DABCO- and DBU-promoted one-pot reaction of N-sulfonyl ketimines with Morita-Baylis-Hillman carbonates: A sequential approach to (2-hydroxyaryl)nicotinate derivatives

Article abstract of DOI:10.3762/bjoc.14.254

An intriguing DABCO-catalyzed and DBU-promoted one-pot synthesis of an important class of (2-hydroxyaryl)pyridine derivatives bearing a carboxylate or a nitrile group suitably placed at C3 position of the aza-ring has been achieved in acceptable chemical yields with a broad functional group tolerance. This sequential C-C/C-N bond making process proceeds through a regioselective allylic alkylation/aza-Michael reaction between MBH carbonates derived from an acrylate/acrylonitrile and N-sulfonyl ketimines as C,N-binucleophiles catalyzed by DABCO, followed by elimination of SO₂ under the influence of base and subsequent aromatization in an open atmosphere.

Full text of DOI:10.3762/bjoc.14.254

DABCO- and DBU-promoted one-pot reaction of
N-sulfonyl ketimines with Morita–Baylis–Hillman
carbonates: a sequential approach to
(2-hydroxyaryl)nicotinate derivatives
Soumitra Guin§, Raman Gupta§, Debashis Majee and Sampak Samanta*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2018, 14, 2771–2778.
Discipline of Chemistry, Indian Institute of Technology Indore, Simrol,
Indore, 453552, Madhya Pradesh, India
doi:10.3762/bjoc.14.254
Received: 13 August 2018
Accepted: 16 October 2018
Published: 02 November 2018
Email:
Sampak Samanta* - sampaks@iiti.ac.in
* Corresponding author
Associate Editor: T. J. J. Müller
§ Both the authors equally contributed to this work.
© 2018 Guin et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
MBH carbonates; metal-free; N-sulfonyl ketimines; one-pot
sequential; pyridines
Abstract
An intriguing DABCO-catalyzed and DBU-promoted one-pot synthesis of an important class of (2-hydroxyaryl)pyridine deriva-
tives bearing a carboxylate or a nitrile group suitably placed at C3 position of the aza-ring has been achieved in acceptable chemi-
cal yields with a broad functional group tolerance. This sequential C–C/C–N bond making process proceeds through a regioselec-
tive allylic alkylation/aza-Michael reaction between MBH carbonates derived from an acrylate/acrylonitrile and N-sulfonyl
ketimines as C,N-binucleophiles catalyzed by DABCO, followed by elimination of SO2 under the influence of base and subsequent
aromatization in an open atmosphere.
Introduction
Substituted pyridines are one of the most fascinating classes of process of living organisms. Consequently, many contributions
heterocyclic molecules which are present in many biologically have been made by synthetic chemists to search for new method
active natural and synthetic products [1-3]. In addition, several for the efficient synthesis and functionalization of pyridines.
pyridine scaffolds have been used in agro-chemical products Among the most significant techniques are condensation reac-
[4], medicines [5], chelating agents in transition metal com- tions between reactive carbonyls and amines (namely Hantzsch
plexes [6,7], and material science [8,9]. Pyridine derivatives [10] and Chichibabin pyridine synthesis [11,12]), transition
such as vitamins B6, B3 (niacin), and nicotinamide adenine metal salts-catalyzed [4 + 2] [13-18], [2 + 2 + 2] [19-26], and
dinucleotide (NAD) play a significant role in the metabolism [3 + 3] cyclization reactions [27], multicomponent reactions
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[28-33], and direct C–H functionalizations on the pyridine rings nicotinate derivatives were developed by Bohlman–Rahtz [39],
[34-36]. Particularly, the fascinating construction of pyridines Bagley [40,41] and other groups independently [42-55]. Simi-
bearing a carboxylate or CN group at C3 position has been a larly, the synthesis of functionalized nicotinonitriles has been
lucrative target for chemists due to the pharmaceutically privi- also greatly explored in the literature [56,57]. Even though great
leged status (Figure 1).
progress, the synthesis of (2-hydroxyaryl)pyridines bearing a
CO2Et/CN group at C3 position remains a daunting task in syn-
In this context, Rodriguez’s group successfully established a thetic organic chemistry [58,59]. A literature study reveals
one-pot three-component reaction between β,γ-unsaturated that a lot of research is focused on the synthesis of (2-hydroxy-
α-ketoesters, 1,3-dicarbonyl compounds, and ammonium aryl)pyridines from 2-arylpyridines via a direct C–H hydroxyl-
acetate promoted by acid under aerobic conditions [37,38]. ation on the aryl ring using several expensive transition metal
Furthermore, Brønsted- and Lewis-acid-catalyzed cyclization salts (e.g., Pd(II) [60-63], Rh(III) [64,65], Ru(II) [66]) as cata-
reactions between β-enamino esters (derived from β-ketoesters lysts (Scheme 1a). However, the above methods have several
and ammonium acetate) and alkynones/α,β-unsaturated drawbacks such as the requirement of high temperatures or use
carbonyls/in situ generated α,β-unsaturated ketones (from alkyl of strong oxidants (H2O2, oxone, K2S2O8, TBHP, PIDA, NHPI
ketones) as Michael acceptors to construct a diverse set of etc.) that are not much compatible with functionality,
Figure 1: Drugs and agrochemicals having a nicotinic acid derivative.
Scheme 1: One-pot access to (2-hydroxyaryl)pyridines.
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precluding late-stage functionalization. Moreover, the scope of and DBU-promoted sequential one-pot procedure for the access
substitution on the pyridine ring is limited which in turn to the interesting class of (2-hydroxyaryl)nicotinates/nicotinoni-
hampers the practical usage. Therefore, we are interested to triles from N-sulfonyl ketimines and MBH adducts as
devise a metal-free based general synthetic technique for the useful synthons [72,73] in the presence of open atmosphere
construction of substituted (2-hydroxyaryl)nicotinate/nicotino- (Scheme 1b).
nitrile scaffolds. In recent years, our research group has been
concentrated on the development of new synthetic methods for Results and Discussion
the preparation of polyfunctionalized pyridine building blocks We have commenced the model reaction between cyclic N-sul-
involving cyclic sulfamidate imines as carbon nucleophiles fonyl imine 1a as interesting C,N-binucleophiles [74] and MBH
[67-71]. In this direction, we recently documented an excellent carbonate of acrylate 2a using 20 mol % of DABCO in toluene
example of an organobase promoted pot-economical approach at room temperature for 14 h. This reaction produced 87% yield
to 4,6-disubstituted nicotinates by choosing 5-membered cyclic of allylic alkylation adduct 3a along with a small amount of
sulfamidate imines and MBH acetates of acrylate as coupling 9,10-dihydro-8H-benzo[e]pyrido[1,2-c]oxathiazine 6,6-dioxide
partners [68]. Herein, we further present a DABCO-catalyzed 4a in 4% yield (entry 1, Table 1).
Table 1: Optimization reaction conditions.
entry
conditions of step I and step II
yield (%)c
3a
4a
5aa
1
2
3
4
[I]a DABCO (20 mol %), toluene, rt, 14 h
[I]a DABCO (20 mol %), toluene, 60 °C, 6 h
[I]d DABCO (1.0 equiv), toluene, 70 °C, 6 h
87
0
4
0
88
85
>2
>4
76
0
[I]a DABCO (20 mol %), toluene, 60 °C, 6 h
[II]b DBU (1.2 equiv), toluene, 60 °C, air, 5 h
5
[I]a DABCO (20 mol %), THF, 60 °C, 6 h
[II]b DBU (1.2 equiv), THF, 60 °C, air, 5 h
68
50
30
19
<7
<5
6
[I]a DABCO (20 mol %), MeCN, 60 °C, 6 h
[II]b DBU (1.2 equiv), MeCN, 60 °C, air, 5 h
7
[I]a DABCO (20 mol %), DMF, 60 °C, 6 h
[II]b DBU (1.2 equiv), DMF, 60 °C, air, 5 h
8
[I]a DABCO (20 mol %), DMSO, 60 °C, 6 h
[II]b DBU (1.2 equiv), DMSO, 60 °C, air, 5 h
9
[I]a Et3N (20 mol %), toluene, 60 °C, 6 h
[II]b DBU (1.2 equiv), toluene, 60 °C, air, 5 h
10
[I]a DMAP (20 mol %), toluene, 60 °C, 6 h
[II]b DBU (1.2 equiv), toluene, 60 °C, air, 5 h
11
12
[I]e DBU (1.0 equiv), toluene, 60 °C, air, 5 h
NDf
21
[I]a PPh3 (20 mol %), toluene, 60 °C, 6 h
[II]b DBU (1.2 equiv), toluene, 60 °C, air, 5 h
aUnless otherwise specified, all of the above reactions were conducted with N-sulfonyl ketimine 1a (0.2 mmol), 2a (0.26 mmol) and base (0.04 mmol,
20 mol %) in the specified dry solvent (1.0 mL) and temperature under atmospheric conditions. bAfter completion of step I, DBU (1.2 equiv) was
added directly to the reaction mixture. cYield of isolated product after column chromatography. dDABCO (1.0 equiv) was used at 70 °C. eReaction was
carried out using 1.0 equiv of DBU. fND = not detected.
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Gratifyingly, high yields (88%) of cyclized product 4a and a lowed by elimination of SO2 to give intermediate 7. Finally, the
trace amount of desired nicotinate 5aa (2% yield) were ob- desired product 5aa is formed from 7 via aerial oxidation under
tained when the reaction was conducted at 60 °C (entry 2, open-flask conditions.
Table 1). By increasing the temperature as well as the loading
of DABCO (1.0 equiv, entry 3, Table 1), a similar result was With the optimization reaction conditions in hand, we decided
observed. At this situation, we surmised that step II may require to explore the generality and scope of the reaction by reacting
a stronger base like DBU which will facilitate the aromatiza- several aryl/heteroaryl-substituted MBH carbonates derived
tion process. For this purpose, DBU (1.2 equiv, entry 4, from acrylates 2a–j and 4-methyl-N-sulfonyl ketimines 1a–e
Table 1) was added to the reaction mixture at 60 °C after under present sequential reaction conditions. The results are in-
completion of step I. Pleasantly, 76% yield of wanted 5aa was corporated in Scheme 3. The regioselective allylic alkylation/
isolated after 5 h. Attempts to optimize the reaction conditions aromatization reaction between 4-methyl-N-sulfonyl ketimine
using several solvents (THF, MeCN, DMF and DMSO) all led 1a and several aryl-substituted MBH carbonates having elec-
to lower yields (19–68%, entries 5–8, Table 1) as compared to tron donating (Me, MeO and BnO) and withdrawing substitu-
the toluene-mediated reaction (76%, entry 4, Table 1). Next, ents (F, Br, CN and NO2) on the benzene rings proceeded
several N/P-containing Lewis bases such as Et3N, DMAP, DBU smoothly under the present conditions. The results showed that
and PPh3 were tested for this reaction in toluene and resulted in electron donating substituents of MBH carbonates produced
very poor yields (5–21%, entries 9–12).
65–73% yields of the corresponding (2-hydroxyphenyl)nicoti-
nates 5ab–5ad which are slightly lower yields as compared to
Based on the above experimental results as well as our previous electron withdrawing ones (74–79% yields, 5ae–5ah) under
report on DABCO-catalyzed reactions of cyclic sulfamidate identical conditions. Furthermore, heteroaryl-substituted MBH
imines with MBH carbonates of isatins [75], a plausible mecha- carbonates 2i and 2j also afforded 68% and 70% yields of 5ai
nism is presented and depicted in Scheme 2. For the first step, and 5aj, respectively.
the nucleophilic Lewis base DABCO reacts with 2a in an SN2'
fashion to make a very reactive allyl ammonium intermediate 6. Interestingly, the coupling reaction proceeded nicely not only
The latter further involves in the SN2' reaction with in situ with N-sulfonyl ketamine 1d bearing an electron poor Br atom
generated carbanion intermediate 1a' forming SN2-adduct 3a. It but also substrates 1b and 1c having electron donating substitu-
undergoes an intramolecular aza-Michael reaction in the pres- ents (Me, MeO) on the aryl rings, although the latter produced
ence of DABCO, leading to tricyclic product 4a. For the second better yields than the former one. By this C–C/C–N bonds
step, DBU (strong base) abstracts an allylic proton of 4a, fol- forming procedure, N-sulfonyl ketimine derived from a bulky
Scheme 2: A possible mechanism for this sequential reaction.
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Scheme 3: Substrate scope for (2-hydroxyaryl)nicotinates syntheses. The reaction was performed with 1a–e (0.2 mmol), 2a–j (0.26 mmol) and
DABCO (0.04 mmol, 20 mol %) in toluene at 60 °C for 6–8 h, followed by the addition of DBU (0.24 mmol, 1.2 equiv) at the same temperature in an
open atmosphere.
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Scheme 4: One-pot synthesis of (2-hydroxyaryl)nicotinonitriles 5ak–5am.
α-naphthol moiety was found to be a suitable coupling reagent, Acknowledgements
leading to the corresponding α-naphthol-substituted nicotinate The authors thank CSIR (Project No. 02(0273)/16/EMR-II)
derivatives 5ea and 5ee in 71% and 74% yields, respectively.
research grant, Govt. of India for generous financial support and
SIC facility, IIT Indore.
Next, we further expanded our present methodology for the syn-
thesis of 2-hydroxyarylated nicotinonitriles by using MBH
carbonates derived from an acrylonitrile. Experimental data
revealed that several aryl-substituted MBH carbonates 2k–2m
underwent [3 + 3] cyclization with N-sulfonyl ketimines 1a and
1c in our established reaction conditions, resulting in good
yields (68–76%) of aforesaid heterocycles 5ak–5am
(Scheme 4).
References
1. Heller, B.; Hapke, M. Chem. Soc. Rev. 2007, 36, 1085–1094.
doi:10.1039/B607877J
2. Allais, C.; Grassot, J.-M.; Rodriguez, J.; Constantieux, T. Chem. Rev.
2014, 114, 10829–10868. doi:10.1021/cr500099b
3. Michael, J. P. Nat. Prod. Rep. 2005, 22, 627–646.
doi:10.1039/B413750G
4. Guan, A.-Y.; Liu, C.-L.; Sun, X.-F.; Xie, Y.; Wang, M.-A.
Bioorg. Med. Chem. 2016, 24, 342–353.
doi:10.1016/j.bmc.2015.09.031
Conclusion
5. Baumann, M.; Baxendale, I. R. Beilstein J. Org. Chem. 2013, 9,
2265–2319. doi:10.3762/bjoc.9.265
In the current manuscript, a unique one-pot two-step sequential
reaction of 4-methyl N-sulfonyl ketimines with MBH carbon-
ates of acrylate/acrylonitrile catalyzed by DABCO, followed by
aromatization using DBU as a base in an open-flask has been
developed. This smart oxidant metal-free C–C/C–N bond
forming process leads to an array of functionalized nicotinates/
nicotinonitriles possessing an interesting phenolic moiety at
C6 position in good to high yields. Moreover, the current
process is mild enough to be applied on a broad range of func-
tional groups. Further studies on the application of this reaction
with broader substrate scope as well as the biological evalua-
tion of the synthesized pyridines are in progress which will be
documented in due course of time.
6. σ-Pyridine Coordination Compounds with Transition Metals. In
Chemistry of Heterocyclic Compounds: Pyridine Metal Complexes;
Tomasik, P.; Ratajewicz, Z.; Newkome, G. R.; Strekowski, L., Eds.;
John Wiley & Sons, Inc., 1985; Vol. 14, pp 186–2067.
doi:10.1002/9780470239674.ch3
Part 6.
7. Sumby, C. J. Coord. Chem. Rev. 2011, 255, 1937–1967.
doi:10.1016/j.ccr.2011.03.015
8. Müller, T. J. J.; Bunz, U. H. F., Eds. Functional Organic Materials;
Wiley-VCH: Weinheim, 2007.
9. Sasabe, H.; Kido, J. Chem. Mater. 2011, 23, 621–630.
doi:10.1021/cm1024052
10.Hantzsch, A. Ber. Dtsch. Chem. Ges. 1881, 14, 1637–1638.
doi:10.1002/cber.18810140214
11.Chichibabin, A. E. J. Russ. Phys.-Chem. Soc. 1906, 37, 1229–1231.
12.Li, Z.; Huang, X.; Chen, F.; Zhang, C.; Wang, X.; Jiao, N. Org. Lett.
2015, 17, 584–587. doi:10.1021/ol5035996
Supporting Information
13.Zhang, Q.-R.; Huang, J.-R.; Zhang, W.; Dong, L. Org. Lett. 2014, 16,
1684–1687. doi:10.1021/ol500345n
Supporting Information File 1
Synthetic protocols, characterization data and copies of 1H
and 13C NMR spectra.
14.Martin, R. M.; Bergman, R. G.; Ellman, J. A. J. Org. Chem. 2012, 77,
2501–2507. doi:10.1021/jo202280e
15.Chen, S.; Bergman, R. G.; Ellman, J. A. Org. Lett. 2015, 17,
2567–2569. doi:10.1021/acs.orglett.5b00979
[https://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-14-254-S1.pdf]
2776

Beilstein J. Org. Chem. 2018, 14, 2771–2778.
16.Neely, J. M.; Rovis, T. J. Am. Chem. Soc. 2014, 136, 2735–2738.
doi:10.1021/ja412444d
45.Kumar, S.; Sawant, A. A.; Chikhale, R. P.; Karanjai, K.; Thomas, A.
J. Org. Chem. 2016, 81, 1645–1653. doi:10.1021/acs.joc.5b02796
46.Reddy, C. R.; Panda, S. A.; Reddy, M. D. Org. Lett. 2015, 17,
896–899. doi:10.1021/ol503752k
17.Too, P. C.; Noji, T.; Lim, Y. J.; Li, X.; Chiba, S. Synlett 2011,
2789–2794. doi:10.1055/s-0031-1289556
18.Wu, J.; Xu, W.; Yu, Z.-X.; Wang, J. J. Am. Chem. Soc. 2015, 137,
9489–9496. doi:10.1021/jacs.5b06400
47.Prechter, A.; Henrion, G.; Faudot dit Bel, P.; Gagosz, F.
Angew. Chem., Int. Ed. 2014, 53, 4959–4963.
19.Goswami, A.; Ohtaki, K.; Kase, K.; Ito, T.; Okamoto, S.
Adv. Synth. Catal. 2008, 350, 143–152. doi:10.1002/adsc.200700380
20.Hapke, M.; Kral, K.; Fischer, C.; Spannenberg, A.; Gutnov, A.;
Redkin, D.; Heller, B. J. Org. Chem. 2010, 75, 3993–4003.
doi:10.1021/jo100122d
doi:10.1002/anie.201402470
48.Tejedor, D.; Méndez-Abt, G.; García-Tellado, F. Eur. J. Org. Chem.
2010, 6582–6587. doi:10.1002/ejoc.201001067
49.Tejedor, D.; Méndez-Abt, G.; García-Tellado, F. Chem. – Eur. J. 2010,
16, 428–431. doi:10.1002/chem.200902140
21.Tanaka, K.; Suzuki, N.; Nishida, G. Eur. J. Org. Chem. 2006,
3917–3922. doi:10.1002/ejoc.200600347
50.Jiang, Y.; Park, C.-M.; Loh, T.-P. Org. Lett. 2014, 16, 3432–3435.
doi:10.1021/ol501010k
22.Komine, Y.; Tanaka, K. Org. Lett. 2010, 12, 1312–1315.
doi:10.1021/ol100182u
51.Jiang, Y.; Park, C.-M. Chem. Sci. 2014, 5, 2347–2351.
doi:10.1039/C4SC00125G
23.Onodera, G.; Shimizu, Y.; Kimura, J.-n.; Kobayashi, J.; Ebihara, Y.;
Kondo, K.; Sakata, K.; Takeuchi, R. J. Am. Chem. Soc. 2012, 134,
10515–10531. doi:10.1021/ja3028394
52.Robert, N.; Bonneau, A.-L.; Hoarau, C.; Marsais, F. Org. Lett. 2006, 8,
6071–6074. doi:10.1021/ol062556i
53.Yu, J.; Kim, K. H.; Lee, H. J.; Kim, J. N. Bull. Korean Chem. Soc. 2013,
34, 3027–3032. doi:10.5012/bkcs.2013.34.10.3027
54.Ling, F.; Xiao, L.; Fang, L.; Lv, Y.; Zhong, W. Adv. Synth. Catal. 2018,
360, 444–448. doi:10.1002/adsc.201701031
24.Kumar, P.; Prescher, S.; Louie, J. Angew. Chem., Int. Ed. 2011, 50,
10694–10698. doi:10.1002/anie.201104475
25.Yamamoto, Y.; Kinpara, K.; Ogawa, R.; Nishiyama, H.; Itoh, K.
Chem. – Eur. J. 2006, 12, 5618–5631. doi:10.1002/chem.200600176
26.Wang, C.; Li, X.; Wu, F.; Wan, B. Angew. Chem., Int. Ed. 2011, 50,
7162–7166. doi:10.1002/anie.201102001
55.Hirai, S.; Horikawa, Y.; Asahara, H.; Nishiwaki, N. Chem. Commun.
2017, 53, 2390–2393. doi:10.1039/C7CC00051K
56.Longstreet, A. R.; Rivalti, D.; McQuade, D. T. J. Org. Chem. 2015, 80,
8583–8596. doi:10.1021/acs.joc.5b01169
27.Tan, W. W.; Ong, Y. J.; Yoshikai, N. Angew. Chem., Int. Ed. 2017, 56,
8240–8244. doi:10.1002/anie.201704378
57.Longstreet, A. R.; Opalka, S. M.; Campbell, B. S.; Gupton, B. F.;
McQuade, D. T. Beilstein J. Org. Chem. 2013, 9, 2570–2578.
doi:10.3762/bjoc.9.292
28.Jiang, H.; Yang, J.; Tang, X.; Li, J.; Wu, W. J. Org. Chem. 2015, 80,
8763–8771. doi:10.1021/acs.joc.5b01621
29.Wu, Q.; Zhang, Y.; Cui, S. Org. Lett. 2014, 16, 1350–1353.
doi:10.1021/ol500094w
58.Shintani, T.; Kadono, H.; Kikuchi, T.; Schubert, T.; Shogase, Y.;
Shimazaki, M. Tetrahedron Lett. 2003, 44, 6567–6569.
doi:10.1016/S0040-4039(03)01695-2
30.Senaiar, R. S.; Young, D. D.; Deiters, A. Chem. Commun. 2006,
1313–1315. doi:10.1039/B515901F
59.Qi, X.; Xiang, H.; He, Q.; Yang, C. Org. Lett. 2014, 16, 4186–4189.
doi:10.1021/ol5018855
31.Sasada, T.; Sakai, N.; Konakahara, T. J. Org. Chem. 2008, 73,
6905–6908. doi:10.1021/jo801090h
60.Das, P.; Saha, D.; Guin, J. ACS Catal. 2016, 6, 6050–6054.
doi:10.1021/acscatal.6b01539
32.He, Z.; Dobrovolsky, D.; Trinchera, P.; Yudin, A. K. Org. Lett. 2013, 15,
334–337. doi:10.1021/ol303246b
61.Dong, J.; Liu, P.; Sun, P. J. Org. Chem. 2015, 80, 2925–2929.
doi:10.1021/acs.joc.5b00167
33.Allais, C.; Constantieux, T.; Rodriguez, J. Chem. – Eur. J. 2009, 15,
12945–12948. doi:10.1002/chem.200902491
62.Yan, Y.; Feng, P.; Zheng, Q.-Z.; Liang, Y.-F.; Lu, J.-F.; Cui, Y.; Jiao, N.
Angew. Chem., Int. Ed. 2013, 52, 5827–5831.
34.Mai, D. N.; Baxter, R. D. Org. Lett. 2016, 18, 3738–3741.
doi:10.1021/acs.orglett.6b01754
doi:10.1002/anie.201300957
35.Stephens, D.; Larionov, O. V. Tetrahedron 2015, 71, 8683–8716.
doi:10.1016/j.tet.2015.08.034
63.Yamaguchi, T.; Yamaguchi, E.; Tada, N.; Itoh, A. Adv. Synth. Catal.
2015, 357, 2017–2021. doi:10.1002/adsc.201500061
64.Wu, Y.; Zhou, B. Org. Lett. 2017, 19, 3532–3535.
doi:10.1021/acs.orglett.7b01494
36.Engle, K. M.; Yu, J.-Q. J. Org. Chem. 2013, 78, 8927–8955.
doi:10.1021/jo400159y
37.Liéby-Muller, F.; Allais, C.; Constantieux, T.; Rodriguez, J.
Chem. Commun. 2008, 4207–4209. doi:10.1039/B805680C
38.Allais, C.; Liéby-Muller, F.; Rodriguez, J.; Constantieux, T.
Eur. J. Org. Chem. 2013, 4131–4145. doi:10.1002/ejoc.201300246
39.Bohlmann, F.; Rahtz, D. Chem. Ber. 1957, 90, 2265–2272.
doi:10.1002/cber.19570901021
65.Kim, K.; Hyun, J.; Kim, J.; Kim, H. Asian J. Org. Chem. 2017, 6,
907–912. doi:10.1002/ajoc.201700196
66.Shome, S.; Singh, S. P. Tetrahedron Lett. 2017, 58, 3743–3746.
doi:10.1016/j.tetlet.2017.08.037
67.Majee, D.; Biswas, S.; Mobin, S. M.; Samanta, S. J. Org. Chem. 2016,
81, 4378–4385. doi:10.1021/acs.joc.6b00472
40.Bagley, M. C.; Glover, C.; Merritt, E. A. Synlett 2007, 2459–2482.
doi:10.1055/s-2007-986674
68.Majee, D.; Biswas, S.; Mobin, S. M.; Samanta, S. Org. Biomol. Chem.
2017, 15, 3286–3297. doi:10.1039/C7OB00240H
69.Majee, D.; Guin, S.; Biswas, S.; Samanta, S. ChemistrySelect 2017, 2,
3423–3427. doi:10.1002/slct.201700733
41.Bagley, M. C.; Chapaneri, K.; Dale, J. W.; Xiong, X.; Bower, J.
J. Org. Chem. 2005, 70, 1389–1399. doi:10.1021/jo048106q
42.Gade, N. R.; Devendram, V.; Pal, M.; Iqbal, J. Chem. Commun. 2013,
49, 7926–7928. doi:10.1039/C3CC44274H
70.Biswas, S.; Majee, D.; Guin, S.; Samanta, S. J. Org. Chem. 2017, 82,
10928–10938. doi:10.1021/acs.joc.7b01792
43.Song, Z.; Huang, X.; Yi, W.; Zhang, W. Org. Lett. 2016, 18,
5640–5653. doi:10.1021/acs.orglett.6b02883
71.Guin, S.; Majee, D.; Biswas, S.; Samanta, S. Asian J. Org. Chem.
2018, 7, 1810–1814. doi:10.1002/ajoc.201800298
72.Langer, P. In Organic Synthesis Highlights V; Schmalz, H.-G.;
Wirth, T., Eds.; Wiley-VCH, 2003; pp 165–177.
44.Wan, J.-P.; Jing, Y.; Hu, C.; Sheng, S. J. Org. Chem. 2016, 81,
6826–6831. doi:10.1021/acs.joc.6b01149
2777

Beilstein J. Org. Chem. 2018, 14, 2771–2778.
73.Langer, P. Angew. Chem., Int. Ed. 2000, 39, 3049–3052.
doi:10.1002/1521-3773(20000901)39:17<3049::AID-ANIE3049>3.0.CO
;2-5
74.Chen, X.-Y.; Gao, Z.-H.; Song, C.-Y.; Zhang, C.-L.; Wang, Z.-X.; Ye, S.
Angew. Chem., Int. Ed. 2014, 53, 11611–11615.
doi:10.1002/anie.201407469
75.Arupula, S. K.; Guin, S.; Yadav, A.; Mobin, S. M.; Samanta, S.
J. Org. Chem. 2018, 83, 2660–2675. doi:10.1021/acs.joc.7b03090
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