A selective removal of the secondary hydroxy group from ortho-dithioacetal-substituted diarylmethanols

Article abstract of DOI:10.3762/bjoc.14.105

We present a successful deoxygenation reaction of ortho-1,3-dithianylaryl(aryl)methanols which enables a selective removal of the secondary hydroxy group in presence of the 1,3-dithianyl moiety under reductive conditions. This reaction proceeds well with

Full text of DOI:10.3762/bjoc.14.105

A selective removal of the secondary hydroxy group from
ortho-dithioacetal-substituted diarylmethanols
Anna Czarnecka1, Emilia Kowalska1, Agnieszka Bodzioch1, Joanna Skalik1,
Marek Koprowski1, Krzysztof Owsianik1 and Piotr Bałczewski*1,2
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2018, 14, 1229–1237.
1Group of Synthesis of Functional Materials, Centre of Molecular and
Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza
112, 90-363 Łódź, Poland, and 2Department of Structural and
Material Research, Institute of Chemistry, Environmental Protection
and Biotechnology, Faculty of Mathematics and Natural Sciences, Jan
Długosz University in Częstochowa, Armii Krajowej 13/15, 42-200
Częstochowa, Poland
doi:10.3762/bjoc.14.105
Received: 26 January 2018
Accepted: 27 April 2018
Published: 29 May 2018
Associate Editor: B. Stoltz
Email:
© 2018 Czarnecka et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Piotr Bałczewski* - pbalczew@cbmm.lodz.pl
* Corresponding author
Keywords:
diarylmethanes; diarylmethanols; 1,3-dithiane; selective reduction;
sodium cyanoborohydride; zinc iodide
Abstract
We present a successful deoxygenation reaction of ortho-1,3-dithianylaryl(aryl)methanols which enables a selective removal of the
secondary hydroxy group in presence of the 1,3-dithianyl moiety under reductive conditions. This reaction proceeds well with
ZnI2/Na(CN)BH3 in dichloroethane or benzene for both unsubstituted and substituted aryls (by electron-rich groups). This is
leading to formyl-protected diarylmethanes with potential application in the synthesis of new pharmaceuticals and optoelectronic
materials. This synthetic approach gives an access to a wide variety of functionalized ortho-1,3-dithianylaryl(aryl)methanes in
26–95% yields and is recommended for the substrates containing sulfur atoms, for which transition metal-induced reactions fail.
Introduction
In last decades, diarylmethanes, such as I–IV and cyclic com- tivities (II) [6]. Other ones have been reported as inhibitors of
pounds possessing a diarylmethyl motif, like podophyllotoxin HIV-1 integrase and viral replication in cells [7] or antituber-
(V) and lasofoxifene (VI), have been a subject of interest as cular agents (III) [8,9]. Various diarylmethane-based mole-
bioactive molecules (Figure 1) [1]. The diarylmethane deriva- cules, like tolterodine (IV) [10], podophyllotoxin (V) [11] and
tives, isolated from natural sources, showed antibacterial [2], lasofoxifene (VI) [12] have been used in the treatment of over-
antiestrogenic and antitumorigenic (I) [3-5] or vasodilating ac- active bladder, external genital warts and osteoporosis
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Beilstein J. Org. Chem. 2018, 14, 1229–1237.
Figure 1: Structures of biologically active diarylmethanes and commercially available pharmaceuticals based on the diarylmethyl moiety.
(Figure 1). The diarylmethyl motif also plays a pivotal role in acid [24]) as well as benzotrifluorides (employed in hydrode-
supramolecular architectures of calixarenes [13] and orthocy- fluorinative Friedel–Crafts alkylations catalyzed by alumenium
clophanes [14].
ions [25]) were interesting, alternative substrates for alcohols,
acetals and esters.
A special, ortho-carbonyl-substituted diarylmethyl scaffold is
present in the key substrates for aromatic cyclodehydration, also A large group of synthetic procedures for the synthesis of
known as the Bradsher reaction [15], which leads to fused, diarylmethanes are deoxygenations of secondary diarylmethyl
polycyclic aromatic hydrocarbons [16-19]. This type of reac- alcohols with hydride sources. These reactions require a prelim-
tion found applications in synthesis of organic, optoelectronic inary C–OH bond activation by Brønsted or Lewis acids.
materials [20-22].
Several reagent systems have recently been employed to
achieve this goal, including: NaBH4–CF3COOH [26],
Metal-catalyzed cross-coupling reactions (e.g., Suzuki–Miyau- ZnI2–NaBH3CN [27], HI–Pred [28], H3PO2–I2 [29,30],
ra, Stille, Kumada, Hiyama or Negishi couplings) play a key Mo(CO)6-Lawesson’s reagent [31], PBr3 [32], BF3·Et2O–di-
role in the preparation of diarylmethanes. However, the reac- butyl ether [33] and silanes (Si–H) in the presence of
tions involving sulfur-containing moieties have not been re- various Lewis acids: B(C6F5)3 [34-36], InCl3 [37,38],
ported yet (Scheme 1) [1]. It is noteworthy that under certain H3[PW12O40]×nH2O [39], Ca(NTf2)2 [40], Bi(OTf)3 [41],
conditions, the Pd-catalyzed cross-coupling reactions of sub- Sn(IV)-montmorillonite [42] and PdCl2 [43]. It is interesting
strates containing an 1,3-dithiane moiety are feasible, like in the that Seto et al. reported that Et3SiH–CF3COOH, TMSCl/NaI
case of the 2-arylation of 2-aryl-substituted 1,3-dithianes. How- failed to reduce secondary OH groups in diheteroaromatic
ever, in the case of 2-benzyl-substituted 1,3-dithianes, a systems and the reduction with H2/Pd/C-ZnBr2 was very slow
tandem elimination/1,3-dithiane ring opening followed [32]. On the other hand, some rigid diarylmethanols were suc-
by a Pd-catalyzed C−S bond formation was observed instead cessfully reduced to benzo[b]indeno[2,1-d]thiophenes using the
[23].
Et3SiH–CF3COOH system which was reported in the patent lit-
erature [44].
Diarylmethanes were also obtained in the Friedel–Crafts reac-
tions of arenes with primary benzyl alcohols, aryl acetals, and Benzophenones were also reduced to diarylmethanes using
benzyl esters [1]. Benzyl fluorides (in 1,1,1,3,3,3-hexafluoroiso- supercritical iPrOH at 350 °C [1], BF3·OEt2/H2O [33] and
propanol in the presence of a catalytic amount of trifluoroacetic PhSiH3/MoCl2O2(H2O)2 [45].
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Beilstein J. Org. Chem. 2018, 14, 1229–1237.
The reductive deoxygenation reactions of diarylmethanols cording to the procedure shown in Scheme 2 including:
proceed via carbocationic species, which are formed by proton- 1) protection of the formyl group in ortho-bromoaldehydes 1
ation or complexation of alcohols by Brønsted or Lewis acids. and 2 with 1,3-propanedithiol, 2) the Br/Li exchange reaction in
Therefore, diarylmethanols bearing electron-donating substitu- the resulting ortho-bromo-1,3-dithianes 3 and 4 with n-BuLi
ents (EDG = methyl, methoxy) are reduced much faster followed by condensation with a second (hetero)aromatic alde-
than diarylmethanols with electron-withdrawing groups hyde Ar2-CHO.
(EWG = CF3, C(O)OR) on (hetero)aryl moieties. Consequently,
dramatically decreased yields have been observed in these cases The reduction of ortho-1,3-dithianylaryl(aryl)methanols 5 and 6
[32,33]. It has also been reported that ortho-substituents on aryl to ortho-1,3-dithianylaryl(aryl)methanes 7 and 8 has been
moieties give lower yields in the reduction processes [33]. carried out using Lau’s procedure with ZnI2 (1.5 equiv) and
Moreover, the OH reduction under acidic conditions cannot be Na(CN)BH3 (7 equiv) in dichloroethane (DCE) and a solvent-
carried out in the presence of other sensitive functional groups. modified protocol employing the same reagents in benzene. In
For instance, ether cleavage and dehalogenation (I but not Cl literature, only few applications of the ZnI2-Na(CN)BH3 system
and Br) are common, side reactions due to either the high in DCE have been described for reduction of diarylmethanols
acidity which is necessary to generate carbocationic species or that do not contain acid-sensitive, formyl protecting, acetal or
due to the use of strongly reducing reaction conditions thioacetal groups [20,27,57-60] and for the reduction of aromat-
[28-30,46-52]. In this context, a serious challenge is still the ic aldehydes and ketones [28]. The bromo function in such
selective and direct removal of the OH group from alcohols diarylmethanols [60], as well as Cl, Br, C(O)OMe, MeO, MeS
Ar2CH(OH) without excessive, side reactions. Especially in the and NO2 groups in aromatic aldehydes and ketones, being
presence of other functionalities such as, for instance, when a reduced to methyl and methylene groups, respectively [27], are
reductively sensitive ortho-1,3-dithianyl group is attached to tolerated by this reagent system.
one of the aryl moieties, side products are to be expected. This
task is additionally difficult to accomplish due to a chemical The use of other procedures for deoxygenation of alcohols 5d,
similarity of oxygen and sulfur, two neighboring heteroatoms 6a and 6b with metal hydride donors, such as NaBH4 and
from the main group VI of the periodic table. A longer atomic LiAlH4 in various combinations with ZnI2 and AlCl3 failed
radius of sulfur than oxygen should make the C–S bond weaker [61-63]. For instance, the reaction with NaBH4 itself and
and more reactive than the C–O bond and consequently the NaBH4/ZnI2/THF at room temperature and reflux only recov-
reduction of the former should a priori occur preferentially ered the substrates. The same result was obtained at room tem-
[53-55].
perature with NaBH4/AlCl3/THF, while at reflux the whole sub-
strate was consumed and three unidentified products were
According to the best of our knowledge, there are no literature formed lacking the SCHS and ArCH2Ar characteristic signals in
reports concerning selective reductions of dibenzylic hydroxy 1H NMR spectra. With NaBH4/CF3COOH/rt, the substrate
groups in the presence of ortho-acetal or ortho-thioacetal func- underwent decomposition.
tions. Such reductions may give an access to new series of
ortho-formyl-protected diarylmethanes as well as their formyl- In our case, the use of the Lau’s procedure in DCE for the re-
modified derivatives, obtained after deprotection of the 1,3- ductive deoxygenation of ortho-1,3-dithianyl-substituted alco-
dithianyl group with one of the available methods [56].
hols 5a–h containing unsubstituted Ar1 phenyl ring and elec-
tron-donating Ar2 groups, gave diarylmethanes 7a–h in
Herein, we present the first example of a selective and efficient 26–95% yields (Table 1, entries 1–9).
reduction of ortho-1,3-dithianylaryl(aryl)methanols leading to
ortho-1,3-dithianylaryl(aryl)methanes using the ZnI2- Surprisingly, the reduction of the Ar1 piperonyl series 6a,b
Na(CN)BH3 reductive system (Scheme 1). The use of zinc failed under the same reaction conditions and only the sub-
iodide is critical in this system. It was used for the first time in strates could be isolated. In this case, a replacement of DCE by
dichloroethane by Lau et al. to reduce aryl ketones, aldehydes, benzene resulted in a successful formation of the desired diaryl-
benzylic, allylic and tertiary alcohols, including the first exam- methanes 8a,b in 95% yield (Table 1, entries 10–12). In addi-
ple of a diarylmethanol (benzhydrol) reduction to diaryl- tion, diarylmethanols 5b and 6b with the bulky group
methane (diphenylmethane) [27].
Ar2 = 3,4,5-trimethoxyphenyl required refluxing in the relevant
solvent (benzene or DCE) to complete the reduction (Table 1,
entries 3 and 12). At room temperature, only 40% of the sub-
Results and Discussion
The synthesis of ortho-1,3-dithianylaryl(aryl)methanols 5 and 6, strates underwent conversion to diarylmethanes 7b and 8b due
as key substrates for the OH reduction, has been realized ac- to their low solubility at this temperature. Attempts to synthe-
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Beilstein J. Org. Chem. 2018, 14, 1229–1237.
Scheme 1: Various synthetic approaches to diarylmethanols (literature review and this work).
Scheme 2: A general strategy for the synthesis of ortho-1,3-dithianylaryl(aryl)methanols 5 and 6, and their reduction to the corresponding ortho-1,3-
dithianylaryl(aryl)methanes.
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Beilstein J. Org. Chem. 2018, 14, 1229–1237.
Table 1: A selective reduction of ortho-1,3-dithianylaryl(aryl)methanols to ortho-1,3-dithianylaryl(aryl)methanes using the ZnI2/Na(CN)BH3 reducing
system.
entry
substrate
solvent
time [h]
temperature [°C]
product
yield
1
2
3
DCE
DCE
DCE
24
72
72
rt
rt
95
95a
85
7a
5a
reflux
7b
5b
4
5
6
DCE
DCE
DCE
72
rt
rt
rt
70
95
26
7c
5c
5d
5e
2
7d
2
7e
7
DCE
1
rt
95
7f
5f
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Beilstein J. Org. Chem. 2018, 14, 1229–1237.
Table 1: A selective reduction of ortho-1,3-dithianylaryl(aryl)methanols to ortho-1,3-dithianylaryl(aryl)methanes using the ZnI2/Na(CN)BH3 reducing
system. (continued)
8
DCE
3
rt
59
7g
5g
9
DCE
5
rt
64
7h
5h
10
C6H6
24
rt
95
6a
8a
11
12
C6H6
C6H6
72
24
rt
95a
60
reflux
6b
8b
aYield calculated based on the consumed substrate.
size diarylmethanols 6 with electron-withdrawing groups
(Ar2 = p-NO2, p-CF3) were also unsuccessful. They proved to
be unstable: the reaction of lithiated 4 with p-nitro and p-tri-
fluoromethylbenzaldehyde gave five products in the crude
reaction mixture and even more complex mixtures of products
after silica gel column chromatography. We also tried to
remove the OH group using the Pd-catalytic hydrogenolysis
(Scheme 3).
In case of 6b (X = S), no reaction occurred and only the sub-
strate was recovered, most probably due to poisoning of the
catalyst by the 1,3-dithianyl sulfur atoms. However, the suc-
cessful catalytic hydrogenolysis (5% Pd/C) of diphenyl-
methanol to diphenylmethane, described in literature [64],
encouraged us to try the Pd-catalyzed reduction of the oxygen
Scheme 3: Attempts of the OH removal in ortho-1,3-dithianyl- 6b and
ortho-1,3-dioxanylaryl(aryl)methanols 9 using the Pd-catalyzed hydro-
genolysis reaction.
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Beilstein J. Org. Chem. 2018, 14, 1229–1237.
analog 9 (X = O) as a representative of the ortho-1,3-dioxanyl Acknowledgements
series. In this case, instead of the expected ortho-1,3-dioxanyl The scientific work was financed from the Science Resources
diarylmethane analog of 8b, 1,3-dihydroisobenzofuran 10 was (National Science Centre-Poland) 2014-2017 as research grant
obtained in 90% yield, within 30 min, as a result of preferential UMO-2013/11/B/ST5/01610.
deacetalization over the dibenzylic OH deoxygenation. This is
References
1. Mondal, S.; Panda, G. RSC Adv. 2014, 4, 28317–28358.
followed by cyclization and final deoxygenation of the second-
ary monobenzylic OH group in the resulting lactol. This prod-
doi:10.1039/C4RA01341G
uct is known in literature and was obtained by hydrogenolysis
2. Sun, H. H.; Paul, V. J.; Fencial, W. Phytochemistry 1983, 22, 743–745.
or pyrolysis of the corresponding ortho-1,3-dioxolanyl [65] and
doi:10.1016/S0031-9422(00)86974-5
ortho-hydroxymethyl [66] substituted diarylmethanols, respec-
3. Chen, I.; McDougal, A.; Wang, F.; Safe, S. Carcinogenesis 1998, 19,
tively. It is worth mentioning that the reduction of 9 with
ZnI2–Na(CN)BH3 caused decomposition of the starting
material. The described reduction process involving 1,3-dithi-
anyl derivatives is facilitated by oxophilic zinc which preferen-
tially binds to the OH oxygen atoms (bond dissociation
energies for Zn–O and Zn–S are 284 and 205 kJ/mol,
respectively) [67]. The weakened C–O bond is thus
more susceptible to the borohydride attack to produce the corre-
sponding diarylmethanes. Most probably, electron-
donating groups on aryls facilitate both Zn complexation
and stabilization of the intermediate carbocationic species
formed.
1631–1639. doi:10.1093/carcin/19.9.1631
4. McDougal, A.; Gupta, M. S.; Ramamoorthy, K.; Sun, G.; Safe, S. H.
Cancer Lett. 2000, 151, 169–179. doi:10.1016/S0304-3835(99)00406-1
5. Abdelrahim, M.; Newman, K.; Vanderlaag, K.; Samudio, I.; Safe, S.
Carcinogenesis 2006, 27, 717–728. doi:10.1093/carcin/bgi270
6. Li, H.; Zhu, X.; Yao, G.; Wang, Z. J. Surg. Res. 2015, 195, 271–276.
doi:10.1016/j.jss.2015.01.016
7. Wai, J. S.; Egbertson, M. S.; Payne, L. S.; Fisher, T. E.;
Embrey, M. W.; Tran, L. O.; Melamed, J. Y.; Langford, H. M.;
Guare, J. P.; Zhuang, L.; Grey, V. E.; Vacca, J. P.; Holloway, M. K.;
Naylor-Olsen, A. M.; Hazuda, D. J.; Felock, P. J.; Wolfe, A. L.;
Stillmock, K. A.; Schleif, W. A.; Gabryelski, L. J.; Young, S. D.
J. Med. Chem. 2000, 43, 4923–4926. doi:10.1021/jm000176b
8. Panda, G.; Parai, M. K.; Das, S. K.; Shagufta; Sinha, M.;
Chaturvedi, V.; Srivastava, A. K.; Manju, Y. S.; Gaikwad, A. N.;
Sinha, S. Eur. J. Med. Chem. 2007, 42, 410–419.
Conclusion
doi:10.1016/j.ejmech.2006.09.020
In summary, a new example of the selective functional group
transformation of diarylmethanols (Ar1Ar2CH(OH)) to diaryl-
methanes (Ar1Ar2CH2) has been performed. It is important for
the sulfur-containing substrates for which metal-catalyzed
cross-coupling reactions fail. The dibenzylic OH group has
been preferentially reduced with the ZnI2/Na(CN)BH3 system
in the presence of an ortho-dithioacetal moiety to give ortho-
1,3-dithianylaryl(aryl)methanes in 26–95% yields under mild
reaction conditions. Thus, the ortho-1,3-dithianyl moiety joins
other functionalities tolerated by this reagent system [47]. Since
analogous 1,3-dioxanyl derivatives, in our hands, decomposed
or led to other products during the attempted catalytic hydro-
genolysis, the elaborated protocol is the only one up to date that
enables synthesis of ortho-formyl-protected diarylmethane de-
rivatives under reductive conditions. The latter may be used as
key substrates both for the synthesis of biologically active
diarylmethanes or for the synthesis of (hetero)acenes via the
Bradsher protocol.
9. Upadhayaya, R. S.; Vandavasi, J. K.; Vasireddy, N. R.; Sharma, V.;
Dixit, S. S.; Chattopadhyaya, J. Bioorg. Med. Chem. 2009, 17,
2830–2841. doi:10.1016/j.bmc.2009.02.026
10.Kerrebroeck, P. V.; Kreder, K.; Jonas, U.; Zinner, N.; Wein, A. Urology
2001, 57, 414–421. doi:10.1016/S0090-4295(00)01113-4
11.Canel, C.; Moraes, R. M.; Dayan, F. E.; Ferreira, D. Phytochemistry
2000, 54, 115–120. doi:10.1016/S0031-9422(00)00094-7
12.Gennari, L.; Merlotti, D.; Martini, G.; Nuti, R. Expert Opin. Invest. Drugs
2006, 15, 1091–1103. doi:10.1517/13543784.15.9.1091
13.Conn, M. M.; Rebek, J., Jr. Chem. Rev. 1997, 97, 1647–1668.
doi:10.1021/cr9603800
14.Lee, W. Y.; Park, C. H.; Kim, H.-J.; Kim, S. J. Org. Chem. 1994, 59,
878–884. doi:10.1021/jo00083a033
15.Bradsher, C. K. J. Am. Chem. Soc. 1940, 62, 486–488.
doi:10.1021/ja01860a006
16.Bradsher, C. K. Chem. Rev. 1987, 87, 1277–1297.
doi:10.1021/cr00082a001
17.Bodzioch, A.; Kowalska, E.; Skalik, J.; Bałczewski, P.
Chem. Heterocycl. Compd. 2017, 53, 11–20.
doi:10.1007/s10593-017-2015-y
18.Bodzioch, A.; Marciniak, B.; Różycka-Sokołowska, E.; Jeszka, J. K.;
Uznański, P.; Kania, S.; Kuliński, J.; Bałczewski, P. Synfacts 2012, 8,
619. doi:10.1055/s-0031-1291065
Supporting Information
19.Bałczewski, P.; Kowalska, E.; Skalik, J. 10-Thiosubstituted
pentahydroxyanthracene derivatives, a method of their preparation and
intermediate compounds. Eur. Pat. Appl. EP 2886539 A1 20150624,
June 24, 2015.
Supporting Information File 1
General experimental information, characterization data
and copies of 1H, 13C NMR spectra.
20.Park, J.-I.; Chung, J. W.; Kim, J.-Y.; Lee, J.; Jung, J. Y.; Koo, B.;
Lee, B.-L.; Lee, S. W.; Jin, Y. W.; Lee, S. Y. J. Am. Chem. Soc. 2015,
137, 12175–12178. doi:10.1021/jacs.5b01108
[https://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-14-105-S1.pdf]
1235

Beilstein J. Org. Chem. 2018, 14, 1229–1237.
21.Bodzioch, A.; Marciniak, B.; Różycka-Sokołowska, E.; Jeszka, J. K.;
Uznański, P.; Kania, S.; Kuliński, J.; Bałczewski, P. Chem. – Eur. J.
2012, 18, 4866–4877. doi:10.1002/chem.201101909
22.Bałczewski, P.; Skalik, J.; Uznański, P.; Guziejewski, D.; Ciesielski, W.
RSC Adv. 2015, 5, 24700–24704. doi:10.1039/C4RA14071K
23.Dockrey, S. A. B.; Makepeace, A. K.; Schmink, J. R. Org. Lett. 2014,
16, 4730–4733. doi:10.1021/ol502428h
48.Mirza-Aghayan, M.; Boukherroub, R.; Rahimifard, M.; Zadmard, R.
J. Iran. Chem. Soc. 2011, 8, 570–573. doi:10.1007/BF03249092
49.Purushothama Chary, K.; Santosh Laxmi, Y. R.; Iyengar, D. S.
Synth. Commun. 1999, 29, 1257–1261.
doi:10.1080/00397919908086100
50.Kotsuki, H.; Ushio, Y.; Yoshimura, N.; Ochi, M. J. Org. Chem. 1987, 52,
2594–2596. doi:10.1021/jo00388a049
24.Hemelaere, R.; Champagne, P. A.; Desroches, J.; Paquin, J.-F.
J. Fluorine Chem. 2016, 190, 1–6. doi:10.1016/j.jfluchem.2016.08.003
25.Forster, F.; Metsänen, T. T.; Irran, E.; Hrobárik, P.; Oestreich, M.
J. Am. Chem. Soc. 2017, 139, 16334–16342.
51.Fleming, B.; Bolker, H. I. Can. J. Chem. 1974, 52, 888–893.
doi:10.1139/v74-143
52.Ishihara, K.; Hanaki, N.; Yamomoto, H. Synlett 1993, 127–129.
doi:10.1055/s-1993-22373
doi:10.1021/jacs.7b09444
53.Luh, T.-Y.; Ni, Z.-J. Synthesis 1990, 89–103.
doi:10.1055/s-1990-26798
26.Gribble, G. W.; Leese, R. M.; Evans, B. E. Synthesis 1977, 172–176.
doi:10.1055/s-1977-24308
54.Rentner, J.; Kljajic, M.; Offner, L.; Breinbauer, R. Tetrahedron 2014,
70, 8983–9027. doi:10.1016/j.tet.2014.06.104
27.Lau, C. K.; Dufresne, C.; Belanger, P. C.; Pietre, S.; Scheigetz, J.
J. Org. Chem. 1986, 51, 3038–3043. doi:10.1021/jo00365a034
28.Dobmeier, M.; Herrmann, J. M.; Lenoir, D.; König, B.
Beilstein J. Org. Chem. 2012, 8, 330–336. doi:10.3762/bjoc.8.36
29.Gordon, P. E.; Fry, A. J. Tetrahedron Lett. 2001, 42, 831–833.
doi:10.1016/S0040-4039(00)02159-6
55.Saito, K.; Kondo, K.; Akiyama, T. Org. Lett. 2015, 17, 3366–3369.
doi:10.1021/acs.orglett.5b01651
56.Burghardt, T. E. J. Sulfur Chem. 2005, 26, 411–427.
doi:10.1080/17415990500195198
57.Alesso, E. N.; Bianchi, D. E.; Finkielsztein, L. M.; Lantaño, B.;
Moltrasio, G. Y.; Aguirre, J. M. Tetrahedron Lett. 1995, 36, 3299–3302.
doi:10.1016/0040-4039(95)00525-H
30.Gordon, P. E.; Fry, A. J.; Hicks, L. D. ARKIVOC 2005, No. 6, 393–400.
doi:10.3998/ark.5550190.0006.634
31.Wu, X.; Mahalingam, A. K.; Alterman, M. Tetrahedron Lett. 2005, 46,
1501–1504. doi:10.1016/j.tetlet.2005.01.012
58.Wex, B.; Kaafarani, B. R.; Neckers, D. C. J. Org. Chem. 2004, 69,
2197–2199. doi:10.1021/jo035769j
32.Nishigaya, Y.; Umei, K.; Watanabe, D.; Kohno, Y.; Seto, S.
Tetrahedron 2016, 72, 1566–1572. doi:10.1016/j.tet.2016.02.005
33.Li, J.; Liu, Q.; Shen, H.; Huang, R.; Zhang, X.; Xiong, Y.; Chen, C.
RSC Adv. 2015, 5, 85291–85295. doi:10.1039/C5RA14775A
34.Gevorgyan, V.; Liu, J.-X.; Rubin, M.; Benson, S.; Yamamoto, Y.
Tetrahedron Lett. 1999, 40, 8919–8922.
59.Wex, B.; Kaafarani, B. R.; Kirschbaum, K.; Neckers, D. C.
J. Org. Chem. 2005, 70, 4502–4505. doi:10.1021/jo048010w
60.Tylleman, B.; Vande Velde, C. M. L.; Balandier, J.-Y.; Stas, S.;
Sergeyev, S.; Geerts, Y. H. Org. Lett. 2011, 13, 5208–5211.
doi:10.1021/ol202089t
61.Pan, X.; Wang, K.; Yu, W.; Zhang, R.; Xu, L.; Liu, F. Chem. Lett. 2015,
44, 1170–1172. doi:10.1246/cl.150390
doi:10.1016/S0040-4039(99)01757-8
35.Gevorgyan, V.; Rubin, M.; Benson, S.; Liu, J.-X.; Yamamoto, Y.
J. Org. Chem. 2000, 65, 6179–6186. doi:10.1021/jo000726d
36.Denancé, M.; Guyot, M.; Samadi, M. Steroids 2006, 71, 599–602.
doi:10.1016/j.steroids.2006.03.002
62.Bhattacharyya, S.; Chatterjee, A.; Williamson, J. S. Synth. Commun.
1997, 27, 4265–4274. doi:10.1080/00397919708005050
63.Ley, S. V.; Tackett, M. N.; Maddess, M. L.; Anderson, J. C.;
Brennan, P. E.; Cappi, M. W.; Heer, J. P.; Helgen, C.; Kori, M.;
Kouklovsky, C.; Marsden, S. P.; Norman, J.; Osborn, D. P.;
Palomero, M. Á.; Pavey, J. B. J.; Pinel, C.; Robinson, L. A.;
Schnaubelt, J.; Scott, J. S.; Spilling, C. D.; Watanabe, H.;
Wesson, K. E.; Willis, M. C. Chem. – Eur. J. 2009, 15, 2874–2914.
doi:10.1002/chem.200801656
37.Miyai, T.; Ueba, M.; Baba, A. Synlett 1999, 182–184.
doi:10.1055/s-1999-2588
38.Baba, A.; Yasuda, M.; Nishimoto, Y.; Saito, T.; Onishi, Y.
Pure Appl. Chem. 2008, 80, 845–854. doi:10.1351/pac200880050845
39.Egi, M.; Kawai, T.; Umemura, M.; Akai, S. J. Org. Chem. 2012, 77,
7092–7097. doi:10.1021/jo300889p
64.Marques, C. A.; Selva, M.; Tundo, P. J. Org. Chem. 1995, 60,
2430–2435. doi:10.1021/jo00113a024
40.Meyer, V. J.; Niggemann, M. Chem. – Eur. J. 2012, 18, 4687–4691.
doi:10.1002/chem.201103691
65.Arnold, B. J.; Mellows, S. M.; Sammes, P. G.
J. Chem. Soc., Perkin Trans. 1 1973, 1266–1270.
doi:10.1039/p19730001266
41.Narayana Kumar, G. G. K. S.; Laali, K. K. Org. Biomol. Chem. 2012,
10, 7347–7355. doi:10.1039/c2ob26046h
42.Tandiary, M. A.; Masui, Y.; Onaka, M. Tetrahedron Lett. 2014, 55,
4160–4162. doi:10.1016/j.tetlet.2014.05.042
66.Galletti, G. C.; Ward, R. S.; Pelter, A.; Goubet, D.
J. Anal. Appl. Pyrolysis 1992, 24, 139–146.
43.Mirza-Aghayan, M.; Boukherroub, R.; Rahimifard, M. Tetrahedron Lett.
2009, 50, 5930–5932. doi:10.1016/j.tetlet.2009.08.043
44.Bell, M. G.; Muehl, B. S.; Winter, M. A.
doi:10.1016/0165-2370(92)85025-G
67.Dean, J. A. Lange’s Handbook of Chemistry, 15th ed.; Section 4;
McGraw-Hill: New York, Montreal, 1998; 4.52.
Dihydrobenzo(B)indeno(2,1-D)thiophene compounds, intermediates,
processes, compositions, and methods. Eur. Pat. EP 832891, April 1,
1998.
45.Sousa, S. C. A.; Fernandes, T. A.; Fernandes, A. C. Eur. J. Org. Chem.
2016, 3109–3112. doi:10.1002/ejoc.201600441
46.Barton, D. H. R.; Jacob, M. Tetrahedron Lett. 1998, 39, 1331–1334.
doi:10.1016/S0040-4039(98)00005-7
47.Shi, Y.; Dayoub, W.; Chen, G.-R.; Lemaire, M. Tetrahedron Lett. 2011,
52, 1281–1283. doi:10.1016/j.tetlet.2011.01.038
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