Oxidative Furan-to-Indole Rearrangement. Synthesis of 2-(2-Acylvinyl)indoles and Flinderole C Analogues

Article abstract of DOI:10.1021/acs.orglett.6b00805

Oxidative rearrangement of 2-(2-aminobenzyl)furans affording 2-(2-acylvinyl)indoles in a stereocontrolled manner in good-to-excellent yields has been developed. Thus, (2-aminobenzyl)furans with electron-releasing alkoxy substituents in the phenyl group fo

Full text of DOI:10.1021/acs.orglett.6b00805

Letter
pubs.acs.org/OrgLett
Oxidative Furan-to-Indole Rearrangement. Synthesis of 2‑(2-
Acylvinyl)indoles and Flinderole C Analogues
Anton S. Makarov,† Anton A. Merkushev,†,‡ Maxim G. Uchuskin,*,† and Igor V. Trushkov§,⊥
†Department of Chemistry, Perm State University, Bukireva st. 15, Perm 614990, Russia
‡Institute of Technical Chemistry UrB RAS, Academika Koroleva st. 3, Perm 614013, Russia
§Department of Chemistry, M.V. Lomonosov Moscow State University, Leninskie gory 1-3, Moscow 119991, Russia
⊥Laboratory of Chemical Synthesis, Federal Research Center of Pediatric Hematology, Oncology and Immunology, Samory Mashela
1, Moscow 117997, Russia
S
* Supporting Information
ABSTRACT: Oxidative rearrangement of 2-(2-aminobenzyl)furans
affording 2-(2-acylvinyl)indoles in a stereocontrolled manner in good-
to-excellent yields has been developed. Thus, (2-aminobenzyl)furans
with electron-releasing alkoxy substituents in the phenyl group form
only E-isomers of 2-(2-acylvinyl)indoles. Conversely, substrates
without such substituents produce target products as Z-isomers
exclusively. A short diastereoselective method for the transformation of
the obtained 2-(2-acylvinyl)indoles into antimalarial bisindole alkaloid flinderole A−C analogues has been developed.
he increasing use of biomass as a renewable source of raw
materials is one of the imperatives of modern industrial
Scheme 1. Furan-to-Azaheterocycle Transformations:
Previous Approaches and This Work
T
organic chemistry due to the restricted supply of fossil resources.
The most important products of biomass processing are referred
to as “molecular platforms”.1 Among these platforms, there are
three furan derivatives (furfural, 5-hydroxymethylfurfural, and
furan-2,5-dicarboxylic acid). Their aromatic reactivity and side
chain functionalization are used to produce a wide range of furan
derivatives, including medicines, photomaterials, and diesel
fuel.2,3
The promising extension of “furan platform” utilization is their
transformations into other heterocyclic compounds, especially
various azaheterocycles.4 The low aromaticity energy of the furan
ring is responsible for the possibility of such transformations,
thereby providing diverse furan reactivities.5 The reactivity of
furans as a synthetic equivalent of 1,4-diketones6 is the most
studied. Ammonia or primary amines can react with both masked
carbonyl groups, affording pyrrole derivatives (Yuriev reaction,
Scheme 1a). Otherwise, azaheterocycles can be formed as a result
of the intramolecular reaction of a nitrogen nucleophile, with a
single latent ketone function while a second masked carbonyl
group evolves in a free form (Butin reaction, Scheme 1b).
Moreover, under oxidative conditions, furan can react as
synthetic equivalent of 2-ene-1,4-dione; corresponding reactions
of furfurylamines afford pyridine derivatives (Scheme 1c, aza-
Achmatowicz reaction).7 In the last process, the nitrogen
nucleophile, separated from the furan ring by a single carbon
atom, can react with the remote masked carbonyl group only.
Nevertheless, if nitrogen and α-carbon are tethered by three
atoms, the nucleophile can react with the proximal latent
carbonyl group, affording a five-membered azaheterocycle.
Inspired by this idea, we devised a new oxidative rearrange-
ment of 2-(2-aminobenzyl)furans 1, which can be synthesized
from furfural in a straightforward manner,8 into 2-(2-acylvinyl)-
indoles 29 (Scheme 1d). Herein, we report the results of our
investigation of this reaction, which opens a simple path from
primary products of biomass processing to indoles constituting
the most privileged class of heterocyclic compounds due to a
broad range of their bioactivities.10 The presence of an α,β-
Received: March 19, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.6b00805
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
unsaturated ketone in indole 2 also opens up opportunities for
diverse and useful transformations.11
Scheme 3. Scope of m-CPBA-Induced Rearrangement of
Furans 1 to Indoles 2
a
Antimalarial bisindole alkaloid flinderoles A−C (Figure 1),
were recently isolated from Flindersia sp.12 To synthesize
Figure 1. Antimalarial alkaloid flinderoles A−C.
flinderoles and their analogues, three “biomimetic” methods
were used.13 The first one is based on the acid-induced
dimerization of borrerine 3 or its derivatives (Figure 1, path
a).14 The key step of the second approach is the acid-catalyzed
reaction of diene 4 with 4-(2-indolyl)-2-methylbut-3-enols 5
(Figure 1, path b).15 Third, a flinderole scaffold was obtained by
dimerization of alcohols 5 (Figure 1, path c).15 Both 4 and 5 can
be easily obtained from the corresponding enones 2.
Accordingly, aimed at expansion of the Flinderole-type products,
we first developed a short diastereoselective method for the
transformation of the obtained 2-(2-acylvinyl)indoles 2 into
flinderole A−C analogues.
We started this work with a search for optimal reaction
conditions using 5-methyl-2-[(2-tosylamino)benzhydryl]furan
1a as a model substrate. A diversity of reagents (Oxone, NaClO2,
Br2, N-bromosuccinimide, etc.), used previously for oxidation of
furans, were studied.16,17 After extensive experiments, we found
that treatment of 1a with m-CPBA at room temperature18 affords
the desired indole 2a in excellent yield as a 2:1 mixture of Z- and
E-isomers (Scheme 2). During further tuning of the reaction
a
Conditions: benzylfuran (0.5 mmol), m-CPBA (0.6 mmol), CH2Cl2
(2 mL), 0 °C, 1 h; then TFA (0.05 mmol), rt, 20 h.
atom of the furan ring and at the nitrogen atom (R1, R3 ≠ H) is
also crucial for a good yield of 2. Significant tarring was observed
for substrates without substituents at these atoms (R1, R3 = H).
Nevertheless, substrates with diverse alkyl substituents in the
furan ring were found to react with a similar efficiency. The
nature of the substituent at the benzylic position (R2) has no
significant influence on the reaction yield.19
If electron-withdrawing groups in the phenyl ring hamper the
studied rearrangement, electron-releasing substituents change
process stereoselectivity. Namely, 5,6-dialkoxyindoles 2l−s were
obtained as E-isomers exclusively. Evidently, electron-donating
substituents in the phenyl ring accelerate acid-induced Z/E-
isomerization in the formed indole 2.17 On the contrary, (Z)-2a
was not converted into an E-isomer even under higher loading
(0.3 equiv) of TFA. Nevertheless, we found that this isomer-
ization proceeds quantitatively under heating with iodine (see
below).
Scheme 2. m-CPBA-Induced Oxidative Rearrangement of 1a
to 2a
During optimization of the reaction conditions, we found that
quenching of the reaction mixture with aq NaHCO3 produces an
unusual spiroindoline 6 (Scheme 4), structure of which was
Scheme 4. Formation of the 6 in the m-CPBA-Induced
Oxidative Transformation of Furan 1a
conditions, we found that indole 2a can be obtained as the Z-
isomer exclusively in 88% isolated yield under 1a oxidation at 0
°C followed by treatment of the reaction mixture with 10 mol %
of TFA.
With the optimized conditions in hand, we studied the scope
of the disclosed reaction (Scheme 3). A broad variety of 2-(2-
aminobenzyl)furans 1 were shown to afford the corresponding
indoles 2 in good-to-excellent yields. A single exception was
compound 2k, which was obtained in 44% yield only. The
presence of the electron-withdrawing substituent in the para-
position to the nucleophilic nitrogen is responsible for the low
yield in this case. The corresponding substrate with a nitro group
in the para-position of the tosylamine moiety failed to produce
the corresponding indole. The presence of a substituent at the C5
unambiguously proven by single-crystal X-ray analysis.20 It is
noteworthy that the treatment of 6 with TFA furnished indole 2a
quantitatively. This indicates that 6 is a tentative reaction
intermediate.
The proposed reaction mechanism for the title rearrangement
includes an epoxidation of the furan ring in 1 with m-CPBA to
form intermediate epoxide A21 followed by an intramolecular
B
DOI: 10.1021/acs.orglett.6b00805
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
nucleophilic attack of the amine moiety, producing 6.
Subsequent protonation of 6 induces dihydrofuran ring opening
and indole moiety aromatization to form (Z)-2 or (E)-2
(Scheme 5).17
Scheme 7. Synthesis of Flinderole C Analogue 10
Scheme 5. Proposed Mechanism for the Formation of Indoles
2
of the opposite diastereomers.14,15,17 The predominant for-
mation of the isomer with cis-arrangement of two alkenyl groups
in the HCl-induced reaction is consistent with the stability of 10
being higher than that of its trans-isomer. Our quantum-chemical
calculations showed that 10 is more stable by 7.5 kJ mol−1 at HF/
6-31G level and 6.2 kJ mol−1 at the B3LYP/6-311G** level.17
Different stereochemical results in the dimerizations of 3 and
5a−c under the effect of other initiators used can be attributed to
the coordination of a catalyst to both molecules in the
dimerization transition state,15a providing greater decrease of
the energy barrier for the formation of trans-10.
With the aim to extend the scope of the reaction applicability,
we decided to study 2-benzylfurans with a nucleophilic moiety
separated from the phenyl group by one or more carbon atoms.
Indeed, we found that N-benzyl-2-(5-methylfurfuryl)benzamide
7 rearranged into the target isoquinolone (Z)-8 in 84% yield
(Scheme 6).22 This demonstrates that the disclosed oxidative
In conclusion, we have developed the m-CPBA-induced
rearrangement of 2-(2-aminobenzyl)furans 1 to 2-(2-acylvinyl)-
indoles 2. The disclosed reaction provides a shortcut to
polyfunctionalized indoles in up to 90% yield starting from
furans 1, which can be easily synthesized from the molecular
platforms of biomass processing. It was found that the reaction
stereoselectivity is governed by substituents in the phenyl group.
Extension of the developed oxidative recyclization for the
synthesis of isoquinolones from the corresponding 2-furfur-
ylbenzamides was demonstrated. A simple, efficient trans-
formation of the obtained indole-derived enones 2 into
analogues of bisindole alkaloid flinderoles A−C was developed.
Scheme 6. Oxidative Rearrangement of 2-Furfurylbenzamide
7
rearrangement has a general character and can be used for the
transformation of a broad variety of furans bearing a nucleophilic
moiety separated from the furan ring by three or more atoms in
the corresponding heterocyclic compounds.
ASSOCIATED CONTENT
■
S
* Supporting Information
Finally, we studied the transformation of indoles 2 into the
Flindersial alkaloid analogues using 2a as a model substrate.
Heating of toluene solution of (Z)-2a with iodine induced its
quantitative isomerization to (E)-2a. A subsequent treatment of
(E)-2a with MeMgI afforded the corresponding tertiary allyl
alcohol 9. Its deprotection with methanolic KOH furnished N-
unsubstituted indole 5a in 87% yield. The indole 5a underwent
acid-induced dimerization to 3-[2-(2-indolyl)vinyl]pyrrolo[1,2-
a]indole derivative 10. The dimerization yield and stereo-
selectivity were found to depend on the conditions applied.
Acidic agents, applied earlier for the dimerization of borrerine 314
and indoles 5b,c (R″ = Me,15a CH2CH2OH),15b afford
flinderoles and their analogues with low diastereoselectivity.
Similarly, under these reaction conditions, dimer 10 was formed
as a mixture of two isomers in a ratio of ca. 1:1. Fortunately, we
have found that use of concentrated HCl in CHCl3 allows target
compound 10 to be produced in excellent yield and a cis/trans
diastereomeric ratio of 6.5:1 (Scheme 7). Moreover, the major
isomer of 10 can be isolated by simple crystallization from
DMSO. It is noteworthy that single-crystal X-ray analysis of 10
revealed that its stereochemistry corresponds to that of flinderole
C,20 while the reported methods usually produced a small excess
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.6b00805.
Experimental procedures and NMR, IR, MS spectra,
elemental analyses (PDF)
X-ray data for 6 (CIF)
X-ray data for 10 (CIF)
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: mu@psu.ru.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Ministry of Education and Science of the Russian
Federation (Project No. 4.246.2014/K) and the Russian
Foundation for Basic Research (Grant No. 13-03-00463 A) for
supporting this work. We thank also Dr. A.E. Rubtsov and Dr.
M.V. Dmitriev (Perm State University) for the preparation of
single-crystal X-ray data.
C
DOI: 10.1021/acs.orglett.6b00805
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Minvielle, M. J.; Melander, C. Tetrahedron 2014, 70, 6363−6372.
(d) Zhang, M.-Z.; Chen, Q.; Yang, G.-F. Eur. J. Med. Chem. 2015, 89,
421−441. (e) Sherer, C.; Snape, T. J. Eur. J. Med. Chem. 2015, 97, 552−
560. (f) Lee, J.-H.; Wood, T. K.; Lee, J. Trends Microbiol. 2015, 23, 707−
718.
DEDICATION
■
This paper is dedicated to the memory of Prof. Alexander V.
Butin (1962−2015), mentor, colleague, and friend.
(11) (a) Zhao, C.; Toste, F. D.; Bergman, R. G. J. Am. Chem. Soc. 2011,
133, 10787−10789. (b) Su, T.; Han, X.; Lu, X. Tetrahedron Lett. 2014,
55, 27−30. (c) Tang, C.-Y.; Tao, Y.; Wu, X.-Y.; Sha, F. Adv. Synth. Catal.
2014, 356, 609−615. (d) Jang, Y.-J.; Chen, Y.-S.; Lee, C.-J.; Chen, C.-H.;
Lin, W. Synthesis 2015, 47, 95−107. (e) Chen, W.; Zhang, H.-H.; Luo,
Y.-C. Synlett 2015, 26, 1687−1692. (f) Swamy, P. M. G.; Prasad, Y. R.;
Ashvini, H. M.; Giles, D.; Shashidhar, B. V.; Agasimundin, Y. S. Med.
Chem. Res. 2015, 24, 3437−3452. (g) Sha, F.; Tao, Y.; Tang, C.-Y.;
Zhang, F.; Wu, X.-Y. J. Org. Chem. 2015, 80, 8122−8133.
REFERENCES
■
(1) Bozell, J. J.; Petersen, G. R. Green Chem. 2010, 12, 539−544.
(2) (a) Rosatella, A. A.; Simeonov, S. P.; Frade, R. F. M.; Afonso, C. A.
M. Green Chem. 2011, 13, 754−793. (b) Gallezot, P. Chem. Soc. Rev.
2012, 41, 1538−1558. (c) Hu, L.; Zhao, G.; Hao, W.; Tang, X.; Sun, Y.;
Lin, L.; Liu, S. RSC Adv. 2012, 2, 11184−11206. (d) van Putten, R. J.;
van der Waal, J. C.; de Jong, E.; Rasrendra, C. B.; Heeres, H. J.; de Vries,
J. G. Chem. Rev. 2013, 113, 1499−1597. (e) Sheldon, R. A. Green Chem.
2014, 16, 950−963. (f) Gidron, O.; Bendikov, M. Angew. Chem., Int. Ed.
2014, 53, 2546−2555.
(3) (a) Wegenhart, B. L.; Yang, L.; Kwan, S. C.; Harris, R.; Kenttamaa,
H. I.; Abu-Omar, M. M. ChemSusChem 2014, 7, 2742−2747.
(b) Balakrishnan, M.; Sacia, E. R.; Bell, A. T. ChemSusChem 2014, 7,
2796−2800. (c) Xia, Q.-N.; Cuan, Q.; Liu, X.-H.; Gong, X.-Q.; Lu, G.-
Z.; Wang, Y.-Q. Angew. Chem., Int. Ed. 2014, 53, 9755−9760.
(d) Thiyagarajan, S.; Genuino, H. C.; Sliwa, M.; van der Waal, J. C.;
de Jong, E.; van Haveren, J.; Weckhuysen, B. M.; Bruijnincx, P. C. A.; van
Es, D. S. ChemSusChem 2015, 8, 3052−3056. (e) Gupta, K.; Tyagi, D.;
Dwivedi, A. D.; Mobin, S. M.; Singh, S. K. Green Chem. 2015, 17, 4618−
4627. (f) Hu, X.; Kadarwati, S.; Song, Y.; Li, C.-Z. RSC Adv. 2016, 6,
4647−4656.
(4) (a) Lichtenthaler, F. W. Acc. Chem. Res. 2002, 35, 728−737.
(b) Guo, J.; Yu, B.; Wang, Y.-N.; Duan, D.; Ren, L.-L.; Gao, Z.; Gou, J.
Org. Lett. 2014, 16, 5088−5091. (c) Xu, L.; Jiang, Y.; Yao, Q.; Han, Z.;
Zhang, Y.; Fu, Y.; Guo, Q.; Huber, G. W. Green Chem. 2015, 17, 1281−
1290. (d) Xu, L.; Yao, Q.; Deng, J.; Han, Z.; Zhang, Y.; Fu, Y.; Huber, G.
W.; Guo, Q. ACS Sustainable Chem. Eng. 2015, 3, 2890−2899.
(e) Sowmiah, S.; Veiros, L. F.; Esperanca, J. M. S. S.; Rebelo, L. P. N.;
Afonso, C. A. M. Org. Lett. 2015, 17, 5244−5247.
(5) (a) Padwa, A.; Flick, A. C. Adv. Heterocycl. Chem. 2013, 110, 1−41.
(b) Parr, B. T.; Green, S. A.; Davies, H. M. L. J. Am. Chem. Soc. 2013,
135, 4716−4718. (c) Kalaitzakis, D.; Noutsias, D.; Vassilikogiannakis, G.
Org. Lett. 2015, 17, 3596−3599. (d) Lopes, S. M. M.; Henriques, M. S.
C.; Paixao, J. A.; Pinho e Melo, M. V. D. Eur. J. Org. Chem. 2015, 2015,
6146−6151. (e) Kalaitzakis, D.; Triantafyllakis, M.; Sofiadis, M.;
Noutsias, D.; Vassilikogiannakis, G. Angew. Chem., Int. Ed. 2016, 55,
4605−4609.
(6) Trushkov, I. V.; Uchuskin, M. G.; Butin, A. V. Eur. J. Org. Chem.
2015, 2015, 2999−3016.
(7) For recent reviews, see: (a) Merino, P. In Organic Reactions;
Denmark, S. E., Ed.; Wiley-VCH: Weinheim, 2015; Vol. 87, pp 1−256.
(b) Deska, J.; Thiel, D.; Gianolio, E. Synthesis 2015, 47, 3435−3450.
(c) van der Pijl, F.; van Delft, F. L.; Rutjes, F. P. J. T. Eur. J. Org. Chem.
2015, 2015, 4811−4829.
(12) Fernandez, L. S.; Buchanan, M. S.; Carroll, A. R.; Feng, Y. J.;
Quinn, R. J.; Avery, V. M. Org. Lett. 2009, 11, 329−332.
(13) The multistep synthesis based on Au-catalyzed allene hydro-
arylation was also reported: Zeldin, R. M.; Toste, F. D. Chem. Sci. 2011,
2, 1706−1709.
(14) (a) Vallakati, R.; May, J. A. J. Am. Chem. Soc. 2012, 134, 6936−
6939. (b) Dethe, D. H.; Erande, R. D.; Dherange, B. D. Org. Lett. 2014,
16, 2764−2767. (c) Vallakati, R.; Lundy, B. J.; Jansone-Popova, S.; May,
J. A. Chirality 2015, 27, 14−17. (d) Kamptmann, S. B.; Ley, S. V. Aust. J.
Chem. 2015, 68, 693−696.
(15) (a) Dethe, D. H.; Erande, R. D.; Ranjan, A. J. Am. Chem. Soc. 2011,
133, 2864−2867. (b) Dethe, D. H.; Erande, R. D.; Ranjan, A. J. Org.
Chem. 2013, 78, 10106−10120.
(16) (a) Asaoka, M.; Yanagida, N.; Sugimura, N.; Takei, H. Bull. Chem.
Soc. Jpn. 1980, 53, 1061−1064. (b) Lepage, L.; Lepage, Y. Synthesis
1983, 1983, 1018−1019. (c) Wu, H.-J.; Huang, F.-J.; Lin, C.-C. J. Chem.
Soc., Chem. Commun. 1991, 770−771. (d) D’Annibale, A.; Scettri, A.
Tetrahedron Lett. 1995, 36, 4659−4660. (e) Sayama, S.; Inamura, Y.
Heterocycles 1996, 43, 1371−1374. (f) Kobayashi, Y.; Nakano, M.;
Kumar, G. B.; Kishihara, K. J. Org. Chem. 1998, 63, 7505−7515.
(g) Raczko, J. Tetrahedron 2003, 59, 10181−10186. (h) Annangudi, S.
P.; Sun, M.; Salomon, R. G. Synlett 2005, 1468−1470. (i) Yu, H.; Zhong,
W.; He, T.; Gu, W.; Yin, B. Tetrahedron Lett. 2013, 54, 1256−1260.
(j) Sivasakthikumaran, R.; Nandakumar, M.; Mohanakrishnan, A. K.
Synlett 2014, 25, 1896−1900. (k) Burki, C.; Bonjoch, J.; Bradshaw, B.;
̈
Villa, G.; Renaud, P. Chem. - Eur. J. 2015, 21, 395−401.
(17) See the Supporting Information for details.
(18) Williams, P. D.; LeGoff, E. J. Org. Chem. 1981, 46, 4143−4147.
(19) Related 2-(2-acylvinyl)-NH-indoles were synthesized by
thermolysis of the corresponding 2-(2-azidobenzyl)furans bearing a
broader scope of substituents in the phenyl ring.9f On the other hand,
only indoles bearing a (hetero)aryl substituent at the C(3) position were
prepared by these methods. Moreover, only E-isomers were obtained in
high yields. Thus, these two methods are complementary.
(20) CCDC 1426892 (6) and 1444841 (10) contain the
supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre.
(21) (a) Gingerich, S. B.; Campbell, W. H.; Bricca, C. E.; Jennings, P.
W.; Campana, C. F. J. Org. Chem. 1981, 46, 2589−2591. (b) Kobayashi,
Y.; Katsuno, H.; Sato, F. Chem. Lett. 1983, 1771−1774. (c) Manfredi, K.
P.; Jennings, P. W. J. Org. Chem. 1989, 54, 5186−5188.
(22) For acid-catalyzed recyclization of 2-furfurylbenzamides, see:
Dmitriev, A. S.; Abaev, V. T.; Bender, W.; Butin, A. V. Tetrahedron 2007,
63, 9437−9447.
(8) (a) Butin, A. V.; Stroganova, T. A.; Lodina, I. V.; Krapivin, G. D.
Tetrahedron Lett. 2001, 42, 2031−2033. (b) Butin, A. V.; Smirnov, S. K.;
Stroganova, T. A.; Bender, W.; Krapivin, G. D. Tetrahedron 2007, 63,
474−491. (c) Nakagawa, Y.; Tamura, M.; Tomishige, K. ACS Catal.
2013, 3, 2655−2668. See the Supporting Information.
(9) For other methods of the synthesis of β-indolyl-α,β-unsaturated
ketones from furans, see: (a) Butin, A. V.; Uchuskin, M. G.; Pilipenko, A.
S.; Tsiunchik, F. A.; Cheshkov, D. A.; Trushkov, I. V. Eur. J. Org. Chem.
2010, 2010, 920−926. (b) El Kaim, L.; Grimaud, L.; Wagschal, S. Chem.
Commun. 2011, 47, 1887−1889. (c) Yin, B.; Cai, C.; Zeng, G.; Zhang,
R.; Li, X.; Jiang, H. Org. Lett. 2012, 14, 1098−1101. (d) Uchuskin, M. G.;
Molodtsova, N. V.; Abaev, V. T.; Trushkov, I. V.; Butin, A. V.
Tetrahedron 2012, 68, 4252−4258. (e) Uchuskin, M. G.; Molodtsova, N.
V.; Lysenko, S. A.; Strel’nikov, V. N.; Trushkov, I. V.; Butin, A. V. Eur. J.
Org. Chem. 2014, 2014, 2508−2515. (f) Abaev, V. T.; Plieva, A. T.;
Chalikidi, P. N.; Uchuskin, M. G.; Trushkov, I. V.; Butin, A. V. Org. Lett.
2014, 16, 4150−4153.
(10) (a) Kochanowska-Karamyan, A. J.; Hamann, M. T. Chem. Rev.
2010, 110, 4489−4497. (b) Ruiz-Sanchis, P.; Savina, S. A.; Albericio, F.;
Alvarez, M. Chem. - Eur. J. 2011, 17, 1388−1408. (c) Melander, R. J.;
D
DOI: 10.1021/acs.orglett.6b00805
Org. Lett. XXXX, XXX, XXX−XXX