A new class of N-doped ionic PAHs: Via intramolecular [4+2]-cycloaddition between arylpyridines and alkynes

Article abstract of DOI:10.1039/c8cc05743e

Reported herein, for the first time, is a copper-promoted intramolecular [4+2]-cycloaddition cascade to access ionic N-doped polycyclic aromatic hydrocarbons (PAHs) with tunable emission wavelengths. It is shown that the reaction can be made catalytic with respect to Cu(OTf)₂ when an external oxidant, Selectfluor, was used.

Full text of DOI:10.1039/c8cc05743e

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: R. D. Mule, A. C.
Shaikh, A. B. Gade and N. Patil, Chem. Commun., 2018, DOI: 10.1039/C8CC05743E.
This is an Accepted Manuscript, which has been through the
Volume 52 Number
1 4 January 2016 Pages 1–216
Royal Society of Chemistry peer review process and has been
accepted for publication.
ChemComm
Accepted Manuscripts are published online shortly after
Chemical Communications
www.rsc.org/chemcomm
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1359-7345
COMMUNICATION
Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc3N@C2n (2n 68 and 80). Synthesis of the
first methanofullerene derivatives of Sc N@D5h-C80
=
3
rsc.li/chemcomm

Please do not adjust margins
ChemComm
Page 1 of 5
View Article Online
DOI: 10.1039/C8CC05743E
ChemComm
COMMUNICATION
A New Class of N-Doped Ionic PAHs via Intramolecular [4+2]-
Cycloaddition between Arylpyridines and Alkynes
Ravindra D. Mule,ab Aslam C. Shaikh,ab Amol B. Gade ab and Nitin T. Patil*c
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Abstract. Reported herein, for the first time, is the copper- the design and development of new class of ionic N-doped PAHs i.e.
promoted intramolecular [4+2]-cycloaddition cascade to access Type (Figure 1b) via Cu-mediated alkyne/azadiene [4+2]-
E
ionic N-doped ionic polycyclic aromatic hydrocarbons (PAHs) with cycloaddition cascades (Scheme 1b). The reaction was proposed to
tunable emission wavelengths. It is showed that the reaction can proceed via initial amino-cupration followed by C-H activation/
be made catalytic with respect to Cu(OTf)2 when external oxidant, reductive elimination sequence to produce ionic N-doped PAHs
Selectfluor, was used.
(Scheme 1b).
Figure 1. N-Doped ionic PAHs: known and present design
Polycyclic aromatic hydrocarbons (PAHs) with annulated
aromatic rings have attracted considerable attention due to their
fascinating structural features and wide application in organic,
optical and electronic material.1 It is known that the incorporation
of heteroatoms in the aromatic framework of PAHs can modulate
their physical, chemical and supramolecular properties.2 As a subset
of these compounds, nitrogen-doped PAHs represent an important
class of molecules that have interesting applications in the field
optoelectronics, light emitting-diodes, supercapacitors and bio-
imaging.3 Recently, it was shown that ionic N-doped PAHs exhibit
interesting optical and aggregation behavior properties.4 Therefore,
it is not surprising why several research group across the globe are
engaged in the design and development of novel ionic N-doped
PAHs (Figure 1a, Type A-D).5 However, most of the approaches to
access N-doped ionic PAHs are based on Rh/Ru catalyzed C-H
activation between arenes/heteroarenes and alkynes.6
a) Previous design for N-doped ionic PAHs:
N
X
X
N
X
N
N
N
Type A
Type B
Type C
b) This design:
Y
OTf
N
R"'
R'
N
R
R
R"
X
D
E
Type
Type
a) Formal [4+2]-cycloaddition via C-H activation (known work)
R'
During the last decades, Rh and Co-catalyzed reactions between
alkynes and azadienes, involving C-H activation, have emerged as an
important tool for accessing heterocyclic quaternary ammonium
salts (Scheme 1a). For instance, the groups of Jones,7 Cheng,8
Huang,9 You10 and Jun11 showed the utility of Rh-complexes for such
reactions. Recently, Pérez-Temprano, 12 Cheng 13 and Wang, 14 in
their independent reports, successfully demonstrated the use of
Co-catalysts for the analogues transformations. Herein, we report
R
cat [M]
¨ cat [Rh] - Ref 7-11
¨ cat [Co] - Ref 12-14
N
R
+
X
N
R"
R"
R'
b) Formal intramolecular [4+2]-cycloaddition via aminocupration/C-H
activation cascade (present work)
OTf
Ar
N
N
Cu(OTf)2
Ar'
Ar
Ar'
1
2
R
R
Scheme 1. Concepts for accessing heterocyclic quaternary
ammonium salts via formal [4+2]-cycloadditions: Known and
present work
Based on our previous report on gold-catalyzed oxidative
intramolecular 1,2-amino-oxygenation reaction of alkynes,15 we
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 5
View Article Online
DOI: 10.1039/C8CC05743E
COMMUNICATION
Journal Name
envisioned that substrate of type 1 would undergo intramolecular the alkyne terminal position of the pyridino alkynes were screened.
[4+2]-cycloaddition reactions to produce ionic N-doped PAHs. For instance, the substrate with sterically demanding 1-Np and
Towards this end, several metal catalysts/oxidants were screened.16 pyrenyl aromatic ring efficiently afforded desired PAHs 2o and 2p in
Our systematic optimization studies revealed that refluxing 1a (Ar' = 80 and 85% yields, respectively. Further, in the cases where
4-OMe-C6H4; R = Ph) in CH3CN in the presence of stoichiometric aliphatic substituents were placed on the alkyne terminus, the
amounts of Cu(OTf)2 is the best the condition to achieve the desired desired PAHs 2q-2s obtained in good yields. Next, we directed our
PAH (2a) in 78% yield. Interestingly, Cu(OTf)2 exhibits dual role by attention to examine the tolerance of the substituents on Ar ring.
mediating the cascade transformation as well as providing counter Pleasingly, the introduction of –Me, –F and –Cl substituents on the
ion. Be noted that the Cu-catalyzed reactions of alkenes, involving ring resulted in the formation of desired PAHs 2t-2x in 60-70%
the simultaneous formation of C-C and C-N bonds, are known in the yields. Similarly, the reaction tolerates di-substitutions at Ar ring to
literature.17 However, to the best of our knowledge, the analogous offer the products 2y-2aa in moderate yields.
reactions of alkynes have never been reported.
Table 2. Substrate scope with Ar' a,b
Table 1. Substrate scope with Ara,b
aReaction conditions: 0.13 mmol 1, 1.0 equiv Cu(OTf)2, CH3CN (2
mL), 80 °C, 12 h. bIsolated yield. cCCDC for 2aj – 1824191.
To understand the tolerance of substituents at Ar′ ring,
substrates 1ab-1am were examined under the optimized reaction
conditions (Table 2). It was observed that 1ab-1ah underwent the
smooth reactions to provide desired PAHs 2ab-2ah in good yields
aReaction conditions: 0.13 mmol 1, 1.0 equiv Cu(OTf)2, CH3CN (2
(58-84%). Moreover, 1-Np, 2-Np, 9-phenanthryl groups were well
tolerated under the present reaction conditions to produce desired
PAHs (2ai-2al) in good yields. Even, the benzothiophenyl moiety
was also well tolerated giving PAH 2am in 65% yield. Scalability of
mL), 80 °C, 12 h. bIsolated yield. cComplex reaction mixture was
obtained.
the methods was demonstrated by the large-scale synthesis
employing 1a (2.7 mmol) as a starting material (2a, 76%).16
With the optimized reaction conditions in hand, we sought to
explore the substrate scope for this reaction. The results are
presented in Table 1. In general, substrates with variation in aryl
ring at alkyne-terminus with varying functional groups, such as alkyl
and –OMe were well tolerated (2b-2d). However, stronger electron
donating group such as –NMe2 was found to be unsuitable for the
reaction. The reaction smoothly tolerated to varying substitution
pattern (ortho, meta, para) on the aforementioned aryl moiety to
furnish the corresponding PAHs in good yields (2f-2n). Next,
substrates bearing bulky aromatics or long-chain/cyclic aliphatics at
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 3 of 5
View Article Online
DOI: 10.1039/C8CC05743E
Journal Name
COMMUNICATION
BF4
N
Cu(OTf)2
(10 mol%)
N
R
R
Selectfluor
(1.0 equiv)
CH3CN, 80 °C, 12 h
R'
1a
; R = OMe, R' = H
2a'
, 75%
R'
1b; R = OMe, R' = Me
2b', 63%
1ag; R, R' = H
2ag', 65%
Scheme 2. Catalytic reactions with respect to Cu(OTf)2 in the
presence of external oxidant
Interestingly, we found that the reaction can be made catalytic
with respect to Cu(OTf)2 when stoichiometric amount oxidant was
used.16 When 1a, 1b and 1ag was treated with 10 mol% Cu(OTf)2 in
the presence of Selectfluor, reaction proceeded smoothly to
produce 2a′, 2b′ and 2ag′ in 75, 63 and 65 % yields, respectively.
A plausible reaction pathway for the present transformation is
depicted in Scheme 3. At first, activation of the alkyne by the
Cu(OTf)2 would occur to enable nucleophilic attack by the pyridyl
nitrogen atom in 5-exo-dig fashion to generate vinyl copper
intermediate I.18 This intermediate would activate C-H bond of
proximal aryl ring and subsequently remove TfOH to generate
copper (II) intermediate II.19 Further, reductive elimination would
occur to form product 2a. The fact that the yield of the reaction was
not hampered in the presence of the radical scavenger such as
2,2,6,6-tetra-methylpiperidine-1-oxyl (TEMPO)16 rules out the
possibility of radical mechanism.
In conclusion, Cu(II)-mediated intramolecular alkynes/azadienes
[4+2]-cycloaddition cascade has been disclosed. The reagent
Cu(OTf)2 exhibits dual role by mediating the cascade transformation
as well as providing counter ion. Further, it is showed that the
reaction can be made catalytic with respect to Cu(OTf)2 in the
presence of external oxidant, Selectfluor. The method provided an
efficient access to ionic N-doped PAHs with tunable emission
wavelengths.
Generous financial support by IISER Bhopal is gratefully
acknowledged. We thank Saibal Bera and Dr. Rahul Banerjee for
providing single crystal X-ray diffraction data. R.D.M., A.C.S. and
A.B.G. thank CSIR for the award of senior research fellowship.
Notes and reference+
OTf
1.0 equiv
Cu(OTf)2
N
N
(1) (a) R. G. Harvey, Polycyclic Aromatic Hydrocarbons; Wiley-
VCH: New York, 1997, 43; (b) A. Narita, X.-Y Wang, X. Feng and
K. Müllen, Chem. Soc. Rev. 2015, 44, 6616; (c) D. Pérez, D.
Peña and E. Guitián, Eur. J. Org. Chem. 2013, 5981; (d) J. Wu,
W. Pisula and K. Müllen, Chem. Rev. 2007, 107, 718; (e) M. D.
Watson, A. Fechtenkötter and K. Müllen, Chem. Rev. 2001,
101, 1267.
(2) For recent reviews, see: (a) M. Stępień, E. Gońka, M. Żyła and
N. Sprutta, Chem. Rev. 2017, 117, 3479; (b) X. Wang, G. Sun,
P. Routh, D.-H. Kim, W. Huang and P. Chen, Chem. Soc. Rev.
2014, 43, 7067; (c) W. Jiang, Y. Li and . Wang, Chem. Soc.
Rev. 2013, 42, 6113.
MeO
MeO
CH3CN
80 °C, 12 h
Ph
Ph
1a
2a
Cu(OTf)2
Cu(0)
C-H
insertion
OTf
OTf
N
N
H
MeO
II
Cu
CuII
-TfOH
MeO
TfO
Ph
Ph
I
II
Scheme 3. A plausible reaction mechanism.
(3) Reviews: (a) Y. Deng, Y. Xie, K. hou and X. Ji, J. Mater. Chem.
A 2016, 4, 1144; (b) A. Mateo-Alonso, Chem. Soc. Rev. 2014,
43, 6311; (c) U. H. F. Bunz, J. U. Engelhart, B. D. Lindner and
M. Schaffroth, Angew. Chem., Int. Ed. 2013, 52, 3810. For
selected examples, see: (d) A. Skabeev, U. schieschang, Y.
agranyarski, H. Klauk K. Müllen, and C. Li, Org. Lett. 2018, 20,
1409; (e) X.-Y. Wang, M. Richter, Y. He, J. Björk, A. Riss, R.
Rajesh, M. Garnica, F. Hennersdorf, J. J. Weigand, A. Narita, R.
Berger, X. Feng, W. Auwärter, J. V. Barth, C.-A. Palma and K.
Müllen, Nat. Commun. 2017, 8, 1948; (f) S. Boldt, S. Parpart,
A. Villinger, P. Ehlers and P. Langer, Angew. Chem., Int. Ed.
2017, 56, 4575; (g) C.-F. Liu, C. Cheng, Y. Jiang, W.-Y. Lai and
W. Huang, New J. Chem. 2017, 41, 13619; (h) M. Richter, K. S.
Schellhammer, P. Machata, G. Cuniberti, A. Popov, F.
Ortmann, R. Berger, K. Müllen and X. Feng, Org. Chem. Front.
2017, 4, 847.
The synthesised PAHs exhibit intense fluorescence and their
photophysical properties were studied in CH2Cl2 solution (Table
S1).16 The PL range covers the visible region, offering a palette of
colors ranging from violet to orange (λem: 434-619 nm, Figure 2).
These fluorophores have good photoluminescence capabilities with
Φf values ranging from 0.06 to 0.88. Next, the electrochemical
properties of representative PAHs were investigated by cyclic
voltammetry and the result indicated that these PAHs have high
electron-accepting abilities.16
Figure 2. Emission spectra of selected ionic PAHs in CH2Cl2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 5
View Article Online
DOI: 10.1039/C8CC05743E
COMMUNICATION
Journal Name
(4) (a) K. Xu, Y. Fu, Y. hou, F. Hennersdorf, P. Machata, I. Vincon, (17) For general reviews, see: (a) X. hu and S. Chiba, Chem. Soc.
J. J. Weigand, A. A. Popov, R. Berger and X. Feng, Angew.
Chem., Int. Ed. 2017, 56, 15876; (b) D. Wu, R. Liu, W. Pisula, X.
Feng and K. Müllen, Angew. Chem., Int. Ed. 2011, 50, 2791; (c)
J. Fortage, F. Tuyèras, P. Ochsenbein, F. Puntoriero, F. Nastasi,
S. Campagna, S. Griveau, F. Bedioui, I. Ciofini and P. P. Lainé,
Chem. Eur. J. 2010, 16, 11047; (d) J. Fortage, C. Peltier, F.
Nastasi, F. Puntoriero, F. Tuyèras, S. Griveau, F. Bedioui, C.
Adamo, I. Ciofini, S. Campagna and P. P. Lainé, J. Am. Chem.
Soc. 2010, 132, 16700; (e) D. Wu, W. Pisula, V. Enkelmann, X.
Feng and K. Müllen, J. Am. Chem. Soc. 2009, 131, 9620; (f) D.
Rev. 2016, 45, 4504; (b) Y. Shimizu and M. Kanai, Tetrahedron
Lett. 2014, 55, 3727; (c) J. P. Wolfe, Top. Heterocycl. Chem.
2013, 32, 1; (d) S.R. Chemler, J. Organomet. Chem, 2011, 696,
150; (e) S. R. Chemler and P. H. Fuller, Chem. Soc. Rev. 2007,
36, 1153. For pertinent reports, see: (f) E. S. Sherman and S. R.
Chemler, Adv. Synth. Catal. 2009, 351, 467; (g) W. eng and S.
R. Chemler, J. Am. Chem. Soc. 2007, 129, 12948; (h) P. H.
Fuller and S. R. Chemler, Org. Lett. 2007, 9, 5477; (i) E. S.
Sherman, P. H. Fuller, D. Kasi and S. R. Chemler, J. Org. Chem.
2007, 72, 3896.
Wu, L. hi, G. J. Bodwell, G. Cui, N. Tsao, and K. Müllen, (18) (a) L. Ouyang, X. Tang, H. He, C. Qi, W. Xiong, Y. Ren and H.
Angew. Chem., Int. Ed. 2007, 46, 5417.
(5) For general reviews, see: (a) D. Sucunza, A. M. Cuadro, J.
Jiang, Adv. Synth. Catal. 2015, 357, 2556; (b) X. hang, R. P.
Hsung, H. Li, Chem. Commun., 2007, 23, 2420.
Alvarez-Builla and J. J. Vaquero, J. Org. Chem. 2016, 81, (19) For selected reviews, see: (a) W.-H. Rao and B.-F. Shi, Org.
10126; For selected examples, see: (b) F. Li, J. Cho, S. Tan,and
S. Kim, Org. Lett. 2018, 20, 824; (c) N. Toriumi, N. Asano, K.
Miyamoto, A. Muranaka, M. Uchiyama, J. Am. Chem. Soc.
2018, 140, 3858 ; (d) J.-R. Deng, C.-S. Tsang, W.-C. Chan, B. C.-
B. Ko, N. C.-H. Lai, S. L.-F. Chan, B. Yang and M.-K. Wong,
Chem. Sci. 2017, 8, 7537; (e) Y. Asanuma, H. Eguchi, H.
Nishiyama, I. Tomita and S. Inagi, Org. Lett. 2017, 19, 1824; (f)
J. M. Villar, J. Suárez, J. A. Varela and C. Saá, Org. Lett. 2017,
19, 1702; (g) Y. Yang, D. Liu, M. Song, D. Shi, B. Liu, K. Cheng,
Y. Lu, H. Liu, M. Yang, W. Wang, J. Li and J. Wei, Chem. Eur. J.
2017, 23, 7409; (h) Q. Ge, Y. Hu, B. Li and B. Wang, Org. Lett.
2016, 18, 2483; (i) B. Feng, D. Wan, L. Yan, V. D. Kadam, J. You
and G. Gao, RSC Adv. 2016, 6, 66407; (j) D. Ghorai, C. Dutta
and J. Choudhury, ACS Catal. 2016, 6, 709; (k) D. Ghorai and J.
Choudhury, ACS Catal. 2015, 5, 2692; (l) D. L. Davies, C. E.
Ellul, S. A. Macgregor, C. L. McMullin and K. Singh, J. Am.
Chem. Soc. 2015, 137, 9659; (m) D. hao, Q. Wu, X. Huang, F.
Song, T. Lv and J. You, Chem. Eur. J. 2013, 19, 6239; (n) G.
hang, L. Yang, Y. Wang, Y. Xie, H. Huang, J. Am. Chem. Soc.
2013, 135, 8850.
Chem. Front., 2016, 3, 1028; (b) X. -X. Guo, D.-W. Gu, . Wu
and W. hang, Chem. Rev., 2015, 115, 1622; (c) Allen, S. E.;
Walvoord, R. R.; Padilla-Salinas, R.; Kozlowski, M. C. Chem.
Rev., 2013, 113, 6234; (d) K. Hirano and M. Miura, Chem.
Commun., 2012, 48, 10704.
(6) For recent reviews, see: (a) J. Jayakumar and C.-H. Cheng, J.
Chin. Chem. Soc. 2018, 65, 11; (b) P. Gandeepan and C.-H.
Cheng, Chem. Asian J. 2016, 11, 448.
(7) L. Li, W. W. Brennessel and W. D. Jones J. Am. Chem. Soc.
2008, 130, 12414.
(8) (a) C.- . Luo, J. Jayakumar, P. Gandeepan, Y.-C. Wu and C.-H.
Cheng, Org. Lett. 2015, 17, 924; (b) C.- . Luo, P. Gandeepan, J.
Jayakumar, K. Parthasarathy, Y.-W. Chang and C.-H. Cheng,
Chem. Eur. J. 2013, 19, 14181.
(9) G. hang, L. Yang, Y. Wang, Y. Xie and H.Huang, J. Am. Chem.
Soc. 2013, 135, 8850.
(10) J. Tang, S. Li, . Liu, Y. hao, . She, V. D. Kadam, G. Gao, J. Lan
and J. You, Org. Lett. 2017, 19, 604.
(11) Y. R. Han, S.-H. Shim, D.-S. Kim and C.-H. Jun, Org. Lett. 2017,
19, 2941.
(12) J. Sanjosé-Orduna, D. Gallego, A. Garcia-Roca, E. Martin, J.
Benet-Buchholz and M. H. Pérez-Temprano, Angew. Chem.,
Int. Ed., 2017, 56, 12137.
(13) S. Prakash, K. Muralirajan and C.-H. Cheng, Angew. Chem., Int.
Ed., 2016, 55, 1844.
(14) Y.-X. Lao, S.-S. hang, X.-G. Liu, C.-Y. Jiang, J.-Q. Wu, Q. Li, .-S.
Huang and H. Wang, Adv. Synth. Catal. 2016, 358, 2186.
(15) A. C. Shaikh, D. S. Ranade, P. R. Rajamohanan, P. P. Kulkarni
and N. T. Patil, Angew. Chem., Int. Ed., 2017, 56, 757.
(16) See supporting information for more details.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 5
ChemComm
View Article Online
DOI: 10.1039/C8CC05743E
Graphical Abstract
A New Class of N-Doped Ionic PAHs via Intramolecular [4+2]-
Cycloaddition between Arylpyridines and Alkynes
Ravindra D. Mule, Aslam C. Shaikh, Amol B. Gade and Nitin T. Patil*