Visible light-mediated, rose Bengal-catalyzed oxidative radical C[sbnd]H cyclization of alkyl 1,1′-biaryl-2-ones: An efficient synthesis of 10-alkylphenanthren-9-ols in water

Article abstract of DOI:10.1016/j.tetlet.2020.151823

A visible light-mediated (blue LED: λ = 455 ± 10 nm), rose bengal-catalyzed intramolecular cycloaromatization reaction of alkyl 1, 1′-biaryl-2-ones for the synthesis of 10-alkylphenanthren-9-ols in water under open air atmosphere at ambient conditions has been developed. Experimental studies demonstrate that the reaction proceeded via a radical pathway. This protocol is applicable to a wide variety of substrates giving expected 10-alkylphenanthren-9-ols in good yields, appropriate for the gram-scale synthesis, atom economy, and eco-friendly as compared to literature reported methodology for the preparation of phenanthrol derivatives. Moreover, to the best of our knowledge, no instance has hitherto been accounted on the visible light-induced transformation of readily available alkyl 1,1′-biaryl-2-ones to 10-alkylphenanthren-9-ols.

Full text of DOI:10.1016/j.tetlet.2020.151823

Journal Pre-proofs
Visible light–mediated, rose Bengal–catalyzed oxidative radical C-H cycliza‐
tion of alkyl 1,1’-biaryl-2-ones: An efficient synthesis of 10-alkylphenanth‐
ren-9-ols in water
Palani Natarajan, Naveen Kumar, Renu Chaudhary, Paloth Venugopalan
PII:
S0040-4039(20)30258-6
DOI:
Reference:
https://doi.org/10.1016/j.tetlet.2020.151823
TETL 151823
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
25 January 2020
6 March 2020
9 March 2020
Please cite this article as: Natarajan, P., Kumar, N., Chaudhary, R., Venugopalan, P., Visible light–mediated, rose
Bengal–catalyzed oxidative radical C-H cyclization of alkyl 1,1’-biaryl-2-ones: An efficient synthesis of 10-
alkylphenanthren-9-ols in water, Tetrahedron Letters (2020), doi: https://doi.org/10.1016/j.tetlet.2020.151823
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Visible light–mediated, rose Bengal–catalyzed oxidative radical CH
cyclization of alkyl 1,1-biaryl-2-ones: An efficient synthesis of 10-
alkylphenanthren-9-ols in water
Palani Natarajan*, Naveen Kumar, Renu Chaudhary, and Paloth Venugopalan
Department of Chemistry & Centre for Advanced Studies in Chemistry, Panjab University,
Chandigarh - 160 014, India.
pnataraj@pu.ac.in
Table of contents
HO
R
O
R
blue LED (5 W,  = 455 nm)
rose bengal (5 mol%)
K2CO3 (1 equiv.)
R'
O , water, 34 h, rt
2
R'
R''
R''
(53-91%)
Abstract
A visible light-mediated (blue LED:  = 45510 nm), rose bengal-catalyzed intramolecular
cycloaromatization reaction of alkyl 1,1-biaryl-2-ones for the synthesis of 10-alkylphenanthren-
9
-ols in water under open air atmosphere at ambient conditions has been developed.
Experimental studies demonstrate that the reaction proceeded via a radical pathway. This
protocol is applicable to a wide variety of substrates giving expected 10-alkylphenanthren-9-ols
in good yields, appropriate for the gram-scale synthesis, atom economy, and eco-friendly as
compared to literature reported methodology for the preparation of phenanthrol derivatives.
Moreover, to the best of our knowledge, no instance has hitherto been accounted on the visible
light-induced transformation of readily available alkyl 1,1-biaryl-2-ones to 10-alkylphenanthren-
9
-ols.
1

Introduction
1
Phenanthrols are important components that are common in many naturally occurring alkaloids
1
and agrochemicals. Besides, the phenanthrols are also utilized in functional materials as
2
biomarkers and smoke sensors. In this context, the development of efficient methods to
synthesize phenanthrols is being effectively sought after.1,2 In 1986, Tantivanich’s group3
showed a nickel(II)-catalyzed method for the conversion of 9-(-bromobenzyl)-9-fluorenols to
4
1
0-arylphenanthren-9-ols at 15 C (Eq 1, Scheme 1). In 2013, Wang et al. uncovered a method
for the synthesis of 10-arylphenanthren-9-ols from 2’-benzoylbiphenyl-2-carbaldehyde as the
carbon unit and N-tosylhydrazones as diazo precursor (Eq 2, Scheme 1). In 2016, Xia et al.5
disclosed a protocol for the synthesis of 10-trifluoroalkylphenanthren-9-ols via cascade
trifluoromethyl radical addition reaction between the aromatic α,β-unsaturated ketones and
6
CF SO Na (Eq 3, Scheme 1). Also in 2016, Ji et al. established a gold-catalyzed methodology
3
2
for the synthesis of 10-substituted phenanthren-9-ols from ynones via oxidation/C-H
7
functionalization reactions (Eq 4, Scheme 1). In 2018, Wang et al. demonstrated a bromide-
induced intramolecular coupling reaction for the synthesis of 10-substituted phenanthren-9-ols
from 1-biphenyl-2-ylethanones as a sole precursor (Eq 5, Scheme 1). Other than in 2018, Zhu’s
8
group reported a rhodium(II)-catalyzed cyclization reaction for the synthesis of 10-substituted
phenanthren-9-ols from biphenyl α-diazoketones at room temperature (Eq 6, Scheme 1). In spite
of some of these protocols with gentle conditions at room temperature, they (Eqs 1-6, Scheme 1)
have downsides, for example, more than stoichiometric amounts of reagents, toxic organic
solvents and reagents, less-practical, low yields, exhaustive work-up procedures, etc. The
development of environmentally friendly and operationally simple approach for the synthesis of
phenanthrols is truly desirable and stays a challenging task for exploration.
Chemical transformations initiated by visible light have pulled in critical consideration in the
9
course of the most recent decade. In continuation of our studies on the visible-light-assisted
1
0
chemical transformations, we demonstrate herein a novel, effective and eco-friendly protocol
for the preparations of 10-alkylphenanthren-9-ols from alkyl 1,1-biaryl-2-ones in the presence of
5
mol% of rose bengal as a catalyst, molecular oxygen as an oxidant, water as a solvent, K CO
2 3
as a base and blue LED (h = 45510 nm) as irradiation source at room temperature (Scheme 2).
2

A plausible mechanism is proposed for the reaction (vide infra). In addition to the use of rose
bengal as an organic photocatalyst, this methodology employs oxygen and water as spotless,
abundant, and sustainable chemical substances.
Br
Ar
OH
Ar
HO
Ni(acac)2
o
i-PrMgBr, -15 C
Eq 1
Ar
i. TsNHNH2
Ar
OH
O
toluene
o
R
7
0 C
R
Eq 2
R
ii. NaOCH3
O
toluene
R
H
o
70 C
F3C
OH
UV-light, BP
CF SO Na
O
3
2
Eq 3
R
CH CN, rt
R
R
3
R
Ar
O
Ar
OH
O
3
Ph PAuNTf2
N-oxide
Eq 4
Eq 5
Eq 6
R
R
C H F, rt
6 5
R
R
R
R
COOR
O
NBS, TBHP
ROOC
OH
OH
NaH PO4
2
o
THF, 66 C
R
R
R
CO(O)R
O
N2
R(O)OC
Rh (CH COO)
4
2
3
R
CH2Cl2, rt
Scheme 1. Literature reported methods of synthesis of 10-substituted phenanthren-9-ols.
3

Cl
O
Cl
Cl
Cl
HO
R
O
R
blue LED (5 W,  = 455 nm)
rose bengal (RB, 5 mol%)
K2CO3 (1 equiv.)
COONa
I
I
R'
NaO
O
I
I
O , water, 34 h, rt
2
R'
R''
R''
Rose Bengal (RB)
Scheme 2. A visible light-assisted intramolecular cyclization reaction of alkyl 1,1-biaryl-2-ones
to 10-alkylphenanthren-9-ols in water at ambient conditions reported in this work.
Results and Discussion
We started this study utilizing commercially accessible 1-([1,1'-biphenyl]-2-yl)propan-1-one (1a)
as a model substrate to streamline the reaction conditions, and the outcomes are listed in Table 1.
For the most part, the model reaction was done within the presence of a photosensitizer, water,
air under the irradiation of a 5 W blue LED ( = 45510 nm). First, a variety of photosensitizers
including porphyrin, rose bengal, methylene blue, fluorescein, eosin and rhodamine were
explored in conjunction with K CO (1 equiv.,) as the base (Table 1 and Entries 1-7). Some of
2
3
the photosensitizers afforded desired 10-methylphenanthren-9-ol (2a) with a marginal yield, yet
rose bengal gave the highest yield, i.e., 66% (Table 1 and Entry 2). The product 2a was
characterized by NMR and mass spectral analysis (Electronic Supporting Information, ESI). The
effect of amount of rose bengal on the product yield was investigated. The reaction time was
shortened (Table 1 and Entries 8-9), when quantity of catalyst was increased from 3.0 mol% to
5
.0 mol% or 10.0 mol%. Nevertheless, only a trace amount of 2a was detected in the lack of rose
bengal (Table 1 and Entry 10). Then, a series of bases were screened (Table 1 and Entries 11-
1
8
4), but the outcomes they gave were inferior compared to those by K CO (Table 1 and Entry
2 3
). Further studies demonstrated that decreasing or increasing the amount of K CO brought
2
3
about a reduced yield of 2a (Table 1 and Entries 15-17). Next, we investigated the impact of
atmosphere on the reaction. Changing the response environment from outdoors to N2,
substandard yields of 2a were obtained (Table 1 and Entry 18). Finally, the control experiments
uncovered that photosensitizer, light, base and oxygen was essential for this reaction to proceed
(Table 1 and Entries 10, 15, 18-19). Thus, the optimized conditions for the synthesis of 10-
alkylphenanthren-9-ol from 1-([1,1'-biphenyl]-2-yl)propan-1-one were 5.0 mol% of rose bengal,
blue LED lights, K CO (1.0 equiv.,), water and molecular oxygen at ambient conditions for
2
3
about 34 h.
4

Table 1. Selected results of screening the optimal conditions for the visible light-assisted
synthesis of 10-alkylphenanthren-9-ols from alkyl 1,1-biaryl-2-ones
O
HO
CH3
blue LED (5 W,  = 455 nm)
dye, base
water, O , rt
2
1a
2a
Entrya Catalyst (mol%)b
Base (equiv.)c Time (h)
Yield (%)
30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
porphyrin (3)
K CO (1)
48
48
48
48
48
48
48
34
31
48
34
34
34
34
34
34
34
34
34
34
30
36
2
3
rose bengal (3)
K CO (1)
66
2
3
methylene blue (3) K CO (1)
46
2
3
fluorescein (3)
rhodamine B (3)
eosin Y (3)
K CO (1)
36
2
3
K CO (1)
trace
38
NRd
2
3
K CO (1)
2
3
eosin B (3)
K CO (1)
2
3
rose bengal (5)
rose bengal (10)
Nil
K CO (1)
2 3
84
K CO (1)
88
2
3
0
1
2
3
4
5
6
7
8
9
0
1
2
K CO (1)
tracee
<5%
NR
NR
41
2
3
rose bengal (5)
rose bengal (5)
rose bengal (5)
rose bengal (5)
rose bengal (5)
rose bengal (5)
rose bengal (5)
rose bengal (5)
rose bengal (5)
rose bengal (5)
rose bengal (5)
rose bengal (5)
NaHCO (1)
3
DBU (1)
DABCO (1)
Cs CO
2
3
K CO (0)
NR
51
2
3
K CO (0.5)
2
3
K CO (1.5)
78
21f
traceg
86h
87i
2
3
K CO (1)
2
3
K CO (1)
2
3
K CO (1)
2
3
K CO (1)
2
3
K CO (1)
76j
2
3
a
Unless stated otherwise all entries were performed in a vial equipped with 1-([1,1'-biphenyl]-
-yl)propan-1-one (1a, 0.3 mmol), K CO (0.3 mmol), 5.0 mol% of rose bengal and water (1
2
2
3
mL), and were irradiated using 5 W blue LEDs for 34 h under an open air atmosphere at room
b
c
temperature. Commercially available high purity dyes were purchased and utilized as such.
d
Commercially available analytical grade substances were purchased and utilized as such. NR
no reaction. Standard conditions without catalyst. Reaction performed under N atmosphere.
Reaction was carried in dark. Reaction performed using oxygen balloon instead of (open) air
atmosphere. Reaction was performed using DMSO as a solvent. Reaction was performed using
e
f
g
2
h
i
j
CH CN as a solvent.
3
5

To investigate the substrate extent of this methodology (Scheme 2), the optimized reaction
conditions (Table 1) were applied to a series of alkyl 1,1-biaryl-2-ones. First, we studied the
effect of the substituents in the aromatic ring with ketone functionality and the results are
summarized in Table 2. Notice that the alkyl 1,1-biaryl-2-ones with either electron-giving (CH3
and OCH ) or electron-withdrawing (F and Cl) substituents on their phenyl ring with a ketone
3
group were efficiently changed over to the desired products in good yield (2b-2e). Then, the
impacts of substituents at the para-position of the aromatic ring without the ketone group were
analyzed. Clearly, both electron-rich and electron-insufficient substrates experienced cyclization
promptly producing the desired products 2f-2j in good yield (Table 2). However, meta-OCH3
substituted alkyl 1,1-biaryl-2-one, such as 1-(3'-methoxy-[1,1'-biphenyl]-2-yl)propan-1-one,
gave two unseparated isomers in a 1.7:1 proportion and 85% overall yield (2j/2j′). The substrate
scope was additionally stretched out to a series of ketones with longer alkyl chains (R = propane,
butane, phenpropane), which were likewise well-endured and afforded the corresponding
products (2l-2n) in significant quantities (Table 2). Unfortunately, no desired products were
detected for the reactions with 1-([1,1'-biphenyl]-2-yl)-2-phenylethanone (1k2k) as a
precursor, most likely due to over oxidation of benzylic radical as well as very high acidity of -
1
1
CH - group of phenylethanone unit.
2
Table 2. Substrate scope for the transformation of alkyl 1,1-biaryl-2-ones into 10-
alkylphenanthren-9-ols
O
R
blue LED (5 W,  = 455 nm)
HO
R
rose bengal (5 mol%)
K CO (1 equiv.)
R'
2
3
O , water, 34 h, rt
2
R'
R''
R''
1
2
6

H C
3
CH3
CH3
H CO
3
CH3
OH
OH
OH
2a, 84%
2b, 80%
2c, 53%
CH3
Cl
CH3
CH3
F
CH3
OH
OH
OH
2d, 88%
2e, 89%
2f, 86%
OCH3
Cl
OCH3
CH3
H CO
3
CH3
CH3
OH
g, 91%
OH
2i, 87%
OH
2h, 89%
2
OCH3
OCH3
+
CH3
C H
6
5
CH3
OH
OH
OH
2j, 54%
2j', 31%
2k, <5%
C H
6
5
OH
OH
OH
2l, 82%
2m, 86%
2n, 84%
Unless stated otherwise all reactions were performed in crimp vials equipped with 1 (0.5 mmol),
K CO (0.5 mmol), and rose bengal (5.0 mol%) in water (3-4 mL) was irradiated using a 5 W
2
3
blue LEDs under an open air/O atmosphere at room temperature for 34 h.
2
To further illustrate the preparative utility of established method, a scale-up synthesis of 2d was
conducted (Scheme 3). A gram-scale reaction of 1d (10.0 mmol, Scheme 3) was done under the
optimized reaction conditions (Table 1), and product 2d was obtained in 85% isolated yield,
which showed the efficacy of the protocol delivered.
7

O
blue LED
HO
CH3
rose bengal (5 mol%)
K CO (1 equiv.)
2
3
Cl
Cl
O , water, 34 h, rt
2
1d
(85%)
2d
Scheme 3. A scale-up synthesis of 2d from 1d using optimized reaction conditions.
To investigate the possible mechanism of this reaction (Scheme 2), a series of control
experiments were performed (Scheme 4). When 1a was stirred in the dark, there was no reaction,
which indicates that the visible light is necessary for the reaction (Table 1 and Entry 19). In
addition, poor yield of 2a was detected when the model reaction was led under an inert
atmosphere (Table 1 and Entry 18), which shows that air is required. Next, when radical inhibitor
TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) was added to the system, the reaction was
suppressed, and only 18% of product 2a was isolated, suggesting that the reaction continue
9
through a radical pathway (Scheme 4, Eq 7). Then again, when 2,6-di-t-butyl-p-cresol (BHT)
was added to the reaction mixture under the standard conditions, the oxidative products BHT-
OOH and BHT-OH were obtained in addition to 2a (16%, Scheme 4, Eq 8). The outcome
1
12
suggests that singlet oxygen ( O ) was formed during the reaction. This was additionally
2
1
affirmed by including O scavenger DABCO, and under these conditions, the reaction was
2
practically inhibited (Scheme 4, Eq 9).9,12,13
8

TEMPO (2 equiv.)
O
blue LED
H C
3
OH
rose bengal (5 mol%)
K CO (1 equiv.)
2
3
Eq 7
O , water, 34 h, rt
2
1a
2a, 18%
BHT (2 equiv.)
O
blue LED
H C
3
OH
O
O
rose bengal (5 mol%)
K CO (1 equiv.)
tBu
tBu
tBu
tBu
2
3
+
+
Eq 8
O , water, 34 h, rt
2
H C
OH
H3C OOH
18%
3
1a
2a, 16%
57%
DABCO (3 equiv.)
O
blue LED
H C
3
OH
rose bengal (5 mol%)
K CO (1 equiv.)
2
3
Eq 9
O , water, 34 h, rt
2
1a
2a, trace
Scheme 4. Control experiments
In view of the experimental results and literature precedent, we propose a reaction mechanism
for the formation of 10-alkylphenanthren-9-ols from alkyl 1,1-biaryl-2-ones (Scheme 5). Upon
illumination by blue LEDs, rose bengal (RB) excites to its excited state species, i.e., RB*. The
energized RB* then interacts with molecular oxygen and produces singlet oxygen via an energy
1
4
transfer pathway. The singlet oxygen quickly reacts with enol form (A) of alkyl 1,1-biaryl-2-
ones and creates the α-carbon radical B and hydroperoxide radical. Afterwards, the radical
intramolecularly attacks the ortho-position of arene unit to produce the intermediate C. At that
point, enolization of the ketone is completes to afford the intermediate D. Subsequently,
hydroperoxide radical abstracts a hydrogen radical to the final product 2 with the formation of
hydrogen peroxide as a byproduct (Scheme 5).
9

3O
O
R
*
RB
2
1
base
enolisation
1O2
RB
blue LED
O
R
HO
R
B
A
O H R
H
HO2
HO
R
HO
R
H
C
D
2
H O
2
2
Scheme 5. A plausible mechanism for the formation of 10-alkylphenanthren-9-ols from alkyl
,1-biaryl-2-ones in the presence of rose bengal (RB) and visible-light.
1
As mentioned in the introduction, there were some methodologies3-8 reported for the synthesis of
0-alkylphenanthren-9-ols, however, strategy reported here is based on the use of alkyl 1,1-
1
biaryl-2-ones as a sole starting materials obtained readily by a reaction between [1,1'-biaryl]-2-
carbaldehyde and alkylmagnesium chloride followed by oxidation. In addition, this protocol
meets a considerable lot of the necessities of green chemistry as: i) the reaction used O from air
2
as the oxidant and water as a solvent; ii) it is atom-economical and iii) organic dye is used as a
catalyst in the reaction. We believe that the present methodology may find a brilliant future
especially in the pharmaceutical companies where the needs for final products have to be
absolutely free of transition metals and volatile organic solvents.
1
0

Conclusion
In conclusion, we have developed a novel, an atom-economical and naturally affable method for
the conversion of alkyl 1,1-biaryl-2-ones to the corresponding 10-alkylphenanthren-9-ols in
good yield. The transformation continues in water utilizing rose bengal as an organic catalyst.
Further use of the strategy to construct other polycyclic aromatic compounds is at present under
investigation and will be uncovered at the appropriate time.
Acknowledgments
The authors gratefully acknowledge the financial support from Council of Industrial Scientific
Research (CSIR), New Delhi, India, through extra mutual research grant with a project number
0
2(0380)/19/EMR-II. In addition, we thank the anonymous reviewers for their many insightful
comments and suggestions.
Electronic supplementary information
Electronic supplementary information (general aspects, procedure and experimental
characterization data) associated with this article can be found in the online version at www.
sciencedirect.com
References
1
. (a) J.-M. Fu, M. J. Sharp and V. Snieckus, Tetrahedron Lett., 1988, 29, 5459; (b) J.-M. Fu and
V. Snieckus, Can. J. Chem., 2000, 78, 905; (c) X. Cai, S. Brown, P. Hodson and V. Snieckus,
Can. J. Chem., 2004, 82, 195; (d) S. Lin and T. You, Tetrahedron Lett., 2008, 64, 9906; (e)
Y. B. Zhao, B. Mariampillai, D. A. Candito, B. Laleu, M. Li and M. Lautens, Angew. Chem.,
2
009, 121, 1881; Angew. Chem., Int. Ed., 2009, 48, 1849; (f) R. Mitsuhashi, Y. Suzuki, Y.
Yamanari, H. Mitamura, T. Kambe, N. Ikeda, H. Okamoto, A. Fujiwara, M. Yamaji, N.
Kawasaki, Y. Maniwa and Y. Kubozono, Nature, 2010, 464, 76; (g) M. G. Banwell, A.
Bezos, C. Burns, I. Kruszelnicki, C. R. Parish, S. Su and M. O. Sydnes, Bioorg. Med. Chem.
Lett., 2006, 16, 181; (h) A. Frstner, M. M. Domostoj and B. Scheiper, J. Am. Chem. Soc.,
2
006, 128, 8087; (i) K. Okano, H. Fujiwara, T. Noji, T. Fukuyama and H. Tokuyama,
Angew. Chem., 2010, 122, 6061; Angew. Chem., Int. Ed., 2010, 49, 5925; (j) D. Mal, A. K.
Jana, P. Mitra and K. Ghosh, J. Org. Chem., 2011, 76, 3392.
2
. (a) E. Elovaara, V. Vaananen and J. Mikkola, Arch Toxicol., 2003, 77, 183; (b) S. S. Hecht, M.
Chen, A. Yoder, J. Jensen, D. Hatsukami, C. Le, and S. G. Carmella, Cancer Epidemiol
1
1

Biomarkers Prev, 2005, 14, 2969; (c) S. S. Hecht, S. G. Carmella, A. Yoder, M. Chen, Z.-ze
Li, C. Le, R. Dayton, J. Jensen, and D. K. Hatsukami, Cancer Epidemiol Biomarkers Prev,
2
006, 15, 1805; (d) S. Dey and S. O. Bajaj, Synth. Commun. 2018, 48, 1.
3
4
. A. Tantivanich and D. Supatimusro, Tetrahedron Lett., 1986, 27, 5301.
. Y. Xia, P. Qu, Z. Liu, R. Ge, Q. Xiao, Y. Zhang, and J. Wang, Angew. Chem., Int. Ed., 2013,
5
2, 2543.
5
6
7
8
9
. B. Li, D. Fan, C. Yang and W. Xia, Org. Biomol. Chem., 2016, 14, 5293.
. K. Ji, F. Yang, S. Gao, J. Tang, and J. Gao, Chem. Eur. J., 2016, 22, 10225.
. Y.-T. Jiang, Z.-Z. Yu, Y.-K. Zhang, and B. Wang, Org. Lett., 2018, 20, 3728.
. K.-H. Chen, Y.-J. Chiang and J.-L. Zhu, Org. Biomol. Chem., 2018, 16, 8353.
. (a) Q.-Q. Zhou, Y.-Q. Zou, L.-Q.Lu and W.-J. Xiao, Angew. Chem., Int. Ed., 2019, 58, 1586;
(b) F. S. Kalthoff, M. J. James, M. Teders, L. Pitzer and F. Glorius, Chem. Soc. Rev., 2018,
4
4
7, 7190; (c) X. Zhang, K. P. Rakesh, L. Ravindar and H.-L. Qin, Green Chem., 2018, 20,
790; (d) C. Bian, A. K. Singh, L. Niu, H. Yi, and A. Lei, Asian J. Org. Chem., 2017, 6, 386;
(e) J. Xie, H. Jinb and A. S. K. Hashmi, Chem. Soc. Rev., 2017, 46, 5193; (f) K. Teegardin, J.
I. Day, J. Chan and J. Weaver, Org. Process Res. Dev., 2016, 20, 1156; (g) D. Ravelli, M.
Fagnoni and A. Albini, Chem. Soc. Rev., 2013, 42, 97.
1
0.(a) P. Natarajan, Manjeet, N. Kumar, S. Devi and K. Mer, Tetrahedron Lett., 2017, 58, 658;
(b) P. Natarajan, Manjeet, Muskan, N. K. Brar and J. J. Kaur, Org. Chem. Front., 2018, 5,
1
527; (c) D. Chuskit, R. Chaudhary, P. Venugopalan, B. König and P. Natarajan, Org. Chem.
Front., 2018, 5, 3553. (d) P. Natarajan, D. Chuskit and Priya, Green Chem., 2019, 21, 4406.
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1. N. A. Romero and D. A. Nicewicz, Chem. Rev., 2016, 116, 10075.
2. (a) Q. Shi, P. Li, X. Zhu, L. Wang, Green Chem., 2016, 18, 4916; (b) C.-H. Tung, L.-Z. Wu,
L.-P. Zhang, B. Chen, Acc. Chem. Res., 2003, 36, 39; (c) D. Ravelli, M. Fagnoni, A. Albini,
Chem. Soc. Rev., 2013, 42, 97; (d) A. A. Ghogare, A. Greer, Chem. Rev., 2016, 116, 9994.
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3. DABCO and related amines are well-known quenchers of singlet oxygen and effective
antioxidants. Basically, they are restricting the singlet oxygen generation. See: (a) P.
Zaltzman-Nirenberg and S. Udenfriend J. Am. Chem. Soc., 1968, 90, 6527; (b) M.
Hajimohammadi, A. V. Sereshk, C. Schwarzinger and G. Knör, Antioxidants, 2018, 7, 194.
4. (a) X.-F. Wang, S.-S. Yu, C. Wang, D. Xue and J. Xiao, Org. Biomol. Chem., 2016, 14,
7
028; (b) J.-G. Sun, H. Yang, P. Li and B. Zhang, Org. Lett., 2016, 18, 5114.
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Declaration of interests
☒
The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐
The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests:
Highlights
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Prepared 10-alkylphenanthren-9-ols from alkyl 1,1-biaryl-2-ones
Employs oxygen and water as sustainable chemical substances
Appropriate for the gram-scale synthesis
Mechanism involves single electron transfer
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