Br?nsted Acid Promoted Thermal-Ring-Rearrangement of Fluorenopyrans to 2-(1H-Inden-3-yl)-9H-fluoren-3-ols Bearing Two All-Carbon-Quaternary Centres

Article abstract of DOI:10.1002/ejoc.202000251

4-Aryl-fluorenopyrans bearing quaternary centre at C2 and C6 positions underwent a thermal-ring-rearrangement with a catalytic amount of pTsOH to furnish 2-(1H-inden-3-yl)-9H-fluoren-3-ols with two all carbon-quaternary centres, in which one is retained a

Full text of DOI:10.1002/ejoc.202000251

A Journal of
Accepted Article
Title: Brønsted acid promoted Thermal-Ring-Rearrangement of
Fluorenopyrans to 2-(1H-inden-3-yl)-9H-fluoren-3-ols bearing two
all-carbon-quaternary centres
Authors: Tabassum Khan, Rajesh P, Dudam Praveen, K. V. Jovan
Jose, and Srinivasarao Yaragorla
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.202000251
Link to VoR: http://dx.doi.org/10.1002/ejoc.202000251
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10.1002/ejoc.202000251
European Journal of Organic Chemistry
Brønsted acid promoted Thermal-Ring-Rearrangement of
Fluorenopyrans to 2-(1H-inden-3-yl)-9H-fluoren-3-ols bearing two
all-carbon-quaternary centres
Tabassum Khan,[a] P. Rajesh,[a] Dudam Praveen,[a] K. V. Jovan Jose*[a] and Srinivasarao Yaragorla*[a]
Abstract: 4-Aryl-fluorenopyrans bearing quaternary centre at C2
OMe
and C6 positions underwent a thermal-ring-rearrangement with a
catalytic amount of p-TsOH to furnish 2-(1H-inden-3-yl)-9H-fluoren-
3-ols with two all carbon-quaternary centres, in which one is retained
and the other is created. Interestingly, these compounds exhibit
atropisomerism, when they have at least one unsymmetrical
quaternary centre. DFT studies of structure and energetics of these
atropisomers were offered, and the calculated 1H-NMR chemical
shifts of the hydroxyl (–OH) functional group in the atropisomers
corroborate well with the experiment.
MeO
O
Ar1
Ar1
Ar1
Ar1
p-TsOH
O
(i)
Toluene, 
Ar2
Ar2
(IB)
only two examples
(IA)
Ar2
OH
Ph
Ar2
OEt
Ph
Ph
O
Sc(OTf)3
(ii)
OH
DCE, 60 o
C
OEt
only one example
(IC)
(ID)
R1
R2
R1
R2
O
Introduction
p-TsOH
(iii)
OH
110 o
C
Ph
large substrate scope
Ring-rearrangement reactions are the ring-opening-cyclization of
a single substrate by means of an acid/base or a metal catalyst
under thermal conditions.[1-4] These ring-rearrangements involve
a cascade of reactions that take place in a single-pot with
maximum atom economy (~100%) and hence fall under green
chemical synthesis.[5] Particularly, the ring rearrangement
(IE)
(IF)
This work
R3
R4
R3 = R4 exhibit
atropisomerism
Me
Me
R4
R3
O
(iv)
-TsOH,

p
I/H
Me
HO
Me
I/H
R1
R2
Solvent-free
R2
R1
reactions of benzochromene derivatives bearing
a
C2-
quaternary centre is depicted in Figure 1. For example, when
naphthopyran [IA] was heated with a catalytic amount of p-TsOH
in toluene, it underwent an irreversible ring-rearrangement to
give highly coloured benzopentaleno-naphthalenones [IB],
however, there are only two examples described using this
method.[2] Later, 3-(2-ethoxyethyl)-2,2-diphenyl-2H-chromene
[IC] was also underwent ring-rearrangement with scandium
R1= R2 exhibit
atropisomerism
both quaternary centers survived
new all-carbon-quaternary center created
Figure 1. Ring-rearrangement reactions of chromenes
Et3N
Me
Me
Me
HO
H
Ph
Ph
Ph
Ph
O
O
o
Ph
Ph
triflate at 60 C to furnish 2-(3-phenyl-1H-inden-1-yl)phenol [ID],
but a single example was demonstrated using this method.[3]
Then a general method was reported by us that a naphthopyran
[IE] can be effectively rearranged to (inden-3-yl)naphthalenol
[IF].[4] On the other hand, while we are working on annulation
reactions to construct the fluorenopyran 1a,[6] we observed that
the addition of trifluoroacetic acid, lead to the formation of an
intense brick red colour solution, and this becomes colourless
when triethylamine was added (Figure 2). This colour changes
can be understood based on the ring-opening of 1a with
protonation and ring closure with base (NEt3) as depicted in
Figure 2. Further investigations on the acidochromic behaviour
[7,8] of this substrate with a series of Bronsted acids,[9] lead to the
formation of a new chemical entity (1H-inden-3-yl)--9H-fluoren-3-
ol through a ring-rearrangement reaction (Figure 1, eq-iv).
Intrigued by this observation, we decided to explore the
generality, scope, limitations and mechanistic insights of this
ring-rearrangement reaction.
Ph
Ph
Ph
Ph
Ph
Me
Ph Me
Ph Me
Ph Ph
1a
TFA
Figure 2. Acidochrmoic nature of 1a
Results and Discussion
To find out the suitable reaction conditions of the ring-
rearrangement reaction, we have selected 5,11-dimethyl-
2,2,4,6,6-pentaphenyl-2,6-dihydroindeno[2,1-g] chromene 1a as
the model substrate, which was synthesized using a reported
method[6]. Among the various reaction conditions studied[9], we
o
found that when 1a was heated at 110 C with 20 mol% of p-
TsOH the reaction gave the best yield, Under these conditions,
compound 1a underwent an irreversible ring-rearrangement via
ring-opening-cyclization to furnish 2-(1,1-diphenyl-1H-inden-3-
yl)-1,4-dimethyl-9,9-diphenyl-9H-fluoren-3-ol 2a in nearly
quantitative yield after 90 minutes. Encouraged by this outcome,
we planned to check the generality of this protocol with
differently substituted fluorenopyrans as depicted in Table 1.
[a] Tabassum Khan, P. Rajesh, Dudam Praveen, Dr. K. V. Jovan
Jose and Dr. Srinivasarao Yaragorla. School of Chemistry,
University of Hyderabad, P.O. Central University, Gachibowli,
Hyderabad- 500046, Telangana State, India.
E-mail: srinivas.yaragorla@uohyd.ac.in, jovanjose@uohyd.ac.in
Home Page: https://sites.google.com/view/srinivasarao-
yaragorla/publications
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10.1002/ejoc.202000251
European Journal of Organic Chemistry
Table 1. Substrate scope of fluorenopyrans in TRR
R5
R5
R4
O
OH
R3
R4
R3
20 mol% p-TsOH
R1
Solvent-Free, 110 oC
R2
Me
1 R2
Me
R
1
2
F
Ph
Ph
Me
OH
Ph
Ph
Ph
Ph
Me
OH
Me
OH
Me
OH
Me
OH
Me
Me
Me
Me
Me
MeO
X
F
Ph
Ph
Ph
Ph
Ph
Ph
F
Ph
Ph
2ea
2ba
2ca
2f
(1 h 45 min, 87%)
2a (90 min, 96%)
(2 h, 80%)
(2 h, 97%);
X=F
F
(90 min, 90%); X=Cl
2da (80 min, 93%); X=Br
2g (90 min, 86%)
Cl
Ph
Ph
Ph
Ph
Me
OH
Ph
Ph
Ph
Me
OH
Ph
Me
OH
Me
OH
Me
Me
OH
Ph
Me
Me
Me
Me
Ph
Ph
Ph
Me
Me
2k
Me
Cl
2la
(2 h, 74%)
Cl
2ia
(2 h, 75%)
2h (2 h 30 min, 73%)
Cl
(2 h , 93%)
2ja (90 min, 85%)
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Me
OH
Me
OH
Me
OH
Ph
Ph
Me
Me
Me
Me
Me
OH
OH
Me
Ph
Ph
Ph
Ph
Ph
Ph
Me
Ph
Ph
X
2s
( 2 h, 93%)
2r (90 min, 88%)
2ma
2na
2oa (2 h, 83%);
MeO
(2 h, 79%); X=Cl
(80 min, 84%); X=F
2q (90 min, 86%)
2pa
(2h, 81%)
X=Br
Conditions: all reactions were performed in a 0.15 mmol scale, amixture of diastereomers
Interestingly, this method showed excellent substrate scope in
delivering the desired products 2a-2s in high yields. The halo-
substitutions such as F, Cl, Br, on the phenyl rings of both the
quaternary centres (2b-2d, 2f, 2g, 2j, 2l-2o) and the methoxy-
substitution on one of the phenyl rings of quaternary centre (2e,
2p) were well tolerated under these conditions. Further at the
quaternary centres, not only aryl-aryl, groups but also aryl-
methyl (2i) and methyl-methyl (2k) groups were also
synthesized with this protocol. Compound 2h indicates that this
rearrangement reaction can facilitate to have a spirocyclic
moiety without much loss of the yield. Unlike other compounds,
the synthesis of 2s indicates the compatibility of benzyl
substitution on fluorenol. Further, we confirmed the adaptability
of this method to have phenyl, methyl substitutions on the
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10.1002/ejoc.202000251
European Journal of Organic Chemistry
indene’s benzene (2q, 2r. A single-crystal X-ray structure of
compound 2c was obtained to conform its structure without any
ambiguity (Figure 4). More interestingly, the H NMR spectra of
Table 2. TRR of 3-iodo-fluorenopyrans
1
the products bearing unsymmetrical substitutions on at least one
of the quaternary centres indicated that the products are formed
as mixture of diastereomers. This could be due to the hindered
rotation of the C-C bond between fluorenol and Indene, which is
[10]
generally known as axial chirality or atropisomerism.
For
example, compounds 2b, 2c, 2d and 2e (bearing unsymmetrical
substitutions at fluorenol quaternary centre) and 2i, 2j, 2l-2p
were isolated as an inseparable diastereomeric mixture. A
similar trend was noticed with compound 2j, bearing two
unsymmetrical quaternary centres. Notably, the hydroxyl-proton
of these compounds in 1H NMR spectrum showed two clear
signals around five ppm, and in case of compounds having a
stereogenic centre on indene the difference of hydroxyl signals
is 0.005-0.007 ppm and that for a stereogenic centre on
fluorenol is in the range of 0.02-0.03 ppm. In addition to this, we
also observed that the compounds bearing a stereogenic centre
on indene part, showed the presence of two compounds on TLC
(Rf≈0.48 and 0.49, mobile phase: 3% EtOAc in hexane),
whereas the diastereomers with chiral centre at 9-fluorenyl
moiety appeared as a single spot on the TLC. Visibility of the
two spots on TLC excited us to separate the diastereomeric
mixture (2o), however our attempts by column chromatography
(100-200 and 230-400 silica mesh, using pure hexane as the
mobile phase), preparative TLC method was unsuccessful. We
also recorded the High-temperature 1H NMR[11] of compound 2o
in CDCl3 (at 50 oC) and DMSO-d6 (at 50 and 80 oC) but it did not
give any conclusion although in DMSO-d6 the signals for
hydroxyl were merged and shifted slightly upfield. However,
LCMS separation using a C8 HPLC column resulted in two
peaks in nearly 1:1 ratio on the chromatogram (Figure 3-top),
which gave the required mass for each peak.[12]
With this success in hand, we further interested to see the TRR
of 3a, because to the best of our knowledge, so far no reports
available on the ring-rearrangement of fully substituted pyran (of
benzo/naphthopyran) systems. Therefore we selected
compound 3a bearing an iodide substitution at C3-position to
test the TRR under standard reaction conditions. Delightfully, the
product 4a was obtained in 62% yield after 2 h (Table 2), in
which the iodide functionality was intact with the final molecule
but on
a newly constructed ring. Encouraged by this
unprecedented observation, we sought the generality of this
reaction, and hence a number of 3-iodo-fluorenopyrans 3b-3f
were subjected to ring-rearrangement reaction and obtained the
respective products 4b-4f in good yields. The structure of these
products was unambiguously determined by a single-crystal X-
ray structure of 4e (CCDC No.1951991) (Figure 4). The 1H
NMR spectra of compounds 4b-4d and 4f indicated that these
compounds exhibit atropisomerism.
Figure 3. Diastereomers (atropisomers) in compound 2o (LCMS
chromatogram-top; 1H NMR showing two compounds-bottom)
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10.1002/ejoc.202000251
European Journal of Organic Chemistry
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10.1002/ejoc.202000251
European Journal of Organic Chemistry
Because of the different chemical environment around the
hydroxy group due to a quaternary center of indene, it is
expected that the molecular conformers exhibit variations in the
Figure 5, Path-a (in green) represents favourable reaction and
Path-b (in red) represents unfavourable reaction.
1
energy and the H-NMR values (0.02-0.003 ppm). The energy
profile of the reaction mechanism (Scheme 4) is depicted in
Figure 5. Energy Profile of two-possible transition states, based on mechanism depicted in scheme 4.The reaction energies are reported in kcal/mol.
The relative energies of the transition states I3 and I4 are −2.6
and 18.8 kcal/mol, respectively concerning the common TS (I2).
The final product (2) is stable relative to 1 with an interaction
energy −7.7 kcal/mol. The less favoured reaction mechanism
depicted in red (Path-b), with transition states (I5, I6) and
product (10) with relative energies 0.3, 26.8, and 3.0 kcal/mol,
respectively. The relative energies of products (2 and 10) are
calculated relative to the initial reactant molecule (1) depicted in
Scheme 4. The final products depicted in Figure 5 differ in
energy by 10.3 kcal/mol. The energy profile evaluated at
M062X/6-31+G(d,p) shows that the mechanism path is shown in
green .i.e. Path-a is more preferred over the Path-b. The
transition states were also characterized by calculating the
imaginary frequencies of I4 (-668.4 cm-1) and I6 (-885.5 cm-1).
The additional information is available in supporting information.
Figure 6 depicts the energy difference (kcal/mol) of two
conformers of molecules 2a, 2c, 2e, 2j, and 2m. The conformers
of molecules (2a, 2c, 2e) show E=0, due to which the
compound 2a was observed as a single compound and 2c and
2e were present as diastereomers with a very minute difference
in the chemical shift values of the hydroxy peak. The conformers
of molecule 2j and 2m show energy differences of -1.34 and -
1.38 respectively (Figure 6).
Scheme 4. The reaction mechanism
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10.1002/ejoc.202000251
European Journal of Organic Chemistry
Conclusion
In conclusion, we have developed a thermal ring rearrangement
reaction of fluorenopyrans to 2-(1H-inden-3-yl)-9H-fluoren-3-ols
using p-TsOH under solvent-free conditions for the first time.
Besides, we have also extended this TRR to 3-
iodofluorenopyrans (3) and obtained the corresponding 2-(2-
iodo-1H-inden-3-yl)-1,4-dimethyl-9H-fluoren-3-ols (4) bearing all
carbon-quaternary centres at C1 and C9 positions. The
presence of asymmetric centre either on indene or fluorine or on
both resulted in the formation of diastereomeric atropisomers,
which were clearly seen in their NMR spectra, also the two
chromatograms in LCMS. DFT calculations were in agreement
with the experimental observations.
Experimental Section
General information: Unless otherwise noted, all reagents were used as
received from commercial suppliers. pTsOH, Ca(OTf)2 and Bu4NPF6,
KOtBu, 2,4-diones, alkyne, and ketones were purchased from
commercial suppliers such as Sigma-Aldrich, Alfa Aesar, TCI chemicals,
and Spectrochem which were used without further purification. Reactions
were performed in flame-dried or oven-dried glassware with magnetic
stirring. Reactions were monitored by thin-layer chromatography (TLC)
using aluminium sheets silica gel 60 F254 from Merck. TLC plates were
visualized with UV light (254 nm), iodine treatment or using p-
anisaldehyde or KMnO4 stain. Column chromatography was carried out
using silica gel 60−120 mesh as the stationary phase. NMR spectra were
recorded at 500 MHz and 400 MHz (1H) and at 125 MHz and 100 MHz
(13C), respectively on Avance Bruker spectrometer. Chemical shifts (δ)
are reported in ppm, using the residual solvent peak in CDCl3 (1H: δ =
7.26 and 13C: δ = 77.16 ppm) as internal standard, and coupling
constants (J) are given in Hz. HRMS were recorded using ESI-TOF
techniques. Melting points were measured with the Labindia MEPA
melting point apparatus.
Figure 6. The energies (E1 and E2) and the relative energy differences (∆E) in
kcal/mol of 2a, 2c, 2e, 2j and 2m. The atom oxygen is depicted in red, the
carbon in grey, hydrogen in white and chlorine in green color, respectively.
Table 3 represents the M062X/6-31+G(d,p) calculated energies
(E1 and E2 in Hartree) of conformers and the difference in
energies in kcal/mol. The NMR chemical shift of –OH functional
group and differences (in ppm) of the selected molecules
depicted in Figure 6. The computational results of the molecules
(2a, 2c, 2e, 2j and 2m) shows that the conformers having a
stereogenic centre on indene, show a difference in energies and
1H-NMR chemical shifts. The theoretical 1H-NMR chemical shifts
corroborate well with the experimental, thus attributing the
difference in NMR chemical shifts as the feature of the
atropisomerism.
Computational Methods: The geometry optimization of the structures
depicted in Figure 1 is performed at M06X/6-31G(d) using the Gaussian
09 suite of packages.[21] A single point energy calculations were carried
out on the optimized structures at M062X[22] density functional, with 6-
31+G(d,p)[23] basis set for the main group atoms, and the LANL2DZ[24]
electron core potential and its associated basis set for the chlorine atom.
The 1H-NMR chemical shifts of atropisomer are calculated at the same
level of theory with chloroform as the solvent. The NMR chemical shifts
reported in Table 3 are calculated relative to the tetramethylsilane (TMS)
molecule. The TMS molecule is optimized and 1H-NMR chemical shift
values evaluated at the same level of theory and basis, the same as that
Table 3. Single point energies of conformers are designated as E1 and E2,
respectively at M062X/6-31+G(d,p). ΔE represents the energy differences (in
kcal/mol) between the two conformers; NMR-1 & NMR-2 are the 1H NMR
chemical shift of the -OH functional groups (in ppm) of the conformers,
respectively. ΔNMR is the difference in the NMR values (in ppm).
Molecules
E1
E2
ΔE
(kcal/mol
)
NMR-1
(ppm)
NMR-2
(ppm)
ΔNMR
(ppm)
for atropisomers. The solvation effect is incorporated using the solvation
(Hartree)
(Hartree)
[25]
model based on the density (SMD) implicit solvation model
with
chloroform as the solvent, as implemented in the Gaussian 09 package.
2a
2c
−1925.29508
−2384.86128
−2039.77480
−2844.43405
−2384.86444
−1925.29508
−2384.86128
−2039.77480
−2844.43191
−2384.86224
0.00
0.00
5.369
5.489
5.336
5.309
5.434
5.369
5.489
5.336
5.075
5.173
0.00
0.00
General experimental procedure for the synthesis of 2-(1,1-diphenyl-
1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-9H-fluoren-3-ol
(2a):
5,11-
dimethyl-2,2,4,6,6-pentaphenyl-2,6-dihydroindeno[2,1-g] chromene 1a
(100 mg, 0.15 mmol) was treated with p-TsOH (20 mol%) at 110 oC in
solvent free condition for 90 min. After completion of the reaction
(monitor by TLC) the crude product was purified by silica gel column
chromatography (0−5 % EtOAc in pet-ether) to obtain the desired product
2a in 96% yield.
2e
0.00
0.00
2j
−1.34
−1.38
0.234
0.262
2m
2-(1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-9H-fluoren-3-ol
(2a): Following general experimental procedure; white solid, mp:
o
246−248 C; yield: 96% (0.096 g). 1H NMR (500 MHz, CDCl3): δ 7.97 (d,
J = 8 Hz, 1H), 7.42−7.40 (m, 1H), 7.39−7.37 (m, 2H), 7.35−7.32 (m, 2H),
7.30−7.28 (m, 4H), 7.27−7.24 (m, 7H), 7.23−7.19 (m, 10H), 6.90 (dd, J1 =
2 Hz, J2 = 6.5 Hz, 1H), 6.83 (s, 1H), 5.13 (s, 1H), 2.68 (s, 3H), 1.74 (s,
3H) ppm; 13C NMR (100 MHz, CDCl3): δ 155.9, 151.2, 150.7, 146.0,
143.5, 142.9, 142.8, 142.7, 142.1, 140.9, 137.9, 132.3, 129.3, 129.0,
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10.1002/ejoc.202000251
European Journal of Organic Chemistry
128.8, 128.6, 128.0, 127.9, 127.8, 127.7, 127.6, 127.5, 127.3, 127.2,
127.0, 126.8, 126.8, 126.5, 126.4, 125.5 (2), 123.4, 121.6, 120.0, 117.2,
66.9, 64.9, 18.0, 12.8 ppm; HRMS (ESI-TOF): m/z calculated for C48H36O
[M+H]+ 629.2844, found 629.2845.
119.8. 117.4, 115.8, 115.7, 115.6, 115.4, 65.6, 65.0, 18.0, 12.8 ppm;
HRMS (ESI-TOF): m/z calculated for C48H34F2O [M+Na]+ 687.9898,
found 687.9812.
2-(1,1-bis(4-fluorophenyl)-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-9H-
fluoren-3-ol (2g): Following general experimental procedure; white solid,
mp: 281−283 oC; yield: 86% (0.086 g). 1H NMR (500 MHz, CDCl3): δ 7.97
(d, J = 7.5 Hz, 1H), 7.38−7.33 (m, 4H), 7.30−7.28 (m, 3H), 7.25−7.17 (m,
11H), 7.15−7.13 (m, 2H), 7.00−6.95 (m, 2H), 6.93−6.86 (m, 3H), 6.75 (s,
1H), 5.04 (s, 1H), 2.68 (s, 3H), 1.72 (s, 3H) ppm; 13C NMR (125 MHz,
CDCl3): δ 163.1, 163.0, 161.1, 161.0, 155.9, 151.2, 150.6, 145.6, 142.9,
142.7, 142.6, 142.3, 140.9, 140.3, 139.0 (2), 138.9, 138.8, 138.2, 132.3,
129.4, 129.3, 129.2, 129.1 (2), 129.0, 128.0, 127.9, 127.8, 127.6, 127.2,
127.0, 126.6, 126.4, 125.5, 125.3, 123.4, 121.8, 119.8. 117.4, 115.8,
2-(1,1-diphenyl-1H-inden-3-yl)-9-(4-fluorophenyl)-1,4-dimethyl-9-phenyl-
9H-fluoren-3-ol (2b): Following general experimental procedure; white
solid, mp: 256−258 oC; yield: 97% (0.097 g); isolated as 1:1.02 of
diastereomer. 1H NMR (400 MHz, CDCl3): δ 7.97 (d, J = 9.5 Hz, 2H),
7.42−7.40 (m, 2H), 7.36−7.33 (m, 4H), 7.32−7.28 (m, 8 H), 7.27−7.24 (m,
15H), 7.23−7.20 (m, 17H), 6.95−6.86 (m, 6H), 6.835 (s, 1H), 6.833 (s,
1H), 5.14 (s, 1H), 5.13 (s, 1H), 2.68 (s, 6H), 1.73 (s, 3H), 1.72 (s, 3H)
ppm; 13C NMR (100 MHz, CDCl3): δ 155.7, 151.3, 150.7, 146.1, 146.0,
143.4, 143.2, 142.7, 142.5, 142.0, 140.8, 140.0, 137.8 (2), 132.2 (2),
130.9 (2), 130.7, 130.6, 129.1, 128.8, 128.6, 128.1, 128.0, 127.7 (2),
127.6, 127.5, 127.3 (2), 127.1, 126.8, 126.7, 126.5, 125.5, 125.3, 123.4,
121.5 (2), 120.1, 117.4, 114.8 (2), 114.6 (2), 66.9, 64.4, 18.0, 12.8 ppm;
HRMS (ESI-TOF): m/z calculated for C48H35FO [M+K]+ 685.2309, found
685.2301.
115.7, 115.6, 115.4, 65.6, 65.0, 18.0, 12.8 ppm; IR: ν m̃ ax = 3512, 3061,
1501, 1226, 828, 773, 572 cm–1; HRMS (ESI-TOF): m/z calculated for
C48H34F2O [M+Na]+ 665.2656, found 665.2653.
1,4-dimethyl-9,9-diphenyl-2-(spiro[fluorene-9,1'-inden]-3'-yl)-9H-fluoren-
3-ol (2h): Following general experimental procedure; white solid, mp:
253−254 oC; yield: 73% (0.073g). 1H NMR (500 MHz, CDCl3): δ 7.99 (d, J
= 7.5 Hz, 1H), 7.83−7.79 (m, 2H), 7.43−7.39 (m, 2H), 7.38−7.36 (m,
2H),7.34−7.27 (m, 6H), 7.24−7.15 (m, 7H), 7.10 (t, J = 7.5 Hz, 1H ), 7.05
(t, J = 7.5 Hz, 1H), 6.97 (d, J = 7.5 Hz, 2H), 6.85 (d, J = 7.5 Hz, 1H),
6.73−6.71 (m, 1H), 6.28 (s, 1H), 5.51 (s, 1H), 2.75 (s, 3H), 1.90 (s, 3H)
ppm; 13C NMR (125 MHz, CDCl3): δ 155.9, 151.0, 148.7, 144.5, 144.2,
142.8, 142.4, 142.3, 142.2, 141.4, 141.2, 141.0, 132.1, 129.3, 129.1,
128.2, 128.1, 128.0, 127.9, 127.8, 127.7, 127.5, 127.2, 127.1, 126.6,
126.4, 125.5, 123.7, 123.4, 123.2, 123.1, 121.0, 120.6, 120.4, 120.3,
117.4, 68.1, 65.0, 18.2, 12.9 ppm; HRMS (ESI-TOF): m/z calculated for
C48H34O [M-H]+ 625.2532, found 625.2525.
9-(4-chlorophenyl)-2-(1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9-phenyl-
9H-fluoren-3-ol (2c): Following general experimental procedure; yellow
viscous liquid; yield: 90% (0.090 g); isolated as 1:1.04 of diastereomer.
1H NMR (500 MHz, CDCl3): δ 7.97 (d, J = 7.5 Hz, 2H), 7.41 (d, J = 7 Hz,
2H), 7.36−7.29 (m, 11H), 7.26−7.24 (m, 12H), 7.23−7.22 (m, 6H),
7.21−7.19 (m, 13H), 7.18−7.15 (m, 6H), 6.92−6.89 (m, 2H), 6.83 (s, 2H),
5.16 (s, 1H), 5.15 (s, 1H), 2.68 (s, 6H), 1.73 (s, 6H) ppm; 13C NMR (125
MHz, CDCl3): δ 155.4, 151.4, 150.7, 146.2, 146.1, 143.4, 143.3, 142.7,
142.4, 142.2, 141.7(2), 141.5, 140.9, 140.0, 137.8, 137.7, 132.4, 132.2,
130.8, 130.4, 129.1, 128.9, 128.8, 128.6 (2), 128.2, 128.1, 127.7 (2),
127.6, 127.4, 127.3, 127.1, 127.0, 126.9, 126.8, 126.7, 126.6, 125.6,
125.3, 123.5, 121.5, 121.4, 120.2, 117.4, 66.9, 64.5, 18.0, 12.8 ppm;
HRMS (ESI-TOF): m/ z calculated for C48H35ClO [M+H]+ 663.2455, found
663.2454.
1,4-dimethyl-2-(1-methyl-1-phenyl-1H-inden-3-yl)-9,9-diphenyl-9H-
fluoren-3-ol (2i): Following general experimental procedure; yellow solid;
mp: 206−208 oC; yield: 75% (0.075g). 1H NMR (500 MHz, CDCl3): δ 7.97
(d, J = 7.5 Hz, 1H), 7.39−7.34 (m, 4H), 7.32−7.26 (m, 6H), 7.25−7.23 (m,
3H),7.22−7.17 (m, 8H), 6.90 −6.89 (m, 1H), 6.59 (s, 1H), 5.32 (s, 1H),
2.70 (s, 3H), 1.76 (s, 3H), 1.71 (s, 3H) ppm; 13C NMR (100 MHz, CDCl3):
δ 155.8, 153.8, 153.5, 151.2, 151.0, 147.8, 147.7, 142.9, 142.8, 142.7 (2),
142.5, 142.4, 142.3, 142.1 (2), 142.0, 141.0, 139.9 (2), 137.0,132.4,
132.2, 129.3 (2), 129.0, 128.9, 128.6, 128.0, 127.9, 127.8, 127.4, 127.2,
127.1, 126.9, 126.8, 126.7, 126.6, 126.5, 126.3, 126.2, 126.0, 125.4,
123.3, 123.2, 121.2 (2), 120.2 (2), 117.1, 64.9, 57.0, 56.9, 23.5, 23.2,
18.1, 17.8, 12.8(2) ppm; HRMS (ESI-TOF): m/z calculated for C43H34O
[M+H]+ 567.2688, found 567.2689.
9-(4-bromophenyl)-2-(1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9-phenyl-
9H-fluoren-3-ol (2d): Following general experimental procedure; white
solid, mp: 269−271 oC yield: 93% (0.093 g); isolated as 1:1.02 of
diastereomer. 1H NMR (500 MHz, CDCl3): δ 7.97 (d, J = 7.5 Hz, 2H), 7.42
(d, J = 7 Hz, 2 H), 7.37−7.33 (m, 7H), 7.32−7.28 (m, 8H), 7.27−7.25 (m,
15H), 7.24−7.23 (m, 4H), 7.21−7.20 (m, 10H), 7.18−7.15 (m, 4H),
6.91−6.87 (m, 2H), 6.836 (s, 1H), 6.832 (s, 1H), 5.15 (s, 1H), 5.14 (s, 1H),
2.68 (s, 6H), 1.72 (s, 6H) ppm; 13C NMR (125 MHz, CDCl3): δ 155.3,
151.4, 150.8, 146.2, 146.1, 146.0, 143.4, 142.7, 142.4, 142.3, 142.2,
141.7, 140.9, 140.0, 137.7, 132.2, 131.2, 131.1, 131.0, 130.8, 129.4,
129.2, 129.0, 128.9, 128.6 (2), 128.2, 128.1, 128.0, 127.9, 127.8, 127.7,
127.6, 127.4, 127.3, 127.1, 126.9, 126.9, 126.8, 126.6, 125.6, 125.3,
123.5, 121.5 (2), 120.5, 120.4, 120.2, 117.5, 67.0, 64.6, 18.0(2), 12.8
9-(4-chlorophenyl)-2-(1-(4-chlorophenyl)-1-phenyl-1H-inden-3-yl)-1,4-
dimethyl-9-phenyl-9H-fluoren-3-ol (2j): Following general experimental
ppm; IR: ν m
̃
ax = 3505, 3057, 2921, 1445, 748, 697 cm–1; HRMS (ESI-
o
procedure; white solid; mp: 220−222 C yield: 85% (0.085g); isolated as
TOF): m/z calculated for C48H35BrO [M+H]+ 707.1950, found 707.1945.
1:1.01 and 1:0.94 of diastereomer. 1H NMR (400 MHz, CDCl3): δ 7.97 (d,
J = 8 Hz, 4H), 7.39−7.37 (m, 4H), 7.36−7.35 (m, 2H), 7.34−7.33 (m, 4H ),
7.32−7.30 (m, 11H), 7.29−7.28 (m, 10H), 7.27−7.25 (m, 18H), 7.24−7.23
(m, 12H), 7.22−7.20 (m, 18H), 7.18−7.15 (m, 12H), 7.14−7.11 (m, 5H),
6.93−6.88 (m, 4H), 6.78 (s, 4H), 5.10 (s, 1H), 5.09 (s, 1H), 5.07, (s, 1H),
5.06 (s, 1H), 2.68 (s, 12H), 1.71 (s, 6H), 1.70 (s, 6H) ppm; 13C NMR (125
MHz, CDCl3): δ 155.4, 151.3, 150.3, 145.6, 142.9, 142.8, 142.6, 142.4,
142.1, 142.0, 141.7, 141.6, 141.4, 140.8, 140.1, 138.1, 133.1, 132.9,
132.4, 132.2, 130.8, 130.4, 129.1 (2), 129.0 (2), 128.8, 128.7, 128.2,
128.1, 127.9, 127.8, 127.7, 127.6, 127.5 (2), 127.4, 127.3, 127.0, 126.8,
126.6, 125.4, 125.3, 123.5, 121.7, 121.6, 119.9, 117.5, 66.4, 64.5, 18.0
(2), 12.8 ppm; HRMS (ESI-TOF): m/z calculated for C48H34Cl2O [M+H]+
697.2065, found 697.2021.
2-(1,1-diphenyl-1H-inden-3-yl)-9-(4-methoxyphenyl)-1,4-dimethyl-9-
phenyl-9H-fluoren-3-ol (2e): Following general experimental procedure;
o
white solid, mp: 268−269 C; yield: 80% (0.080 g); isolated as 1:0.99 of
diastereomer. 1H NMR (500 MHz, CDCl3): δ 7.96 (d, J = 7.5 Hz, 2H),
7.42−7.41 (m, 2 H), 7.37 (d, J = 7 Hz, 2H), 7.34−7.31 (m, 3H), 7.30−7.29
(m, 4H), 7.28−7.27 (m, 9H), 7.26−7.22 (m, 8H), 7.21−7.19 (m, 15H),
7.18−7.15 (m, 3H), 6.93−6.90 (m, 2H), 6.83 (d, J = 1 Hz, 2H), 6.79−6.74
(m, 4H), 5.14 (s, 1H), 5.13 (s, 1H), 3.77 (s, 3H), 3.75 (s, 3H), 2.68 (s, 6H),
1.74 (s, 3H), 1.74 (s, 3H) ppm; 13C NMR (125 MHz, CDCl3): δ 158.2,
158.0, 156.2, 156.1, 151.1, 150.7, 146.0 (2), 143.5, 143.3, 143.2, 143.0,
142.8, 142.3, 140.8, 140.0, 137.9 (2), 134.7, 134.5, 132.3, 130.4, 130.1,
129.3, 128.9, 128.8, 128.6, 128.0, 127.9, 127.7 (2), 127.6, 127.5, 127.2,
127.1, 127.0, 126.8, 126.5, 126.3, 125.5, 125.3, 123.3, 121.6, 120.0,
117.2, 113.3, 113.2, 66.9, 64.3, 18.0, 17.9, 12.8 ppm; HRMS (ESI-TOF):
m/z calculated for C49H38O2 [M-H]+ 657.2794, found 657.2822.
2-(1,1-dimethyl-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-9H-fluoren-3-ol
(2k): Following general experimental procedure; yellowish solid; mp:
217−219 oC yield: 74% (0.074g). 1H NMR (500 MHz, CDCl3): δ 8.00 (d, J
= 8.0 Hz, 1H), 7.40−7.39 (m, 3H), 7.37−7.35 (m, 1H), 7.34−7.31 (m, 3H),
7.27−7.24 (m, 3H), 7.23−7.17 (m, 6H), 6.87 (d, J = 7.5 Hz, 1H), 6.44 (s,
1H), 5.36 (s, 1H), 2.74 (s, 3H), 1.69 (s, 3H), 1.48 (s, 3H), 1.38 (s, 3H)
ppm; 13C NMR (100 MHz, CDCl3): δ 155.9, 153.8, 151.1, 148.2, 143.0,
142.7, 142.0, 141.9, 141.1, 139.8, 136.4, 132.0, 129.4, 129.2, 129.0,
128.0, 127.8, 127.4, 127.1, 126.9, 126.5, 126.3, 126.2, 125.4, 123.3,
121.5, 121.0, 120.5, 117.0, 65.0, 49.6, 24.9, 24.8, 17.8, 12.9 ppm; HRMS
(ESI-TOF): m/z calculated for C38H32O [M+Na]+ 433.1568, found
433.1563.
2-(1,1-diphenyl-1H-inden-3-yl)-9,9-bis(4-fluorophenyl)-1,4-dimethyl-9H-
fluoren-3-ol (2f): Following general experimental procedure; white solid;
mp: 186−188 oC yield: 87% (0.087 g). 1H NMR (500 MHz, CDCl3): δ 7.97
(d, J = 8 Hz, 1H), 7.38−7.37 (m, 2H), 7.36−7.34 (m, 2H), 7.32−7.31 (m,
1H), 7.30−7.28 (m, 2H), 7.26−7.23 (m, 5H), 7.21−7.18 (m, 6H),
7.15−7.13 (m, 2H), 6.98 (t, J = 8.5 Hz, 2H), 6.93−6.91 (m, 1H), 6.88 (t, J
= 8.5 Hz, 2H), 6.75 (s, 1H), 5.04 (s, 1H), 2.68 (s, 3H), 1.72 (s, 3H) ppm;
13C NMR (125 MHz, CDCl3): δ 163.1, 163.0, 161.1, 161.0, 155.9, 151.1,
150.5, 145.6, 142.9, 142.6, 142.6, 142.3, 140.9, 140.3, 139.0 (2), 138.9,
138.8, 138.2, 132.3, 129.4, 129.3, 129.2, 129.1 (2), 129.0, 128.0, 127.9,
127.8, 127.6, 127.2, 127.0, 126.6, 126.4, 125.5, 125.3, 123.4, 121.8,
2-(1-(3,4-dichlorophenyl)-1-phenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-
diphenyl-9H-fluoren-3-ol (2l): Following general experimental procedure;
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000251
European Journal of Organic Chemistry
white solid, mp: 256−258 oC; yield: 93% (0.093g); isolated as 1:0.90 of
diastereomer. 1H NMR (400 MHz,CDCl3): δ 7.97 (d, J = 7.6 Hz, 2H),
7.39−7.36 (m, 9H), 7.34−7.33 (m, 2 H), 7.31−7.28 (m, 10H), 7.27−7.24
(m, 11H), 7.22−7.20 (m, 8H), 7.197−7.190 (m, 3H), 7.17−7.15 (m, 3H),
7.10−7.08 (m, 1H), 7.03−7.00 (m, 1H), 6.94−6.92 (m, 2H), 6.756 (s, 1H),
6.751 (s, 1H), 5.04 (s, 1H), 5.01 (s, 1H), 2.69 (s, 3H), 2.68 (s, 3H), 1.73
(s, 3H), 1.72 (s, 3H) ppm; 13C NMR (100 MHz, CDCl3): δ 155.9, 151.1 (2),
149.8, 149.7, 144.8, 144.7, 144.0, 143.8, 142.8 (2), 142.7, 142.6, 142.4,
142.3, 142.1, 140.8, 138.9 (2), 132.6, 132.3, 132.2, 130.7, 130.5, 129.7,
129.5, 129.3, 129.1, 129.0, 128.8, 128.0, 127.9, 127.7, 127.6, 127.5,
127.2, 127.1, 126.6, 126.4 (2), 125.5, 125.3, 123.4, 121.9, 119.7 (2),
117.4, 66.1, 65.0, 18.0, 12.8 ppm; IR (KBr): ῠ 3528, 2958, 1585, 1157,
761cm-1; HRMS (ESI-TOF): m/z calculated for C48H34Cl2O [M+Na]+
697.2065, found 697.2014.
J1 = 1.2 Hz, J2 = 6.4 Hz, 1H), 7.40−7.36 (m, 5H), 7.34−7.29 (m, 8H),
7.28−7.22 (m, 7H), 7.22−7.17 (m, 6H), 6.97 (d, J = 7.6 Hz, 1H), 6.85 (s,
1H), 5.16 (s, 1H), 2.70 (s, 3H), 1.77 (s, 3H) ppm; 13C NMR (100 MHz,
CDCl3): δ 155.9, 151.4, 151.2, 146.2, 143.4, 143.3, 142.9, 142.7, 142.3,
142.1, 140.2, 140.0, 137.7, 132.4, 129.3, 129.0, 128.9, 128.8, 128.6,
128.0, 127.9, 127.8, 127.7, 127.5, 127.4, 127.3, 127.2, 127.1, 126.8,
126.6, 126.4, 125.5, 124.4, 123.4, 121.8, 120.1, 117.3, 67.1, 65.0, 18.1,
12.8 ppm; HRMS (ESI-TOF): m/z calculated for C54H40O [M+K]+
743.2716, found 743.2712.
1,4-dimethyl-2-(6-methyl-1,1-diphenyl-1H-inden-3-yl)-9,9-diphenyl-9H-
fluoren-3-ol (2r): Following general experimental procedure; yellow solid;
1
mp: 280−281oC; yield: 86% (0.086 g). H NMR (500 MHz, CDCl3 δ 7.96
(d, J = 8 Hz, 1H), 7.38−7.33 (m, 3H), 7.31−7.28 (m, 4H), 7.27−7.24 (m,
6H), 7.22−7.16 (m, 11H), 7.02 (d, J = 7 Hz, 1H), 6.78 (d, J = 7.5 Hz, 1H),
6.74 (s, 1H), 5.17 (s, 1H), 2.68 (s, 3H), 2.33 (s, 3H), 1.73 (s, 3H) ppm;
13C NMR (125 MHz, CDCl3): δ 155.9, 151.23, 151.0, 145.0, 143.7, 143.5,
142.9, 142.7, 142.1, 141.0, 140.1, 140.0, 137.7, 136.7, 132.3, 129.3,
129.0, 128.8, 128.5, 128.3, 128.0, 127.9, 127.8, 127.7, 127.4, 127.1,
126.9, 126.5, 126.3, 125.4, 123.3, 121.3, 120.2, 117.2, 66.7, 64.9, 21.8,
2-(1-(4-chlorophenyl)-1-phenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-
9H-fluoren-3-ol (2m): Following general experimental procedure; yellow
solid, mp: 246−248 oC; yield: 79% (0.079g); isolated as 1:0.92 of
diastereomer. 1H NMR (400 MHz, CDCl3): δ 7.97 (d, J = 7.6 Hz, 2H),
7.38−7.35 (m, 7H), 7.33−7.26 (m,12H), 7.24−7.23 (m, 12H), 7.21−7.17
(m, 15H), 7.15−7.11 (m, 4H), 6.90−6.91 (m, 2H), 6.78 (s, 2H), 5.09 (s,
1H), 5.06 (s, 1H), 2.68 (s, 6H), 1.73 (s, 3H), 1.70 (s, 3H) ppm; 13C NMR
(100 MHz, CDCl3): δ 155.9, 151.2, 150.4, 145.5, 143.0, 142.9, 142.7,
142.6, 142.2, 142.1, 141.9, 140.9, 140.2, 138.4, 138.3, 133.1, 132.9,
132.3, 132.2, 129.3, 129.1, 129.0, 128.7, 128.0, 127.9, 127.8, 127.6,
127.5 (2), 127.3, 127.2, 126.9, 126.6, 126.4, 125.5, 125.4, 123.4, 121.7,
18.0, 12.8 ppm; IR: ν m̃
ax = 3497, 3052, 1489, 759, 744, 694, 479 cm–1;
HRMS (ESI-TOF): m/z calculated for C49H38O [M+H]+ 643.3001, found
643.001.
4-benzyl-2-(1,1-diphenyl-3a,7a-dihydro-1H-inden-3-yl)-1-methyl-9,9-
diphenyl-9H-fluoren-3-ol (2s): Following general experimental procedure;
yellow viscous liquid; yield: 93% (0.093 g). 1H NMR (400 MHz, CDCl3): δ
7.70 (d, J = 5.6, 1H), 7.42−7.36 (m, 4H), 7.34−7.32 (m, 4H), 7.27−7.26
(m, 8H), 7.24−7.15 (m, 12H), 7.13−7.11 (m, 3H), 6.90−6.88 (m, 1H), 6.86
(s, 1H), 5.16 (s, 1H), 4.60 (s, 2H), 1.79 (s, 3H) ppm;13C NMR (125 MHz,
CDCl3): δ 156.0, 151.9, 150.7, 146.0, 143.5, 143.1, 142.9, 142.8, 142.6,
142.5, 140.7, 140.0, 139.7, 137.7, 133.6, 129.9, 129.4, 129.0, 128.9,
128.8, 128.7, 128.6, 128.5, 128.2, 128.1, 128.0, 127.8, 127.7, 127.6,
127.5, 127.3, 127.2, 127.0, 126.8, 126.6, 126.4, 126.1, 125.6, 125.4,
123.3, 121.5, 120.3, 119.0, 67.0, 65.0, 32.1, 18.3 ppm; HRMS (ESI-
TOF): m/z calculated for C54H40O [M+H]+ 705.3157, found 705.3122.
119.8, 117.3, 66.4, 65.0, 18.0, 12.8 ppm; IR: ν m̃ ax = 3503, 3056, 1445,
748, 696 cm–1; HRMS (ESI-TOF): m/z calculated for C48H35ClO [M+Na]+
663.2454, found 663.2411.
2-(1-(4-fluorophenyl)-1-phenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-
9H-fluoren-3-ol (2n): Following general experimental procedure; white
solid, mp: 238−240 oC; yield: 84% (0.084g); isolated as 1:0.91 of
diastereomer. 1H NMR (500 MHz, CDCl3): δ 7.97 (d, J = 8 Hz, 2H),
7.38−7.32 (m, 10H), 7.31−7.27 (m, 10H), 7.25−7.21 (m, 14H), 7.20−7.19
(m, 8H), 7 .17−7.14 (m, 4H), 6.97 (t, J = 8.5 Hz, 2H), 6.92−6.88 (m, 4H),
6.79 (s, 2H), 5.10 (s, 1H), 5.08 (s, 1H), 2.68 (s, 6H), 1.73 (s, 3H), 1.72 (s,
3H) ppm; 13C NMR (125 MHz, CDCl3): δ 155.9, 151.2, 151.1, 150.6,
145.8, 143.3, 143.1, 142.9, 142.7, 142.6, 142.3, 142.2, 140.9, 140.2,
139.2, 139.0, 138.1, 138.0, 132.3, 132.2, 129.4, 129.3, 129.2 (2), 129.0,
128.9, 128.7, 128.0, 127.9, 127.7, 127.6, 127.5, 127.4, 127.2, 126.9,
126.5, 126.4, 125.5, 125.4, 123.4, 121.7, 119.9, 117.3, 115.7, 115.5 (2),
115.3, 66.3, 65.0, 18.0, 12.8 ppm; HRMS (ESI-TOF): m/z calculated for
C48H35FO [M-H]+ 645.2594, found 645.2592.
General experimental procedure for the synthesis of 2-(2-iodo-1,1-
diphenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-9H-fluoren-3-ol (4a): 3-
iodo-5,11-dimethyl-2,2,4,6,6-pentaphenyl-2,6-dihydroindeno[2,1-
g]chromene 3a (100 mg, 0.13 mmol) was treated with p-TsOH (20 mol%)
at 110 oC in solvent free condition for 2 h. After completion of the reaction
(monitor by TLC) the crude product was purified by silica gel column
chromatography (0−5 % EtOAc in pet-ether) to obtain the desired product
4a in 62% yield.
2-(1-(4-bromophenyl)-1-phenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-
9H-fluoren-3-ol (2o): Following general experimental procedure; white
solid, mp: 274−276 oC; yield: 83% (0.083 g); isolated as 1:0.94 of
2-(2-iodo-1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-9H-
fluoren-3-ol (4a): Following general experimental procedure; white solid,
mp: 130−131 oC; yield: 62% (0.062 g). 1H NMR (500 MHz, CDCl3): δ 7.98
(d, J = 8 Hz, 1H), 7.42−7.40 (m, 2H), 7.37 (d, J = 7.0 1H), 7.33−7.29 (m,
8H), 7.26−7.25 (m, 4H), 7.23−7.19 (m, 9H), 7.16−7.13 (m, 2H),
6.88−6.87 (m, 1H), 4.76 (s, 1H), 2.72 (s, 3H), 1.68 (s, 3H) ppm; 13C NMR
(125 MHz, CDCl3): δ 156.0, 152.4, 150.7, 146.4, 143.2, 142.6, 142.3,
142.2, 142.1, 141.7, 140.9, 132.4, 130.7, 129.4, 129.1, 128.8, 128.7,
128.5, 128.4, 128.0, 127.9, 127.8, 127.7, 127.6, 127.5, 127.2, 126.9,
126.5, 126.4, 125.5, 125.4, 123.4, 122.0, 121.4, 120.8, 117.7, 80.1, 71.0,
1
diastrereomer. H NMR (500 MHz, CDCl3): δ 7.97 (d, J = 7 Hz, 2H),
7.41−7.35 (m, 8H), 7.36−7.28 (m, 14H), 7.25−7.23 (m, 10H), 7.21−7.16
(m, 14H), 7.14−7.13 (m, 2H), 7.07−7.06 (m, 2H), 6.93−6.91 (m, 2H), 6.77
(s, 2H), 5.09 (s, 1H), 5.05 (s, 1H), 2.68 (d, J = 1.5, 6H), 1.73 (s, 3H), 1.71
(s, 3H) ppm; 13C NMR (125 MHz, CDCl3): δ 155.9, 151.1, 150.2, 145.4,
142.9, 142.7, 142.6, 142.5, 140.9, 140.2, 138.3, 131.9, 131.7, 129.5,
129.4, 129.3, 129.0, 128.7, 128.0, 127.9, 127.8, 127.6, 127.5 (2), 127.3,
127.2, 127.0, 126.6, 126.4, 125.5, 125.4, 123.4, 121.7, 121.0, 119.8,
117.3, 66.4, 64.9, 18.0, 12.8 ppm; IR: ν m̃ ax = 3514, 2919, 2360, 1487,
64.9, 17.4, 12.8 ppm; IR: ν m̃ ax = 3534, 3058, 2959, 1597, 1446, 744,
748, 699, 577 cm–1; HRMS (ESI-TOF): m/z calculated for C48H35BrO
698, 579 cm–1; HRMS (ESI-TOF): m/z calculated for C48H35IO [M+H]+
[M+Na]+ 707.1949, found 707.1917.
755.1811, found 755.1807.
2-(1-(4-methoxyphenyl)-1-phenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-
9-(4-fluorophenyl)-2-(2-iodo-1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9-
phenyl-9H-fluoren-3-ol (4b): Following general experimental procedure;
white solid, mp: 141−142 oC; yield: 65% (0.065 g); isolated as 1:0.93 of
diastereomer. 1H NMR (400 MHz, CDCl3): δ 7.98 (d, J = 8.4 Hz, 2H),
7.41−7.37 (m, 3H), 7.36−7.34 (m, 5H), 7.33−7.29 (m, 14H), 7.28−7.27 (m,
5H), 7.247−7.241 (m, 4H), 7.23−7.22 (m, 3H), 7.20−7.18 (m, 8H),
7.12−7.13 (m, 4H), 6.92−6.87 (m, 6H), 4.77 (s, 1H), 4.76 (s, 1H), 2.72 (s,
6H), 1.67 (s, 6H) ppm; 13C NMR (100 MHz, CDCl3): δ 155.7, 151.3, 150.7,
146.1, 143.4, 143.3, 142.7, 142.1, 140.8, 140.0, 137.8, 132.2, 131.7,
130.9 (2), 130.7, 130.6, 129.1, 128.8, 128.6, 128.4, 128.2, 128.1, 128.0,
127.7 (2), 127.6, 127.3, 127.1, 127.0, 126.8, 126.7, 126.5, 125.5, 125.3,
123.4, 123.3, 122.0, 121.5, 120.2, 117.4, 114.8 (2), 114.6 (2), 90.7, 88.5,
66.9, 64.4, 23.6, 18.0, 12.8 ppm; HRMS (ESI-TOF): m/z calculated for
C48H34FIO [M+H]+ 755.1811, found 755.1806.
diphenyl-9H-fluoren-3-ol (2p): Following general experimental procedure;
white solid; mp: 254−256 oC yield: 81% (0.081 g). 1H NMR (500 MHz,
CDCl3,): δ 7.90 (d, J = 8 Hz, 2H), 7.33−7.28 (m, 8H), 7.24−7.19 (m, 12H),
7.17−7.13 (m, 12H), 7.12−7.09 (m, 13H),7.03 (d, J = 8.5 Hz, 2H), 6.82 (d,
J = 6.5 Hz, 2H), 6.75−6.73 (m, 3H), 6.66 (s, 1H), 6.65 (s, 1H), 5.08 (s,
2H), 3.70 (s, 3H), 3.65 (s, 3H), 2.61 (s, 6H), 1.67 (s, 3H), 1.65 (s, 3H)
ppm; 13C NMR (100 MHz, CDCl3): δ 158.8, 158.6, 155.9, 151.2, 1561.1,
146.2, 143.7, 143.5, 142.9, 142.7, 142.1, 141.0, 140.1, 137.5, 135.3,
135.0, 132.3, 129.3, 129.0, 128.8, 128.7, 123.3, 121.5, 120.1, 117.2,
114.2, 113.9, 66.2, 65.0, 55.4, 55.3, 29.8, 18.0, 12.8 ppm; IR: ν m̃ ax =
3501, 2953, 1597, 1446, 1294, 775, 699 cm–1; HRMS (ESI-TOF): m/z
calculated for C49H38O2 [M+H]+ 659.2950, found 659.2864.
1,4-dimethyl-9,9-diphenyl-2-(1,1,6-triphenyl-1H-inden-3-yl)-9H-fluoren-3-
ol (2q): Following general experimental procedure; yellow solid, mp:
284−286 oC; yield: 88% (0.088 g). 1H NMR (400 MHz, CDCl3,): δ 7.98 (d,
J = 8 Hz, 1H), 7.62 (d, J = 0.8 Hz, 1H), 7.52 (d, J = 7.2 Hz, 2H), 7.45 (dd,
9-(4-bromophenyl)-2-(2-iodo-1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9-
phenyl-9H-fluoren-3-ol (4c): Following general experimental procedure;
yellow viscous liquid; yield: 90% (0.090 g); isolated as 1:1.08 of
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000251
European Journal of Organic Chemistry
diastereomer. 1H NMR (400 MHz, CDCl3): δ 7.98 (d, J = 8.4 Hz, 2H),
7.40−7.37 (m, 2H), 7.35−7.31 (m, 14H), 7.27−7.25 (m, 4H), 7.24−7.22 (m,
12H), 7.21−7.19 (m, 8H), 7.18−7.16 (m, 6H), 7.15−7.13 (m, 4H),
6.89−6.86 (m, 2H), 4.78 (s, 1H), 4.77 (s, 1H), 2.72 (s, 6H), 1.68 (s, 6H)
ppm; 13C NMR (125 MHz, CDCl3): δ 155.5, 152.4 (2), 150.9, 146.2, 142.7,
142.1 (2),142.0 (3), 141.7 (2), 141.6, 141.0, 140.8, 140.6, 132.4, 132.3,
132.2, 130.8, 130.5, 129.2, 128.9, 128.7 (2), 128.5, 128.4 (2), 128.2 (2),
128.1, 127.7 (2), 127.5 (2), 127.4, 127.1, 127.0, 126.8, 126.6, 125.4,
125.3, 123.5, 122.2, 122.1, 121.5, 120.7 (2), 117.8, 71.0, 64.4, 17.4, 12.8
ppm; HRMS (ESI-TOF): m/ z calculated for C48H34ClIO [M+H]+ 343.2061,
found 343.2061.
General Experimental Procedure for the Synthesis of 2-(2-iodo-1,1-
diphenyl-1H-inden-3-yl)-3-methoxy-1,4-dimethyl-9,9-diphenyl-9H-
fluorene (6): To a stirring solution of 2-(2-iodo-1,1-diphenyl-1H-inden-3-
yl)-1,4-dimethyl-9,9-diphenyl-9H-fluoren-3-ol 4a (100 mg, 0.13 mmol) in
anhydrous acetone (5.0 mL), K2CO3 (45.75 mg, 0.33 mmol) and Me2SO4
(0.26 mmol) were added. The resulting reaction mixture was heated at
80 °C for 3 h. After completion of the reaction, it was filtered through a
short plug of celite, and the filtrate was concentrated in a rotary
evaporator and purified by silica gel column chromatography to afford the
methyl protected compound 6 as a white solid in 87% yield.
2-(2-iodo-1,1-diphenyl-1H-inden-3-yl)-3-methoxy-1,4-dimethyl-9,9-
diphenyl-9H-fluorene (6): White solid, mp: 268−270 oC; yield: 96% (0.088
g). 1H NMR (500 MHz, CDCl3): δ 7.95 (d, J = 7.5 Hz, 1H), 7.42−7.40 (m,
2H), 7.39−7.37 (m, 3H), 7.33−7.29 (m, 6H), 7.27−7.24 (m, 2H),
7.22−7.21 (m, 6H), 7.21−7.16 (m, 5H), 7.12−7.08 (m, 2H), 6.87−6.85 (m,
1H), 2.89 (s, 3H), 2.75 (s, 3H), 1.72 (s, 3H) ppm; 13C NMR (125 MHz,
CDCl3): δ 156.6, 155.9, 152.0, 148.1, 146.2, 143.7, 142.9, 142.5, 142.3,
141.9, 140.9, 140.8, 133.4, 129.5, 129.4, 129.1, 129.0 (2), 128.5, 128.4,
128.3, 128.2, 128.1, 127.9 (2), 127.6, 127.4, 127.3, 127.2 (2), 126.6,
126.5, 126.2, 125.5, 125.1, 124.5, 123.3, 120.5, 118.8, 70.7, 65.2, 61.7,
9-(4-chlorophenyl)-2-(2-iodo-1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9-
phenyl-9H-fluoren-3-ol (4d): Following general experimental procedure;
yellow viscous liquid; yield: 89% (0.089 g); isolated as 1:0.7 of
diastereomer. 1H NMR (500 MHz, CDCl3): δ 7.98 (d, J = 8.5 Hz, 2H),
7.39−7.37 (m, 2H), 7.34−7.30 (m, 19H), 7.29−7.27 (m, 3H), 7.26−7.25 (m,
2H), 7.25−7.23 (m, 6H), 7.22−7.21 (m, 3H), 7.21−7.20 (m, 6H),
7.19−7.17 (m, 4H), 7.16−7.13 (m, 5H), 6.89−6.86 (m, 2H), 4.78 (s, 1H),
4.77 (s, 1H), 2.72 (s, 6H), 1.67 (s, 6H) ppm; 13C NMR (125 MHz, CDCl3):
δ 155.4, 152.4, 150.9, 146.2, 142.6 (2), 142.1, 142.0 (2), 141.7, 141.6,
140.8, 140.6, 132.3, 131.2, 131.1, 130.9 (2), 129.2, 128.9, 128.8, 128.7,
128.5, 128.4 (2), 128.2, 128.0, 127.8, 127.7, 127.5, 127.4, 127.1, 127.0,
126.8, 126.6, 125.5, 125.3, 123.5, 122.2, 122.1, 121.5, 120.7, 120.3,
117.8, 71.0, 64.5, 17.4, 12.8 ppm; HRMS (ESI-TOF): m/z calculated for
C48H34BrIO [M+H]+ 363.1748, found 363.1748.
17.2, 13.5 ppm; IR: ν m̃ ax = 3396, 3056, 2923, 1594, 1443, 1029, 743,
724, 646 cm–1; HRMS (ESI-TOF): m/z calculated for C49H37IO [M+H]+
769.1967, found 769.1927.
Experimental Procedure for the Synthesis of 2-(1,1-diphenyl-1H-
inden-3-yl)-1,4-dimethyl-9,9-diphenyl-3-(prop-2-yn-1-yloxy)-9H-fluorene
(7): To a stirring solution of 2-(1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-
9,9-diphenyl-9H-fluoren-3-ol 2a (100 mg, 0.16 mmol) in anhydrous
acetone (5.0 mL), K2CO3 (54.9 mg, 0.39 mmol) and propargyl bromide
(0.23 mmol) were added. The resulting reaction mixture was heated at
80 °C for 4 h. After completion of the reaction, it was filtered through a
short plug of celite, and the filtrate was concentrated in a rotary
evaporator and purified by silica gel column chromatography to afford the
propargyl protected compound 7 as a white solid in 98% yield.
2-(2-iodo-6-methyl-1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-
diphenyl-9H-fluoren-3-ol (4e): Following general experimental procedure;
colorless viscous liquid; mp: 284−285 oC; yield: 79% (0.079 g). 1H NMR
(400 MHz, CDCl3): δ 7.98 (d, J = 6.6 Hz, 1H), 7.42−7.36 (m, 5H),
7.32−7.29 (m, 7H), 7.26−7.23 (m, 5H), 7.22−7.17 (m, 6H), 7.10 (s, 1H),
6.95 (d, J = 6.6 Hz, 1H), 6.79−6.76 (m, 1H), 4.77 (s, 1H), 2.72 (s, 3H),
2.25 (s, 3H), 1.68 (s, 3H) ppm; 13C NMR (100 MHz, CDCl3): δ 156.0,
152.6, 150.7, 146.2, 143.2, 142.5, 142.4, 142.3, 141.9, 140.9, 140.6,
139.6, 137.1, 132.4, 129.4, 129.1, 128.8, 128.7, 128.6, 128.4, 128.0,
127.8, 127.6, 127.5, 127.4, 127.2, 126.5, 126.4, 126.2, 125.5, 123.4,
121.5, 120.5, 117.6, 76.8, 70.8, 64.9, 21.7, 17.4, 12.8 ppm; IR: ν m̃ ax =
2-(1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-3-(prop-2-yn-1-
yloxy)-9H-fluorene (7): White solid, mp: 273−275 oC; yield: 98% (0.110 g).
1H NMR (500 MHz, CDCl3): δ 7.96 (d, J = 7.5 Hz, 1H), 7.38−7.34 (m, 6H),
7.31 (d, J = 8 Hz, 1H), 7.29−7.25 (m, 6H), 7.24−7.21 (m, 3H), 7.20−7.17
(m, 10H), 6.85−6.84 (m, 1H), 6.67 (s, 1H), 4.11−4.10 (m, 2H), 2.79, (s,
3H), 2.35−2.34 (m, 1H), 1.72 (s, 3H) ppm; 13C NMR (125 MHz, CDCl3): δ
155.7, 154.8, 150.2, 146.4, 144.4, 144.0, 143.8, 142.4, 142.2, 140.7,
140.1, 138.3, 133.5, 129.3, 129.0, 128.5, 128.4 (2), 128.0, 127.9 (2),
127.6, 127.3, 127.2, 126.8, 126.7, 126.6, 126.5, 125.9, 125.5, 125.3,
125.0, 123.3, 121.2, 79.3, 74.9, 66.8, 65.2, 61.1, 17.8, 14.2 ppm; IR:
3534, 3056, 2922, 1595, 1445, 741, 696, 642, cm–1; HRMS (ESI-TOF):
m/z calculated for C49H37IO [M+H]+ 331.1697, found 331.1697.
2-(1-(4-chlorophenyl)-2-iodo-1-phenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-
diphenyl-9H-fluoren-3-ol (4f): Following general experimental procedure;
yellow viscous liquid; yield: 53% (0.053 g); isolated as 1:1.06 of
diastereomer. 1H NMR (500 MHz, CDCl3): δ 7.98 (d, J = 8 Hz, 2H),
7.42−7.37 (m, 6H), 7.33−7.31 (m, 5H), 7.30−7.28 (m, 8H), 7.25−7.24 (m,
11H), 7.23−7.20 (m, 10H), 7.19−7.18 (m, 4H), 7.16−7.14 (m, 4H), 7.11 (d,
J = 8.5 Hz, 2H), 6.90−6.88 (m, 2H), 4.74 (s, 1H), 4.69 (s, 1H), 2.72 (s,
6H), 1.68 (s, 3H), 1.65 (s, 3H) ppm; 13C NMR (125 MHz, CDCl3): δ 156.0,
151.9, 150.6, 143.1, 142.6, 140.8, 130.1, 130.0, 129.4, 129.0, 128.9,
128.6, 128.4, 128.1, 127.8, 127.6, 127.2, 127.1, 126.6, 126.4, 125.4,
125.3, 123.4, 121.2, 120.9, 117.6, 70.4, 64.9, 17.4, 12.8 ppm; HRMS
(ESI-TOF): m/z calculated for C48H34ClIO [M+Na]+ 433.1568, found
433.1563.
ν m̃
ax = 3276, 1489, 1445, 1078, 756, 747, 699, 652 cm–1; HRMS (ESI-
TOF): m/z calculated for C51H38O [M+K]+ 705.2560, found 705.2586.
Experimental Procedure for the Synthesis of (E)-3-((2,3-
diiodoallyl)oxy)-2-(1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-9,9-diphenyl-
9H-fluorene (9): To the solution of 2-(1,1-diphenyl-1H-inden-3-yl)-1,4-
dimethyl-9,9-diphenyl-3-(prop-2-yn-1-yloxy)-9H-fluorene 7 (100 mg, 0.15
mmol) in ethyl acetate (5.0 mL), I2 (76.0 mg, 0.30 mmol) was added and
refluxed for 12 h. After completion of the reaction, it was quenched with
hypo and extracted with ethyl acetate thrice, the organic layer was
concentrated in rotary evaporator and purified by silica gel column
chromatography to afford the 3-((2,3-diiodoallyl)oxy)-2-(1,1-diphenyl-1H-
inden-3-yl)-1,4-dimethyl-9,9-diphenyl-9H-fluorene 9 as white solid in 83%
yield.
Experimental Procedure for the Synthesis of 7-(4-chlorophenyl)-5,12-
dimethyl-7,13,13-triphenyl-7,13-dihydrofluoreno[3,2-b]indeno[1,2-d]furan
(5): To a stirring solution of 2-(1-(4-chlorophenyl)-2-iodo-1-phenyl-1H-
inden-3-yl)-1,4-dimethyl-9,9-diphenyl-9H-fluoren-3-ol 4f (100 mg, 0.12
mmol) in DMSO (3.0 mL), Cu2O (18.0 mg, 0.12 mmol) and quinoline (1
ml) were added. The resulting reaction mixture was heated at 170 °C for
16 h. After completion purified by silica gel column chromatography to
afford the polycyclic compound 5 as white solid in 86% yield.
(E)-3-((2,3-diiodoallyl)oxy)-2-(1,1-diphenyl-1H-inden-3-yl)-1,4-dimethyl-
9,9-diphenyl-9H-fluorene (9): White solid, mp: 295−296 oC; yield: 83%
(0.114 g). 1H NMR (500 MHz, CDCl3): δ 7.95 (d, J = 7.8 Hz, 1H),
7.39−7.34 (m, 6H), 7.31 (d, J = 7.5 Hz, 1H), 7.28−7.23 (m, 6H),
7.22−7.19 (m, 5H), 7.18−7.15 (m, 8H), 6.93 (d, J = 7 Hz, 1H), 6.86 (s,
1H), 6.70 (s, 1H), 4.19 (d, J = 12.5 Hz, 1H), 4.06 (dd, J1 = 1 Hz, J2 = 11
Hz, 1H), 2.80 (s, 3H), 1.72 (s, 3H) ppm; 13C NMR (100 MHz, CDCl3): δ
155.8, 154.8, 150.3, 146.6, 144.6, 144.2, 143.9, 143.8, 142.4, 142.2,
140.7, 140.1, 138.4, 133.8, 129.3, 129.0, 128.7, 128.3, 128.0 (2), 127.9,
127.6, 127.4, 127.2, 126.9, 126.7, 126.5, 125.8, 125.5 (2), 124.5, 123.3,
121.5, 98.0, 81.0, 79.1, 66.7, 65.2, 17.8, 14.5 ppm; HRMS (ESI-TOF):
m/z calculated for C51H38I2O [M+K]+ 959.0649, found 959.0690.
7-(4-chlorophenyl)-5,12-dimethyl-7,13,13-triphenyl-7,13-
dihydrofluoreno[3,2-b]indeno[1,2-d]furan (5): White solid, mp: >300 oC;
yield: 86% (0.085 g). 1H NMR (400 MHz, CDCl3): δ 7.92 (d, J = 8 Hz, 1H),
7.68 (d, J = 7.2 Hz, 1H), 7.37−7.36 (m, 2H), 7.35−7.34 (m, 3 H),
7.30−7.24 (m, 7H), 7.23 (d, J = 1.2 Hz, 5H), 7.21 (s, 2H), 7.21−7.18 (m,
4H), 7.16−7.12 (m, 2H), 2.88 (s, 3H), 2.49 (s, 3H) ppm; 13C NMR (100
MHz, CDCl3): δ 168.9, 159.9, 155.3, 149.9, 145.6, 142.9 (2), 141.8,
141.0, 140.9, 135.9 (2), 133.2, 129.7, 129.1, 128.7 (2), 128.2, 128.0,
127.8, 127.5, 127.3, 127.2, 126.5 (2), 125.5, 125.4, 124.9, 124.3, 122.7,
121.5, 115.8, 64.8, 59.9, 19.6, 13.1 ppm; HRMS (ESI-TOF): m/z
calculated for C48H33ClO [M+H]+ 661.2298, found 661.2323.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000251
European Journal of Organic Chemistry
Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M.
Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J.
Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R.
Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G.
Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A.
D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D.
J. Fox, Gaussian, Inc., Wallingford CT, 2009.
Acknowledgements
The authors acknowledge the funding from CSIR no-
02/333/EMR-II. JJKV and DP thank the centre for modelling
simulation and design (CMSD), the University of Hyderabad for
computing time, and UGC-FRPS for research grants.
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Keywords: all-carbon-quaternary centre, Bronsted acid, Ring-
Rearrangement, Fluorenol, Indene, Friedel-Crafts annulation.
24. P. Jeffery Hay and Willard R. Wadt, J. Chem. Phys. 1985, 85, 299-310.
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10.1002/ejoc.202000251
European Journal of Organic Chemistry
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Thermal Ring Rearrangement Reaction
Tabassum Khan, P. Rajesh, Dudam
Praveen, K. V. Jovan Jose,* Srinivasarao
Yaragorla*
Page No. – Page No.
Brønsted acid promoted Thermal-Ring-
Rearrangement of Fluorenopyrans to 2-
(1H-inden-3-yl)-9H-fluoren-3-ols bearing
two all-carbon-quaternary centers
4-Aryl-fluorenopyrans bearing quaternary centre at C2 and C6 positions underwent a thermal-ring-rearrangement with a catalytic amount of p-
TsOH to furnish 2-(1H-inden-3-yl)-9H-fluoren-3-ols with two all carbon-quaternary centres, in which one is retained and the other is created.
Interestingly, these compounds exhibit atropisomerism, when they have at least one unsymmetrical quaternary centre.
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