Triflic acid-Mediated Expedient Synthesis of Benzo[a]fluorenes and Fluorescent Benzo[a]fluorenones

Article abstract of DOI:10.1002/adsc.201701516

Fluorene-based polyaromatic hydrocarbons are renowned compounds for materials applications. Herein, a straightforward route via in situ acetal formation has been presented to access benzo[a]fluorenes by a triflic acid promoted cationic cycloisomerization

Full text of DOI:10.1002/adsc.201701516

Title: Triflic acid-Mediated Expedient Synthesis of Benzo[a]fluorenes
and Fluorescent Benzo[a]fluorenones
Authors: Mou Mandal and Balamurugan Rengarajan
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201701516
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10.1002/adsc.201701516
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Triflic acid-Mediated Expedient Synthesis of Benzo[a]fluorenes
and Fluorescent Benzo[a]fluorenones
Mou Mandala and Rengarajan Balamurugana,*
a
School of Chemistry, University of Hyderabad, Gachibowli, Hyderabad-500046, India.
Email: bala@uohyd.ac.in
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract. Fluorene-based polyaromatic hydrocarbons are
renowned compounds for materials applications. Herein, a
straightforward route via in situ acetal formation has been
presented to access benzo[a]fluorenes by a triflic acid
promoted cationic cycloisomerization of enynones in
presence of trimethyl orthoformate under metal-free
conditions. In the absence of trimethyl orthoformate, the same
reaction results in benzo[a]fluorenones. All the synthesized
benzo[a]fluorenones are highly fluorescent in solution phase
with high Stokes shift while the corresponding
benzo[a]fluorenes are not fluorescent.
Keywords: benzo[a]fluorene; benzo[a]fluorenone; triflic
acid; acetal; Stokes shift
benzaldehydes with alkynes in the presence of
trimethyl orthoformate via in situ acetal formation.[9]
An ,-unsaturated ketone intermediate was proposed
in resulting the benzo[a]fluorene product (Scheme 1).
In this manuscript we present our studies on the
reaction of a different ,-unsaturated ketone system
having the carbonyl and double bond positions
interchanged. It was found that these substrates form a
different benzo[a]fluorene derivative via in situ
formed acetals.
Polycyclic aromatic hydrocarbons (PAHs) have
engrossed increasing attention in the field of organic
materials.[1] In the fortress of PAHs family, fluorene[2]
and fluorenone[3] based compounds show tremendous
potential due to their extended -conjugation which
contributes to their unique optoelectronic properties.[4]
This is evident from a range of potential applications
of benzofluorenes such as organic lasers, blue light
emitting OLEDs, in electroluminescent devices, in
photochromic devices, in the treatment of osteoporosis
etc.[5] In addition, this structural motif occurs in
biologically active compounds as well.[6] Because of
these broad utilities, synthesis of such polyarylated
functional organic cores is in high need. For the
synthesis of the title benzo[a]fluorenones, only three
reports are available so far.[5e, 7] Two of these three
known methods are not general and are used to make
a
specific derivative of benzo[a]fluorenones
containing additional substituents such as sulfonyl and
dimethylamine groups compulsorily.[7] In comparison
to available methods for synthesis of benzo[b] and
benzo[c] fluorenes, the methods for synthesis of
benzo[a]fluorenes are less developed. Thus,
development of efficient strategies to synthesize
benzofluorenes and benzofluorenones[8] that have the
scope for introducing different substituents in order to
tune their optical properties is a worthy task.
We have reported the synthesis of benzo[a]fluorene[8g]
by a triflic acid-catalyzed reaction of o-alkynyl
1
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10.1002/adsc.201701516
Advanced Synthesis & Catalysis
Scheme 1. Synthesis of benzo[a]fluorenes and
benzo[a]fluorenones.
benzo[a]fluorenone 3a in 97% yield in 2 h (Table 1,
entry 14). The reaction is high yielding only when 1
equivalent of TfOH was used in solvent HFIP. When
we have used different solvents, low to moderate
yields were obtained. But to our delight, HFIP
solvent[12] has provided exceptionally high yield (97%).
As HFIP is a highly polar solvent it stabilizes the polar
intermediates involved in the present reaction more,
thereby giving high yield of products. Reactions
involving other solvents, Brønsted acids, and Lewis
acids were found to be less effective. The optimized
reaction conditions presented in entries 5 and 14 of
Table 1 were used to evaluate the substrate scope for
In extension, we have also carried out the synthesis of
benzo[a]fluorenones under the same reaction
condition in the absence of trimethyl orthoformate.
Moreover, the benzo[a]fluorenones synthesized by us
are fluorescent having high Stokes shifts which is a
beneficial property in developing imaging materials,
fluorescence sensors and solid state emitters etc.[10]
Importantly, fluorescent active benzofluorenones
(including all its sub-classes) have not been reported
so far.
The enynone derivative 1a was subjected to
treatment with trimethyl orthoformate and triflic acid.
It resulted in the formation of benzo[a]fluorene
derivative 2a. Interestingly, the same reaction in the
absence of trimethyl orthoformate resulted in the
formation of benzo[a]fluorenone 3a. A striking feature
of this compound 3a is that it does not enolize under
the reaction condition to result in the highly
conjugated fluorenol system and, notably, it is
fluorescent. The reaction of 1a with TfOH was studied
under different conditions in the presence and absence
of trimethyl orthoformate (TMOF). Selected screening
results are presented in table 1.[11] It was found that in
the
synthesis
of
benzo[a]fluorenes
and
benzo[a]fluorenones respectively from the starting
materials that could easily be accessed from o-bromo
acetophenones or o-bromobenzaldehydes.
Table 2. Substrate scope for benzo[a]fluorene synthesisa
the presence of
3
equivalents of TMOF
benzo[a]fluorene 2a was obtained in 98% isolated
yield in 3 h (Table 1, entry 5) as only 75% of the
benzo[a]fluorene 2a along with 24% of
benzo[a]fluorenone 3a were isolated with 2 equivalent
of trimethyl orthoformate (Table 1, entry 6).
Table 1. Selected optimization data
Sl. Condition
No.
Time Yield
(h)
(%)a
2a
35
4
3a
8
-
1
CH2Cl2+TMOF (3 equiv.) 20
CH3CN+TMOF (3 equiv.) 72
2
3
4
5
6
DCE+TMOF (3 equiv.)
THF+TMOF (3 equiv.)
HFIP+TMOF (3 equiv.)
HFIP+TMOF (2 equiv.)
HFIP+TMOF (3 equiv.)
HFIP+TMOF (3 equiv.)
CH2Cl2
CH3NO2
Dioxane
CH3CN
5
48
3
3
3
48
12
3
24
12
2
33
NR
98
75
73
-
-
-
-
-
-
-
-
24
-
7b
8c
9
-
53
45
NR
5
80
97
10
11
12
13b HFIP
-
-
14
HFIP
2
an
b
c
isolated yield. 50 mol% of TfOH was used.
AgSbF6 (0.2 equiv.) was used in the place of TfOH.
a isolated yield.
On the other hand, in the absence of TMOF, the
reaction resulted in the formation of fluorescent active
2
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10.1002/adsc.201701516
Advanced Synthesis & Catalysis
A wide range of substrates having substituents with
different electronic effects that can influence the
reactivities of all the three aryl rings was subjected to
TfOH-promoted benzo[a]fluorene synthesis via in situ
formed acetal (Table 2). The yields were generally
very high with most of the substrates studied. When
electron withdrawing groups are present on the aryl
rings attached to alkynyl and alkenyl carbons
decreased yields of benzo[a]fluorenes (2c, 2d, 2m and
2r) were observed.
formation of benzo[a]fluorene and electron
withdrawing substituents in it will suppress it. On the
contrary, electron withdrawing fluoro group on the
aryl ring of o-alkynylaryl ketone portion of the starting
substrate did not have any noticeable negative effect
on the yield of benzo[a]fluorene product (2g, 2p, and
2t). Whereas, an electron donating OMe group on the
aryl ring of o-alkynylaryl ketone reduced the yield of
the product appreciably (2f vs 2a, 2r vs 2b and 2s vs
2h). It may be due to increase in reactivity because of
the presence of OMe group which can be seen from the
lesser reaction times taken by the substrates with OMe
substituents (2 h vs 3 h). It was noted that several
minor products were also formed in these reactions.
As mentioned in table 1, the same reactants in absence
of trimethyl orthoformate resulted in the formation of
corresponding fluorenone derivative (Table 1, entry
14). The scope of this reaction was also explored using
substrates containing diverse substituents with
different electronic effects in presence of triflic acid[13]
(Table 3). The yields of the benzo[a]fluorenones are
comparatively higher than that of the corresponding
benzo[a]fluorenes which were obtained in the
presence of trimethyl orthoformate. As observed in the
benzo[a]fluorene formation, yields were dropped to
moderate or poor whenever there were electron
withdrawing substituents on the -aryl ring of the
enone moiety (3d, 3p, 3u and 3w). In a similar way,
the substrate containing electron withdrawing NO2
group in the aryl ring attached to alkyne moiety
resulted in a a poor yield of the product (3g, 36%) due
to destabilization of the benzylidene carbocation
intermediate which is expected to be formed after the
first cyclization. Fluoro substituent is a p-donor and
electrophilic aromatic substitutions are favored at the
para position by a fluoro substituent.[14] The fluoro
group, during the formation of 3e, might not facilitate
the cyclization as it has to happen at the meta position.
Therefore the yield 3e was poor (38%). However, a
fluoro substituent on the aryl ring of o-alkynylaryl
ketone did not decrease the yield of 3i (82%) much.
Electron donating groups on the aryl rings, on the other
hand, facilitated the reaction and resulted in excellent
yields of the products. Here the -OMe group present in
the aryl ring of alkynylaryl ketone did not reduce the
yields of the reactions more as [C] type intermediate
was not forming in this case.
Table 3. Substrate scope for benzo[a]fluorenone synthesisa
The structures of the compounds were further
confirmed by X-ray crystallographic analysis (2a, 2j,
3a, and 3j). The CCDC numbers for these compounds
are 1560544, 1560552, 1560545 and 1560546
respectively.
a isolated yield.
This is not surprising as this aromatic ring undergoes
electrophilic aromatic substitution during the
3
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10.1002/adsc.201701516
Advanced Synthesis & Catalysis
Scheme 2. Plausible reaction mechanism for the synthesis
of benzo[a]fluorenes.
On the other hand, the plausible mechanistic pathway
for the synthesis of benzo[a]fluorenone (3a) is
illustrated in Scheme 3. 1a undergoes triflic acid
catalyzed keto-enol tautomerism to produce the
intermediate [G] via the formation of intermediate [F].
Both the transformations i.e., benzo[a]fluorenone and
benzo[a]fluorene formation were not feasible in
presence of strong electron withdrawing substituent
like 4-NO2 as R2. Also, this reaction failed to give any
of the desired product from the substrate made from
Table
4
Stokes Shifts (nm) of the synthesized
benzo[a]fluorenones in CH2Cl2, CHCl3, CH3CN and MeOH
pyrene
aldehyde
and
1-(2-
(phenylethynyl)phenyl)ethan-1-one and resulted in the
complex product mixture. In addition, the reaction was
not working when any one of the three aryl moieties
was replaced by cyclic/acyclic aliphatic group.
3a (122, 92, 111, 206 )
3c (83, 66, 100, 136)
3e (54, 83, 99, 146)
3g (106, 111, 72, 149)
3b (70, 120, 99, 135)
3d (81, 154, 28, 12)
3f (143, 136, 127, 165)
3h (173, 196, 198, 225)
3i (192, 207, 206, 211) 3j (129, 128, 122, 160)
3k (218, 143, 151, 226) 3l (244, 211, 182, 223)
3m (101, 154, 54, 52)
3n (137, 179, 129, 207)
3o (155, 105, 152, 163) 3p (108, 119, 123, 67)
3q (251, 222, 201, 216) 3r (183, 137, 180, 218)
3s (165, 179, 209, 212) 3t (200, 202, 172, 203)
3u (168, 143, 159, 193) 3v (191, 207, 186, 216)
3w (104, 126, 98, 153)
3y (130, 239, 248, 167)
3x (251, 205, 215, 208)
Scheme 3. Plausible reaction mechanism for the synthesis
of benzo[a]fluorenones.
The first annulation takes place in a similar fashion
like benzo[a]fluorene case by the intramolecular
attack of the alkyne in the intermediate [G] leads to the
formation of vinyl carbocation [H]. The vinyl
carbocation is then trapped by the aryl group by
aromatic electrophilic substitution reaction to form the
intermediate [I]. Finally the intermediate [I] will
undergo tautomerization to result in the formation of
benzo[a]fluorenone derivative (3a).
A tentative mechanism for the formation of
benzo[a]fluorene (2a) can be proposed as shown in
Scheme 2. The acetal [A] is formed from 1a in the
presence of trimethyl orthoformate and TfOH. Then
one -OMe group is protonated and departed as MeOH
leading to the formation of oxonium ion intermediate
[C] from the intermediate [B]. Intramolecular attack of
the alkyne leads to the first annulation producing vinyl
carbocation [D] which will further undergo annulation
through aromatic electrophilic substitution reaction to
form the intermediate [E]. Finally, benzo[a]fluorene
derivative (2a) is formed from [E] through
isomerization.
1.0
Stokes Shift = 191 nm
(a)
0.8
0.6
0.4
0.2
0.0
400
450
500
550
600
650
700
750
Wavelength (nm)
(b)
Figure 1. (a) Absorption and emission spectra of compound
3v in CH2Cl2. (b) Solvent-dependent fluorescence activity
of compound 3v.
Scheme 4. Conversions of benzo[a]fluorene and fluorenone
derivatives.
It is interesting that none of the benzo[a]fluorenones
3a-3y isomerized to corresponding fluorenol
4
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10.1002/adsc.201701516
Advanced Synthesis & Catalysis
J = 6.6, 2H), 5.17 (s, 1H), 4.09 (s, 3H); 13C NMR (125 MHz,
CDCl3): 156.5, 149.7, 142.0, 141.4, 139.3, 134.7, 131.0,
128.9, 128.0, 127.1, 126.9, 126.8, 126.7, 125.8, 124.9, 124.6,
124.4, 123.2, 119.3, 96.6, 55.8, 53.7; IR (Neat, cm-1): 3023,
1696, 1629, 1587, 1396, 1216, 1148, 1097, 1019, 983, 823,
766, 689; HRMS: m/z [M+H]+ calcd for C24H18O: 323.1430;
found: 323.1433.
derivative under the reaction conditions. However,
treatment of benzo[a]fluorene 2a with BBr3 resulted in
the corresponding benzo[a]fluorenol derivative 4a
which is a stable compound (Scheme 4). Remarkably,
the benzo[a]fluorenone 3a upon heating in a closed
vessel at 180 °C under nitrogen atmosphere resulted in
the formation of 4a without any side reaction. To our
surprise, both 3a and 4a transformed into a red colored
solid 5a at 300 °C in an open atmosphere by
dehydrogenation. The structure of compound 5a was
further confirmed by X-ray crystallographic analysis
and its CCDC number is 1560547.
The above procedure was followed to prepare the other
benzo[a]fluorene derivatives 2b-2t from their respective
starting materials.
9-Bromo-5-methoxy-11-phenyl-11H-benzo[a]fluorene
(2b, Table 2): Brownish yellow solid (yield = 75%); M.P.
o
= 230 - 231 C; Rf value = 0.69 (10% EtOAc in hexanes);
1H NMR (400 MHz, CDCl3): 8.30 (d, J = 8.1 Hz, 1H),
7.64 (d, J = 8.0 Hz, 1H), 7.54 (d, J = 7.7 Hz, 1H), 7.49 (dd,
J = 8.2, 1.5 Hz, 1H), 7.42 (s, 1H), 7.40 - 7.36 (m, 1H), 7.35
- 7.30 (m, 1H), 7.26 (s, 2H), 7.24 (s, 1H), 7.23 (s, 1H), 7.09
(dd, J = 7.7, 1.6 Hz, 2H), 5.23 (s, 1H), 4.14 (s, 3H); 13C
NMR (100 MHz, CDCl3): 156.6, 151.5, 141.0, 140.4,
138.3, 134.5, 130.8, 130.2, 129.0, 128.1, 127.9, 127.1, 127.0,
125.9, 124.9, 124.3, 123.2, 120.58, 120.57, 96.3, 55.8, 53.6;
IR (Neat, cm-1): 1577, 1463, 1407, 1376, 1272, 1216, 1086,
1024, 813, 751, 704; HRMS: m/z [M+Na]+ calcd for
C24H17BrO: 423.0355; found: 423.0359.
The benzo[a]fluorenones 3a-3y are highly fluorescent
in a solution state and have high Stokes shifts in
different solvents (Table 4).[15]
For example,
compound 3a has Stokes shifts of 122, 92, 111 and 206
nms in CH2Cl2, CHCl3, CH3CN and MeOH
respectively when excited at 359, 361, 353 and 354
nms corresponding to the n to * transition.
In a similar fashion, all the other benzo[a]fluorenones
also have high Stokes shifts as shown in table 4. A
representative plot containing the absorption and
emission spectra of compound 3v in CH2Cl2 is
presented in Figure 1 (a). As seen in the plot, the
overlapping region of absorption and emission peaks
is very small which is highly desired for efficient
applications such as fluorescent imaging and OLED
etc.
In conclusion, the synthesis of benzo[a] fluorenes and
fluorescent benzo[a]fluorenones have been achieved
by a cationic cycloisomerization of easily accessible
enynones using triflic acid as the promoter. The broad
substrate scope with a tolerance of a wide array of
functional groups and the moderate to high isolated
yields of both the desired PAHs in lower reaction time
of 1-4 h made this protocol more attractive. The
synthesized benzo[a]fluorenones are highly florescent
in solution state with high Stokes shifts. The high
florescent properties of these compounds might find
potential applications in imaging and sensing areas.
Studies in these lines are currently in progress.
9-Chloro-5-methoxy-11-phenyl-11H-benzo[a]fluorene
(2c, Table 2): Brownish yellow solid (yield = 70%); M.P. =
208 - 209 oC; Rf value = 0.75 (10% EtOAc in hexanes); 1H
NMR (500 MHz, CDCl3): 8.29 (d, J = 8.1 Hz, 1H), 7.64
(d, J = 8.1 Hz, 1H), 7.51 (d, J = 8.3 Hz, 1H), 7.40 - 7.35 (m,
1H), 7.33 - 7.29 (m, 2H), 7.25 - 7.19 (m, 4H), 7.17 (s, 1H),
7.05 (dd, J = 7.9, 1.5 Hz, 2H), 5.12 (s, 1H), 4.10 (s, 3H); 13
C
NMR (125 MHz, CDCl3): 156.6, 151.2, 141.1, 139.9,
138.3, 134.6, 132.5, 130.9, 129.0, 127.9, 127.4, 127.1, 127.0,
125.8, 125.3, 124.8, 124.3, 123.3, 120.2, 96.4, 55.8, 53.5;
IR (Neat, cm-1): 3049, 2941, 1577, 1463, 1396, 1376, 1262,
1210, 1143, 1092, 1071, 1019, 983, 818; HRMS: m/z [M]+
calcd for C24H17ClO: 356.0968; found: 356.0967.
5-Methoxy-11-phenyl-9-(trifluoromethyl)-11H-
benzo[a]fluorene (2d, Table 2): Brownish yellow solid
o
(yield = 17%); M.P. = 188 - 189 C; Rf value = 0.69 (10%
EtOAc in hexanes); 1H NMR (400 MHz, CDCl3): 8.32 (d,
J = 7.3 Hz, 1H), 7.85 (s, 1H), 7.74 - 7.51 (m, 5H), 7.49 -
7.31 (m, 4H), 7.10 (s, 2H), 5.29 (s, 1H), 4.16 (s, 3H); 13C
NMR (100 MHz, CDCl3): 156.7, 149.8, 144.9, 140.7,
139.9, 139.2, 137.9, 136.0, 130.8, 129.6, 129.1, 127.9, 127.2,
127.1, 126.3, 125.3, 124.5, 123.3, 121.6 (q, J = 3.5 Hz),
119.3, 96.5, 55.8, 53.7; 19F NMR (376 MHz, CDCl3):  -
62.9; IR (Neat, cm-1): 3059, 1618, 1582, 1433, 1402, 1329,
1272, 1143, 1117, 1061, 828, 746, 694; HRMS: m/z
[M+Na]+ calcd for C25H17F3O: 413.1124; found: 413.1125.
11-(4-Chlorophenyl)-5-methoxy-11H-
benzo[a]fluorene (2e, Table 2): Reddish solid (yield =
84%); M.P. = 190 - 191 oC; Rf value = 0.66 (5% EtOAc in
1
hexanes); H NMR (500 MHz, CDCl3): 8.29 (d, J = 8.5
Hz, 1H), 7.74 (d, J = 7.5 Hz, 1H), 7.49 (d, J = 7.7 Hz, 1H),
7.39 - 7.29 (m, 3H), 7.24 (d, J = 7.4 Hz, 1H), 7.22 - 7.20 (m,
2H), 7.17 (d, J = 8.5 Hz, 2H), 6.99 (d, J = 8.4 Hz, 2H), 5.11
(s, 1H), 4.09 (s, 3H); 13C NMR (125 MHz, CDCl3): 156.6,
149.2, 141.4, 140.7, 139.4, 134.1, 132.4, 130.9, 129.3, 129.1,
127.3, 127.1, 127.0, 125.9, 124.8, 124.7, 124.2, 123.3, 119.4,
96.6, 55.8, 52.9; IR (Neat, cm-1): 3065, 1624, 1582, 1448,
1402, 1221, 1148, 1097, 1014, 802, 756; HRMS: m/z
[M+Na]+ calcd for C24H17ClO: 379.0860; found: 379.0861.
Experimental Section
Representative procedure for the synthesis of
benzo[a]fluorene derivative 5-methoxy-11-phenyl-11H-
benzo[a]fluorene 2a: To a solution of compound 1a (100
mg, 0.325 mmol, 1.0 equiv.) in hexafluoroisopropanol
solvent (1.5 mL), trimethyl orthoformate (107 L, 0.974
mmol, 3 equiv.) followed by triflic acid (29 L, 0.325 mmol,
1 equiv.) were added at room temperature (25 oC) under
nitrogen atmosphere. The reaction mixture was stirred and
the progress of the reaction was monitored by TLC. After
completion of the reaction (after 3 hrs), it was quenched
with a saturated NaHCO3 solution (20 mL). Then it was
extracted using ethyl acetate. The combined organic layers
was washed with saturated brine solution and dried over
anhydrous Na2SO4. The solvents were evaporated under
reduced pressure. The crude product was purified by column
chromatography using silica gel, 5% EtOAc/hexanes eluent
to get the pure 5-methoxy-11-phenyl-11H-benzo[a]fluorene
2a (103 mg, 98%). Pale white solid (yield = 98%); M.P. =
194 - 195 oC; Rf value = 0.84 (10% EtOAc in hexanes); 1H
NMR (400 MHz, CDCl3): 8.29 (d, J = 8.2 Hz, 1H), 7.75
(d, J = 7.5 Hz, 1H), 7.55 (d, J = 8.2 Hz, 1H), 7.38 - 7.31 (m,
2H), 7.28 (d, J = 7.3 Hz, 2H), 7.22 - 7.13 (m, 5H), 7.07 (d,
3,5-Dimethoxy-11-phenyl-11H-benzo[a]fluorene
(2f,
Table 2): Yellow solid (yield = 54%); M.P. = 249 - 250 oC;
1
Rf value = 0.40 (10% EtOAc in hexanes); H NMR (400
MHz, CDCl3): 7.67 (d, J = 7.5 Hz, 1H), 7.53 (d, J = 2.6
Hz, 1H), 7.41 (d, J = 9.1 Hz, 1H), 7.27 (t, J = 7.4 Hz, 1H),
7.22 - 7.08 (m, 6H), 7.01 (d, J = 6.4 Hz, 2H), 6.91 (dd, J =
9.1, 2.7 Hz, 1H), 5.13 (s, 1H), 4.06 (s, 3H), 3.83 (s, 3H); 13
C
NMR (100 MHz, CDCl3): 157.0, 155.4, 149.3, 142.1,
141.6, 137.1, 135.0, 128.8, 128.0, 127.0, 126.8, 126.7, 126.4,
126.3, 126.0, 124.8, 119.3, 119.0, 101.9, 97.2, 55.8, 55.3,
53.6; IR (Neat, cm-1): 2920, 1587, 1474, 1371, 1210, 1174,
1019, 833, 808, 761, 730; HRMS: m/z [M]+ calcd for
C25H20O2: 352.1463; found: 352.1461.
3-Fluoro-5-methoxy-11-phenyl-11H-benzo[a]fluorene
(2g, Table 2): Off-white solid (yield = 87%); M.P. = 224 -
225 oC; Rf value = 0.69 (10% EtOAc in hexanes); 1H NMR
(400 MHz, CDCl3): 7.89 (dd, J = 10.8, 2.7 Hz, 1H), 7.75
5
This article is protected by copyright. All rights reserved.

10.1002/adsc.201701516
Advanced Synthesis & Catalysis
o
(d, J = 7.6 Hz, 1H), 7.53 (dd, J = 9.1, 5.6 Hz, 1H), 7.36 (t, J
= 7.4 Hz, 1H), 7.28 (d, J = 7.0 Hz, 1H), 7.26 - 7.17 (m, 5H),
7.10 - 7.04 (m, 3H), 5.17 (s, 1H), 4.10 (s, 3H); 13C NMR
(100 MHz, CDCl3): 161.4, 158.9, 155.9 (d, J = 5.1 Hz),
149.4, 141.8, 141.2, 138.7 (d, J = 2.5 Hz), 134.8, 128.9,
128.0, 127.95, 127.1, 126.9, 126.8, 126.6 (d, J = 8.7 Hz),
124.8, 119.3, 116.9 (d, J = 25.0 Hz), 107.4 (d, J = 22.6 Hz),
97.5, 55.8, 53.7; IR (Neat, cm-1): 2925, 1587, 1520, 1407,
1371, 1205, 1076, 931, 756, 730; HRMS : m/z [M]+ calcd
for C24H17FO: 340.1263; found: 340.1263.
(yield = 59%); M.P. = 187 - 188 C; Rf value = 0.56 (5%
EtOAc in hexanes); 1H NMR (400 MHz, CDCl3): 8.25 (d,
J = 7.9 Hz, 1H), 7.64 (d, J = 8.0 Hz, 1H), 7.57 (d, J = 8.0
Hz, 1H), 7.47 (d, J = 8.0 Hz, 1H), 7.40 - 7.30 (m, 2H), 7.20
- 7.12 (m, 3H), 7.12 - 7.07 (m, 3H), 5.25 (s, 1H), 4.09 (s,
3H); 13C NMR (100 MHz, CDCl3): 156.6, 148.5, 142.5,
138.8, 137.0, 136.2, 130.8, 130.5, 130.0, 129.6, 129.1, 128.4,
127.3, 126.8, 126.1, 125.1, 123.9, 123.2, 118.1, 96.1, 55.7,
54.4; IR (Neat, cm-1): 2925, 1577, 1453, 1417, 1396, 1221,
1128, 1030, 880, 823, 761; HRMS: m/z [M+Na]+ calcd for
5,8,10-Trimethoxy-11-phenyl-11H-benzo[a]fluorene (2h, C24H16Cl2O: 413.0470; found: 413.0471.
Table 2): Brownish-yellow solid (yield = 98%); M.P. = 278
- 279 oC; Rf value = 0.25 (5% EtOAc in hexanes); 1H NMR
(500 MHz, CDCl3): 8.26 (d, J = 8.0 Hz, 1H), 7.61 (d, J =
7.7 Hz, 1H), 7.36 - 7.27 (m, 2H), 7.20 (s, 1H), 7.17 - 7.08
(m, 5H), 6.96 (d, J = 1.9 Hz, 1H), 6.34 (d, J = 1.9 Hz, 1H),
5.28 (s, 1H), 4.13 (s, 3H), 3.92 (s, 3H), 3.66 (s, 3H); 13C
NMR (125 MHz, CDCl3): 161.4, 156.8, 156.2, 143.7,
5,8,10-Trimethoxy-11-(p-tolyl)-11H-benzo[a]fluorene
(2n, Table 2): Off-white solid (yield = 98%); M.P. = 162 -
163 oC; Rf value = 0.30 (10% EtOAc in hexanes); 1H NMR
(500 MHz, CDCl3): 8.26 (d, J = 7.9 Hz, 1H), 7.63 (dd, J =
7.5, 1.4 Hz, 1H), 7.36 - 7.28 (m, 2H), 7.21 (s, 1H), 7.01 -
6.93 (m, 5H), 6.34 (d, J = 2.0 Hz, 1H), 5.27 (s, 1H), 4.13 (s,
3H), 3.92 (s, 3H), 3.68 (s, 3H), 2.24 (s, 3H); 13C NMR (125
141.5, 138.9, 136.8, 130.8, 129.5, 128.5, 128.1, 126.9, 126.0, MHz, CDCl3): 161.3, 156.8, 156.1, 143.7, 138.8, 138.3,
125.8, 124.5, 124.2, 123.1, 98.0, 96.63, 96.55, 55.8, 55.7,
55.5, 51.4; IR (KBr, cm-1): 2930, 1582, 1489, 1447, 1419,
1344, 1246, 1210, 1132, 1075, 1034, 936, 838, 750, 693,
543, 476; HRMS: m/z [M+H]+ calcd for C26H22O3:
383.1642; found: 383.1641.
136.9, 135.3, 130.8, 129.6, 128.8, 128.3, 126.8, 125.8, 124.5,
124.3, 123.0, 98.0, 96.6, 96.5, 55.8, 55.7, 55.5, 51.0, 21.1;
IR (Neat, cm-1): 2956, 1582, 1453, 1278, 1252, 1200, 1148,
1071, 1040; HRMS: m/z [M+H]+ calcd for C27H24O3:
397.1798; found: 397.1794.
5,8,9,10-Tetramethoxy-11-phenyl-11H-
5-(5,8,10-Trimethoxy-11H-benzo[a]fluoren-11-
yl)benzo[d][1,3]dioxole (2o, Table 2): Brownish yellow
benzo[a]fluorene (2i, Table 2): Brownish yellow solid
o
o
(yield = 99%); M.P. = 278 - 279 C; Rf value = 0.15 (10%
solid (yield = 84%); M.P. = 206 - 207 C; Rf value = 0.21
EtOAc in hexanes); 1H NMR (500 MHz, CDCl3): 8.26 (d,
J = 7.8 Hz, 1H), 7.64 (d, J = 7.6 Hz, 1H), 7.36 - 7.28 (m,
2H), 7.22 - 7.16 (m, 3H), 7.16 - 7.11 (m, 4H), 5.32 (s, 1H),
4.14 (s, 3H), 4.02 (s, 3H), 3.87 (s, 3H), 3.29 (s, 3H); 13C
NMR (125 MHz, CDCl3): 156.4, 154.2, 150.4, 141.8,
(10% EtOAc in hexanes); H NMR (500 MHz, CDCl3):
1
8.27 (d, J = 7.4 Hz, 1H), 7.68 (d, J = 7.2 Hz, 1H), 7.39 -
7.32 (m, 2H), 7.20 (s, 1H), 6.95 (d, J = 2.0 Hz, 1H), 6.77
(dd, J = 8.0, 1.7 Hz, 1H), 6.65 (d, J = 8.0 Hz, 1H), 6.40 (d,
J = 1.6 Hz, 1H), 6.36 (d, J = 2.0 Hz, 1H), 5.83 (dd, J = 8.4,
141.7, 138.8, 137.4, 136.0, 134.9, 130.8, 128.5, 128.4, 127.0, 1.4 Hz, 2H), 5.23 (s, 1H), 4.14 (s, 3H), 3.93 (s, 3H), 3.72 (s,
126.4, 125.4, 124.4, 124.0, 123.1, 99.0, 96.3, 60.9, 60.0,
56.4, 55.8, 51.9; IR (KBr, cm-1): 3070, 1603, 1587, 1453,
1412, 1365, 1319, 1247, 1205, 1123, 1035, 983, 823, 756,
699, 570, 513; HRMS: m/z [M+Na]+ calcd for C27H24O4:
435.1567; found: 435.1567.
3H); 13C NMR (125 MHz, CDCl3): 161.4, 156.8, 156.2,
147.2, 145.7, 143.6, 138.8, 136.6, 135.2, 130.8, 129.3, 126.9,
125.8, 124.5, 124.2, 123.1, 121.9, 108.5, 107.9, 100.6, 97.9,
96.6, 96.5, 55.8, 55.7, 55.5, 51.0; IR (Neat, cm-1): 2930,
1582, 1484, 1453, 1247, 1195, 1138, 1035, 926, 828, 735;
HRMS: m/z [M+Na]+ calcd for C27H22O5: 449.1359; found:
449.1354.
5-Methoxy-13-phenyl-13H-dibenzo[a,i]fluorene
(2j,
Table 2): Yellow solid (yield = 67%); M.P. = 250 - 251 oC;
1
Rf value = 0.51 (10% EtOAc in hexanes); H NMR (400
3-Fluoro-5-methoxy-9-methyl-11-phenyl-11H-
benzo[a]fluorene (2p, Table 2): White solid (yield = 83%);
MHz, CDCl3): 8.28 - 8.24 (m, 1H), 7.87 (s, 2H), 7.83 (dd,
J = 8.0, 1.6, Hz, 2H), 7.78 - 7.74 (m, 1H), 7.36 - 7.27 (m,
4H), 7.21 (s, 1H), 7.17 - 7.11 (m, 4H), 7.10 - 7.05 (m, 1H),
5.36 (s, 1H), 4.06 (s, 3H); 13C NMR (100 MHz, CDCl3):
156.3, 145.3, 142.1, 139.5, 139.1, 136.8, 133.3, 130.8,
o
M.P. = 209 - 210 C; Rf value = 0.66 (5% EtOAc in
1
hexanes); H NMR (500 MHz, CDCl3): 7.93 (d, J = 10.8
Hz, 1H), 7.68 (d, J = 7.7 Hz, 1H), 7.58 - 7.53 (m, 1H), 7.30
- 7.23 (m, 4H), 7.21 (d, J = 7.8 Hz, 1H), 7.15 - 7.08 (m, 4H),
130.2, 129.0, 128.8, 128.7, 128.6, 127.0, 126.5, 126.4, 125.5, 5.18 (s, 1H), 4.15 (s, 3H), 2.38 (s, 3H); 13C NMR (125 MHz,
125.0, 124.4, 123.9, 123.6, 123.2, 118.2, 96.6, 55.7, 53.6;
IR (KBr, cm-1): 3064, 1582, 1515, 1458, 1380, 1220, 1096,
1019, 812, 755, 698, 631, 590, 435; HRMS: m/z [M]+ calcd
for C28H20O: 372.1514; found: 372.1518.
CDCl3): 161.0, 159.0, 155.8 (d, J = 5.2 Hz), 149.6, 142.1,
138.6 (d, J = 27.1 Hz), 136.8, 134.4, 128.9, 128.1, 128.0,
127.9, 126.8, 126.5 (d, J = 8.3 Hz), 126.4, 125.6, 119.0,
116.8 (d, J = 25.1 Hz), 107.3 (d, J = 22.6 Hz), 97.5, 55.8,
53.5, 21.6; IR (Neat, cm-1): 3008, 1593, 1525, 1484, 1458,
1407, 1195, 1174, 1086, 988, 926, 813, 715; HRMS: m/z
[M]+ calcd for C25H14FO: 354.1420; found: 354.1418.
3,5-Dimethoxy-9-methyl-11-phenyl-11H-
5-Methoxy-9,11-diphenyl-11H-benzo[a]fluorene
(2k,
Table 2): Dull-white solid (yield = 73%); M.P. = 248 - 249
oC; Rf value = 0.41 (10% EtOAc in hexanes); 1H NMR (500
MHz, CDCl3): 8.31 (d, J = 7.7 Hz, 1H), 7.84 (d, J = 7.9
Hz, 1H), 7.61 (dd, J = 8.1, 1.7 Hz, 1H), 7.59 - 7.55 (m, 3H),
7.52 (s, 1H), 7.42 - 7.36 (m, 3H), 7.35 - 7.28 (m, 3H), 7.23
(d, J = 7.6 Hz, 2H), 7.21 - 7.17 (m, 1H), 7.15 (d, J = 6.8 Hz,
2H), 5.31 (s, 1H), 4.16 (s, 3H); 13C NMR (125 MHz,
CDCl3): 156.5, 150.3, 141.9, 141.4, 140.7, 140.0, 139.0,
135.0, 131.0, 128.9, 128.7, 128.1, 127.14, 127.06, 127.0,
126.7, 126.3, 125.8, 124.6, 124.4, 123.7, 123.2, 119.5, 96.7,
55.8, 53.8; IR (KBr, cm-1): 1587, 1474, 1396, 1216, 1117,
1092, 828, 756, 694, 632, 503; HRMS: m/z [M+Na]+ calcd
for C30H22O: 421.1563; found: 421.1562.
benzo[a]fluorene (2q, Table 2): Yellow solid (yield =
77%); M.P. = 260 - 261 oC; Rf value = 0.67 (10% EtOAc in
1
hexanes); H NMR (400 MHz, CDCl3): 7.63 (d, J = 7.7
Hz, 1H), 7.60 (d, J = 2.6 Hz, 1H), 7.46 (d, J = 9.1 Hz, 1H),
7.22 (d, J = 7.3 Hz, 3H), 7.19 (d, J = 6.8 Hz, 1H), 7.15 (d, J
= 8.0 Hz, 1H), 7.10 (d, J = 6.3, 3H), 6.97 (dd, J = 9.1, 2.6
Hz, 1H), 5.18 (s, 1H), 4.13 (s, 3H), 3.90 (s, 3H), 2.33(s, 3H);
13C NMR (100 MHz, CDCl3): 156.8, 155.4, 149.5, 142.4,
138.9, 137.2, 136.2, 134.6, 128.8, 128.0, 127.8, 126.6, 126.5,
126.4, 125.9, 125.5, 119.3, 118.7, 97.2, 55.7, 55.3, 53.5,
21.6; IR (Neat, cm-1): 2920, 1593, 1484, 1376, 1272, 1205,
1174, 1102, 839, 808, 678; HRMS: m/z [M]+ calcd for
C26H22O2: 366.1620; found: 366.1621.
11-(2,4-Dimethylphenyl)-5-methoxy-11H-
benzo[a]fluorene (2l, Table 2): Reddish yellow solid (yield
o
= 76%); M.P. = 171 - 172 C; Rf value = 0.63 (5% EtOAc
in hexanes); 1H NMR (400 MHz, CDCl3): 8.30 (d, J = 7.8
Hz, 1H), 7.78 (d, J = 7.5 Hz, 1H), 7.62 (d, J = 7.7 Hz, 1H),
7.40 - 7.29 (m, 4H), 7.28 (s, 1H), 7.24 - 7.19 (m, 1H), 6.82
(s, 1H), 6.71 (s, 2H), 5.16 (s, 1H), 4.14 (s, 3H), 2.19 (s, 6H);
13C NMR (100 MHz, CDCl3): 156.3, 149.9, 141.7, 141.3,
139.2, 138.2, 134.9, 131.1, 128.5, 126.93, 126.9, 126.8,
125.7, 124.8, 124.6, 124.5, 123.1, 119.2, 96.6, 55.8, 53.6,
21.3; IR (Neat, cm-1): 3003, 1587, 1448, 1402, 1371, 1216,
1143, 1102, 1024, 828, 715, 699; HRMS: m/z [M]+ calcd for
C26H22O: 350.1671; found: 350.1668.
9-Bromo-3,5-dimethoxy-11-phenyl-11H-
benzo[a]fluorene (2r, Table 2): Off-white solid (yield =
46%); M.P. = 263 - 264 oC; Rf value = 0.74 (10% EtOAc in
hexanes); 1H NMR (400 MHz, CDCl3): 7.61 (s, 1H), 7.59
(d, J = 5.8 Hz, 1H), 7.49 - 7.43 (m, 2H), 7.38 (s, 1H), 7.26 -
7.19 (m, 4H), 7.07 (dd, J = 7.7, 1.6 Hz, 2H), 6.99 (dd, J =
9.1, 2.6 Hz, 1H), 5.17 (s, 1H), 4.13 (s, 3H), 3.91 (s, 3H); 13
C
NMR (100 MHz, CDCl3): 157.2, 155.6, 151.1, 141.2,
140.6, 136.1, 134.8, 130.2, 129.0, 128.0, 127.9, 127.0,
126.97, 126.1, 125.9, 120.2, 120.0, 119.5, 101.9, 96.9, 55.8,
55.3, 53.5; IR (Neat, cm-1): 2920, 1732, 1587, 1458, 1262,
9,10-Dichloro-5-methoxy-11-phenyl-11H-
benzo[a]fluorene (2m, Table 2): Brownish yellow solid
6
This article is protected by copyright. All rights reserved.

10.1002/adsc.201701516
Advanced Synthesis & Catalysis
1210, 1185, 1035, 813, 699; HRMS: m/z [M]+ calcd for
C25H19BrO2: 430.0568; found: 430.0565.
7.35 (m, 3H), 7.32 (d, J = 7.3 Hz, 3H), 7.27 (d, J = 9.8 Hz,
2H), 7.24 - 7.17 (m, 2H), 7.07 (d, J = 6.7 Hz, 1H), 4.03 (dd,
J = 14.2, 5.4 Hz, 1H), 3.41 (dd, J = 15.9, 5.4 Hz, 1H), 2.38
(dd, J = 15.8, 14.3 Hz, 1H); 13C NMR (100 MHz, CDCl3):
197.0, 148.5, 144.5, 139.6, 138.5, 136.7, 134.1, 133.5,
130.9, 129.3, 128.9, 128.8, 128.4, 128.2, 127.9, 126.9, 124.5,
124.2, 121.7, 48.6, 42.7; IR (Neat, cm-1): 3070, 1680, 1448,
1283, 1241, 1138, 1061, 926, 782, 746, 704; HRMS: m/z
[M+Na]+ calcd for C23H15BrO: 409.0198; found: 409.0194.
9-Chloro-11-phenyl-6,6a-dihydro-5H-benzo[a]fluoren-
5-one (3c, Table 3): Red solid (yield = 90%); M.P. = 209 -
3,5,8,10-Tetramethoxy-11-phenyl-11H-
benzo[a]fluorene (2s, Table 2): Brown solid (yield =
75%); M.P. = 237 - 238 oC; Rf value = 0.5 (10% EtOAc in
1
hexanes); H NMR (400 MHz, CDCl3): 7.57 (d, J = 2.6
Hz, 1H), 7.53 (d, J = 9.1 Hz, 1H), 7.21 (s, 1H), 7.18 - 7.08
(m, 5H), 6.97 (dd, J = 9.1, 2.7 Hz, 1H), 6.94 (d, J = 2.0 Hz,
1H), 6.32 (d, J = 2.0, 1H), 5.26 (s, 1H), 4.14 (s, 3H), 3.92 (s,
3H), 3.89 (s, 3H), 3.66 (s, 3H); 13C NMR (100 MHz,
CDCl3): 161.3, 157.0, 156.8, 155.2, 143.9, 141.7, 137.1,
136.7, 129.0, 128.5, 128.1, 126.7, 126.1, 126.0, 125.8, 119.3, 210 oC; Rf value = 0.84 (10% EtOAc in hexanes); 1H NMR
101.7, 97.5, 97.2, 96.3, 55.8, 55.7, 55.5, 55.3, 51.3; IR (Neat, (500 MHz, CDCl3): 8.11 - 8.08 (m, 1H), 7.54 - 7.45 (m,
cm-1): 3424, 1591, 1460, 1269, 1205, 1138, 988, 844, 734;
HRMS: m/z [M]+ calcd for C27H24O4: 412.1675; found:
412.1673.
3H), 7.41 (d, J = 7.7 Hz, 2H), 7.35 - 7 .28 (m, 2H), 7.27 -
7.24 (m, 2H), 7.19 (d, J = 1.8 Hz, 1H), 7.18 - 7.15 (m, 1H),
4.14 (dd, J = 14.0, 5.3 Hz, 1H), 3.50 (dd, J = 16, 5.5 Hz, 1H),
2.47 (dd, J = 16, 14.2 Hz, 1H); 13C NMR (125 MHz,
CDCl3): 197.0, 148.2, 144.0, 139.7, 138.6, 136.8, 134.1,
133.7, 133.5, 130.9, 129.3, 128.9, 128.4, 128.2, 127.9, 126.9,
125.9, 123.8, 121.6, 48.6, 42.8; IR (Neat, cm-1): 3054, 2915,
1680, 1489, 1448, 1283, 1241, 1071, 818, 771, 735, 709;
HRMS: m/z [M+H]+ calcd for C23H15ClO: 343.0884; found:
343.0884.
3-Fluoro-5,8,9,10-tetramethoxy-11-phenyl-11H-
benzo[a]fluorene (2t, Table 2): Yellow solid (yield =
68%); M.P. = 231 - 232 oC; Rf value = 0.38 (20% EtOAc in
hexanes); 1H NMR (500 MHz, CDCl3): 7.85 (dd, J = 10.8,
2.7 Hz, 1H), 7.59 (dd, J = 9.1, 5.6 Hz, 1H), 7.19 (d, J = 7.7
Hz, 2H), 7.17 - 7.13 (m, 2H), 7.12 (d, J = 1.5 Hz, 1H), 7.10
(s, 2H), 7.09 - 7.04 (m, 1H), 5.26 (s, 1H), 4.11 (s, 3H), 4.01
(s, 3H), 3.87 (s, 3H), 3.29 (s, 3H); 13C NMR (125 MHz,
11-Phenyl-9-(trifluoromethyl)-6,6a-dihydro-5H-
CDCl3): 161.0, 159.1, 155.8, 154.2, 150.4, 141.7, 138.2 (d, benzo[a]fluoren-5-one (3d, Table 3): Dark red solid (yield
J = 2.4 Hz), 137.2, 136.0, 134.6, 128.5 (d, J = 8.5 Hz), 127.8,
126.5, 126.3, 126.25 (d, J = 8.6 Hz), 126.24, 116.9 (d, J =
25.2 Hz), 107.2 (d, J = 22.7 Hz), 98.9, 97.2, 60.9, 60.0, 56.4,
55.8, 51.9; IR (Neat, cm-1): 2997, 1593, 1520, 1463, 1407,
1355, 1267, 1112, 1035, 988, 833, 730, 694; HRMS: m/z
[M]+ calcd for C27H23FO4: 430.1580; found: 430.1576.
Representative procedure for the synthesis of
benzo[a]fluorenone derivative 11-phenyl-6,6a-dihydro-
5H-benzo[a]fluoren-5-one 3a: To a solution of compound
1a (100 mg, 0.325 mmol, 1.0 equiv.) in
hexafluoroisopropanol solvent (1.5 mL), triflic acid (29 L,
0.325 mmol, 1 equiv.) was added and the contents were
stirred at room temperature (25 oC) under nitrogen
atmosphere. The progress of the reaction was monitored by
TLC. After completion of the reaction (after 2 hrs), it was
quenched with saturated NaHCO3 solution. Then it was
extracted using ethyl acetate. The combined organic layer
was washed with saturated brine solution and dried over
anhydrous Na2SO4. The solvents were evaporated under
reduced pressure. The crude was purified by column
chromatography (using silica gel, 5% EtOAc/hexanes
eluent) to get pure 11-phenyl-6,6a-dihydro-5H-
benzo[a]fluoren-5-one 3a (97 mg, 97%). Orange yellow
= 54%); M.P. = 171 - 172 oC; Rf value = 0.36 (10% EtOAc
in hexanes); 1H NMR (400 MHz, CDCl3): 8.13 - 8.09 (m,
1H), 7.61 (d, J = 8.0 Hz, 1H), 7.58 - 7.47 (m, 4H), 7.46 -
7.41 (m, 3H), 7.37 - 7.29 (m, 2H), 7.18 (d, J = 7.0 Hz, 1H),
4.21 (dd, J = 14.1, 5.5 Hz, 1H), 3.54 (dd, J = 16.0, 5.5 Hz,
1H), 2.50 (dd, J = 16.0, 14.1 Hz, 1H);
13C NMR (100
MHz, CDCl3):  196.8, 149.2, 147.0, 139.7, 138.6, 136.6,
133.9, 133.6, 130.9, 130.4, 129.4, 128.9, 128.5, 128.3, 127.9,
126.9, 125.7, 123.0, 122.95, 118.0 (q, J = 4.0 Hz), 48.9,
42.5; 19F NMR (376 MHz, CDCl3):  -61.9; IR (Neat, cm-1):
3059, 2925, 1686, 1433, 1319, 1278, 1174, 1123, 1055, 895,
844, 771; HRMS: m/z [M+H]+ calcd for C24H15F3O:
377.1148; found: 377.1148.
9-Fluoro-11-phenyl-6,6a-dihydro-5H-benzo[a]fluoren-
5-one (3e, Table 3): Red solid (yield = 38%); M.P. = 169 -
o
1
170 C; Rf value = 0.59 (5% EtOAc in hexanes); H NMR
(500 MHz, CDCl3): 8.11 - 8.08 (m, 1H), 7.54 - 7.49 (m,
2H), 7.47 (d, J = 7.3 Hz, 1H), 7.45 - 7.40 (m, 3H), 7.35 -
7.28 (m, 2H), 7.19 - 7.16 (m, 1H), 7.00 - 6.95 (m, 1H), 6.92
(dd, J = 9.1, 2.4 Hz, 1H), 4.13 (dd, J = 14.1, 5.5 Hz, 1H),
3.50 (dd, J = 16.0, 5.5 Hz, 1H), 2.48 (dd, J = 16.0, 14.1 Hz,
1H); 13C NMR (100 MHz, CDCl3): 197.1, 161.9, 148.5 (d,
J = 10.1 Hz), 141.2, 140.1, 138.8 (d, J = 2.9 Hz), 136.9,
134.2, 133.4, 130.9, 129.2, 128.9, 128.4,
o
solid (yield = 97%); M.P. = 189 - 190 C; Rf value = 0.39
1
(10% EtOAc in hexanes); H NMR (500 MHz, CDCl3):
128.1, 127.8, 126.9, 123.6 (d, J = 9.1 Hz), 112.7 (d, J = 23.2
Hz), 108.5 (d, J = 23.6 Hz), 48.4, 43.0; IR (Neat, cm-1): 2961,
2930, 1686, 1458, 1278, 1138, 1014, 864, 777; HRMS: m/z
[M+H]+ calcd for C24H15FO: 327.1180; found: 327.1180.
11-(4-Chlorophenyl)-6,6a-dihydro-5H-benzo[a]fluoren-
5-one (3f, Table 3): Red solid (yield = 85%); M.P. = 112 -
113 oC; Rf value = 0.71 (10% EtOAc in hexanes); 1H NMR
(500 MHz, CDCl3): 8.11 - 8.08 (m, 1H), 7.52 (d, J = 5.6
8.10 - 8.06 (m, 1H), 7.51 - 7.46 (m, 3H), 7.46 - 7.40 (m,
3H), 7.31 - 7.25 (m, 4H), 7.25 - 7.21 (m, 1H), 7.18 - 7.15
(m, 1H), 4.12 (dd, J = 14.1, 5.5 Hz, 1H), 3.50 (dd, J = 16,
5.5 Hz, 1H), 2.47 (dd, J = 16, 14.2 Hz, 1H); 13C NMR (125
MHz, CDCl3): 197.5, 146.5, 146.0, 139.5, 138.1, 137.3,
134.8, 133.4, 131.0, 129.1, 129.0, 128.2, 127.83, 127.76,
127.6, 126.9, 126.1, 122.9, 121.4, 49.0, 43.0; IR (KBr, cm-
1): 1660, 1479, 1443, 1340, 1200, 1097, 1014, 973, 756, 704, Hz, 1H), 7.48 (d, J = 8.6 Hz, 2H), 7.38 (d, J = 8.1 Hz, 2H),
565, 529; HRMS: m/z [M+H]+ calcd for C23H16O:
309.1274; found: 309.1271.
7.34 - 7.29 (m, 4H), 7.23 - 7.20 (m, 1H), 7.18 - 7.14 (m, 1H),
4.16 (dd, J = 14.0, 5.5 Hz, 1H), 3.52 (dd, J = 16.0, 5.5 Hz,
1H), 2.48 (dd, J = 16.0, 14.0 Hz, 1H); 13C NMR (100 MHz,
CDCl3): 197.2, 146.0, 145.9, 138.7, 138.1, 136.9, 134.1,
133.5, 133.3, 131.0, 130.5, 129.5, 128.0, 127.9, 127.6, 126.7,
126.2, 122.9, 121.2, 49.1, 42.9; IR (Neat, cm-1): 2915, 2853,
1680, 1489, 1283, 1241, 1092, 1009, 844, 813, 751; HRMS:
m/z [M+H]+ calcd for C23H15ClO: 343.0884; found:
343.0880.
1
The structure of 2a is also established with H-1H COSY,
HETCOR and NOESY studies; intramolecular NOEs
between CH2 (δ = 2.47 and 3.50 ppm) and CH (δ = 4.12
ppm) was observed.
11-(3-Nitrophenyl)-6,6a-dihydro-5H-benzo[a]fluoren-5-
one (3g, Table 3): Reddish yellow solid (yield = 36%); M.P.
o
= 207 - 208 C; Rf value = 0.47 (10% EtOAc in hexanes);
1H NMR (400 MHz, CDCl3): 8.36 - 8.32 (m, 2H), 8.12 (dd,
J = 7.8, 1.5 Hz, 1H), 7.79 (d, J = 7.6 Hz, 1H), 7.70 (t, J =
8.0 Hz, 1H), 7.57 - 7.53 (m, 1H), 7.39 - 7.29 (m, 4H), 7.21
- 7.17 (m, 1H), 7.05 (d, J = 7.5 Hz, 1H), 4.22 (dd, J = 14.0,
5.5 Hz, 1H), 3.56 (dd, J = 16.1, 5.6 Hz, 1H), 2.51 (dd, J =
16.1, 14.1 Hz, 1H); 13C NMR (125 MHz, CDCl3): 196.8,
149.0, 145.8, 145.4, 140.0, 136.8, 136.6, 136.3, 135.4, 133.6,
131.1, 130.3, 128.5, 128.2, 127.8, 126.6, 126.4, 124.2, 123.2,
123.1, 120.8, 49.3, 42.9; IR (Neat, cm-1): 3070, 2925, 1706,
The above procedure was followed to prepare the other
benzo[a]fluorenone derivatives 3b-3y from their respective
starting materials.
9-Bromo-11-phenyl-6,6a-dihydro-5H-benzo[a]fluoren-
5-one (3b, Table 3): Red solid (yield = 95%); M.P. = 226 -
227 oC; Rf value = 0.69 (10% EtOAc in hexanes); 1H NMR
(400 MHz, CDCl3): 8.00 (dd, J = 7.0, 1.8 Hz, 1H), 7.46 -
7
This article is protected by copyright. All rights reserved.

10.1002/adsc.201701516
Advanced Synthesis & Catalysis
1531, 1453, 1345, 1278, 1081, 813, 766; HRMS: m/z
[M+Na]+ calcd for C23H15NO3: 376.0944; found: 376.0944.
3-Methoxy-11-phenyl-6,6a-dihydro-5H-
2H), 7.31 (d, J = 7.6 Hz, 1H), 7.29 - 7.22 (m, 2H), 7.18 -
7.13 (m, 1H), 6.97 - 6.93 (m, 1H), 4.25 (dd, J = 14.1, 5.4 Hz,
1H), 3.62 (dd, J = 15.8, 5.5 Hz, 1H), 2.46 (dd, J = 15.8, 14.2
Hz, 1H); 13C NMR (125 MHz, CDCl3): 197.5, 145.0,
141.4, 140.7, 139.6, 138.1, 137.4, 134.0, 133.5, 130.7, 130.0,
129.3, 128.9, 128.6, 128.3, 127.8, 127.4, 127.2, 126.5, 125.8,
125.2, 123.8, 120.8, 49.2, 43.0; IR (Neat, cm-1): 3426, 3049,
2920, 1627, 1582, 1463, 1272, 1117, 1081, 735, 699;
HRMS: m/z [M+H]+ calcd for C27H18O: 359.1430; found:
359.1432.
benzo[a]fluoren-5-one (3h, Table 3): Brownish yellow
o
solid (yield = 99%); M.P. = 230 - 231 C; Rf value = 0.57
1
(10% EtOAc in hexanes); H NMR (500 MHz, CDCl3):
7.56 (d, J = 2.9 Hz, 1H), 7.49 (d, J = 7.1 Hz, 3H), 7.46 -
7.41 (m, 3H), 7.32 - 7.26 (m, 2H), 7.23 - 7.20 (m, 1H), 7.11
(d, J = 8.8 Hz, 1H), 6.87 (dd, J = 8.7, 2.8 Hz, 1H), 4.13 (dd,
J = 14.1, 5.4, Hz, 1H), 3.85 (s, 3H), 3.52 (dd, J = 16.0, 5.4
Hz, 1H), 2.49 (dd, J = 16.0, 14.1 Hz, 1H); 13C NMR (125
MHz, CDCl3): 197.5, 159.2, 146.7, 145.5, 138.0, 137.7,
135.0, 132.2, 130.6, 129.09, 129.06, 128.3, 128.0, 127.5,
125.6, 122.7, 121.7, 121.0, 109.8, 55.5, 49.1, 43.0; IR (Neat,
cm-1): 2956, 2848, 1680, 1603, 1484, 1453, 1319, 1278,
1221, 1143, 1019, 875, 751, 704; HRMS: m/z [M+H]+ calcd
for C24H18O2: 339.1380; found: 339.1384.
9,11-Diphenyl-6,6a-dihydro-5H-benzo[a]fluoren-5-one
(3n, Table 3): Yellow solid (yield = 94%); M.P. = 147 - 148
oC; Rf value = 0.33 (10% EtOAc in hexanes); 1H NMR (400
MHz, CDCl3): 8.12 - 8.08 (m, 1H), 7.60 - 7.55 (m, 2H),
7.54 - 7.50 (m, 4H), 7.49 - 7.44 (m, 3H), 7.43 - 7.38 (m, 3H),
7.35 - 7.28 (m, 3H), 7.19 - 7.16 (m, 1H), 4.22 (dd, J = 14.0,
5.3 Hz, 1H), 3.55 (dd, J = 16.0, 5.5 Hz, 1H), 2.55 (dd, J =
16.0, 14.2 Hz, 1H); 13C NMR (125 MHz, CDCl3): 197.4,
147.1, 144.9, 141.4, 141.2, 139.5, 138.8, 137.2, 134.7, 133.4,
131.0, 129.2, 129.0, 128.7, 128.2, 127.82, 127.81, 127.4,
127.3, 126.9, 125.3, 123.0, 120.2, 48.8, 43.1; IR (KBr, cm-
1): 2925, 2858, 1680, 1458, 1288, 1138, 1076, 1009, 751,
699; HRMS: m/z [M+H]+ calcd for C29H20O: 385.1587;
found: 385.1580.
3-Fluoro-11-phenyl-6,6a-dihydro-5H-benzo[a]fluoren-
5-one (3i, Table 3): Brownish solid (yield = 82%); M.P. =
185 - 186 oC; Rf value = 0.56 (10% EtOAc in hexanes); 1H
NMR (500 MHz, CDCl3): 7.73 (dd, J = 9.1, 2.8 Hz, 1H),
7.53 - 7.40 (m, 6H), 7.33 - 7.27 (m, 2H), 7.25 - 7.22 (m, 1H),
7.16 (dd, J = 8.7, 5.2 Hz, 1H), 6.99 (td, J = 8.2, 2.9 Hz, 1H),
4.13 (dd, J = 14.2, 5.4 Hz, 1H), 3.52 (dd, J = 16.1, 5.5 Hz,
1H), 2.47 (dd, J = 16.1, 14.3 Hz, 1H); 13C NMR (100 MHz,
CDCl3):  196.5, 163.6, 160.8, 146.3, 145.5, 139.3, 137.0,
134.6, 133.6, 132.9 (d, J = 6.1 Hz), 129.1 (d, J = 26.1 Hz),
129.0, 128.3, 127.6, 126.1, 122.9, 121.4, 120.9 (d, J = 22.6
11-(2,4-Dimethylphenyl)-6,6a-dihydro-5H-
benzo[a]fluoren-5-one (3o, Table 3): Red solid (yield =
96%); M.P. = 180 - 181 oC; Rf value = 0.45 (10% EtOAc in
1
hexanes); H NMR (400 MHz, CDCl3): 8.11 - 8.05 (m,
Hz), 113.8 (d, J = 22.3 Hz), 48.9, 42.8; IR (Neat, cm-1): 3054, 1H), 7.49 (d, J = 6.7 Hz, 1H), 7.31 - 7.27 (m, 4H), 7.25 -
2956, 1660, 1593, 1474, 1293, 1262, 1169, 1019, 926, 740,
704; HRMS: m/z [M+H]+ calcd for C23H15FO: 327.1180;
found: 327.1180.
7.22 (m, 2H), 7.08 (s, 1H), 7.04 (s, 2H), 4.13 (dd, J = 14.2,
5.4 Hz, 1H), 3.50 (dd, J = 15.9, 5.4 Hz, 1H), 2.47 (dd, J =
16, 14.2 Hz, 1H), 2.36 (s, 6H); 13C NMR (100 MHz,
CDCl3): 197.6, 146.7, 145.9, 139.9, 138.6, 137.6, 137.4,
134.7, 133.3, 130.9, 129.7, 128.5, 128.4, 127.7, 127.6, 127.4,
126.9, 126.5, 125.9, 122.7, 121.5, 48.9, 43.0, 21.4; IR (Neat,
cm-1): 3023, 2915, 1680, 1463, 1283, 1205, 1014, 978, 849,
756, 694; HRMS: m/z [M+H]+ calcd for C25H20O: 337.1587;
found: 337.1587.
11-Phenyl-6,6a-dihydro-5H-
indeno[2',1':5,6]naphtho[2,3-d][1,3]dioxol-5-one
(3j,
Table 3): Dark brown solid (yield = 54%); M.P. = 235 - 236
oC; Rf value = 0.56 (10% EtOAc in hexanes); 1H NMR (500
MHz, CDCl3): 7.52 (s, 1H), 7.51 (s, 1H), 7.50 - 7.40 (m,
5H), 7.32 - 7.27 (m, 2H), 7.23 - 7.20 (m, 1H), 6.54 (s, 1H),
5.96 (d, J = 2.9 Hz, 2H), 4.12 (dd, J = 14.0, 5.5 Hz, 1H),
3.47 (dd, J = 16.0, 5.5 Hz, 1H), 2.43 (dd, J = 16.0, 14.0 Hz,
1H); 13C NMR (100 MHz, CDCl3): 196.1, 151.9, 147.8,
9,10-Dichloro-11-phenyl-6,6a-dihydro-5H-
benzo[a]fluoren-5-one (3p, Table 3): Red solid (yield =
27%); M.P. = 192 - 193 oC; Rf value = 0.38 (5% EtOAc in
1
146.5, 145.6, 138.7, 138.1, 134.6, 134.3, 129.2, 129.0, 128.2, hexanes); H NMR (500 MHz, CDCl3): 8.11 - 8.08 (m,
127.5, 126.8, 125.9, 122.7, 121.2, 106.8, 106.0, 101.7, 49.3,
42.6; IR (Neat, cm-1): 3337, 1664, 1608, 1470, 1371, 1260,
1034, 931, 751, 699; HRMS: m/z [M+H]+ calcd for
C24H16O3: 353.1172; found: 353.1173.
1H), 7.56 (s, 1H), 7.55 - 7.46 (m, 3H), 7.40 (d, J = 6.9 Hz,
2H), 7.36 - 7.28 (m, 2H), 7.27 (s, 1H), 7.15 (d, J = 7.4 Hz,
1H), 4.15 (dd, J = 14.0, 5.5 Hz, 1H), 3.48 (dd, J = 16.1, 5.6
Hz, 1H), 2.49 (dd, J = 16.0, 14.2 Hz, 1H); 13C NMR (125
MHz, CDCl3): 196.4, 146.4, 145.2, 139.8, 138.0, 136.5,
133.8, 133.5, 131.9, 130.9, 130.0, 129.4, 128.8, 128.6, 128.4,
127.9, 126.9, 124.8, 122.9, 48.5, 42.5; IR (Neat, cm-1): 3054,
2915, 1737, 1660, 1598, 1474, 1288, 1262, 1107, 1024, 952,
880, 771; HRMS: m/z [M+H]+ calcd for C23H14Cl2O:
377.0494; found: 377.0494.
8,10-Dimethoxy-11-phenyl-6,6a-dihydro-5H-
benzo[a]fluoren-5-one (3k, Table 3): Yellow solid (yield
= 76%); M.P. = 184 - 185 oC; Rf value = 0.45 (10% EtOAc
in hexanes); 1H NMR (500 MHz, CDCl3): 8.04 - 8.00 (m,
1H), 7.37 (s, 5H), 7.21 - 7.14 (m, 2H), 6.90 - 6.87 (m, 1H),
6.69 (d, J = 1.3 Hz, 1H), 6.37 (d, J = 1.2 Hz, 1H), 4.05 (dd,
J = 14.2, 5.4 Hz, 1H), 3.84 (s, 3H), 3.50 (s, 3H), 3.41 (dd, J
= 15.9, 5.4 Hz, 1H), 2.47 (dd, J = 15.8, 14.3 Hz, 1H); 13C
NMR (125 MHz, CDCl3): 197.6, 160.4, 156.1, 149.7,
8,10-Dimethoxy-11-(p-tolyl)-6,6a-dihydro-5H-
benzo[a]fluoren-5-one (3q, Table 3): Yellow solid (yield
= 98%); M.P. = 205 - 206 oC; Rf value = 0.18 (10% EtOAc
139.4, 137.9, 137.2, 135.1, 133.2, 130.6, 129.1, 128.0, 127.6, in hexanes); 1H NMR (400 MHz, CDCl3): 8.04 - 8.00 (m,
127.23, 127.17, 126.8, 126.6, 100.8, 98.5, 55.7, 55.5, 49.2,
43.4; IR (Neat, cm-1): 3059, 2930, 1685, 1458, 1292, 1205,
1148, 1101, 827, 765, 693; HRMS: m/z [M+H]+ calcd for
C25H20O3: 369.1485; found: 369.1483.
1H), 7.26 - 7.16 (m, 6H), 6.95 - 6.91 (m, 1H), 6.69 (dd, J =
2.0, 0.8 Hz, 1H), 6.38 (d, J = 2.0 Hz, 1H), 4.05 (dd, J = 14.1,
5.4 Hz, 1H), 3.86 (s, 3H), 3.54 (s, 3H), 3.41 (dd, J = 15.9,
5.5 Hz, 1H), 2.48 (dd, J = 15.9, 14.2 Hz, 1H), 2.43 (s, 3H);
13C NMR (100 MHz, CDCl3): 197.7, 160.3, 156.1, 149.7,
139.4, 138.0, 136.8, 135.0, 134.0, 133.2, 130.6, 128.7, 127.6,
127.2, 126.7, 126.6, 100.7, 98.5, 55.7, 55.5, 49.1, 43.4, 21.4;
IR (KBr, cm-1): 1680, 1453, 1355, 1283, 1205, 1154, 1040,
947, 833, 766, 653, 554; HRMS: m/z [M+H]+ calcd for
C26H22O3: 383.1642; found: 383.1645.
8,9,10-Trimethoxy-11-phenyl-6,6a-dihydro-5H-
benzo[a]fluoren-5-one (3l, Table 3): Pale yellow solid
o
(yield = 84%); M.P. = 224 - 225 C; Rf value = 0.09 (10%
1
EtOAc in hexanes); H NMR (400 MHz, CDCl3): 8.06 -
8.02 (m, 1H), 7.43 (s, 5H), 7.24 - 7.18 (m, 2H), 6.94 - 6.90
(m, 1H), 6.88 (s, 1H), 4.07 (dd, J = 14.0, 5.4 Hz, 1H), 3.93
(s, 3H), 3.84 (s, 3H), 3.44 (dd, J = 15.9, 5.4 Hz, 1H), 3.35
(s, 3H), 2.50 (dd, J = 15.8, 14.2 Hz, 1H); 13C NMR (100
MHz, CDCl3): 197.5, 153.2, 149.4, 142.6, 142.5, 139.1,
11-(Benzo[d][1,3]dioxol-5-yl)-8,10-dimethoxy-6,6a-
dihydro-5H-benzo[a]fluoren-5-one (3r, Table 3):
Greenish yellow solid (yield = 52%); M.P. = 183 - 184 oC;
1
137.5, 136.8, 136.5, 133.3, 131.9, 130.6, 129.3, 128.3, 127.6, Rf value = 0.21 (10% EtOAc in hexanes); H NMR (400
127.5, 127.1, 126.6, 103.1, 61.1, 61.0, 56.4, 49.1, 43.4; IR
(KBr, cm-1): 2920, 2853, 1675, 1458, 1360, 1334, 1283,
1138, 1102, 1024, 993, 890, 751, 704, 663; HRMS: m/z
[M+H]+ calcd for C26H22O4: 399.1591; found: 399.1590.
13-Phenyl-6,6a-dihydro-5H-dibenzo[a,i]fluoren-5-one
(3m, Table 3): Yellow solid (yield = 30%); M.P. = 123 -
MHz, CDCl3): 8.05 - 8.01 (m, 1H), 7.25 - 7.19 (m, 2H),
7.02 (d, J = 7.5 Hz, 1H), 6.97 - 6.72 (m, 3H), 6.68 (dd, J =
2.0, 0.7 Hz, 1H), 6.39 (d, J = 2.0 Hz, 1H), 6.04 (s, 2H), 4.04
(dd, J = 14.2, 5.4 Hz, 1H), 3.86 (s, 3H), 3.59 (s, 3H), 3.40
(dd, J = 15.9, 5.4 Hz, 1H), 2.46 (dd, J = 15.9, 14.3 Hz, 1H);
13C NMR (100 MHz, CDCl3): 197.6, 160.4, 156.0, 151.9,
149.6, 147.4, 146.8, 138.8, 137.8, 135.3, 133.3, 130.7, 130.6,
127.6, 127.1, 126.9, 126.6, 110.0, 108.2, 101.0, 100.7, 98.5,
55.7, 55.6, 49.0, 43.3; IR (Neat, cm-1): 2961, 2920, 1675,
1484, 1433, 1324, 1231, 1143, 1097, 1040, 942, 761, 735;
o
1
124 C; Rf value = 0.57 (5% EtOAc in hexanes); H NMR
(500 MHz, CDCl3): 8.10 - 8.07 (m, 1H), 7.88 (d, J = 8.2,
1H), 7.81 (d, J = 8.2 Hz, 1H), 7.72 - 7.65 (m, 3H), 7.57 (tt,
J = 7.3, 1.5 Hz, 1H), 7.53 - 7.47 (m, 1H), 7.44 - 7.34 (m,
8
This article is protected by copyright. All rights reserved.

10.1002/adsc.201701516
Advanced Synthesis & Catalysis
1
HRMS: m/z [M+H]+ calcd for C26H20O5: 413.1384; found:
413.1385.
Rf value = 0.22 (10% EtOAc in hexanes); H NMR (500
MHz, CDCl3):  7.46 (s, 1H), 7.44 - 7.34 (m, 4H), 7.26 (s,
1H), 6.67 (d, J = 1.3 Hz, 1H), 6.37 (d, J = 2 Hz, 1H), 6.26
(s, 1H), 5.90 (q, J = 1.3 Hz, 2H), 4.03 (dd, J = 14.0, 5.5 Hz,
1H), 3.86 (s, 3H), 3.51 (s, 3H), 3.37 (dd, J = 15.9, 5.5 Hz,
1H), 2.42 (dd, J = 15.9, 14.0 Hz, 1H); 13C NMR (100 MHz,
CDCl3): 196.1, 160.3, 155.9, 151.7, 149.3, 147.1, 138.5,
137.0, 135.1, 135.0, 128.1, 127.3, 127.1, 126.3, 106.6, 105.7,
101.5, 100.7, 98.5, 55.7, 55.5, 49.4, 42.9; IR (Neat, cm-1):
3054, 2915, 1670, 1613, 1469, 1329, 1257, 1205, 1148,
1035, 931, 839, 735, 699; HRMS: m/z [M]+ calcd for
C26H20O5: 412.1311; found: 412.1311.
3-Fluoro-9-methyl-11-phenyl-6,6a-dihydro-5H-
benzo[a]fluoren-5-one (3s, Table 3): Brownish yellow
o
solid (yield = 99%); M.P. = 140 - 141 C; Rf value = 0.73
1
(10% EtOAc in hexanes); H NMR (400 MHz, CDCl3):
7.72 (dd, J = 9.1, 2.8 Hz, 1H), 7.54 - 7.43 (m, 3H), 7.42 (s,
1H), 7.38 (d, J = 7.7 Hz, 2H), 7.16 - 7.09 (m, 2H), 7.03 (s,
1H), 6.97 (td, J = 8.3, 2.8 Hz, 1H), 4.09 (dd, J = 14.1, 5.4
Hz, 1H), 3.50 (dd, J = 16.1, 5.4 Hz, 1H), 2.45 (dd, J = 16.1,
14.2 Hz, 1H), 2.35 (s, 3H); 13C NMR (100 MHz, CDCl3):
196.6, 163.2, 160.7, 146.6, 142.8, 139.3, 137.5, 137.3,
134.8, 133.7 (d, J = 3.1 Hz), 132.9 (d, J = 6.3 Hz), 129.1 (d,
J = 22.9 Hz), 128.9, 128.2, 126.9, 122.6, 122.0, 120.9 (d, J
9-Methyl-11-phenyl-6,6a-dihydro-5H-
indeno[2',1':5,6]naphtho[2,3-d][1,3]dioxol-5-one
(3y,
= 22.7 Hz), 113.8 (d, J = 22.3 Hz), 48.6, 43.0, 21.5; IR (Neat, Table 3): Brown solid (yield = 88%); M.P. = 291 - 292 oC;
1
cm-1): 2961, 2915, 1686, 1603, 1458, 1298, 1262, 1019, 895, Rf value = 0.28 (10% EtOAc in hexanes); H NMR (500
823, 704; HRMS: m/z [M]+ calcd for C24H17FO: 340.1263;
found: 340.1260.
MHz, CDCl3): 7.56 - 7.51 (m, 3H), 7.50 - 7.46 (m, 1H),
7.43 (d, J = 6.8 Hz, 2H), 7.39 (d, J = 7.5 Hz, 1H), 7.12 (d, J
= 7.5 Hz, 1H), 7.02 (s, 1H), 6.53 (s, 1H), 5.97 (d, J = 2.3 Hz,
2H), 4.11 (dd, J = 13.9, 5.5 Hz, 1H), 3.46 (dd, J = 16.0, 5.5
3-Methoxy-9-methyl-11-phenyl-6,6a-dihydro-5H-
benzo[a]fluoren-5-one (3t, Table 3): Brownish white solid
o
(yield = 83%); M.P. = 183 - 184 C; Rf value = 0.58 (10%
Hz, 1H), 2.43 (dd, J = 16.0, 13.9 Hz, 1H), 2.37 (s, 3H); 13
C
EtOAc in hexanes); 1H NMR (400 MHz, CDCl3): 7.55 (d,
J = 2.8 Hz, 1H), 7.53 - 7.40 (m, 5H), 7.37 (d, J = 7.5 Hz,
1H), 7.08 (d, J = 8.8 Hz, 2H), 7.02 (s, 1H), 6.86 (dd, J = 8.8,
2.8 Hz, 1H), 4.09 (dd, J = 14.0, 5.4 Hz, 1H), 3.84 (s, 3H),
3.49 (dd, J = 16.0, 5.4 Hz, 1H), 2.47 (dd, J = 15.9, 14.1 Hz,
1H), 2.35 (s, 3H); 13C NMR (100 MHz, CDCl3): 197.7,
159.1, 146.9, 142.7, 138.3, 137.7, 137.3, 135.1, 132.2, 130.7,
129.11, 129.07, 128.3, 127.9, 126.4, 122.4, 121.71, 121.66,
109.7, 55.5, 48.7, 43.2, 21.5; IR (KBr, cm-1): 1685, 1592,
1499, 1468, 1323, 1220, 1153, 1019, 884, 807, 750, 704,
595; HRMS: m/z [M]+ calcd for C25H20O2: 352.1463; found:
352.1465.
NMR (125 MHz, CDCl3): 196.2, 151.8, 147.7, 146.7,
142.8, 138.7, 138.4, 137.3, 134.8, 134.4, 129.8, 129.2, 129.0,
128.1, 126.7, 122.4, 121.8, 106.8, 106.0, 101.7, 49.0, 42.8,
21.5; IR (KBr, cm-1): 3385, 1701, 1629, 1484, 1267, 1169,
1035, 870, 808, 766; HRMS: m/z [M+H]+ calcd for
C25H18O3: 367.1329; found: 367.1329.
Synthetic Procedure for the preparation of
benzo[a]fluorenol (4a) and benzo[a]fluorenone (5a):
Heating Method: Benzo[a]fluorenone 3a was heated under
N2 atmosphere in a closed vessel neatly. After 1 hour, 3a
was found to be fully converted into 11-phenyl-11H-
benzo[a]fluoren-5-ol, 4a. In an open vessel when 3a was
9-Bromo-3-methoxy-11-phenyl-6,6a-dihydro-5H-
benzo[a]fluoren-5-one (3u, Table 3): Greenish yellow
o
heated at 300 C, compound 11-phenyl-6,6a-dihydro-5H-
o
solid (yield = 58%); M.P. = 202 - 203 C; Rf value = 0.76
benzo[a]fluoren-5-one (5a) was obtained after 1 hour. The
1
o
(10% EtOAc in hexanes); H NMR (400 MHz, CDCl3):
compound 4a upon heating at 300 C in open atmosphere
7.56 (d, J = 2.8 Hz, 1H), 7.54 - 7.44 (m, 3H), 7.42 - 7.30
(m, 5H), 7.09 (d, J = 8.7 Hz, 1H), 6.88 (dd, J = 8.7, 2.9 Hz,
1H), 4.08 (dd, J = 14.0, 5.4 Hz, 1H), 3.85 (s, 3H), 3.49 (dd,
converted into compound 5a.
Chemical Method:
J = 16.0, 5.5 Hz, 1H), 2.47 (dd, J = 16.0, 14.1 Hz, 1H); 13
C
Synthesis of (11-Phenyl-11H-benzo[a]fluoren-5-ol) (4a):
In a round bottom flask, benzo[a]fluorene 2a (50 mg, 0.155
mmol) was dissolved in CH2Cl2 (1 mL) solvent under
NMR (100 MHz, CDCl3): 197.0, 159.5, 148.8, 144.1,
139.5, 136.7, 134.3, 132.3, 130.0, 129.3, 129.0, 128.4,
128.33, 128.29, 124.1, 124.0, 121.8, 121.7, 109.8, 55.6, 48.7, nitrogen atmosphere at 0 oC. Then BBr3 (268 L, 0.31 mmol,
42.7; IR (Neat, cm-1): 3018, 2930, 1680, 1587, 1484, 1453,
1319, 1283, 1241, 1210, 1040, 1014, 931, 870, 818, 746,
699; HRMS: m/z [M+H]+ calcd for C24H17BrO2: 417.0485;
found: 417.0485.
1.16 M BBr3 in CH2Cl2.) was added to it and allowed to stir
at room temperature for 3 hours. Then the reaction mixture
was quenched by a saturated NaHCO3 solution and
extracted with EtOAc. Then the organic layer was washed
with saturated brine solution, dried over anhydrous Na2SO4
and the solvent was evaporated under reduced pressure.
Finally, the crude product was purified by column
chromatography (silica gel, hexanes/EtOAc) to get pure 11-
phenyl-11H-benzo[a]fluoren-5-ol 4a (45.1 mg, 94%)
3,8,10-Trimethoxy-11-phenyl-6,6a-dihydro-5H-
benzo[a]fluoren-5-one (3v, Table 3): Greenish yellow
o
solid (yield = 79%); M.P. = 208 - 209 C; Rf value = 0.42
1
(10% EtOAc in hexanes); H NMR (400 MHz, CDCl3):
7.50 (d, J = 2.6 Hz, 1H), 7.38 (s, 5H), 6.84 - 6.76 (m, 2H),
6.69 (d, J = 1.3 Hz, 1H), 6.38 (d, J = 2 Hz, 1H), 4.04 (dd, J
= 14.1, 5.4 Hz, 1H), 3.86 (s, 3H), 3.81 (s, 3H), 3.52 (s, 3H),
3.42 (dd, J = 15.9, 5.4 Hz, 1H), 2.49 (dd, J = 15.9, 14.2 Hz,
1H); 13C NMR (100 MHz, CDCl3): 197.7, 160.1, 158.5,
o
Brown solid; M.P. = 208 - 209 C; Rf value = 0.20 (10%
EtOAc in hexane); 1H NMR (400 MHz, CDCl3): 8.25 (d,
J = 8.5 Hz, 1H), 7.75 (d, J = 7.6 Hz, 1H), 7.62 (d, J = 8.2
Hz, 1H), 7.45 - 7.32 (m, 5H), 7.27 - 7.21 (m, 4H), 7.14 (d, J
155.8, 149.1, 137.5, 137.3, 135.0, 131.8, 131.3, 128.0, 127.3, = 6.5 Hz, 2H), 5.47 (s, 1H), 5.30 (s, 1H); 13C NMR (100
127.1, 121.7, 109.5, 100.8, 98.5, 55.7, 55.5, 55.46, 49.2,
43.3; IR (Neat, cm-1): 2961, 2837, 1675, 1587, 1479, 1309,
1278, 1200, 1143, 1035, 823, 699; HRMS: m/z [M+H]+
calcd for C26H22O4: 399.1591; found: 399.1590.
MHz, CDCl3):  152.2, 149.6, 141.9, 140.9, 139.4, 136.1,
131.2, 128.9, 128.0, 127.1, 127.0, 126.7, 125.9, 124.9,
124.59, 124.55, 122.8, 119.8, 119.4, 101.4, 53.7; IR (Neat,
cm-1): 2930, 1660, 1587, 1417, 1293, 1102, 1014, 864, 751,
663; HRMS: m/z [M+Na]+ calcd for C23H16O: 331.1093;
found: 331.1092.
9-Chloro-11-phenyl-6,6a-dihydro-5H-
indeno[2',1':5,6]naphtho[2,3-d][1,3]dioxol-5-one
(3w,
Table 3): Brown solid (yield = 53%); M.P. = 265 - 266 oC;
Rf value = 0.5 (10% EtOAc in hexanes); 1H NMR (500 MHz, Synthesis of 11-Phenyl-5H-benzo[a]fluoren-5-one (5a):
CDCl3): 8.07 (s, 1H), 7.82 (d, J = 8.6 Hz, 1H), 7.63 - 7.60
(m, 1H), 7.55 - 7.50 (m, 1H), 7.41 - 7.34 (m, 2H), 7.24 (dd,
J = 7.9, 1.9 Hz, 1H), 7.17 - 7.15 (m, 1H), 6.53 (s, 1H), 5.97
(s, 2H), 5.67 (s, 1H), 4.09 (dd, J = 13.9, 5.2 Hz, 1H), 3.44
(dd, J = 16.0, 5.6 Hz, 1H), 2.41 (dd, J = 16, 13.9 Hz, 1H);
13C NMR (100 MHz, CDCl3): 195.6, 151.9, 148.6, 143.7,
Benzo[a]fluorenone 3a (50 mg, 0.162 mmol) was dissolved
in DMF (1 mL) in a round bottom flask. Then DABCO (6.4
mg, 0.032 mmol) was added to the reaction mixture and
o
refluxed at 90 C for 1 hour in an open atmosphere. After
the completion of the reaction water was then added to the
reaction mixture. It was extracted with EtOAc. The organic
140.0, 137.7, 133.8, 132.0, 129.7, 129.5, 128.9, 128.5, 126.8, layer was washed with dil. HCl solution followed by
125.8, 123.6, 121.4, 117.5, 106.9, 106.0, 101.8, 48.9, 42.4;
IR (Neat, cm-1): 2920, 1706, 1670, 1593, 1469, 1262, 1035,
942, 839, 813, 746, 699; HRMS: m/z [M+H]+ calcd for
C24H15ClO3: 387.0782; found: 387.0783.
saturated NaHCO3 solution. Then the organic layer was
washed with saturated brine solution, dried over Na2SO4 and
the solvent was evaporated under reduced pressure. Finally,
the crude product was purified by column chromatography
(silica gel, hexaness/EtOAc) to get pure 11-phenyl-5H-
benzo[a]fluoren-5-one 5a (48 mg, 96%). Dark red solid
(yield = 96% in chemical method); M.P. = 190 - 191 oC; Rf
8,10-Dimethoxy-11-phenyl-6,6a-dihydro-5H-
indeno[2',1':5,6]naphtho[2,3-d][1,3]dioxol-5-one
(3x,
Table 3): Green solid (yield = 98%); M.P. = 199 - 200 oC;
9
This article is protected by copyright. All rights reserved.

10.1002/adsc.201701516
Advanced Synthesis & Catalysis
value = 0.31 (10% EtOAc in hexanes); 1H NMR (500 MHz,
CDCl3): 8.10 (d, J = 8.0 Hz, 1H), 7.60 - 7.55 (m, 2H), 7.55
- 7.51 (m, 2H), 7.49 (d, J = 1.6 Hz, 1H), 7.48 - 7.46 (m, 1H),
7.27 (s, 1H), 7.26 (s, 1H), 7.22 - 7.16 (m, 3H), 6.88 (t, J =
4.1 Hz, 2H); 13C NMR (100 MHz, CDCl3):  186.4, 153.0,
149.0, 146.0, 135.7, 134.3, 133.4, 132.3, 130.8, 130.5, 129.3,
129.2, 128.2, 127.84, 127.78, 127.5, 125.2, 122.4, 122.0,
121.3; IR (Neat, cm-1): 2956, 1644, 1593, 1407, 1262, 1097,
1014, 802, 704; HRMS: m/z [M+H]+ calcd for C23H14O:
307.1117; found: 307.1118.
Uckert, Y. -H. Tak, K. Müllen, H. Bassler, Adv. Mater.
2000, 12, 905.
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Acknowledgements
This work was supported by the grants received from SERB-India.
M. M. is grateful to the University Grants Commission (UGC-BSR),
New Delhi for her fellowship.
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10.1002/adsc.201701516
Advanced Synthesis & Catalysis
FULL PAPER
Triflic acid-Mediated Expedient Synthesis of
Benzo[a]fluorenes and Fluorescent
Benzo[a]fluorenones
Adv. Synth. Catal. Year, Volume, Page – Page
Mou Mandala and Rengarajan Balamurugana*
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