An efficient approach to isoquinoline via AgNO3-promoted 6-endo-dig cyclization followed by oxidative elimination of o-alkynylarylaldimines and its application in fluoride recognition

Article abstract of DOI:10.1016/j.tetlet.2019.151187

A novel 6-endo-dig cyclization followed by oxidation/elimination of o-alkynylarylaldimines with 4-hydroxybenzylamine was developed for preparation of isoquinolines. The intermediates of this tandem reaction were monitored by mass spectroscopy (MS) to confirm the reaction pathway. This methodology was further applied to the design and synthesis of a novel ratiometric chemosensor for determination of fluoride.

Full text of DOI:10.1016/j.tetlet.2019.151187

Tetrahedron Letters xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An efficient approach to isoquinoline via AgNO3-promoted 6-endo-dig
cyclization followed by oxidative elimination of o-alkynylarylaldimines
and its application in fluoride recognition
a
Yongxing Tang a,1, Yajun Yu a,1, Xinyu Wei a, Jin Yang a, Yeting Zhu a, Yun-Hui Zhao a,b,c, , Zilong Tang ,
⇑
Zhihua Zhou a,c, Xiaofang Li a, Xianyong Yu a,
⇑
a School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan, Hunan 411201, PR China
b Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, PR China
c Hunan Provincial Key Laboratory of Controllable Preparation and Functional Application of Fine Polymers, Hunan University of Science and Technology, Xiangtan, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel 6-endo-dig cyclization followed by oxidation/elimination of o-alkynylarylaldimines with 4-
hydroxybenzylamine was developed for preparation of isoquinolines. The intermediates of this tandem
reaction were monitored by mass spectroscopy (MS) to confirm the reaction pathway. This methodology
was further applied to the design and synthesis of a novel ratiometric chemosensor for determination of
fluoride.
Received 6 August 2019
Revised 17 September 2019
Accepted 20 September 2019
Available online xxxx
Ó 2019 Published by Elsevier Ltd.
Keywords:
Isoquinoline
Oxidative elimination
Fluoride recognition
Fluorescent chemosensor
Isoquinoline and its derivatives have gained widespread atten-
tion due to their extensive range of therapeutic and biological
activities, such as antimicrobial, anti-HIV-1, antifungal and anti-
tumour properties [1]. Isoquinolinium salts, formed by N-alkyla-
tion of isoquinolines, are also important alkaloids with numerous
valuable biological activities and other applications in dyes and
paints [2]. In addition to the excellent bioactivities of these com-
pounds, they also are versatile intermediates for the synthesis of
therapeutic agents [3].
A number of methods for the preparation of isoquinoline and
derivative compounds have been reported because of their remark-
able physiological properties and significant role in organic synthe-
sis. Among the wide range of strategies employed, catalysis of 6-
endo-dig ring closures of 2-(1-alkynyl) arene carboxaldehyde imi-
nes by metal ions or other cations have emerged as some of the
most efficient, owing to their high selectivity and mild conditions
(Scheme 1a) [4]. These reactions are mainly restricted to transition
metals such as Cu, Ag, Pd and Au, with Ag-catalysed ring closure
reactions giving the best results [5]. For an example, Liang devel-
oped an efficient method for the synthesis of substituted isoquino-
line via silver catalyzed cyclization of 2-alkynyl benzyl azides
(Scheme 1a). But the synthesis of substrates 2-alkynyl benzyl
azides was complicated and needed dangerous azides as raw mete-
rials (Scheme 1a) [6]. Another method that has been employed is
transition metal-catalysed direct CAH bond functionalisation of
arenes bearing nitrogen-containing directing groups, followed by
cyclisation with the resulting internal alkynes. This approach has
enabled the highly efficient preparation of diverse isoquinolines
containing a wide range of functional groups [7]. However,
noble-metal rhodium catalysts were usually required to achieve
CAH functionalization in some reactions (Scheme 1b). Other nitro-
gen-containing compounds, such as 2-(cyanomethyl)-benzoni-
triles, 3-aminopyrazine-2-carbohydrazide and tert-butylamine/
benzamidine were also used to prepare isoquinolines [8]. Ammo-
nium salts, ammonia were reported as efficient nitrogen sources
to synthesize isoquinolines catalyzed by transition metals [9]. In
our previous studies, methods for the synthesis of isoquinoline
derivatives by Ag-mediated annulation/NAN bond cleavage were
reported [10].
Methylene benzoquinone is an excellent synthetic intermediate
that is often used as the Michael receptor in the synthesis of vari-
ous compounds [11]. This unit is a very good leaving molecule via
oxidation/elimination because of its stable electronic structure
[12]. Therefore, this motif or a similar unit has been incorporated
⇑
Corresponding authors.
E-mail addresses: zhao_yunhui@163.com (Y.-H. Zhao), yu_xianyong@163.com
(X. Yu).
1
These authors contributed equally to this work.
https://doi.org/10.1016/j.tetlet.2019.151187
0040-4039/Ó 2019 Published by Elsevier Ltd.
Please cite this article as: Y. Tang, Y. Yu, X. Wei et al., An efficient approach to isoquinoline via AgNO3-promoted 6-endo-dig cyclization followed by oxida-
tive elimination of o-alkynylarylaldimines and its application in fluoride recognition, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151187

2
Y. Tang et al. / Tetrahedron Letters xxx (xxxx) xxx
Scheme 1. Synthetic routes for isoquinolines.
Table 1
into many fluorescent molecules for recognition of reactive oxygen
species [13]. When these chemosensors are subjected to an oxidant
they release methylene benzoquinone (or similar unit) as a result
of the change of probe structure. Accordingly, the fluorescence
wavelength and intensity will change as a result of the change in
conjugation in the structure.
Optimisation of reaction conditions for synthesis of isoquinolines.a
Derivatives of 4-hydroxybenzylamine on N atom have the
potential to release methylene benzoquinone and to provide nitro-
gen source under certain oxidation conditions. Therefore, this
study reports a novel methodology for the synthesis of isoquinoli-
nes via 6-endo-dig cyclisation followed by oxidation/elimination
based on 4-hydroxybenzylamine. 2-(1-Alkynyl) arene carboxalde-
hyde imines were generated in situ from o-alkynyl benzaldehydes
and amines and then catalyzed by Ag to afford the benzyl isoquino-
linium salts, which were oxidised immediately under oxidation
conditions to eliminate methylene benzoquinone and provide iso-
quinolines (Scheme 1c).
Entry
Catalyst
Solvent
Proportion
(1a:2)
Yield %b
1
2
3
4
5
6
7
8
AgNO3 (30%)
AgOTf (30%)
AgTFA (30%)
CuI (30%)
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1.5
42
35
24
15
8
11
Trace
20%
66
74
80
82
86
81
77
CoCl2 (30%)
Ni(AcO)2 (30%)
Zn(NO3)2 (30%)
PdCl2 (30%)
AgNO3(30%)
AgNO3(50%)
AgNO3(80%)
AgNO3(90%)
AgNO3(100%)
AgNO3(120%)
AgNO3(100%)
To verify the practicability of this route, a set of experiments
was performed using 2-((4-methoxyphenyl)ethynyl)benzaldehyde
1a and 4-hydroxybenzylamine 2 as model substrates. Optimisation
of the reaction conditions was carried out with respect to different
Lewis acids, solvents and temperatures (Table 1). Silver is an effi-
cient catalyst and has been known to activate alkynes, which
prompted the exploration of different methodologies for the syn-
thesis of heterocycles. Initially, 30 mol% AgNO3 in 1,2-dichlor-
oethane (DCE) was selected to catalyze this reaction, resulting in
a 42% yield of designed product 3 (Entry 1, Table 1). Other Lewis
acids (AgOTf, AgTFA, CuI, CoCl2, Ni(OAc)2, Zn(NO3)2, and PdCl2)
were somewhat inferior (Entries 2–8, Table 1). The efficiency of
AgNO3 was greatly improved in EtOH resulted in a yield of 66%
(Entry 9, Table 1). Next, the catalyst loading was found to have a
significant effect on the conversion: 100 mol% AgNO3 was found
to be optimum for the highest conversion of 1a and 2 in EtOH at
80 °C (Entry 13, Table 1). Increasing the amount of 4-hydroxyben-
zylamine had negative effect on the yield of the desired product
(Entry 15, Table 1). Decreasing or increasing the temperature had
a negative effect on the yield of target product 3 (not shown).
The scope of the reaction was explored next using the optimised
reaction conditions (Scheme 2). Generally, the domino reactions
provided the desired isoquinolines in moderate to good yields. Var-
ious R1 and R2 substituents on the phenyl ring, including chloro,
methyl, fluoro and methoxy groups, were well tolerated. As seen
from Scheme 2, the electronic effects of R1 and R3 had significant
influence on the reaction efficiency: the yields of desired products
increased from 62% to 78% and then 88% when the substituents at
9
10
11
12
13
14
15
Bold display is to highlight the best reaction condition.
The reactions were performed using 0.3 mmol of 2-(phenylethynyl)benzalde-
hyde 1a and 2 in 2.0 mL of solvent at 80 °C for 12 h.
a
b
Isolated yield.
R1 changed from methoxyl (3c) to methyl (3b) to chloro (3d),
respectively (Scheme 2). The results indicated that the electron
withdrawing groups at R1 provided better product yields than elec-
tron donating groups. Indeed, a similar trend was observed for the
compound series 3f, 3k and 3g. An opposite phenomenon was
observed for substituents at R3. The yields of targeted products
decreased from 86% to 69% and 62% when the substituents at R3
changed from methoxy (3a) to methyl (3 h) and chloro (3 k),
respectively, indicating that electron donating groups at R3
resulted in greater reaction efficiency than electron withdrawing
groups. This result may be explained by the fact that the higher
the density of the electron cloud on the triple bond, the stronger
the 6-endo-dig cyclisation ability of substrate 1 with the amine 2
[14].
Please cite this article as: Y. Tang, Y. Yu, X. Wei et al., An efficient approach to isoquinoline via AgNO3-promoted 6-endo-dig cyclization followed by oxida-
tive elimination of o-alkynylarylaldimines and its application in fluoride recognition, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151187

Y. Tang et al. / Tetrahedron Letters xxx (xxxx) xxx
3
Scheme 2. Substrate scope of different 2-alkynylbenzaldehydes with 4-hydroxybenzylamine in the presence of AgNO3.
Scheme 3. Synthetic route of isoquinolinium salt 5.
It was discovered that protection of the benzylamine hydroxyl
group resulted in halting of the reaction at the isoquinolinium salt.
Enlightened by this, a novel ratiometric fluorescent probe based on
an isoquinolinium salt was designed and synthesized for determi-
nation of fluoride. 4-Hydroxybenzylamine was protected as the
diphenyl-t-butylsilyl (DPTBS) ether, then reacted with 2-((4-meth-
oxyphenyl)ethynyl)benzaldehyde 1a to provide probe 5 under the
optimized reaction conditions (Scheme 3).
With fluorescent probe 5 in hand, it was expected that depro-
tection with fluoride would produce the 4-hydroxybenzyl iso-
quinolinium salt intermediate, which was then applied to detect
reactive oxygen species. Unexpectedly, the colour of the probe sys-
tem changed from yellow-green to blue immediately after the
addition of fluoride. This phenomenon meant that there had been
significant changes to the conjugated structure, not simply arising
from DPTBS removal. It was proposed that the probe had been oxi-
dised, eliminating methylene benzoquinone to form the isoquino-
line unit; this was confirmed by the fluorescent emission spectra of
compounds 5 and 3a (Fig. 1). Therefore, probe 5 was successfully
applied to detect fluoride [15].
Fig. 1. Fluorescent emission of compounds 5, 3a and the emission changes of 5
(10 l
mol LÀ1) in the presence of increasing amounts of FÀ.
Fluorescence recognition experiments were performed via the
addition of fluoride to 5 in MeCN/H2O (9:1 v/v). As shown in
Fig. 1, the fluorescence emission peak for 5 was at 522 nm with a
large Stokes shift of 172 nm (kex = 350 nm, Fig. S1). When FÀ was
added into the solution, the peak at 522 nm weakened dramati-
cally and a new peak at 394 nm began to appear with a blue shift
of 128 nm. The large shift would decrease the interference of back-
ground noise and improve the sensitivity of detection, which is
highly advantageous compared to general ratiometric or single
signal probes [16]. With an increased amount of FÀ (from 0 to 4,
6, 9
mol LÀ1), the peak at 394 nm increased accordingly, and the
peak at 522 nm disappeared gradually. Consequently, chemosen-
sor 5 could be used in quantitative determination of fluoride.
Further quantitative determinations and selectivity investigations
on this probe for fluoride are underway.
l
The possible reaction pathway of this tandem reaction
was demonstrated by monitoring reaction intermediates using
Please cite this article as: Y. Tang, Y. Yu, X. Wei et al., An efficient approach to isoquinoline via AgNO3-promoted 6-endo-dig cyclization followed by oxida-
tive elimination of o-alkynylarylaldimines and its application in fluoride recognition, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151187

4
Y. Tang et al. / Tetrahedron Letters xxx (xxxx) xxx
Fig. 2. The reaction pathway of this tandem reaction was confirmed by TOF-MS.
(c) J.E. Anthony, Angew. Chem., Int. Ed. 47 (2008) 452;
(d) J. Fortage, C. Peltier, F. Nastasi, F. Puntoriero, F. Tuye`ras, S. Griveau, F.
Bedioui, C. Adamo, I. Ciofini, S. Campagna, P.P. Laine´, J. Am. Chem. Soc. 132
(2010) 16700;
TOF-MS. A small amount of the reaction solution was decanted for
MS monitoring. As shown in Fig. 2, the AgNO3-catalyzed reaction of
o-alkynylarylaldehyde 1a with 4-hydroxybenzylamine produced a
cationic intermediate A, corresponding to the signal at 342.0.
Because of the driving force of aromatisation induced by FÀ, the
intermediate immediately decomposed into isoquinoline and
methylene benzoquinone B, corresponding to the peaks at 236.1
and 107.0, respectively. This reaction process was consistent with
the proposed reaction pathway.
(e) Y. Ni, H. Liu, D. Dai, X. Mu, J. Xu, S. Shao, Anal. Chem. 90 (2018) 10152.
[3] (a) G.E. Lee, H.S. Lee, S.D. Lee, J.-H. Kim, W.-K. Kim, Y.-C. Kim, Bioorg. Med.
Chem. Lett. 19 (2009) 954;
(b) P. Hewavitharanage, E.O. Danilov, D.C. Neckers, J. Org. Chem. 2005 (70)
(2005) 10653;
(c) Z. Chen, X. Yang, J. Wu, Chem. Commun. 45 (2009) 3469;
(d) H. Waldmann, L. Eberhardt, K. Wittstein, K. Kumar, Chem. Commun. 46
(2010) 4622;
In summary, an efficient silver nitrate-promoted 6-endo-dig
cyclisation followed by oxidation/elimination of o-alkynylary-
laldimines with 4-hydroxybenzylamine for the efficient synthesis
of isoquinolines in moderate to good yields is reported. A novel flu-
orescent probe is designed and synthesised for recognition of fluo-
ride, and this process further confirms the reaction pathway.
Further study on the efficiency of isoquinolinium salt 5 for deter-
mination of fluoride is underway.
(e) N.T. Patil, A.K. Mutyala, G.V.V. Lakshmi, P.V.K. Raju, B. Sridhar, Eur. J. Org.
Chem. 2010 (1999);
(f) R.R. Jha, R.K. Saunthwal, A.K. Verma, Org. Biomol. Chem. 12 (2014) 552;
(g) T. Guo, Y. Liu, Y.-H. Zhao, P.-K. Zhang, S.-L. Han, H.-M. Liu, Tetrahedron Lett.
57 (2016) 3920;
(h) T. Guo, X.-N. Wei, H.-Y. Wang, Y.-L. Zhu, Y.-H. Zhao, Y.-C. Ma, Org. Biomol.
Chem. 15 (2017) 9455.
[4] (a) D.D. Vachhani, V.P. Mehta, S.G. Modha, K. Van Hecke, L. VanMeervelt, E.V.
Van der Eycken, Adv. Synth. Catal. 354 (2012) 1593;
(b) K.R. Roesch, R.C. Larock, J. Org. Chem. 67 (2002) 86;
(c) Y.-H. Zhao, Y. Li, T. Guo, Z. Tang, K. Deng, G. Zhao, Synth. Commun. 46
(2016) 355;
Acknowledgments
(d) Y.-H. Zhao, Y. Li, T. Guo, Z. Tang, W. Xie, G. Zhao, Tetrahedron Lett. 57
(2016) 2257.
[5] (a) For selected examples, see: Z. Chen, X. Yang, J. Wu Chem. Commun. 45
(2009) 3469;
The generous financial support from the National Natural
Science Foundation of China (Nos. 51773057 and 21877034), the
Hunan Provincial Education Department Scientific Research Fund
(No. 18B221, 18A192) are gratefully acknowledged.
(b) H. Ren, S. Ye, F. Liu, J. Wu, Tetrahedron 66 (2010) 8242;
(c) S. Ye, X. Yang, J. Wu, Chem. Commun. 46 (2010) 5238;
(d) S. Li, Y. Luo, J. Wu, Org. Lett. 13 (2011) 4312;
(e) G. Qiu, Y. He, J. Wu, Chem. Commun. (2012) 3836;
(f) S. Ye, G. Liu, S. Pu, J. Wu, Org. Lett. 14 (2012) 70;
(g) Y.-H. Zhao, M. Luo, Y. Li, X. Liu, Z. Tang, K. Deng, G. Zhao, Chin. J. Chem. 34
(2016) 857;
Appendix A. Supplementary data
(h) Y. Li, Y. Zhao, M. Luo, Z. Tang, C. Cao, K. Deng, Chin. J. Org. Chem. 36 (2016)
2504.
[6] Y.-N. Niu, Z.-Y. Yan, G.-Y. Gao, H.-L. Wang, X.-Z. Shu, K.-G. Ji, Y.-M. Liang, J. Org.
Chem. 74 (2009) 2893.
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2019.151187.
[7] (a) R. He, Z.-T. Huang, Q.-Y. Zheng, C. Wang, Angew. Chem. Int. Ed. 53 (2014)
4950;
References
(b) B. Zhou, H. Chen, C. Wang, J. Am. Chem. Soc. 135 (2013) 1264;
(c) M. Dell’Acqua, G. Abbiati, E. Rossi, Synlett (2010) 2672;
(d) S. Dhiman, N.K. Nandwana, H.K. Saini, D. Kunar, K. Rangan, K.N. Rovertson,
M. Jha, A. Kumar, Adv. Synth. Catal. 360 (2018) 1973;
(e) J. Cheng, J. Xie, C. Zhu, Chem. Commun. 54 (2018) 1655;
(f) G. Zhang, L. Yang, Y. Wang, Y. Xie, H. Huang, J. Am. Chem. Soc. 135 (2013)
8850;
[1] (a) V.K. Pandey, A. Shukla, Indian J. Chem., Sect. B: Org. Chem. Incl. Med. Chem.
38 (1999) 1381;
(b) S.M. Rida, S.A.M. El-Hawash, H.T.Y. Fahmy, A.A. Hazzaa, M.M.M. El-Meligy,
Arch. Pharmacal Res. 29 (2006) 826;
(c) R.L. Weinkauf, A.Y. Chen, C. Yu, L. Liu, L. Barrows, E. LaVoie, Bioorg. Med.
Chem. 2 (1994) 781;
(d) L.W. Deady, T. Rodemann, G.J. Finlay, B.C. Baguley, W.A. Denny, Anti-
Cancer Drug Des. 15 (2001) 339.
(g) M. Kienle, S.R. Dubbaka, K. Brade, P. Knochel, Eur. J. Org. Chem. (2007) 4166.
[8] (a) K. Hu, L. Qi, S. Yu, T. Cheng, X. Wang, Z. Li, Y. Xia, J. Chen, H. Wu, Green
Chem. 19 (2017) 1740;
[2] (a) B.D. Krane, M.O. Fagbule, M. Shamma, B.J. Gozler, Nat. Prod. 47 (1984) 1;
(b) W.-C. Pan, J.-Q. Liu, X.-S. Wang, Tetrahedron 74 (2018) 1468;
(c) K. Shekarrao, P.P. Kaishap, S. Gogoi, R.C. Boruah, RSC Adv. 4 (2014) 14013.
(b) D. Wu, L. Zhi, G.J. Bodwell, G. Cui, N. Tsao, K. Mu
46 (2007) 5417;
̈llen, Angew. Chem., Int. Ed.
Please cite this article as: Y. Tang, Y. Yu, X. Wei et al., An efficient approach to isoquinoline via AgNO3-promoted 6-endo-dig cyclization followed by oxida-
tive elimination of o-alkynylarylaldimines and its application in fluoride recognition, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151187

Y. Tang et al. / Tetrahedron Letters xxx (xxxx) xxx
5
[9] (a) V. Guguloth, N.S. Thirukovela, R. Balaboina, S. Paidakula, R. Vadde,
(b) J. Liu, J. Liang, C. Wu, Y. Zhao, Anal. Chem. 91 (2019) 6902;
(c) Z. Xu, L. Xu, Chem. Commun. 52 (2016) 1094;
Tetrahedron Lett. 60 (2019) 297;
(b) D. Yang, S. Burugupalli, D. Daniel, Y. Chen, J. Org. Chem. 77 (2012) 4466;
(c) S. Dhara, R. Singha, Y. Nuree, J.K. Ray, Tetrahedron Lett. 55 (2014) 795.
[10] (a) Y.-H. Zhao, Y. Li, M. Luo, Z. Tang, K. Deng, Synlett 27 (2016) 2597;
(b) Y.-H. Zhao, Y. Luo, Y. Zhu, H. Wang, H. Zhou, H. Tan, Z. Zhou, Y.-C. Ma, W.
Xie, Z. Tang, Synlett 29 (2018) 773.
[11] (a) M.M. Toteva, J.P. Richard, Adv. Phys. Org. Chem. 45 (2011) 39;
(b) M. Freccero, C.D. Valentin, M. Sarzi-Amade, J. Am. Chem. Soc. 125 (2003)
3544;
(d) C. Chen, F. Wang, J.Y. Hyun, T. Wei, J. Qiang, X. Ren, I. Shin, J. Yoon, Chem.
Soc. Rev. 45 (2016) 2976;
(e) X. Qiu, C. Xin, W. Qin, Z. Li, G. Zhang, B. Peng, X. Han, C. Yu, L. Li, W. Huang,
Talanta 199 (2019) 628.
[14] Y.-H. Zhao, Y. Luo, H. Wang, H. Wei, T. Guo, H. Tan, L. Yuan, X.-B. Zhang, Anal.
Chim. Acta 1065 (2019) 134.
[15] (a) Y.-H. Zhao, Y. Li, Y. Long, Z. Zhou, Z. Tang, K. Deng, S. Zhang, Tetrahedron
Lett. 58 (2017) 1351;
(c) Y. Chiang, A.J. Kresge, Y. Zhu, J. Am. Chem. Soc. 122 (2000) 9854;
(d) M.S. Singh, A. Nagaraju, N. Anand, S. Chowdhury, RSC Adv. 4 (2014) 55924;
(e) N.J. Willis, C.D. Bray, Chem. Eur. J. 18 (2012) 9160;
(b) O.A. Bozdemir, F. Sozmen, O. Buyukcakir, R. Guliyev, Y. Cakmak, E.U.
Akkaya, Org. Lett. 12 (2010) 1400;
(c) F. Qi, F. Zhang, L. Mo, X. Ren, Y. Wang, X. Li, X. Liu, Y. Zhang, Z. Yang, X.
Song, Spectrochim. Acta A 219 (2019) 547, For selected examples, see:.
[16] (a) Y.-H. Zhao, Y. Luo, H. Wang, T. Guo, H. Zhou, H. Tan, Z. Zhou, Y. Long, Z.
Tang, ChemistrySelect 3 (2018) 1521;
(f) T.P. Pathak, M.S. Sigman, J. Org. Chem. 76 (2011) 9210.
[12] (a) J.P. Richard, T.L. Amyes, M.M. Toteva, Acc. Chem. Res. 34 (2001) 981;
(b) J.P. Richard, M.M. Toteva, J. Crugeiras, J. Am. Chem. Soc. 122 (2000) 1664;
(c) M.M. Toteva, J.P. Richard, J. Am. Chem. Soc. 122 (2000) 11073;
(d) W.J. Bai, J.G. David, Z.G. Feng, M.G. Weaver, K.L. Wu, T.R.R. Pettus, Acc.
Chem. Res. 47 (2014) 3655.
(b) P.P. Zhang, S. Chen, Y.F. Kang, Y.F. Long, Spectrochim. Acta A 99 (2012) 347;
(c) L. Yang, Y. Su, Y. Geng, H. Xiong, J. Han, Q. Fang, X. Song, Org. Biomol. Chem.
16 (2018) 5036;
[13] (a) For selected examples, see: L. Yuan, W. Lin, Y. Xie, B. Chen, S. Zhu J. Am.
Chem. Soc. 134 (2012) 1305;
(d) Y.-H. Zhao, Y. Luo, T. Guo, Z. Tang, Z. Zhou, ChemistrySelect 4 (2019) 5195.
Please cite this article as: Y. Tang, Y. Yu, X. Wei et al., An efficient approach to isoquinoline via AgNO3-promoted 6-endo-dig cyclization followed by oxida-
tive elimination of o-alkynylarylaldimines and its application in fluoride recognition, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151187