Regiodivergent Aromatic Electrophilic Substitution Using Nitrosoarenes in Hexafluoroisopropanol: A Gateway for Diarylamines and p-Iminoquinones Synthesis

Article abstract of DOI:10.1002/adsc.201900788

A metal-free aromatic electrophilic substitution reaction using nitrosoarenes as the electrophile in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) is reported. HFIP activates nitrosoarene towards the electrophilic C?H amination followed by a concomitant N?O bo

Full text of DOI:10.1002/adsc.201900788

Title: Regiodivergent Aromatic Electrophilic Substitution Using
Nitrosoarenes in Hexafluoroisopropanol: A Gateway for
Diarylamines and p-Iminoquinones Synthesis
Authors: Indranil Chatterjee, Suman Pradhan, Sourav Roy, and
Soumen Ghosh
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201900788
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10.1002/adsc.201900788
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Regiodivergent Aromatic Electrophilic Substitution Using
Nitrosoarenes in Hexafluoroisopropanol: A Gateway for
Diarylamines and p-Iminoquinones Synthesis
Suman Pradhan,a Sourav Roy,a Soumen Ghosh,a and Indranil Chatterjeea*
a
Department of Chemistry, Indian Institute of Technology Ropar, Nangal Road, Rupnagar, Punjab-140001, India
E-mail: indranil.chatterjee@iitrpr.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######.
Abstract. A metal-free aromatic electrophilic substitution p-iminoquinones following a unique mechanistic rationale
reaction using nitrosoarenes as the electrophile in of two consecutive [2,3] sigmatropic rearrangement in
1,1,1,3,3,3-hexafluoroisopropanol (HFIP) is reported. HFIP nitroso-chemistry.
activates nitrosoarene towards the electrophilic C–H
amination followed by a concomitant N–O bond cleavage to
deliver diarylamines without requiring any extra reagent or
further treatment. The dual electrophilic nature of
nitrosoarene permits a switchover of selectivity to C–H
oxygenation furnishing dearomatized
Keywords: Aromatic electrophilic substitution;
hexafluoroisopropanol; nitrosoarenes; C–H amination; C–H
oxygenation
challenging.[11] If possible, HFIP will activate the
Introduction
heteroatoms
of
nitroso-functionality
and
consequently provide an avenue for regiochemically
divergent electrophilic C–N bond formation along
with the construction of C–O bond. The dual
electrophilic nature of nitroso-functionality and
unique features of HFIP have prompted us to devise a
mild, regioselective and straightforward method en
route to various diarylamines via C–H amination and
p-iminoquinones via C–H oxygenation of arenes
(Scheme 1, bottom, this work). Both the diarylamines
and iminoquinones are ubiquitous motifs in several
natural products such as marine-alkaloids,
pharmaceuticals, agrochemicals and materials.[12],[13]
While diarylamines are synthesized by transition-
metal catalyzed C–N coupling[14] or radical-based
direct C–H aminations including photoredox
Functionalization of native C–H bonds represents one
of the central goals in advanced organic synthesis. In
this regard, the Lewis acid-mediated or catalyzed
Friedel-Crafts
(FC)
reactions
constitute
a
conventional route to deliver industrially relevant
functionalized arenes with structural diversity via C–
C bond formation.[1] Recently, in search of a milder,
efficient and benign activator, fluorinated alcohol
1,1,1,3,3,3-hexafluoro-isopropanol
(HFIP)
has
emerged as a potential alternative to promote intra-
and intermolecular FC acylation as well as FC
alkylation with large set of electrophiles, such as acid
chlorides,[2]
alcohols/halides,[4]
allylic
epoxides,[5]
alcohols,[3]
and
benzyl
even
cyclopropane[6] via ring-opening (Scheme 1, left side). catalysis,[15] iminoquinones are usually obtained via
The exotic reactivity of HFIP has been ascribed to its
mild acidity, low nucleophilicity, the high dielectric
constant for cation stabilization and moreover, strong
hydrogen-bond donor ability.[7] When the HFIP is
studied significantly for forging C–C bonds (Scheme
1, top left), the HFIP-mediated C–X (X = N or O)
bond formation remains rarely explored except recent
reports on C–H amination of free anilines using
azodicarboxylic esters as electrophiles and C–H
oxygenation of arenes using methanesulfonic
peroxyanhydride (Scheme 1, top right).[8],[9], [10]
oxidation of aniline derivatives.[16] However, this
metal-free approach is portrayed by: (1) direct
synthesis of diarylamines without requiring additional
reagent or treatment for N–O bond cleavage (step-
economic); (2) rarely explored HFIP-activated double
C–H oxidation of arene via two consecutive [2,3]
sigmatropic rearrangement in nitroso-chemistry for
the direct synthesis of p-iminoquinones; (3) switching
of regioselectivity by altering reactants and
imperative role of HFIP in the activation of
nitrosoarene (sometimes, the catalytic amount of
TfOH is needed for p-iminoquinones); (4) easy
recovery via rotary evaporator and reuse of HFIP
solvent.
In this line, developing
a
C–H bond
functionalization using nitrosoarenes as an
electrophile in HFIP (a strong hydrogen-bond donor
solvent as well as a mild Brønsted acid) will be
highly
fascinating,
yet
regiochemically
1
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10.1002/adsc.201900788
Advanced Synthesis & Catalysis
remained detrimental to the overall reactivity
(Table 1, entries 7–8). However, monitoring the
concentration (0.75 to 0.15 M) resulted in a
drastic improvement of the reactivity, delivering
the desired diarylamine product (3a) in 47%
isolated yield and good selectivity (10:1) (Table
1, entry 9
).[17] Excess of 1a is necessary to achieve
acceptable yield. Nevertheless, the presence of p-
iminoquinone (4a) in a tiny amount in the
reaction mixture encouraged us to develop an
alternative set of conditions for its exclusive
formation. Since the Brønsted acidity of HFIP
promotes the C–H oxygenation, we envisioned that
an acid additive might selectively protonate N-
atom of nitrosobenzene for the C–H oxygenation.
Indeed, this switchover of selectivity was feasible
in the presence of catalytic amount of TfOH (20
mol%) and by the reversal of stoichiometry of
1,3,5-trimethoxybenzene (1a, 1.0 equiv) and
nitrosobenzene (2a, 3.0 equiv) affording p-
iminoquinone (4a) as sole product (47%) (Table
1, entry 12).[18] All the components and
parameters, such as the utilization of HFIP, the
stoichiometry of reactants and concentration,
remain crucial in achieving the desired reactivity
and selectivity. Notably, this method is
distinguished by the imperative role of HFIP in
the activation of nitrosoarene through H-bonding
and furthermore, in situ N–O bond cleavage
without requiring an additional reagent to deliver
direct C–H amination product. Additionally, later,
the C–H oxygenation followed by the shifting of
nitrogen counterpart to provide p-iminoquinone is
excelled by the presence of HFIP.
Scheme 1. HFIP-mediated aromatic electrophilic
substitution reactions.
Table 1. Optimization study and reaction set up.
Results and Discussion
We initiated our investigation by reacting 1,3,5-
trimethoxybenzene (1a, 3.0 equiv) as the model
substrate with nitrosobenzene (2a, 1.0 equiv) as
the electrophilic reagent in a series of solvents
(0.75 M) at 55 °C (Table 1, entries 1-6). While
most of the solvents provided a little or no
conversion, HFIP surprisingly, promoted the
reaction significantly delivering diarylamine (3a
)
as the major product via C–H amination along
with the additional formation of p-iminoquinone
(
4a) as minor product via C–H oxygenation. We
attribute this regioselectivity due to the dual
nature of HFIP. HFIP activates nitrosobenzene
through H-bonding with more electronegative O-
atom delivering 3a via C–H amination, whereas
mild Brønsted acidity of HFIP results in the
protonation of the more basic N-atom of
nitrosobenzene that leads to the attack of the arene
[a]
Reaction condition A (entry 1-9): 1a (3.0 equiv, 0.45
mmol) and 2a (1.0 equiv, 0.15 mmol) stirred in solvent;
condition B (entry 10-12): 1a (1.0 equiv, 0.15 mmol) and
2a (3.0 equiv, 0.45 mmol) stirred in HFIP in the presence
of TfOH (0-20 mol%); yield determined by 1H NMR using
CH2Br2 as internal standard; isolated yields in parentheses.
at the nitroso O-atom for the C–H oxygenation.
Guided by the notion to suppress the side
reactions of reactive nitrosobeneze, the lowering
of reaction temperature (55 °C to 25 °C)
2
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10.1002/adsc.201900788
Advanced Synthesis & Catalysis
[b] 1 mmol scale reaction provided 52% isolated yield of 3a. employed as a substrate, the amination products
[c]
[d]
15 mol% TfOH as additive.
20 mol% TfOH as
(even more electron-rich) preceded further reaction,
delivering N-arylamine functionalized p-
[e]
additive.
yield of 4a.
1 mmol scale reaction provided 40% isolated
iminoquinone derivatives (Scheme 2, 6a–6c). C–H
amination at 4-position of α-naphthol led to the
formation of p-iminoquinones 6a’–6c’. With phenol
and thioanisole, we obtained colored complex
reaction mixture without detecting any isolable
desired product. To our delight, 2,6-di-tert-
butylphenol afforded p-iminoquinone 7 in 61% yield.
When electron-rich heterocyclic compounds indole
and benzothiophene were tested, no desired product
was detected instead a colored complex reaction
mixture was obtained.
Contrastingly, the presence of TfOH (20 mol%)
and switching the stoichiometry of reactants at a
slightly reduced temperature in HFIP, p-
iminoquinones were obtained in complete
regioselectivity via C–H oxygenation (under
condition B) (Scheme 2, 4a–4i). The nitrosoarenes
decorated with electron-withdrawing groups worked
well yielding corresponding p-iminoquinones in
excellent yields, such as furnishing 4d and 4i in 72%
and 74% respectively.
With these two different sets of optimized
conditions, we set out to explore the scope and
limitations of C–H amination as well as C–H
oxygenation protocols with several arene partners and
variety of nitrosoarenes decorated with diverse
functionality, as summarized in Scheme 2. Initially,
various nitrosoarenes with different functional groups
such as halide, (trifluoro)methyl, nitrile, ester (2a–2h)
reacted well with 1,3,5-trimethoxy benzene (1a) to
afford corresponding diarylamines (3a–3h) in 40-
55% yields (under condition A), accompanied by the
formation of p-iminoquinones as side products, albeit
in lower amounts. Nitrosoarenes featuring electron-
withdrawing nitrile and ester groups delivered the
corresponding diarylamines (3g and 3h) almost
exclusively. However, to our delight, the reaction of
β-naphthol derivatives with nitrosoarenes resulted in
various aminonaphthols (5a–5e) as sole products in
good yields. Interestingly, while α-naphthol was
Scheme 2. HFIP-assisted C–H amination and C–H oxygenation of arenes with nitrosoarenes.
o
Condition A for diarylamine synthesis: 1a or β-naphthol (0.45-0.75 mmol) and 2a–h (0.15 mmol) HFIP (0.15 M), 55 C,
40 h (10 h for β-naphthol); condition B for p-iminoquinone synthesis: 1a (0.15 mmol) and 2a–i (0.45 mmol), TfOH (20
mol%), HFIP (0.75 M), 40 oC, 12 h; isolated yields unless otherwise mentioned. [a] using condition B. [b] using α-naphthol
(0.15 mmol) and nitrosoarene (0.30 mmol) for 10 h. cm = complex mixture. X-ray structure of 3h and 4b. [19]
3
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10.1002/adsc.201900788
Advanced Synthesis & Catalysis
Aside from 1,3,5-trimethoxybenzene and naphthols, position. However, moving to tri-substituted arenes
other electron-rich alkylated arenes remained
competent for the synthesis of p-iminoquinones via
C–H oxygenation with exquisite selectivity (Scheme
3). Interestingly, the reaction could be performed in
the absence of TfOH, since its utilization was found
for the formation of the products 13–14, the
regioselectivity is found to be controlled by the steric
factor irrespective of substitution at para-position.
Interestingly, 8a was formed together with 14 from 2-
methoxy-1,4-dimethylbenzene
via
the
C–H
to be deleterious for this set of arenes. We reason that, oxygenation at the para-position of the OMe group
it is due to the Brønsted acidity of HFIP that followed by the shifting of nitrogen counterpart
protonates N-atom of nitrosoarene for the C–H and release of methanol. While o-xylene and m-
oxygenation. It is notable to mention that according
to our mechanistic rationale, two equivalents of
nitrosoarene were consumed to construct one
equivalent of p-iminoquinone via double C–H bond
functionalization, thus obtaining the product in 50%
yield (based on nitrosoarene) would reveal for
achieving the highest efficiency. Taking it into
account, at first, p-xylene was tested for the
formation of the iminoquinone 8a and 8b as sole
regioisomer. Furthermore, the unsymmetrical di-
substituted arenes appeared to be viable substrates
delivering product 9a–9b and 12 as regioisomeric
mixtures in moderate to good yields. The exclusive
regiochemical outcome was obtained for p-
iminoquinone 10a–10b, and 11. In this regard, the
site selectivity of oxygenation event was dictated by
the more electron-donating substituent to its ortho-
xylene remained unreacted under this condition, to
our delight, 1,2,4-trimethoxybenzene and 1,4-
dimethoxybenzene delivered the identical p-
iminoquinone 15. It was surprising to find this
different reactivity between 1,2,4-trimethoxybenzene
and 1,3,5-trimethoxybenzene. We think it was the
nucleophilicity of the reactive carbons of the
substrates as mentioned above that was highly
influenced by the characteristic of HFIP (H-bonding
vs.
Brønsted
acidity).
Importantly,
1,3-
dimethoxybenzene provides p-iminoquinone 4a, and
even anisole were converted to corresponding p-
iminoquinone 16 without detecting any diarylamine
formation. Interestingly, as such, this external
oxidant-free protocol offers the first example of
metal-free dearomatization of arenes via double C–H
bond
functionalization.
4
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10.1002/adsc.201900788
Advanced Synthesis & Catalysis
Scheme 3. C–H oxygenation for the synthesis of p-iminoquinone.
o
Reaction conducted on 0.15 mmol scale using 1.0 equiv of nitrosoarene, 5.0 equiv of arene in HFIP (0.75 M) at 55 C, 40
h. isolated yields unless otherwise mentioned. (maximum expected yield = 50%). rr = regioisomeric ratio determined by
1H NMR analysis of crude reaction mixture.[a] Performed at 80 oC.
Additionally, the synthetic potential of this
methodology was demonstrated by converting p-
iminoquinone to p-aminophenol by the reduction
with Na2S2O4 in good yield (Scheme 4, top). As proof
of practicability, the nitrosoarenes were generated in
situ from anilines and transformed into the desired
amination as well as p-iminoquinone products via a
one-pot sequential operation (Scheme 4, bottom).
5
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10.1002/adsc.201900788
Advanced Synthesis & Catalysis
generates intermediate 23 as detected in MS and
GCMS analysis.[21] The release of hexafluoroacetone
(not able to detect) from the intermediate 23 results
the formation of diarylamine. However, the
involvement of arylhydroxylamine formed via auto
reduction-oxidation of nitrosoarenes cannot be ruled
out in the reduction process through the intermediate
22.
Scheme 4. Synthetic application of the developed
methodology: Reduction of p-iminoquinones (top); one-pot
sequential synthesis of diarylamines and p-iminoquinones
(bottom).
Based on the experimental evidence and previous
reports, [2,4,8a] we propose tentative mechanisms for
the formation of both diarylamine and p-
iminoquinone. At first, the O-atom of nitrosobenzene
is activated by the H-bonding interaction with HFIP
1
as corroborated by recording H NMR spectra of
nitrosobenzene in the presence of variable amounts of
HFIP exhibiting an apparent shift of O–H signal of
HFIP and a new set of aromatic signals (Scheme 5a).
We believe that two or higher number of HFIP
molecules engage in activation of nitroso moiety
through H-bonding with O-atom. We presume the
formation of 9- or higher-membered ring system 19
involving o-hydrogen of nitrosobenzene (the identical
structure was previously proposed by Yamamoto and
his group).[20] This solvation cluster breaks the
symmetry of nitrosobenzene (through locked
conformation) and displays chemically distinguished
two sets of aromatic protons (o, m and p) of
nitrosobenzene. The aforementioned interpretation
supports the shifting of aromatic protons towards
upfield in 1H NMR.
For the diarylamine synthesis, a nucleophilic attack
by the highly electron-rich arenes (1,3,5-
trimethoxybenzene and naphthol derivatives) onto the
N-center of activated nitrosoarene generates
hydroxylamine intermediate 20 (Scheme 5b), which
is further activated by HFIP making the N–O bond
cleavage facile to deliver iminoquinone intermediate
21. The trapping of intermediate 21 by HFIP
Scheme 5. a) 1H NMR experiment for the activation of
nitrosobenzene in HFIP. b) Plausible mechanism for C–H
amination.
While the H-bond drives the C–N bond formation,
the generation of iminoquinone is triggered by the
protonation of the N-atom of nitrosoarene either by
TfOH or by HFIP alone (pKa = 9.3)[22] for the C–O
bond formation (Scheme 6a). A nucleophilic attack
by the arenes onto the O-center of N-protonated
nitrosoarene generates hydroxylamine intermediate
24 (detected in MS and GCMS analysis, see SI),
which readily reacts with another molecule of
nitrosoarene to form intermediate 25. At this stage,
two successive [2,3] sigmatropic rearrangements of
6
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10.1002/adsc.201900788
Advanced Synthesis & Catalysis
this intermediate 25 furnish the intermediate 27 via
the formation of intermediate 26.[23] When the para-
position is substituted with a methoxy group, the
intermediate 27a releases methanol providing p-
iminoquinone. On the other hand, when the para
position is free, the intermediate 27b liberates a
molecule of hydroxylamine delivering the
dearomatized p-iminoquinone product. The formation
of nitrone 28 from 3-methylanisole reinforces the
involvement of intermediate 26 via the C–H
oxygenation followed by the first [2,3] sigmatropic
rearrangement.
charge on the para-position of the arene to which the
aniline released in the previous step can add to form
intermediate 29 (Scheme 6b). When the para-position
is substituted with methoxy group (R3 = OMe),
intermediate 29 can release methanol to furnish p-
iminoquinone. Whereas, when R3 = H, intermediate
29 can react with another molecule of nitrosoarene
forming 30, which eventually liberates hydroxyamine
providing the p-iminoquinone product. The same
hydroxylamine intermediate 24 can undergo N–O
bond cleavage, generating a partial positive charge on
the ortho-carbon followed by the attack of another
molecule of nitrosoarene, delivering the nitrone 28
after tautomerization (Scheme 6c).
Alternatively, hydroxylamine intermediate 24 can
undergo N–O bond cleavage by the involvement of
the electron-rich arene. This creates a partial positive
Scheme 6. a) Mechanistic proposal for the formation of p-iminoquinone via two consecutive [2,3] sigmatropic
rearrangement. b) An alternative mechanism for the formation of p-iminoquinone. c) An alternative mechanism for the
nitrone formation.
the dearomatizing difunctionalization of arenes to
furnish p-iminoquinones, where consecutive [2,3]
Conclusion
sigmatropic rearrangements remain mechanistically
intriguing in nitroso-regime. Furthermore, the
significant characteristics of HFIP meticulously guide
the regioselectivity of an aromatic C–H bond
functionalization in a metal-free pathway.
We have depicted a rarely explored metal-free
aromatic C–H bond functionalization utilizing
nitrosoarenes as dual electrophiles and conducting the
reaction in HFIP, which serves as an activator for
nitroso-functionality. Notably, nitrosoarene, being a
single entity, can deliver regioselective divergent C–
H amination and/or C–H oxygenation outcome.
While the C–H amination directly affords Experimental Section
diarylamines via the scission of N–O bond without
any external reagent, the C–H oxygenation results in
7
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10.1002/adsc.201900788
Advanced Synthesis & Catalysis
Representative procedure for the synthesis of
diarylamines from 1,3,5-trimethoxybenzene and
nitrosobenzene: An oven-dried glass vial is charged with
a magnetic stir bar, 1a (75.0 mg, 0.45 mmol, 3.0 equiv),
and 2a (16.0 mg, 0.15 mmol, 1.0 equiv). 1,1,1,3,3,3-
Hexafluoro-2-propanol (HFIP) (0.2 mL, 0.15 M) is added
to the mixture in argon atmosphere. The vial is maintained
for 40 h at 55oC. The reaction mixture is then passed
through a plug of silica. The vial is rinsed with CH2Cl2 (2
X 2 mL), and the collected organic phases are evaporated
under reduced pressure. The analytically pure product 3a is
obtained by column chromatography on silica gel using
petroleum ether and ethyl acetate (20:1, v/v) as eluent.
[4] Selected reports on FC reaction with benzylic
systems: a) P. A. Champagne, Y. Benhassine, J.
Desroches, Paquin; Angew. Chem. Int. Ed. 2014, 53,
1383–13839; b) N. Weisner, M. G. Khaledi, Green
Chem. 2016, 18, 681–685; c) V. D. Vuković, E.
Richmond, E. Wolf, J. Moran, Angew. Chem. Int. Ed.
2017, 56, 3085–3089.
[5] Selected report on FC reaction with epoxides: a) G.-X.
Li, J. Qu, Chem. Commun. 2010, 46, 2653–2655; b)
Y. Tian, X. Xu, L. Zhang, J. Qu, Org. Lett. 2016, 18,
268–271.
Representative procedure for the synthesis of
iminoquinone
from
1,3,5-trimethoxybenzene,
[6] Selected reports on FC reaction with cyclopropane:
a)E. Richmond, V. D. Vuković, J. Moran, Org. Lett.
2018, 20, 574–577; b) E. Richmond, J. Yi, V. D.
Vuković, F. Sajadi, C. N. Rowley, J. Moran, Chem.
Sci. 2018, 9, 6411–6416.
nitrosobenzene and TfOH as an additive: An oven-dried
glass vial is charged with a magnetic stir bar, 1a (25.0 mg,
0.15 mmol, 1.0 equiv), and 2a (48.0 mg, 0.45 mmol, 3.0
equiv). A solution of TfOH (150.0 µl, 20 mol%, 0.2 M in
HFIP) in 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP) (50.0
µl, 0.75 M) is added to the mixture. The vial is maintained
o
for 12 h at 40 C.The reaction mixture is then passed
[7] For a recent review on HFIP as a solvent, see: a) I.
Colomer, A. E. R. Chamberlain, M. B. Haughey, T. J.
Donohoe, Nat. Rev. Chem. 2017, 1, 1–12 and
references cited thereafter; b) S. K. Sinha, T.
Bhattacharya, D. Maiti, React. Chem. Eng. 2019, 4,
244–253.
through a plug of silica. The vial is rinsed with CH2Cl2 (2
X 2mL), and the collected organic phases are evaporated
under reduced pressure. The analytically pure product 4a is
obtained by column chromatography on silica gel using
petroleum ether and ethylacetate (1:1, v/v) as eluent.
Representative procedure for the synthesis of
iminoquinone from p-xylene and nitrosobenzene: An
oven-dried glass vial is charged with a magnetic stir bar, p-
xylene (90.0µl, 0.75 mmol, 5.0 equiv), and 2a (16.0 mg,
0.15 mmol, 1.0 equiv). 1,1,1,3,3,3-Hexafluoro-2-propanol
(HFIP) (0.2 mL, 0.75 M) is added to the mixture in argon
atmosphere. The vial is maintained for 40 h at 55oC. The
reaction mixture is then passed through a plug of silica.
The vial is rinsed with CH2Cl2 (2 X 2 mL), and the
collected organic phases are evaporated under reduced
pressure. The analytically pure product 8a is obtained by
column chromatography on silica gel using petroleum
ether and ethyl acetate (40:1, v/v) as eluent.
[8] Selected reports on HFIP mediated C–H amination:
a) R. -J. Tang, T. Milcent, B. Crousse, Eur. J. Org.
Chem. 2017, 4753–4757; b) Nitrosopyridine was used
for the annulation reaction with alkynes in HFIP; S.
Manna, R. Narayan, C. Golz, C. Strohmann, A. P.
Antonchick, Chem. Commun. 2015, 51, 6119–6122.
[9] For the synthesis of diarylamines using
nitrosobenzene and arene based organometallics
reagents see: a) Y. Yu, J. Srogl, L. S. Liebeskind,
Org. Lett. 2004, 6, 2631–2634;b) B. Zhou, J. Du, Y.
Yang, H. Feng, Y. Li, Org. Lett. 2013,15, 6302–
6305; c) J. Du, Y. Yang, H. Feng, Y. Li, B. Zhou,
Chem.–Eur. J. 2014, 20, 5727–5731; d) V. Dhayalan,
C. Sämann, P. Knochel, Chem. Commun. 2015, 51,
3239–3242; e) S. Roscales, A. G. Csákÿ, Org. Lett.
2018, 20, 1667–1671.
Acknowledgements
The authors wish to acknowledge financial assistance from
Indian Institute of Technology, Ropar and SERB, DST, India
(ECR/2018/000098). S.P., S. R. and S.G. thank IIT Ropar and
UGC, New Delhi, respectively, for their research fellowships.
[10] J. Börgel, L. Tanwar, F. Berger, T. Ritter, J. Am.
Chem. Soc. 2018, 140, 16026−16031.
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10.1002/adsc.201900788
Advanced Synthesis & Catalysis
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9
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Advanced Synthesis & Catalysis
FULL PAPER
Regiodivergent Aromatic Electrophilic Substitution
Using Nitrosoarenes in Hexafluoroisopropanol: A
Gateway for Diarylamines and p-Iminoquinones
Synthesis
Adv. Synth. Catal.Year, Volume, Page – Page
Suman Pradhan, Sourav Roy, Soumen Ghosh, and
Indranil Chatterjee*
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