Article abstract of DOI:10.1021/acs.joc.0c00790

A three-component synthesis of multisubstituted fluorene derivatives has been developed by devising a rhodium-catalyzed stitching reaction/remote nucleophilic substitution sequence. A variety of nucleophiles can be installed in the second step including both heteroatom and carbon nucleophiles. An efficient synthesis of 5H-benzo[a]fluoren-5-ones has also been realized using N-(2-alkynyl)benzoylpyrrole as the reaction partner through a new reaction pathway.

Full text of DOI:10.1021/acs.joc.0c00790

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Article
Intermolecular Three-Component Synthesis of
Fluorene Derivatives by Rhodium-Catalyzed Stitching
Reaction/Remote Nucleophilic Substitution Sequence
Masaki Nishida, Donghyeon Lee, and Ryo Shintani
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.0c00790 • Publication Date (Web): 08 Jun 2020
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Intermolecular Three-Component Synthesis of Fluorene Derivatives by Rhodium-
Catalyzed Stitching Reaction/Remote Nucleophilic Substitution Sequence
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Masaki Nishida, Donghyeon Lee, and Ryo Shintani*
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Division of Chemistry, Department of Materials Engineering Science, Graduate School of
Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
Three-Component Fluorene Synthesis
OH
Rh cat.
Nu H
O
B(OR)2
Nu
nucleophilic substitution
stitching reaction
Abstract: A three-component synthesis of multi-substituted fluorene derivatives has been
developed by devising a rhodium-catalyzed stitching reaction/remote nucleophilic substitution
sequence. A variety of nucleophiles can be installed in the second step including both
heteroatom and carbon nucleophiles. An efficient synthesis of 5H-benzo[a]fluoren-5-ones has
also been realized by using N-(2-alkynyl)benzoylpyrrole as the reaction partner through a new
reaction pathway.
Introduction
Catalytic intermolecular multi-component reactions represent a convergent and efficient
approach for the synthesis of complex organic molecules from relatively simple precursors
with minimal synthetic operations.1 Such a synthetic approach also allows for a rapid
preparation of a diverse array of analogs by modifying each reaction component, and is
therefore particularly desirable for the synthesis of functional organic compounds where
utilities and properties can be altered through the change of positions and types of substituents.
Among the functional π-conjugated organic compounds, fluorenes constitute one of the
basic structures that can be utilized as luminescent or electronic materials in the form of small
molecules as well as polymers/oligomers.2 In addition, anionic forms of fluorene derivatives
are often employed as effective ligands to transition metals, and some of those metal complexes
can be used as catalysts for organic transformations including olefin polymerization.3
Furthermore, some fluorenes having a heteroatom substituent at their bridging carbon (9-
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position) are known to exhibit biological activity.4 Because of the high utility of this structural
motif, various synthetic methods of fluorenes and their derivatives have been developed to
date,5 but most of the existing methods rely on the use of intramolecular processes as
exemplified in the classical Friedel–Crafts cyclization,6 radical cyclization,7 and more recent
transition-metal-catalyzed cyclization involving C–H bond activation.8 With regard to the more
desirable intermolecular processes in view of convergent nature and structural diversity,
several approaches have been reported, including palladium-catalyzed tandem cross-
coupling/cyclization reactions to give 9H-fluorenones9 or 9-unsubstituted 9H-fluorenes,10
palladium-catalyzed methylenation reactions of 2-halobiaryls to give 9-unsubstituted 9H-
fluorenes11 or 9,9-disubstituted 9H-fluorenes,12 and Brønsted acid-catalyzed three-component
reactions to give 11-methoxy-11-aryl-11H-benzo[a]fluorenes.13 Despite these recent
progresses,14 development of new and efficient intermolecular synthetic methods of fluorene
derivatives continues to be of high importance to diversify accessible structures from easily
available fragments.
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In this context, we recently reported an intermolecular synthesis of fluorene derivatives by
employing a sequence of rhodium-catalyzed stitching reaction followed by alkene
isomerization (Scheme 1a).15 This method realized unprecedented bond connections toward
the formation of a fluorene skeleton in a convergent manner to give a variety of 11-
monosubstituted 11H-benzo[a]fluorenes and their analogs. Based on this synthetic approach,
we imagined that it could be further extended to the synthesis of more substituted
(benzo)fluorenes by combining the stitching reaction of 2-alkynylarylboronates and 2-
alkynylaryl ketones/aldehydes under rhodium catalysis with a subsequent aromatization-driven
remote nucleophilic substitution reaction. In this article, we describe our accomplishment of
this new mode of intermolecular three-component synthesis of 11,11-disubstituted 11H-
benzo[a]fluorenes and their analogs.
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Scheme 1. (a) Previous Synthesis of (Benzo)fluorenes by Rhodium-Catalyzed Stitching
Reaction Followed by Alkene Isomerization (X = O, NR, etc.) (b) Newly Devised Synthesis
of (Benzo)fluorenes by Rhodium-Catalyzed Stitching Reaction Followed by Remote
Nucleophilic Substitution
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(a) Previous Work
stitching reaction
alkene isomerization
H
XH
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XH
Rh cat.
X
base
B(OR)2
H
H
(b) This Work
B(OR)2
stitching reaction
nucleophilic substitution
OH
Rh cat.
O
Nu H
Nu
Results and Discussion
Initially, we chose 2-(phenylethynyl)phenylboronate 1a and o-(1-pentynyl)acetophenone
(2a; 0.500 mmol scale) as a model substrate combination for the rhodium-catalyzed stitching
reaction (eq 1),16 and found that, similarly to our previous report,15 the reaction proceeded
smoothly at 40 °C by using catalytic [Rh(OH)(cod)]2 with additional 1,5-cyclooctadiene in the
presence of H2O in THF to cleanly provide corresponding stitched product 3aa. Subsequent
addition of H2O as the nucleophile and a catalytic amount of H2SO4 in a one-pot manner
without isolation of 3aa led to the formation of 11H-benzo[a]fluoren-11-ol 4aa in 82% overall
yield through an aromatization-driven conjugate 1,5-nucleophilic substitution reaction.17 The
reaction can be readily scaled up and compound 4aa was obtained in 78% overall yield on a
3.00 mmol scale.
[Rh(OH)(cod)]2
(8 mol% Rh)
cod (40 mol%)
Ph
O
Me
+
B
O
H2O (1.3 equiv)
THF, 40 °C, 16 h
O
nPr
1a (1.3 equiv)
2a (0.10 M)
Ph
Ph
Me
Me
OH
H2SO4 (10 mol%)
(1)
THF/H2O (10/1)
rt, 2 h
HO nPr
nPr
3aa
4aa: 82% overall yield
(0.500 mmol scale)
78% overall yield
(3.00 mmol scale)
The present reaction sequence using H2O as the nucleophile under acidic conditions in the
second step was found to be readily applicable to the synthesis of various substituted 11H-
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benzo[a]fluoren-11-ol derivatives as summarized in Scheme 2.18 For example, substituents on
the alkyne of ketones 2 can be either an alkyl group (2a–b) or a silyl group (2c), which is
removable by treatment with nBu4NF after the stitching reaction, to give corresponding
benzofluorenes 4aa, 4ab, and 4bc in relatively high overall yields (68–82% yield).19 In addition,
phenyl ketone 2d as well as aldehyde 2e are similarly applicable to this reaction, giving 4bd
and 4ae, respectively (83–87% yield). It is worth noting that, under our previous conditions,15
selective alkene isomerization took place from stitched product 3ae to give 11H-
benzo[a]fluoren-5-ol 4ae’, but isomeric 11H-benzo[a]fluoren-11-ol 4ae was exclusively
obtained under the present nucleophilic substitution conditions, showing the complementary
nature of these two systems (Scheme 3). Furthermore, compounds 2 having substituents on the
benzene ring (2f–h) as well as an heteroaryl group (2i) can also be used to give substituted
benzofluorenes 4af–ah and heteroarene-fused fluorene 4ai in uniformly high yields (78–86%
yield). With regard to the variation of arylboronates 1, substituents on the alkyne can be
changed from phenyl to tert-butyl group (1b) or a silyl group (1c) with similarly high efficiency
(82–88% yield), but somewhat smaller substituents such as cyclohexyl group (1d) significantly
decrease the reaction efficiency (30% yield) and even smaller n-propyl group cannot be
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1
effectively employed in the present reaction (16% H NMR yield, not shown in Scheme 2).
Electronically different arylboronates (1e–g) are well tolerated, giving corresponding products
4ea–ga in 75–88% yield.
Scheme 2. Scope of Rhodium-Catalyzed Stitching Reaction Followed by Nucleophilic
Substitution with H2O
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X
R
[Rh(OH)(cod)]2
(4–8 mol% Rh)
cod (20–40 mol%)
R
R2
B(neop)
1 (1.3 equiv)
H2SO4
THF/H2O, rt
X
+
H2O (1.3 equiv)
THF, 20–40 °C
O
7
R2
R1
HO
Y
8
9
(neop = OCH2CMe2CH2O)
4
R1
Y
2 (0.10 M)
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Ph
Ph
tBu
Me
Me
Me
HO nPr
HO Me
HO
H
4bc (R1 = SiMe3): 68% yield
4aa: 82% yield
4ab: 81% yield
Ph
H
tBu
Ph
H
Ph
HO nPr
HO nPr
HO nPr
Cl
4bd: 87% yield
4ae: 83% yield
4af: 78% yield
Ph
Ph
Me
Ph
Me
Me
N
NO2
HO nPr
HO nPr
Me
4ai: 82% yield
HO nPr
OMe
4ag: 83% yield
4ah: 86% yield
tBu
tBuMe2Si
Cy
Me
Me
Me
HO nPr
HO nPr
HO nPr
4ba: 88% yield
4ca: 82% yield
4da: 30% yield
Ph
tBu
tBu
Me MeO
Me
F
Me
Me2N
F
HO nPr
HO nPr
HO nPr
4ea: 75% yield
4fa: 77% yield
4ga: 86% yield
Scheme 3. Complementary Conversion of Stitched Product 3ae to 11H-Benzo[a]fluoren-5-ol
4ae’ (left: previous work) and 11H-Benzo[a]fluoren-11-ol 4ae (right: this work)
Ph
Ph
Ph
H
H
OH
nBu4NF
•3H2O
OH
H2SO4
THF/H2O
THF
H
nPr
4ae’
HO nPr
4ae
nPr
3ae
(previous work)
(this work)
Importantly, the nucleophile that can be used in the second step of the present reaction
sequence is not limited to H2O. As shown in Table 1, several other heteroatom nucleophiles
can be effectively employed as well to install OMe (5),20 SCH2Ph (6),21 N3 (7),22 and Cl (8)23
at 11-position of 11H-benzo[a]fluorenes (71–88% yield; entries 1–4). It is worth comparing
the reactivity between non-aromatized stitched product 3aa and aromatized 11H-
benzo[a]fluoren-11-ol 4aa toward nucleophilic substitution with MeOH (Scheme 4). While
3aa can be readily converted to compound 5 at room temperature, 4aa shows much lower
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reactivity under the same conditions, indicating that aromatization from 3aa functions as the
driving force in the present conjugate nucleophilic substitution reaction. In addition to the
heteroatom nucleophiles described above, allylation and hydride reduction can also take place
to give compounds 9 and 10, respectively, in high yields (77–78% yield; entries 5 and 6).
Furthermore, treatment of 3aa with p-toluenesulfonic acid in the absence of a nucleophile led
to stereoselective 1,6-elimination to give 11-alkylidene-11H-benzo[a]fluorene (E)-11 in 74%
yield (eq 2).24
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Table 1. Scope of Nucleophiles
Ph
Ph
Me
OH
Me
same
as eq 1
1a (1.3 equiv)
conditions
+
2a (0.10 M)
Nu nPr
nPr
3aa
yield
(%)a
entry
conditions
product (Nu)
5 (OMe)
6 (SCH2Ph)
MeOH (20 equiv), H2SO4 (10 mol%),
THF, rt
PhCH2SH (1.0 equiv), CF3CO2H (1.0
1b
2
78
78
equiv), CH2Cl2, 0 °C®rt
1. HCl (1.0 equiv), dioxane, rt;
3
2. NaN3 (2.0 equiv), ZnCl2 (1.0 equiv), 7 (N3)
DMF, 40 °C
71
88
4
5
HClaq (20 equiv), toluene, rt
8 (Cl)
CH2=CHCH2SiMe3 (2.0 equiv),
CF3CO2H (3.0 equiv), CH2Cl2, 0 °C®rt
HSiEt3 (2.0 equiv), CF3CO2H (3.0
equiv), CH2Cl2, 0 °C®rt
9 (CH2CH=CH2) 77
10 (H) 78
6
a Overall isolated yield. b The stitching reaction was conducted in the presence of MeOH
(20 equiv) instead of H2O (1.3 equiv) and H2SO4 was subsequently added to the reaction
mixture.
Scheme 4. Comparison of Nucleophilic Substitution of 3aa and 4aa with MeOH to Give 5
Ph
Ph
Ph
Me
OH
Me
Me
MeOH
H2SO4
MeOH
H2SO4
THF, rt
THF, rt
MeO nPr
HO nPr
nPr
3aa
100% conv. (2 h)
2% conv. (3.5 h)
5
4aa
Ph
Ph
Me
Me
OH
1a
same
as eq 1
TsOH•H2O
(1.0 equiv)
(1.3 equiv)
+
(2)
toluene
80 °C
2a
(0.10 M)
nPr
3aa
Et
11: 74% yield
(E/Z = 97/3)
The present stitching reaction/nucleophilic substitution sequence can be extended to the
synthesis of a more complex spirocyclic compound by using an o-alkynylacetophenone
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possessing a pronucleophile. For example, a rhodium-catalyzed stitching reaction of
arylboronate 1a with compound 2j bearing 3,5-dimethoxyphenyl group gave intermediate 3aj,
which smoothly underwent intramolecular Friedel–Crafts-type substitution reaction by treating
it with BF3•OEt2 to give corresponding spirocycle 12 in 77% yield (eq 3).25
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O
[Rh(OH)(cod)]2
Me
(8 mol% Rh)
MeO
Ph
cod (40 mol%)
+
H2O (1.3 equiv)
THF, 40 °C, 16 h
B(neop)
MeO
1a (1.3 equiv)
2j (0.10 M)
Ph
Me
OH
Ph
Me
BF3•OEt2 (1.0 equiv)
CH2Cl2, 0 °C, 1 h
MeO
(3)
MeO
12: 77% overall yield
MeO
OMe
3aj
During the course of our study, we found that the use of N-(2-alkynyl)benzoylpyrrole 2k
for the stitching reaction of arylboronate 1b led to the formation of 5H-benzo[a]fluoren-5-one
13bk26 in 95% yield via elimination of the pyrrole moiety (eq 4). A similarly high yield of
13ck was also achieved for the reaction of 1c with 2k, and these reactions represent the first
example where N-acylpyrroles act as an acyl-donor in the rhodium-catalyzed carbon–carbon
bond-forming reaction as far as we are aware.27 Based on the fact that N-
(hydroxymethyl)pyrroles are usually stable once they are formed28 and that the reaction of 1b
with 2k in the absence of H2O shows much lower reactivity (28% yield of 13bk under
otherwise the same conditions), a proposed catalytic cycle of this transformation is illustrated
in Scheme 5.29 Initially, transmetalation of 1 with a hydroxorhodium catalyst gives arylrhodium
species A. Insertion of alkyne of 2k then leads to alkenylrhodium species B, which undergoes
five-membered ring-forming intramolecular insertion of alkyne derived from 1 to give another
alkenylrhodium species C. Subsequent intramolecular insertion of the carbonyl moiety in a
stitching manner gives alkoxorhodium species D, and b-nitrogen elimination from this
intermediate generates product 13 along with the formation of a rhodium pyrrolide species.
Finally, hydrolysis with H2O gives pyrrole and a hydroxorhodium species to close the catalytic
cycle.30
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[Rh(OH)(cod)]2
(4 mol% Rh)
cod (20 mol%)
R
O
O
N
R
+
(4)
H2O (1.3 equiv)
THF, 40 °C, 16 h
nPr
B(neop)
nPr
(1.3 equiv)
1b: R = tBu
1c: R = SiMe2tBu
2k (0.10 M)
13bk: 95% yield
13ck: 93% yield
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Scheme 5. Proposed Catalytic Cycle for the Reaction of 1 with to Give 13 (Rh = Rh(cod))
HN
1
Rh OH
H2O
R
Rh
N
Rh
A
2k
13
Rh
R
P
R
O
Rh P
O
nPr
nPr
D
B
R
Rh
P
O
P =
N
nPr
C
Conclusion
We have developed a three-component synthesis of fluorene derivatives by devising a
rhodium-catalyzed stitching reaction/remote nucleophilic substitution sequence. A variety of
nucleophiles can be installed in the second step including both heteroatom and carbon
nucleophiles. We have also found that 5H-benzo[a]fluoren-5-ones, which were previously
difficult to synthesize, can be readily prepared by using N-(2-alkynyl)benzoylpyrrole as the
reaction partner through a new reaction pathway. Future studies will be directed toward further
development of new and efficient synthetic methods for other functional organic compounds.
Experimental Section
General Methods. All air- and moisture-sensitive manipulations were carried out with
standard Schlenk techniques under nitrogen. The reactions with heating were performed using
an oil bath. Et3N was distilled over KOH under vacuum. MeOH was distilled over Mg turnings
under nitrogen. Dehydrated THF, Et2O, CH2Cl2, DMF, 1,4-dioxane, and toluene were degassed
by purging nitrogen. 1a,31 1c,16b 2e,32 2f,15 PdCl2(PPh3)2,33 Pd(PPh3)4,34 and [Rh(OH)(cod)]2
35
were synthesized following the literature procedures. All other commercial chemicals and
solvents were used as received.
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2-(tert-Butylethynyl)phenylboronic acid neopentylglycol ester (1b). nBuLi (6.26 mL,
9.70 mmol; 1.55 M solution in hexane) was added slowly over 1 h to a solution of 1-bromo-2-
(tert-butylethynyl)benzene36 (2.19 g, 9.24 mmol) and triisopropyl borate (2.34 mL, 10.2 mmol)
in THF (40 mL) at –78 °C, and the mixture was stirred for 30 min at –78 °C and for 1.5 h at
room temperature. The reaction was quenched with 1 M HClaq and this was extracted with
Et2O. The organic layer was washed with saturated NaClaq, dried over MgSO4, filtered, and
concentrated under vacuum. The residue was chromatographed on silica gel with hexane/Et2O
= 7/2. The resulting boronic acid and 2,2-dimethyl-1,3-propanediol (897 mg, 8.61 mmol) were
dissolved in CH2Cl2 (40 mL) and MgSO4 (3.11 g, 25.8 mmol) was added to it, and the mixture
was stirred for 2 h at room temperature. The solids were filtered off with CH2Cl2 and the
solvents were removed under vacuum. The residue was dissolved in pentane, filtered through
a PTFE membrane (pore size: 0.22 µm), and concentrated under vacuum to afford compound
1b as a white solid (2.32 g, 8.59 mmol; 93% yield). 1H NMR (CDCl3, 400 MHz): δ 7.64 (dd,
J = 7.4, 1.4 Hz, 1H), 7.39 (dd, J = 6.9, 1.4 Hz, 1H), 7.28 (td, J = 7.6, 1.4 Hz, 1H), 7.21 (td, J =
7.3, 1.4 Hz, 1H), 3.79 (s, 4H), 1.33 (s, 9H), 1.06 (s, 6H). 13C{1H} NMR (CDCl3, 101 MHz): δ
134.1, 132.6, 129.6, 128.1, 126.6, 99.7, 80.3, 72.4, 31.9, 31.2, 28.2, 22.1. Mp: 90–92 °C.
HRMS (FAB, sector) calcd for C17H23BO2 (M+) 270.1786, found 270.1791.
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2-(Cyclohexylethynyl)phenylboronic acid neopentylglycol ester (1d). This was
synthesized following the procedure for compound 1b. 92% yield (908 mg). 1H NMR (CDCl3,
400 MHz): δ 7.64 (dd, J = 7.3, 0.9 Hz, 1H), 7.40 (dd, J = 7.8, 0.9 Hz, 1H), 7.28 (td, J = 7.6,
1.4 Hz, 1H), 7.21 (td, J = 7.3, 1.4 Hz, 1H), 3.78 (s, 4H), 2.68-2.57 (m, 1H), 1.93-1.73 (m, 4H),
1.63-1.49 (m, 3H), 1.43-1.30 (m, 3H), 1.06 (s, 6H). 13C{1H} NMR (CDCl3, 101 MHz): δ 134.1,
132.7, 129.6, 128.2, 126.6, 95.7, 81.8, 72.5, 32.9, 31.9, 30.0, 26.2, 24.9, 22.1. HRMS (FAB,
sector) calcd for C19H25BO2 (M+) 296.1942, found 296.1947.
2-(Phenylethynyl)-5-(dimethylamino)phenylboronic acid neopentylglycol ester (1e).
This was synthesized following the procedure for compound 1b. 86% yield (498 mg). 1H NMR
(CDCl3, 400 MHz): δ 7.51-7.45 (m, 2H), 7.43 (d, J = 8.7 Hz, 1H), 7.34-7.28 (m, 2H), 7.28-
7.22 (m, 1H), 7.07 (d, J = 2.7 Hz, 1H), 6.71 (dd, J = 8.7, 2.8 Hz, 1H), 3.83 (s, 4H), 3.00 (s, 6H),
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1.08 (s, 6H). C{1H} NMR (CDCl3, 101 MHz): δ 149.5, 133.9, 131.3, 128.2, 127.2, 125.2,
117.7, 114.4, 113.7, 92.4, 88.6, 72.6, 40.4, 31.9, 22.1. Mp: 137–139 °C. HRMS (FAB, sector)
calcd for C21H24BNO2 (M+) 333.1895, found 333.1904.
2-(tert-Butylethynyl)-4-methoxyphenylboronic acid neopentylglycol ester (1f). This
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was synthesized following the procedure for compound 1b. 88% yield (817 mg). H NMR
(CDCl3, 400 MHz): δ 7.60 (d, J = 8.2 Hz, 1H), 6.92 (d, J = 2.7 Hz, 1H), 6.78 (dd, J = 8.2, 2.7
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Hz, 1H) 3.79 (s, 3H), 3.76 (s, 4H), 1.33 (s, 9H), 1.04 (s, 6H). C{1H} NMR (CDCl3, 101
MHz): δ 160.8, 136.0, 129.8, 117.4, 113.5, 99.6, 80.3, 72.4, 55.2, 31.9, 31.2, 28.2, 22.1. Mp:
90–92 °C. HRMS (FAB, sector) calcd for C18H25BO3 (M+) 300.1891, found 300.1903.
2-(tert-Butylethynyl)-4,5-difluorophenylboronic acid neopentylglycol ester (1g). This
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was synthesized following the procedure for compound 1b. 91% yield (457 mg). H NMR
(CDCl3, 400 MHz): δ 7.44 (dd, J = 11.4, 9.2 Hz, 1H), 7.17 (dd, J = 11.4, 7.8 Hz, 1H), 3.77 (s,
4H), 1.31 (s, 9H), 1.04 (s, 6H). 13C{1H} NMR (CDCl3, 101 MHz): δ 151.0 (dd, J = 251, 13.4
Hz), 149.5 (dd, J = 250, 12.5 Hz), 125.4 (dd, J = 7.7, 3.8 Hz), 123.0 (d, J = 15.3 Hz), 121.4 (d,
J = 17.3 Hz), 100.3 (d, J = 1.9 Hz), 78.6 (d, J = 3.8 Hz), 72.5, 31.9, 31.0, 28.2, 22.1. Mp: 90–
91 °C. HRMS (FAB, sector) calcd for C17H21BF2O2 (M+) 306.1597, found 306.1604.
1-(2-(1-Pentynyl)phenyl)ethanone (2a) (CAS no. 1858190-38-1). 1-Pentyne (352 µL,
3.60 mmol) was added to a mixture of 1-(2-iodophenyl)ethanone37 (738 mg, 3.00 mmol),
PdCl2(PPh3)2 (42.1 mg, 60.0 µmol), CuI (22.9 mg, 120 µmol), and Et3N (1.25 mL, 9.00 mmol)
in THF (3 mL), and the mixture was stirred for 5 h at room temperature. The reaction mixture
was directly passed through a pad of silica gel with EtOAc. After removal of the solvent under
vacuum, the residue was chromatographed on silica gel with hexane/EtOAc = 25/1 to afford
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compound 2a as a pale yellow oil (535 mg, 2.87 mmol; 96% yield). H NMR (CDCl3, 400
MHz): δ 7.66 (dd, J = 7.8, 1.4 Hz, 1H), 7.49 (dd, J = 7.8, 1.4 Hz, 1H), 7.40 (td, J = 7.6, 1.4 Hz,
1H), 7.32 (td, J = 7.6, 1.4 Hz, 1H), 2.72 (s, 3H), 2.44 (t, J = 7.1 Hz, 2H), 1.66 (sext, J = 7.2 Hz,
2H), 1.06 (t, J = 7.3 Hz, 3H). 13C{1H} NMR (CDCl3, 101 MHz): δ 201.0, 141.2, 134.1, 131.1,
128.4, 127.6, 122.5, 96.8, 79.9, 30.1, 22.0, 21.8, 13.7.
1-(2-(1-Propynyl)phenyl)ethanone (2b) (CAS no. 171258-00-7). Iodomethane (191 µL,
3.00 mmol) was added dropwise to a stirring suspension of Mg turnings (80.2 mg, 3.30 mmol)
in Et2O (1.0 mL), and the mixture was stirred for 20 min at room temperature. This was then
added dropwise with the aid of additional Et2O (1.0 mL) to a solution of 2-(1-
propynyl)benzaldehyde15 (288 mg, 2.00 mmol) in Et2O (3.0 mL) at 0 °C, and the mixture was
stirred for 4 h at 0 °C. The reaction was quenched with saturated NH4Claq and this was
extracted with Et2O. The organic layer was washed with saturated NaClaq, dried over MgSO4,
filtered, and concentrated under vacuum. The residue was dissolved in CH2Cl2 (6.0 mL) and
pyridinium chlorochromate (647 mg, 3.00 mmol) was added to it, and the mixture was stirred
for 4 h at room temperature. The reaction mixture was directly passed through a pad of silica
gel with CH2Cl2. After removal of the solvent under vacuum, the residue was chromatographed
on silica gel with hexane/EtOAc = 15/1 to afford compound 2b as a pale yellow oil (291 mg,
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1.84 mmol; 92% yield). H NMR (CDCl3, 400 MHz): δ 7.66 (dd, J = 7.8, 1.4 Hz, 1H), 7.48
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(dd, J = 7.8, 1.4 Hz, 1H), 7.40 (td, J = 7.6, 1.4 Hz, 1H), 7.32 (td, J = 7.6, 1.4 Hz, 1H), 2.71 (s,
3H), 2.10 (s, 3H). 13C{1H} NMR (CDCl3, 101 MHz): δ 201.0, 141.1, 134.0, 131.2, 128.4, 127.6,
122.5, 92.3, 78.9, 30.0, 4.7.
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1-(2-(Trimethylsilylethynyl)phenyl)ethanone (2c) (CAS no. 202871-98-5). This was
synthesized following the procedure for compound 2a. 96% yield (529 mg). 1H NMR (CDCl3,
498 MHz): δ 7.68 (dd, J = 7.8, 1.4 Hz, 1H), 7.55 (dd, J = 7.6, 1.4 Hz, 1H), 7.42 (td, J = 7.4,
1.5 Hz, 1H), 7.38 (td, J = 7.5, 1.4 Hz, 1H), 2.74 (s, 3H), 0.26 (s, 9H). 13C{1H} NMR (CDCl3,
101 MHz): δ 200.6, 141.7, 134.3, 131.1, 128.6, 128.5, 121.5, 104.0, 101.1, 30.2, –0.2.
(2-(1-Pentynyl)phenyl)(phenyl)methanone (2d) (CAS no. 1006056-21-8). This was
synthesized following the procedure for compound 2a. 78% yield (486 mg). 1H NMR (CDCl3,
400 MHz): δ 7.85-7.79 (m, 2H), 7.56 (tt, J = 7.3, 1.4 Hz, 1H), 7.51-7.33 (m, 6H), 2.08 (t, J =
6.9 Hz, 2H), 1.26 (sext, J = 7.2 Hz, 2H), 0.78 (t, J = 7.6 Hz, 3H). 13C{1H} NMR (CDCl3, 101
MHz): δ 197.4, 141.8, 137.4, 133.0, 132.6, 130.2, 130.0, 128.3, 128.1, 127.4, 122.6, 96.5, 78.8,
21.7, 21.3, 13.4.
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1-(4-Methoxy-2-(1-pentynyl)phenyl)ethanone (2g). This was synthesized following the
procedure for compound 2b. 88% yield (177 mg). 1H NMR (CDCl3, 400 MHz): δ 7.75 (d, J =
8.7 Hz, 1H), 6.97 (d, J = 2.8 Hz, 1H), 6.85 (dd, J = 8.7, 2.8 Hz, 1H), 3.84 (s, 3H), 2.70 (s, 3H),
2.45 (t, J = 7.1 Hz, 2H), 1.67 (sext, J = 7.2 Hz, 2H), 1.07 (t, J = 7.3 Hz, 3H). 13C{1H} NMR
(CDCl3, 101 MHz): δ 198.8, 161.9, 133.4, 131.3, 125.1, 118.6, 114.1, 96.9, 80.4, 55.6, 30.0,
22.0, 21.8, 13.8. HRMS (FAB, sector) calcd for C14H17O2 (M+H+) 217.1223, found 217.1229.
1-(5-Nitro-2-(1-pentynyl)phenyl)ethanone (2h). This was synthesized following the
procedure for compound 2a. 64% yield (148 mg). 1H NMR (CDCl3, 400 MHz): δ 8.51 (d, J =
2.3 Hz, 1H), 8.23 (dd, J = 8.7, 2.3 Hz, 1H), 7.64 (d, J = 8.7 Hz, 1H), 2.76 (s, 3H), 2.50 (t, J =
7.1 Hz, 2H), 1.69 (sext, J = 7.2 Hz, 2H), 1.07 (t, J = 7.3 Hz, 3H). 13C{1H} NMR (CDCl3, 101
MHz): δ 198.5, 146.6, 141.9, 135.2, 129.0, 125.3, 123.7, 103.3, 79.0, 29.9, 22.0, 21.8, 13.7.
HRMS (FAB, sector) calcd for C13H14NO3 (M+H+) 232.0968, found 232.0971.
1-(1-Methyl-2-(1-pentynyl)-1H-3-indolyl)ethanone (2i). Iodomethane (210 µL, 3.30
mmol) was added dropwise to a stirring suspension of Mg turnings (88.2 mg, 3.63 mmol) in
Et2O (2.0 mL), and the mixture was stirred for 20 min at room temperature. This was then
added dropwise with the aid of additional Et2O (1.0 mL) to a solution of 1-methyl-2-(1-
pentynyl)-1H-indole-3-carbaldehyde15 (495 mg, 2.20 mmol) in Et2O (12 mL) at 0 °C, and the
mixture was stirred for 6 h at 0 °C. The reaction was quenched with saturated NH4Claq and
this was extracted with Et2O. The organic layer was washed with saturated NaClaq, dried over
MgSO4, filtered, and concentrated under vacuum. The residue was dissolved in CH2Cl2 (10
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mL) and 4-methylmorpholine N-oxide (531 mg, 4.40 mmol) and tetrapropylammonium
perruthenate (39.9 mg, 0.110 mmol) were added to it at 0 °C, and the mixture was stirred for 3
h at 0 °C. The reaction mixture was directly passed through a pad of silica gel with EtOAc.
After removal of the solvent under vacuum, the residue was chromatographed on silica gel
with hexane/EtOAc = 5/1, and the solid thus obtained was washed with pentane to afford
compound 2i as a white solid (328 mg, 1.37 mmol; 62% yield). 1H NMR (CDCl3, 400 MHz):
δ 8.47-8.42 (m, 1H), 7.35-7.25 (m, 3H), 3.83 (s, 3H), 2.73 (s, 3H), 2.61 (t, J = 7.1 Hz, 2H),
1.75 (sext, J = 7.2 Hz, 2H), 1.12 (t, J = 7.3 Hz, 3H). 13C{1H} NMR (CDCl3, 101 MHz): δ 193.9,
136.7, 127.9, 125.9, 124.1, 123.1, 122.9, 119.0, 109.3, 104.6, 72.6, 31.0, 29.8, 22.0, 21.9, 13.8.
Mp: 103–104 °C. HRMS (FAB, sector) calcd for C16H18NO (M+H+) 240.1383, found 240.1387.
1-(2-(4-(3,5-Dimethoxyphenyl)-1-butynyl)phenyl)ethanone (2j). HgCl2 (11.3 mg, 41.6
µmol) was added to a stirring suspension of Mg turnings (128 mg, 5.28 mmol) in Et2O (2.0
mL), and the mixture was stirred for 30 min at room temperature. This was cooled to 0 °C and
propargyl bromide (361 µL, 4.80 mmol) was added slowly over 1 h and the mixture was stirred
for 30 min at 0 °C. This was then added dropwise with the aid of THF (1.5 mL) to a solution
of 3,5-dimethoxybenzyl bromide (739 mg, 3.20 mmol) in THF (2.0 mL) at 0 °C, and the
mixture was stirred for 30 min at 0 °C and for 24 h at 40 °C. The reaction was quenched with
saturated NH4Claq and this was extracted with Et2O. The organic layer was washed with
saturated NaClaq, dried over MgSO4, filtered, and concentrated under vacuum. The residue
was chromatographed on silica gel with hexane/EtOAc = 20/1 to afford 1-(3-butynyl)-3,5-
dimethoxybenzene as a colorless oil (577 mg, 3.03 mmol; 95% yield). 1H NMR (CDCl3, 400
MHz): δ 6.39 (d, J = 2.3 Hz, 2H), 6.33 (t, J = 2.3 Hz, 1H), 3.78 (s, 6H), 2.79 (t, J = 7.8 Hz,
2H), 2.48 (td, J = 7.8, 2.8 Hz, 2H), 1.99 (t, J = 2.8 Hz, 1H). 13C{1H} NMR (CDCl3, 101 MHz):
δ 160.9, 142.9, 106.6, 98.4, 83.9, 69.0, 55.3, 35.2, 20.4.
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1-(3-Butynyl)-3,5-dimethoxybenzene (457 mg, 2.40 mmol) was added to a mixture of 1-
(2-iodophenyl)ethanone (492 mg, 2.00 mmol), Pd(PPh3)4 (46.2 mg, 40.0 µmol), CuI (15.2 mg,
80.0 µmol), and Et3N (834 µL, 6.00 mmol) in THF (2 mL), and the mixture was stirred for 12
h at room temperature and for 24 h at 40 °C. The reaction mixture was directly passed through
a pad of silica gel with EtOAc. After removal of the solvent under vacuum, the residue was
chromatographed on silica gel with hexane/EtOAc = 8/1 to afford compound 2j as a red oil
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(477 mg, 1.55 mmol; 77% yield). H NMR (CDCl3, 400 MHz): δ 7.65 (dd, J = 7.8, 1.4 Hz,
1H), 7.46 (dd, J = 7.8, 1.4 Hz, 1H), 7.39 (td, J = 7.6, 1.4 Hz, 1H), 7.33 (td, J = 7.6, 1.4 Hz, 1H),
6.43 (d, J = 2.3 Hz, 2H), 6.34 (t, J = 2.3 Hz, 1H), 3.78 (s, 6H), 2.89 (t, J = 7.3 Hz, 2H), 2.76 (t,
J = 7.3 Hz, 2H), 2.63 (s, 3H). 13C{1H} NMR (CDCl3, 101 MHz): δ 200.8, 160.9, 142.8, 141.1,
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134.1, 131.1, 128.4, 127.7, 122.2, 106.6, 98.4, 95.8, 80.5, 55.3, 35.1, 29.9, 21.7. HRMS (FAB,
sector) calcd for C20H21O3 (M+H+) 309.1485, found 309.1489.
(2-(1-Pentynyl)phenyl)(1H-1-pyrrolyl)methanone (2k). nBuLi (4.62 mL, 7.35 mmol;
1.59 M solution in hexane) was added slowly over 8 min to a solution of 1-bromo-2-(1-
pentynyl)benzene38 (1.56 g, 7.00 mmol) in THF (35 mL) at –78 °C, and the mixture was stirred
for 30 min at –78 °C. CO2 was then bubbled through the mixture for 30 min while gradually
raising the temperature to room temperature. The reaction was quenched with 1 M HClaq and
this was extracted with Et2O. The organic layer was washed with saturated NaClaq, dried over
MgSO4, filtered, and concentrated under vacuum to afford 2-(1-pentynyl)benzoic acid as a red
oil. This was dissolved in CH2Cl2 (30 mL), and DMF (12.0 µL, 0.156 mmol) and oxalyl
chloride (1.20 mL, 14.0 mmol) were added to it, and the mixture was stirred for 3 h at room
temperature. The volatiles were removed under vacuum to afford 2-(1-pentynyl)benzoyl
chloride as a purple oil. Separately, NaH (267 mg, 6.68 mmol; 60 wt% in mineral oil) was
added to a solution of pyrrole (440 µL, 6.36 mmol) in THF (20 mL) at 0 °C, and the mixture
was stirred for 30 min at 0 °C and for 30 min at room temperature. After cooled to 0 °C, a
solution of 2-(1-pentynyl)benzoyl chloride obtained above in THF (10 mL) was added to it and
the mixture was stirred for 20 h at room temperature. The reaction was quenched with 1 M
HClaq and this was extracted with Et2O. The organic layer was washed with saturated NaClaq,
dried over MgSO4, filtered, and concentrated under vacuum. The residue was chromatographed
on silica gel with hexane/EtOAc = 20/1 to afford compound 2k as a yellow oil (1.25 g, 5.27
mmol; 83% yield). 1H NMR (CDCl3, 400 MHz): δ 7.53-7.42 (m, 3H), 7.41-7.34 (m, 1H), 7.15
(bs, 2H), 6.33-6.26 (m, 2H), 2.21 (t, J = 6.9 Hz, 2H), 1.40 (sext, J = 7.2 Hz, 2H), 0.87 (t, J =
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7.3 Hz, 3H). C{1H} NMR (CDCl3, 101 MHz): δ 167.3, 136.8, 132.5, 130.4, 127.8, 127.5,
122.7, 120.7, 113.3, 96.2, 77.4, 21.8, 21.4, 13.4. HRMS (FAB, sector) calcd for C16H16NO
(M+H+) 238.1226, found 238.1231.
Procedure for Equation 1. 1,5-Cyclooctadiene (24.5 µL, 0.200 mmol), H2O (11.7 µL,
0.649 mmol), and THF (0.5 mL) were added to a solution of [Rh(OH)(cod)]2 (9.1 mg, 40 µmol
Rh), compound 1a (189 mg, 0.650 mmol), and compound 2a (93.1 mg, 0.500 mmol) in THF
(4.5 mL), and the mixture was stirred for 16 h at 40 °C. After cooled to room temperature, H2O
(0.50 mL) and conc. H2SO4 (2.8 µL, 50 µmol) were added to it and the mixture was stirred for
2 h at room temperature. The reaction was quenched with saturated NaHCO3aq and this was
extracted with Et2O. The organic layer was washed with saturated NaClaq, dried over MgSO4,
filtered, and concentrated under vacuum. The residue was chromatographed on silica gel with
hexane/EtOAc = 10/1, and the solid thus obtained was washed with cold pentane to afford 5-
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methyl-6-phenyl-11-propyl-11H-benzo[a]fluoren-11-ol (4aa) as a white solid (149 mg, 0.409
mmol; 82% yield). The reaction on a 3.00 mmol scale of 2a gave compound 4aa in 78% yield
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(848 mg). H NMR (CDCl3, 400 MHz): δ 8.62 (dd, J = 7.3, 1.8 Hz, 1H), 8.14 (dd, J = 7.8, 1.8
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0.9 Hz, 1H), 6.03 (d, J = 7.8 Hz, 1H), 2.56 (ddd, J = 12.4, 10.0, 4.6 Hz, 1H), 2.47 (s, 3H), 2.46-
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2.35 (m, 1H), 2.15 (s, 1H), 0.81-0.59 (m, 5H). C{1H} NMR (CDCl3, 101 MHz): δ 150.9,
141.2, 140.9, 140.4, 135.6, 135.0, 133.6, 132.8, 129.8, 129.6, 129.3, 129.0, 128.9, 128.4, 127.6,
127.0, 126.1, 125.9, 125.6, 125.2, 122.8, 122.6, 84.2, 42.4, 17.4, 16.3, 14.3. Mp: 132–134 °C.
HRMS (FAB, sector) calcd for C27H24O (M+) 364.1822, found 364.1832.
General Procedure for Scheme 2. 1,5-Cyclooctadiene (4.9–9.8 µL, 40–80 µmol), H2O
(4.7 µL, 0.26 mmol), and THF (0.5 mL) were added to a solution of [Rh(OH)(cod)]2 (1.8–3.6
mg, 7.9–16 µmol Rh), compound 1 (0.260 mmol), and compound 2 (0.200 mmol) in THF (1.5
mL), and the mixture was stirred for 16 h at 40 °C. After cooled to room temperature, H2O
(0.20 mL) and conc. H2SO4 (5.0 µL, 90 µmol) were added to it and the mixture was stirred for
1–5 h at room temperature. The reaction was quenched with saturated NaHCO3aq and this was
extracted with Et2O. The organic layer was washed with saturated NaClaq, dried over MgSO4,
filtered, and concentrated under vacuum. The residue was chromatographed on silica gel to
afford compound 4.
5,11-Dimethyl-6-phenyl-11H-benzo[a]fluoren-11-ol (4ab). 8 mol% Rh and 40 mol% cod
were used. The crude material was purified by silica gel chromatography with hexane/EtOAc
= 9/1, and the solid thus obtained was washed with cold pentane. Pale orange solid. 81% yield
(54.4 mg). 1H NMR (CDCl3, 400 MHz): δ 8.62 (dd, J = 7.8, 1.4 Hz, 1H), 8.16 (dd, J = 8.2, 1.4
Hz, 1H), 7.67-7.48 (m, 6H), 7.38-7.29 (m, 2H), 7.21 (td, J = 7.3, 0.9 Hz, 1H), 6.98 (td, J = 7.6,
1.4 Hz, 1H), 6.06 (d, J = 7.8 Hz, 1H), 2.47 (s, 3H), 2.07 (s, 1H), 1.97 (s, 3H). 13C{1H} NMR
(CDCl3, 101 MHz): δ 152.3, 142.2, 140.8, 139.3, 135.2, 134.5, 133.7, 132.9, 129.7, 129.6,
129.03, 128.95, 128.4, 127.7, 127.1, 126.1, 125.9, 125.6, 125.4, 123.0, 122.4, 81.0, 27.2, 16.2.
Mp: 113–115 °C. HRMS (FAB, sector) calcd for C25H20O (M+) 336.1509, found 336.1516.
6-(tert-Butyl)-5-methyl-11H-benzo[a]fluoren-11-ol (4bc). 8 mol% Rh and 40 mol% cod
were used. After rhodium catalysis, the reaction mixture was passed through a pad of silica gel
with EtOAc and concentrated under vacuum. This was dissolved in Et2O, washed with H2O,
dried over MgSO4, filtered, and concentrated under vacuum. The residue was dissolved in THF
(0.6 mL) and nBu4NF•3H2O (63.1 mg, 0.200 mmol) in THF (0.4 mL) was added to it at 0 °C,
and the mixture was stirred for 24 h at 30 °C. After cooled to room temperature, THF (1.0 mL),
H2O (0.20 mL) and conc. H2SO4 (0.20 mL, 3.6 mmol) were added to it and the mixture was
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stirred for 2 h at room temperature. The reaction was quenched with saturated NaHCO3aq and
this was extracted with Et2O. The organic layer was washed with saturated NaClaq, dried over
MgSO4, filtered, and concentrated under vacuum. The residue was chromatographed on silica
gel with hexane/EtOAc = 10/1, and the solid thus obtained was washed with cold pentane. Pale
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yellow solid. 68% yield (41.3 mg). H NMR (CDCl3, 400 MHz): δ 8.38-8.32 (m, 1H), 8.10-
8.03 (m, 1H), 8.01 (d, J = 7.8 Hz, 1H), 7.70 (d, J = 7.4 Hz, 1H), 7.57-7.47 (m, 2H), 7.38 (td, J
= 7.8, 1.4 Hz, 1H), 7.28 (td, J = 7.3, 0.9 Hz, 1H), 5.91 (d, J = 10.5 Hz, 1H), 2.87 (s, 3H), 1.767
(d, J = 10.1 Hz, 1H), 1.765 (s, 9H). 13C{1H} NMR (CDCl3, 101 MHz): δ 146.9, 143.9, 143.0,
141.0, 137.5, 134.5, 134.3, 128.1, 128.0, 127.3, 126.3, 126.1, 125.8, 125.2, 124.6, 124.5, 74.6,
37.9, 32.8, 20.6. Mp: 149–150 °C. HRMS (FAB, sector) calcd for C22H22O (M+) 302.1665,
found 302.1673.
6-(tert-Butyl)-5-phenyl-11-propyl-11H-benzo[a]fluoren-11-ol (4bd). 4 mol% Rh and 20
mol% cod were used. 3.60 mmol of conc. H2SO4 was used in the subsequent step. The crude
material was purified by silica gel chromatography with hexane/CH2Cl2 = 1/1. White solid.
87% yield (70.6 mg). 1H NMR (CDCl3, 400 MHz): δ 8.66 (d, J = 8.3 Hz, 1H), 8.08 (d, J = 7.8
Hz, 1H), 7.65 (dd, J = 7.3, 1.4 Hz, 1H), 7.51-7.36 (m, 6H), 7.36-7.21 (m, 4H), 2.65-2.54 (m,
1H), 2.48-2.36 (m, 1H), 2.13 (s, 1H), 1.43 (s, 9H), 0.87-0.62 (m, 5H). 13C{1H} NMR (CDCl3,
101 MHz): δ 151.3, 145.5, 142.5, 142.3, 141.6, 139.2, 137.0, 134.5, 132.5, 131.6, 128.2, 127.81,
127.78, 127.7, 127.5, 127.4, 127.2, 126.5, 125.8, 125.5, 124.6, 122.4, 83.9, 42.9, 37.6, 34.3,
17.4, 14.3. Mp: 218–219 °C. HRMS (FAB, sector) calcd for C30H30O (M+) 406.2291, found
406.2300.
6-Phenyl-11-propyl-11H-benzo[a]fluoren-11-ol (4ae). 8 mol% Rh and 40 mol% cod
were used and conducted for 20 h at 20 °C. The crude material was purified by silica gel
chromatography with hexane/EtOAc = 12/1. Pale yellow solid. 83% yield (58.3 mg). 1H NMR
(CDCl3, 400 MHz): δ 8.57 (d, J = 8.2 Hz, 1H), 7.89 (d, J = 8.2 Hz, 1H), 7.71 (s, 1H), 7.65-7.45
(m, 8H), 7.23 (t, J = 7.3 Hz, 1H), 7.06 (t, J = 7.6 Hz, 1H), 6.73 (d, J = 7.8 Hz, 1H), 2.66-2.52
(m, 1H), 2.51-2.37 (m, 1H), 2.15 (bs, 1H), 0.92-0.61 (m, 5H). C{1H} NMR (CDCl3, 101
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MHz): δ 150.9, 144.1, 140.9, 139.9, 136.1, 135.0, 133.5, 130.7, 129.7, 129.2, 129.0, 128.9,
128.6, 128.44, 128.35, 127.8, 127.2, 126.5, 126.0, 124.6, 122.9, 122.8, 84.2, 42.3, 17.4, 14.3.
Mp: 134–136 °C. HRMS (FAB, sector) calcd for C26H22O (M+) 350.1665, found 350.1671.
2-Chloro-6-phenyl-11-propyl-11H-benzo[a]fluoren-11-ol (4af). 8 mol% Rh and 40
mol% cod were used and conducted for 20 h at 20 °C. The crude material was purified by silica
gel chromatography with hexane/EtOAc = 10/1, and the solid thus obtained was washed with
cold pentane. Yellow solid. 78% yield (60.3 mg). 1H NMR (CDCl3, 400 MHz): δ 8.55 (s, 1H),
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7.81 (d, J = 8.7 Hz, 1H), 7.68 (s, 1H), 7.56 (d, J = 7.4 Hz, 1H), 7.55-7.46 (m, 5H), 7.44 (dd, J
= 8.7, 2.3 Hz, 1H), 7.25 (t, J = 7.6 Hz, 1H), 7.06 (t, J = 7.6 Hz, 1H), 6.73 (d, J = 7.8 Hz, 1H),
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2.58-2.33 (m, 2H), 2.19 (d, J = 5.5 Hz, 1H), 0.93-0.61 (m, 5H). C{1H} NMR (CDCl3, 101
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MHz, 60 °C): δ 151.0, 143.6, 140.7, 139.6, 136.5, 136.2, 132.6, 131.8, 130.6, 130.5, 129.7,
129.4, 128.7, 128.6, 128.0, 127.6, 127.0, 123.6, 123.2, 122.9, 84.3, 42.6, 17.5, 14.2. Mp: 110–
112 °C. HRMS (FAB, sector) calcd for C26H21ClO (M+) 384.1275, found 384.1281.
2-Methoxy-5-methyl-6-phenyl-11-propyl-11H-benzo[a]fluoren-11-ol (4ag). 8 mol%
Rh and 40 mol% cod were used. The crude material was purified by silica gel chromatography
with hexane/EtOAc = 7/1, and the solid thus obtained was washed with cold pentane. Pale
yellow solid. 83% yield (65.3 mg). 1H NMR (CDCl3, 400 MHz): δ 8.04 (d, J = 9.6 Hz, 1H),
7.94 (d, J = 2.8 Hz, 1H), 7.58-7.47 (m, 4H), 7.36-7.27 (m, 2H), 7.22 (dd, J = 9.4, 2.7 Hz, 1H),
7.18 (td, J = 7.3, 0.9 Hz, 1H), 6.96 (td, J = 7.6, 0.9 Hz, 1H), 6.04 (d, J = 7.8 Hz, 1H), 4.03 (s,
3H), 2.65-2.51 (m, 1H), 2.47-2.32 (m, 1H), 2.43 (s, 3H), 2.12 (s, 1H), 0.79-0.60 (m, 5H).
13C{1H} NMR (CDCl3, 101 MHz): δ 157.5, 150.9, 140.9, 140.4, 139.8, 136.0, 133.5, 132.9,
130.4, 130.0, 129.8, 129.0, 128.8, 128.3, 128.2, 127.5, 127.1, 126.9, 122.8, 122.5, 118.3, 103.5,
84.1, 55.5, 41.8, 17.4, 16.3, 14.3. Mp: 195–197 °C. HRMS (FAB, sector) calcd for C28H26O2
(M+) 394.1927, found 394.1931.
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5-Methyl-3-nitro-6-phenyl-11-propyl-11H-benzo[a]fluoren-11-ol (4ah). 8 mol% Rh
and 40 mol% cod were used. 0.45 mmol of conc. H2SO4 was used in the subsequent step. The
crude material was purified by silica gel chromatography with hexane/CH2Cl2 = 1/2, and the
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solid thus obtained was washed with pentane. Yellow solid. 86% yield (70.5 mg). H NMR
(CDCl3, 400 MHz): δ 9.12 (d, J = 2.3 Hz, 1H), 8.74 (d, J = 9.2 Hz, 1H), 8.34 (dd, J = 9.2, 2.3
Hz, 1H), 7.63-7.51 (m, 4H), 7.38-7.23 (m, 3H), 7.01 (td, J = 7.6, 0.9 Hz, 1H), 6.08 (d, J = 7.8
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Hz, 1H), 2.56 (s, 3H), 2.55-2.35 (m, 2H), 2.18 (s, 1H), 0.79-0.55 (m, 5H). C{1H} NMR
(CDCl3, 101 MHz): δ 151.1, 145.2, 141.4, 139.7, 139.6, 139.4, 137.1, 136.6, 131.83, 131.76,
129.5, 129.4, 129.28, 129.26, 128.8, 128.24, 128.22, 126.7, 123.6, 122.8, 122.7, 119.5, 84.1,
42.7, 17.4, 16.5, 14.2. Mp: 252–255 °C (dec). HRMS (FAB, sector) calcd for C27H24NO3
(M+H+) 410.1751, found 410.1755.
6,11-Dimethyl-5-phenyl-12-propyl-11,12-dihydroindeno[2,1-a]carbazol-12-ol (4ai). 8
mol% Rh and 40 mol% cod were used. The crude material was purified by silica gel
chromatography with hexane/EtOAc = 8/1, and the solid thus obtained was washed with
pentane. White solid. 82% yield (68.4 mg). 1H NMR (CDCl3, 400 MHz): δ 8.25 (d, J = 7.8 Hz,
1H), 7.59-7.45 (m, 6H), 7.39-7.31 (m, 2H), 7.31-7.24 (m, 1H), 7.16 (td, J = 7.6, 0.9 Hz, 1H),
6.94 (td, J = 7.8, 1.4 Hz, 1H), 6.03 (d, J = 7.8 Hz, 1H), 4.46 (s, 3H), 2.63 (s, 3H), 2.57-2.46 (m,
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1H), 2.46-2.35 (m, 1H), 2.35 (s, 1H), 0.89-0.60 (m, 5H). 13C{1H} NMR (CDCl3, 101 MHz): δ
149.8, 143.1, 140.8, 140.7, 137.9, 136.4, 132.8, 130.8, 130.4, 129.3, 129.0, 128.9, 128.5, 127.4,
127.0, 126.9, 125.5, 124.2, 122.9, 122.8, 122.4, 119.4, 108.9, 83.3, 42.8, 33.8, 18.0, 17.5, 14.3.
Mp: 122–125 °C. HRMS (FAB, sector) calcd for C30H27NO (M+) 417.2087, found 417.2093.
6-(tert-Butyl)-5-methyl-11-propyl-11H-benzo[a]fluoren-11-ol (4ba). 4 mol% Rh and 20
mol% cod were used. 0.45 mmol of conc. H2SO4 was used in the subsequent step. The crude
material was purified by silica gel chromatography with hexane/EtOAc = 14/1. White solid.
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88% yield (60.7 mg). H NMR (CDCl3, 400 MHz): δ 8.56-8.49 (m, 1H), 8.12-8.05 (m, 1H),
7.93 (d, J = 7.8 Hz, 1H), 7.58 (dd, J = 7.4, 1.4 Hz, 1H), 7.53-7.45 (m, 2H), 7.33 (td, J = 7.6,
1.4 Hz, 1H), 7.25 (t, J = 7.3 Hz, 1H), 2.86 (s, 3H), 2.54 (td, J = 12.4, 4.6 Hz, 1H), 2.40 (ddd, J
= 12.8, 11.4, 4.6 Hz, 1H), 1.97 (bs, 1H), 1.75 (s, 9H), 0.95-0.70 (m, 2H), 0.68 (t, J = 7.1 Hz,
3H). 13C{1H} NMR (CDCl3, 101 MHz): δ 151.0, 143.8, 143.5, 142.8, 136.9, 134.20, 134.16,
127.5, 127.2, 126.8, 126.1, 125.6, 125.2, 125.0, 124.5, 122.5, 84.4, 42.6, 37.7, 32.6, 20.5, 17.5,
14.3. Mp: 181–182 °C. HRMS (FAB, sector) calcd for C25H28O (M+) 344.2135, found
344.2147.
6-(tert-Butyldimethylsilyl)-5-methyl-11-propyl-11H-benzo[a]fluoren-11-ol (4ca). 4
mol% Rh and 20 mol% cod were used. 0.40 mL of H2O and 0.45 mmol of conc. H2SO4 were
used in the subsequent step. The crude material was purified by silica gel chromatography with
hexane/EtOAc = 14/1. White solid. 82% yield (66.1 mg). 1H NMR (CDCl3, 400 MHz): δ 8.56
(d, J = 8.2 Hz, 1H), 8.11 (d, J = 7.8 Hz, 1H), 7.85 (d, J = 7.4 Hz, 1H), 7.61-7.48 (m, 3H), 7.32
(td, J = 7.4, 0.9 Hz, 1H), 7.28 (dd, J = 7.3, 1.4 Hz, 1H), 2.92 (s, 3H), 2.57-2.46 (m, 1H), 2.46-
2.35 (m, 1H), 2.03 (s, 1H), 1.33 (s, 9H), 0.93-0.61 (m, 5H), 0.354 (s, 3H), 0.346 (s, 3H).
13C{1H} NMR (CDCl3, 101 MHz): δ 151.0, 144.6, 142.5, 142.2, 141.9, 132.34, 132.32, 129.5,
127.0, 126.8, 126.7, 125.7, 125.11, 125.06, 124.6, 122.5, 84.4, 42.5, 30.6, 24.2, 18.3, 17.5, 14.3,
2.9, 2.4. Mp: 186–188 °C. HRMS (FAB, sector) calcd for C27H34OSi (M+) 402.2373, found
402.2376.
6-Cyclohexyl-5-methyl-11-propyl-11H-benzo[a]fluoren-11-ol (4da). 8 mol% Rh and 40
mol% cod were used on a 0.400 mmol scale. 0.90 mmol of conc. H2SO4 was used in the
subsequent step. The crude material was purified by silica gel chromatography with
hexane/CH2Cl2 = 1/1 and further purified by silica gel preparative TLC with hexane/EtOAc =
10/1. Yellow amorphous. 30% yield (44.0 mg). 1H NMR (CDCl3, 400 MHz): δ 8.60-8.53 (m,
1H), 8.13-8.07 (m, 1H), 7.84 (d, J = 7.8 Hz, 1H), 7.63 (dd, J = 7.4, 1.4 Hz, 1H), 7.55-7.46 (m,
2H), 7.40 (td, J = 7.6, 1.4 Hz, 1H), 7.33 (t, J = 7.3, 1H), 3.84 (tt, J = 12.6, 3.0, 1H), 2.86 (s,
3H), 2.57-2.44 (m, 1H), 2.43-2.32 (m, 1H), 2.30-2.15 (m, 2H), 2.09 (s, 1H), 2.06-1.84 (m, 5H),
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1.68-1.38 (m, 3H), 0.78-0.50 (m, 5H). 13C{1H} NMR (CDCl3, 101 MHz): δ 151.5, 142.0, 141.1,
138.8, 136.6, 134.0, 133.8, 128.8, 128.2, 126.9, 125.7, 125.3, 125.1, 124.6, 123.5, 123.1, 83.9,
42.5, 41.7, 31.1, 30.7, 27.8, 27.6, 26.4, 17.8, 17.4, 14.2. HRMS (FAB, sector) calcd for
C27H30O (M+) 370.2291, found 370.2295.
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9-(Dimethylamino)-5-methyl-6-phenyl-11-propyl-11H-benzo[a]fluoren-11-ol (4ea). 8
mol% Rh and 40 mol% cod were used and conducted for 20 h at 20 °C. The crude material
was purified by silica gel chromatography with hexane/EtOAc = 5/1, and further purified by
GPC with CHCl3. White solid. 75% yield (61.2 mg). 1H NMR (CDCl3, 400 MHz): δ 8.56 (d, J
= 7.8 Hz, 1H), 8.11 (d, J = 8.2 Hz, 1H), 7.60-7.45 (m, 5H), 7.38-7.27 (m, 2H), 6.97 (s, 1H),
6.34 (d, J = 7.3 Hz, 1H), 5.89 (d, J = 8.7 Hz, 1H), 2.96 (s, 6H), 2.63-2.51 (m, 1H), 2.45 (s, 3H),
2.39-2.27 (m, 1H), 2.19 (s, 1H), 0.86-0.60 (m, 5H). 13C{1H} NMR (CDCl3, 101 MHz): δ 152.8,
150.0, 141.2, 139.5, 136.5, 134.5, 133.2, 131.9, 129.9, 129.7, 129.4, 128.9, 128.8, 127.4, 125.8,
125.6, 124.9, 124.7, 123.3, 112.2, 107.4, 84.2, 42.8, 41.0, 17.4, 16.2, 14.3. Mp: 162–164 °C
(dec). HRMS (FAB, sector) calcd for C29H29NO (M+) 407.2244, found 407.2250.
6-(tert-Butyl)-8-methoxy-5-methyl-11-propyl-11H-benzo[a]fluoren-11-ol (4fa).
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mol% Rh and 40 mol% cod were used. 0.45 mmol of conc. H2SO4 were used in the subsequent
step. The crude material was purified by silica gel chromatography with hexane/EtOAc = 6/1,
and the solid thus obtained was washed with cold pentane. White solid. 77% yield (57.5 mg).
1H NMR (CDCl3, 400 MHz): δ 8.55-8.48 (m, 1H), 8.12-8.04 (m, 1H), 7.54-7.43 (m, 4H), 6.80
(dd, J = 8.2, 2.3 Hz, 1H), 3.88 (s, 3H), 2.86 (s, 3H), 2.52 (ddd, J = 12.4, 11.4, 4.2 Hz, 1H), 2.37
(ddd, J = 12.8, 11.0, 4.6 Hz, 1H), 1.92 (s, 1H), 1.75 (s, 9H), 0.95-0.63 (m 5H). 13C{1H} NMR
(CDCl3, 101 MHz): δ 159.2, 144.2, 144.0, 143.7, 143.1, 136.4, 134.2, 134.0, 127.0, 125.6,
125.1, 124.9, 124.4, 122.6, 113.9, 110.5, 83.7, 55.5, 42.7, 37.5, 32.5, 20.4, 17.5, 14.2. Mp:
154–156 °C. HRMS (FAB, sector) calcd for C26H30O2 (M+) 374.2240, found 374.2244.
6-(tert-Butyl)-8,9-difluoro-5-methyl-11-propyl-11H-benzo[a]fluoren-11-ol (4ga). 4
mol% Rh and 20 mol% cod were used. 1.80 mmol of conc. H2SO4 was used in the subsequent
step. The crude material was purified by silica gel chromatography with hexane/EtOAc = 11/1,
and the solid thus obtained was washed with cold pentane. White solid. 86% yield (65.7 mg).
1H NMR (CDCl3, 400 MHz): δ 8.51-8.44 (m, 1H), 8.12-8.05 (m, 1H), 7.72 (dd, J = 12.4, 7.3
Hz, 1H), 7.55-7.47 (m, 2H), 7.35 (dd, J = 9.2, 7.8 Hz, 1H), 2.86 (s, 3H), 2.58-2.45 (m, 1H),
2.39-2.26 (m, 1H), 1.98 (s, 1H), 1.72 (s, 9H), 0.91-0.63 (m, 5H). 13C{1H} NMR (CDCl3, 101
MHz): δ 149.7 (dd, J = 244, 13.4 Hz), 149.0 (dd, J = 249, 13.4 Hz), 147.5 (dd, J = 4.8, 2.9 Hz),
143.84, 143.82, 143.3, 138.7 (dd, J = 6.7, 2.9 Hz), 135.2, 134.7, 134.2, 126.9, 126.1, 125.6,
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124.7, 115.8 (d, J = 21.1 Hz), 111.3 (d, J = 18.2 Hz), 83.9, 42.5, 37.6, 32.6, 20.5, 17.4, 14.2.
Mp: 208–209 °C. HRMS (FAB, sector) calcd for C25H26F2O (M+) 380.1946, found 380.1942.
Procedure for Table 1, Entry 1. 1,5-Cyclooctadiene (24.5 µL, 0.200 mmol), MeOH (410
µL, 10.1 mmol), and THF (1.0 mL) were added to a solution of [Rh(OH)(cod)]2 (9.1 mg, 40
µmol Rh), compound 1a (189 mg, 0.650 mmol), and compound 2a (93.1 mg, 0.500 mmol) in
THF (4.0 mL), and the mixture was stirred for 16 h at 40 °C. After cooled to room temperature,
conc. H2SO4 (2.8 µL, 50 µmol) was added to it and the mixture was stirred for 2 h at room
temperature. The reaction was quenched with saturated NaHCO3aq and this was extracted with
Et2O. The organic layer was washed with saturated NaClaq, dried over MgSO4, filtered, and
concentrated under vacuum. The residue was chromatographed on silica gel with
hexane/EtOAc = 50/1, and the solid thus obtained was washed with cold pentane to afford 11-
methoxy-5-methyl-6-phenyl-11-propyl-11H-benzo[a]fluorene (5) as a pale yellow solid (147
mg, 0.388 mmol; 78% yield). 1H NMR (CDCl3, 400 MHz): δ 8.60-8.52 (m, 1H), 8.15 (dd, J =
7.4, 1.8 Hz, 1H), 7.64-7.49 (m, 5H), 7.47 (d, J = 7.3 Hz, 1H), 7.40-7.29 (m, 2H), 7.19 (td, J =
7.6, 1.4 Hz, 1H), 6.98 (td, J = 7.6, 1.4 Hz, 1H), 6.07 (d, J = 7.3 Hz, 1H), 2.83 (s, 3H), 2.48 (s,
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3H), 2.48-2.37 (m, 1H), 2.37-2.27 (m, 1H), 0.81-0.56 (m, 5H). C{1H} NMR (CDCl3, 101
MHz): δ 147.6, 141.6, 140.9, 138.4, 137.0, 135.1, 133.5, 132.4, 129.9, 129.7, 129.6, 129.0,
128.9, 128.3, 127.6, 126.7, 126.3, 126.0, 125.6, 124.7, 123.0, 122.7, 90.3, 51.8, 42.9, 17.1, 16.3,
14.3. Mp: 143–145 °C. HRMS (FAB, sector) calcd for C28H26O (M+) 378.1978, found
378.1988.
General Procedure for Table 1, Entries 2–6 and Equation 2. 1,5-Cyclooctadiene (98.1
µL, 0.800 mmol), H2O (46.9 µL, 2.60 mmol), and THF (2.0 mL) were added to a solution of
[Rh(OH)(cod)]2 (36.5 mg, 0.160 mmol Rh), compound 1a (754 mg, 2.60 mmol), and
compound 2a (373 mg, 2.00 mmol) in THF (18 mL), and the mixture was stirred for 16 h at
40 °C. The reaction mixture was directly passed through a pad of silica gel with EtOAc and
concentrated under vacuum. The residue was dissolved in Et2O, washed with H2O, dried over
MgSO4, filtered, and concentrated under vacuum. The solid thus obtained was washed with
cold pentane to afford compound 3aa as a crude product (749 mg). 1/10 of this material (74.9
mg) was used for each subsequent step.
Entry 2 (11-Benzylthio-5-methyl-6-phenyl-11-propyl-11H-benzo[a]fluorene (6)).
Trifluoroacetic acid (15.3 µL, 0.200 mmol) was added dropwise to a solution of crude product
3aa (74.9 mg) and benzyl mercaptan (23.5 µL, 0.200 mmol) in CH2Cl2 (1.0 mL) at 0 °C, and
the mixture was stirred for 3 h at room temperature. The reaction was quenched with saturated
NaHCO3aq and this was extracted with CH2Cl2. The organic layer was washed with saturated
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NaClaq, dried over MgSO4, filtered, and concentrated under vacuum. The residue was
chromatographed on silica gel with hexane/EtOAc = 50/1 to afford compound 6 as a white
solid (73.2 mg, 0.156 mmol; 78% yield). 1H NMR (CDCl3, 400 MHz): δ 8.84 (d, J = 8.2 Hz,
1H), 8.14 (d, J = 8.2 Hz, 1H), 7.66 (d, J = 6.8 Hz, 1H), 7.65-7.49 (m, 5H), 7.41-7.31 (m, 2H),
7.23 (t, J = 7.6 Hz, 1H), 7.01-6.88 (m, 4H), 6.76-6.65 (m, 2H), 6.07 (d, J = 7.8 Hz, 1H), 2.80
(d, J = 12.4 Hz, 1H), 2.76 (d, J = 12.4 Hz, 1H), 2.70-2.57 (m, 1H), 2.47 (s, 3H), 2.43-2.32 (m,
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1H), 0.69-0.53 (m, 5H). C{1H} NMR (CDCl3, 101 MHz): δ 150.6, 141.12, 141.09, 139.0,
137.5, 136.9, 134.8, 133.1, 132.7, 129.9, 129.7, 129.3, 129.03, 128.96, 128.7, 127.8, 127.6,
127.3, 126.9, 126.3, 125.74, 125.66, 125.6, 125.0, 123.4, 122.4, 61.2, 41.2, 33.7, 17.4, 16.3,
14.2. Mp: 166–168 °C. HRMS (FAB, sector) calcd for C34H30S (M+) 470.2063, found 470.2064.
Entry 3 (11-Azido-5-methyl-6-phenyl-11-propyl-11H-benzo[a]fluorene (7)). HCl (50.0
µL, 0.200 mmol; 4.0 M solution in 1,4-dioxane) was added to a solution of crude product 3aa
(74.9 mg) in 1,4-dioxane (1.0 mL), and the mixture was stirred for 3 h. The volatiles were then
removed under vacuum. ZnCl2 (27.3 mg, 0.200 mmol) and DMF (1.0 mL) were added to it,
and NaN3 (26.0 mg, 0.400 mmol) was added to this mixture. After stirring for 24 h at 40 °C,
the reaction was quenched with saturated NaHCO3aq and this was extracted with EtOAc. The
organic layer was washed with H2O, dried over MgSO4, filtered, and concentrated under
vacuum. The residue was chromatographed on silica gel with hexane/EtOAc = 50/1 to afford
compound 7 as a pale yellow solid (55.5 mg, 0.142 mmol; 71% yield). 1H NMR (CDCl3, 400
MHz): δ 8.45 (dd, J = 7.8, 1.4 Hz, 1H), 8.17 (dd, J = 7.8, 1.4 Hz, 1H), 7.68-7.49 (m, 6H), 7.41-
7.30 (m, 2H), 7.24 (td, J = 7.6, 0.9 Hz, 1H), 7.02 (td, J = 7.6, 0.9 Hz, 1H), 6.09 (d, J = 7.8 Hz,
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1H), 2.55-2.40 (m, 1H), 2.49 (s, 3H), 2.37-2.25 (m, 1H), 0.82-0.58 (m, 5H). C{1H} NMR
(CDCl3, 101 MHz): δ 146.9, 141.3, 140.6, 137.7, 136.8, 135.0, 134.3, 132.9, 129.8, 129.7,
129.04, 129.02, 128.9, 128.8, 127.8, 127.1, 126.5, 126.1, 125.9, 124.6, 123.1, 122.9, 75.2, 41.3,
17.1, 16.4, 14.1. Mp: 149–151 °C. HRMS (FAB, sector) calcd for C27H23N3 (M+) 389.1887,
found 389.1888.
Entry 4 (11-Chloro-5-methyl-6-phenyl-11-propyl-11H-benzo[a]fluorene (8)). Crude
product 3aa (74.9 mg) was further washed with hexane and the resulting solid was dissolved
in toluene (1.0 mL). Conc. HCl (360 µL, 4.32 mmol) was then added to it, and the mixture was
stirred for 1 h at room temperature. The reaction was quenched with saturated NaHCO3aq and
this was extracted with Et2O. The organic layer was washed with saturated NaClaq, dried over
Na2SO4, filtered, and concentrated under vacuum to afford compound 8 as an orange solid
(67.2 mg, 0.175 mmol; 88% yield). 1H NMR (CDCl3, 400 MHz): δ 8.57 (d, J = 8.2 Hz, 1H),
8.18 (d, J = 8.2 Hz, 1H), 7.70-7.47 (m, 6H), 7.39-7.29 (m, 2H), 7.23 (t, J = 7.6 Hz, 1H), 6.98
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(t, J = 7.8 Hz, 1H), 6.05 (d, 3JHH = 7.8 Hz, 1H), 3.01-2.86 (m, 1H), 2.77-2.63 (m, 1H), 2.48 (s,
3H), 0.75-0.56 (m, 5H). 13C{1H} NMR (CDCl3, 101 MHz): δ 149.4, 140.6, 139.9, 138.6, 136.0,
135.0, 134.7, 133.0, 129.74, 129.70, 129.1, 129.0, 128.8, 128.6, 127.8, 127.3, 126.3, 126.0,
125.9, 124.8, 123.3, 122.9, 73.8, 45.2, 18.2, 16.4, 13.9. Mp: 74–76 °C. HRMS (FAB, sector)
calcd for C27H23 (M–Cl–) 347.1794, found 347.1798.
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Entry
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(11-Allyl-5-methyl-6-phenyl-11-propyl-11H-benzo[a]fluorene
(9)).
Trifluoroacetic acid (45.9 µL, 0.600 mmol) was added dropwise to a solution of crude product
3aa (74.9 mg) and allyltrimethylsilane (63.7 µL, 0.400 mmol) in CH2Cl2 (0.5 mL) at 0 °C, and
the mixture was stirred for 2 h at room temperature. The reaction was quenched with saturated
NaHCO3aq and this was extracted with CH2Cl2. The organic layer was washed with saturated
NaClaq, dried over MgSO4, filtered, and concentrated under vacuum. The residue was
chromatographed on silica gel with hexane to afford compound 9 as a white solid (59.6 mg,
0.153 mmol; 77% yield). 1H NMR (CDCl3, 400 MHz): δ 8.32 (d, J = 8.7 Hz, 1H), 8.19 (dd, J
= 7.8, 1.4 Hz, 1H), 7.65-7.48 (m, 5H), 7.42 (d, J = 7.8 Hz, 1H), 7.38-7.31 (m, 2H), 7.19 (td, J
= 7.3, 0.9 Hz, 1H), 6.94 (td, J = 7.6, 0.9 Hz, 1H), 6.10 (d, J = 7.8 Hz, 1H), 5.06-4.89 (m, 1H),
4.64 (dd, J = 17.0, 2.3 Hz, 1H), 4.51 (dd, J = 10.1, 2.3 Hz, 1H), 3.16 (dd, J = 14.2, 7.3 Hz, 1H),
3.03 (dd, J = 13.8, 6.9 Hz, 1H), 2.62-2.42 (m, 1H), 2.48 (s, 3H), 2.31-2.16 (m, 1H), 0.68-0.38
(m, 5H). 13C{1H} NMR (CDCl3, 101 MHz): δ 152.1, 141.94, 141.93, 141.4, 137.5, 135.3, 133.7,
132.5, 131.8, 129.9, 129.8, 128.92, 128.90, 127.5, 126.5, 126.1, 125.6, 125.2, 124.3, 122.6,
122.1, 116.6, 56.5, 44.6, 42.2, 17.3, 16.3, 14.5. Mp: 139–141 °C. HRMS (FAB, sector) calcd
for C30H28 (M+) 388.2186, found 388.2192.
Entry 6 (5-Methyl-6-phenyl-11-propyl-11H-benzo[a]fluorene (10)). Trifluoroacetic
acid (45.9 µL, 0.600 mmol) was added dropwise to a solution of crude product 3aa (74.9 mg)
and triethylsilane (63.5 µL, 0.400 mmol) in CH2Cl2 (1.0 mL) at 0 °C, and the mixture was
stirred for 2 h at room temperature. The reaction was quenched with saturated NaHCO3aq and
this was extracted with CH2Cl2. The organic layer was washed with saturated NaClaq, dried
over MgSO4, filtered, and concentrated under vacuum. The residue was chromatographed on
silica gel with hexane to afford compound 10 as a white solid (54.2 mg, 0.156 mmol; 78%
1
yield). H NMR (CDCl3, 400 MHz): δ 8.25-8.13 (m, 2H), 7.66-7.49 (m, 6H), 7.44-7.37 (m,
1H), 7.36-7.30 (m, 1H), 7.18 (td, J = 7.6, 0.9 Hz, 1H), 6.97 (td, J = 7.6, 0.9 Hz, 1H), 6.18 (d, J
= 7.8 Hz, 1H), 4.44 (dd, J = 6.9, 3.7 Hz, 1H), 2.49 (s, 3H), 2.43-2.28 (m, 1H), 2.23-2.08 (m,
1H), 1.03 (sext, J = 7.6 Hz, 2H), 0.79 (t, J = 7.3 Hz, 3H). 13C{1H} NMR (CDCl3, 101 MHz):
δ 149.3, 142.4, 141.7, 141.3, 137.0, 135.4, 132.3, 131.5, 129.9, 129.73, 129.71, 129.0, 128.9,
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127.5, 126.5, 125.84, 125.81, 125.77, 125.5, 124.9, 123.8, 122.7, 46.7, 36.6, 18.2, 16.1, 14.5.
Mp: 114–116 °C. HRMS (FAB, sector) calcd for C27H24 (M+) 348.1873, found 348.1878.
Equation 2 ((E)-5-Methyl-6-phenyl-11-propylidene-11H-benzo[a]fluorene (11)). A
solution of crude product 3aa (74.9 mg) and p-toluenesulfonic acid (38.0 mg, 0.200 mmol;
monohydrate) in toluene (2.0 mL) was stirred for 12 h at 80 °C. The reaction was quenched
with saturated NaHCO3aq and this was extracted with Et2O. The organic layer was washed
with saturated NaClaq, dried over MgSO4, filtered, and concentrated under vacuum. The
residue was chromatographed on silica gel with hexane/EtOAc = 100/1 to afford compound 11
as a yellow solid (51.4 mg, 0.148 mmol; 74% yield, E/Z = 97/3). The major structure of 11 was
determined by X-ray crystallographic analysis after recrystallizations from hexane. E-isomer:
1H NMR (CDCl3, 400 MHz): δ 8.62 (d, J = 7.8 Hz, 1H), 8.15 (dd, J = 8.7, 0.9 Hz, 1H), 7.80
(d, J = 7.8 Hz, 1H), 7.63-7.47 (m, 5H), 7.37-7.31 (m, 2H), 7.28 (t, J = 7.3 Hz, 1H), 7.16 (td, J
= 7.6, 0.9 Hz, 1H), 6.93 (td, J = 7.6, 0.9 Hz, 1H), 6.14 (d, J = 7.8 Hz, 1H), 2.98 (quint, J = 7.4
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Hz, 2H), 2.45 (s, 3H), 1.37 (t, J = 7.6 Hz, 3H). C{1H} NMR (CDCl3, 101 MHz): δ 141.3,
140.9, 139.2, 138.8, 137.8, 135.7, 135.1, 132.9, 132.8, 132.2, 129.8, 129.0, 128.9, 127.5, 127.1,
126.5, 126.0, 125.9, 125.3, 125.2, 124.5, 122.8, 24.1, 16.4, 14.7. Mp: 110–112 °C. HRMS
(FAB, sector) calcd for C27H22 (M+) 346.1716, found 346.1723.
Procedure for Equation 3. 1,5-Cyclooctadiene (9.8 µL, 80 µmol), H2O (4.7 µL, 0.26
mmol), and THF (0.5 mL) were added to a solution of [Rh(OH)(cod)]2 (3.6 mg, 16 µmol Rh),
compound 1a (75.4 mg, 0.260 mmol), and compound 2j (61.7 mg, 0.200 mmol) in THF (1.5
mL), and the mixture was stirred for 16 h at 40 °C. The reaction mixture was directly passed
through a pad of silica gel with EtOAc and concentrated under vacuum. The residue was
dissolved in CH2Cl2 (2.0 mL) and boron trifluoride diethyl etherate (25.1µL, 0.200 mmol) was
added to it at 0 °C. The mixture was stirred for 1 h at 0 °C, and the reaction was quenched with
saturated NaHCO3aq. After extraction with CH2Cl2, the organic layer was washed with
saturated NaClaq, dried over MgSO4, filtered, and concentrated under vacuum. The residue
was chromatographed on silica gel with hexane/EtOAc = 14/1 to afford 5',7'-dimethoxy-5-
methyl-6-phenyl-2',3'-dihydrospiro[benzo[a]fluorene-11,1'-indene] (12) as a white solid (72.5
mg, 0.155 mmol; 77% yield). 1H NMR (CDCl3, 400 MHz): δ 8.14 (d, J = 8.3 Hz, 1H), 7.62 (d,
J = 8.7 Hz, 1H), 7.60-7.50 (m, 3H), 7.49-7.36 (m, 3H), 7.31 (t, J = 7.6 Hz, 1H), 7.09 (d, J =
7.3 Hz, 1H), 7.03 (t, J = 7.1 Hz, 1H), 6.91 (t, J = 7.6 Hz, 1H), 6.65 (d, J = 1.8 Hz, 1H), 6.15 (d,
J = 7.8 Hz, 1H), 6.11 (d, J = 1.8 Hz, 1H), 3.85 (s, 3H), 3.55 (dt, J = 16.0, 9.6 Hz, 1H), 3.41
(ddd, J = 16.5, 9.6, 2.3 Hz, 1H), 3.07-2.95 (m, 1H), 3.01 (s, 3H), 2.50 (s, 3H), 2.31 (ddd, J =
13.3, 9.2, 2.3 Hz, 1H). 13C{1H} NMR (CDCl3, 101 MHz): δ 161.3, 157.0, 154.8, 147.1, 145.2,
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141.6, 140.1, 136.0, 135.2, 132.6, 131.3, 129.91, 129.86, 129.0, 128.9, 128.8, 128.1, 127.4,
126.3, 126.2, 125.7, 125.3, 125.1, 124.3, 122.4, 122.0, 101.4, 98.1, 61.7, 55.6, 55.5, 39.8, 32.7,
16.2. Mp: 254–256 °C (dec). HRMS (FAB, sector) calcd for C34H28O2 (M+) 468.2084, found
468.2085.
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General Procedure for Equation 4. 1,5-Cyclooctadiene (7.4 µL, 60 µmol), H2O (7.0 µL,
0.39 mmol), and THF (0.6 mL) were added to a solution of [Rh(OH)(cod)]2 (2.7 mg, 12 µmol
Rh), compound 1 (0.390 mmol), and compound 2k (71.1 mg, 0.300 mmol) in THF (2.4 mL),
and the mixture was stirred for 16 h at 40 °C. The reaction mixture was directly passed through
a pad of silica gel with EtOAc and concentrated under vacuum. The residue was
chromatographed on silica gel with hexane/CH2Cl2 to afford compound 13.
6-(tert-Butyl)-11-propyl-5H-benzo[a]fluoren-5-one (13bk). The crude material was
purified by silica gel chromatography with hexane/CH2Cl2 = 5/4. Red solid. 95% yield (93.4
mg). 1H NMR (CDCl3, 400 MHz): δ 7.88 (dd, J = 7.8, 1.4 Hz, 1H), 7.75 (d, J = 7.3 Hz, 1H),
7.69 (d, J = 7.8 Hz, 1H), 7.50 (td, J = 7.6, 1.4 Hz, 1H), 7.31 (t, J = 7.3 Hz, 1H), 7.23-7.13 (m,
13
3H), 2.92-2.83 (m, 2H), 1.85-1.72 (m, 2H), 1.60 (s, 9H), 1.16 (t, J = 7.3 Hz, 3H). C{1H}
NMR (CDCl3, 101 MHz): δ 190.5, 151.1, 147.4, 146.6, 146.2, 135.9, 133.4, 132.5, 132.2, 129.3,
129.0, 127.3, 127.1, 126.8, 124.4, 120.3, 35.6, 30.9, 29.1, 21.4, 14.8. Mp: 173–175 °C. HRMS
(FAB, sector) calcd for C24H25O (M+H+) 329.1900, found 329.1903.
6-(tert-Butyldimethylsilyl)-11-propyl-5H-benzo[a]fluoren-5-one (13ck). The crude
material was purified by silica gel chromatography with hexane/CH2Cl2 = 3/2. Red solid. 93%
yield (108 mg). 1H NMR (CDCl3, 400 MHz): δ 8.05 (dd, J = 7.8, 1.4 Hz, 1H), 7.75 (d, J = 7.8
Hz, 1H), 7.71 (d, J = 7.8 Hz, 1H), 7.52 (td, J = 7.8, 1.8 Hz, 1H), 7.32 (t, J = 7.6 Hz, 1H), 7.25-
7.17 (m, 2H), 7.11 (td, J = 7.3, 1.8 Hz, 1H), 2.96-2.87 (m, 2H), 1.87-1.72 (m, 2H), 1.18 (t, J =
7.3 Hz, 3H), 1.16 (s, 9H), 0.33 (s, 6H). 13C{1H} NMR (CDCl3, 101 MHz): δ 191.1, 160.7,
149.7, 146.1, 140.5, 136.8, 134.2, 132.5, 130.6, 130.1, 128.1, 127.7, 127.2, 126.8, 125.9, 124.6,
120.4, 29.2, 28.9, 21.1, 19.3, 14.9, 0.1. Mp: 180–181 °C. HRMS (FAB, sector) calcd for
C26H31OSi (M+H+) 387.2139, found 387.2146.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website.
Crystallographic data, NMR spectra (PDF)
Accession Codes
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CCDC 1992334 contains the supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: shintani@chem.es.osaka-u.ac.jp.
ORCID
Ryo Shintani: 0000-0002-3324-9393
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
Support has been provided in part by JSPS KAKENHI Grant Number JP18H04653 (Hybrid
Catalysis), Nagase Science Technology Foundation, and Tokuyama Science Foundation. We
thank Mr. Tomohiro Tsuda for the help of X-ray crystallographic analysis.
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perfluoroalkylated fluorenes via a one-pot two-step three-component process. Tetrahedron
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