Novel stereocontrolled syntheses of tashiromine and epitashiromine

Article abstract of DOI:10.3762/bjoc.11.66

A novel stereocontrolled approach has been developed for the syntheses of tashiromine and epitashiromine alkaloids from cyclooctene β-amino acids. The synthetic concept is based on the azetidinone opening of a bicyclic β-lactam, followed by oxidative ring

Full text of DOI:10.3762/bjoc.11.66

Novel stereocontrolled syntheses of tashiromine
and epitashiromine
Loránd Kiss1, Enikő Forró1 and Ferenc Fülöp*1,2
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2015, 11, 596–603.
1Institute of Pharmaceutical Chemistry, University of Szeged, H-6720
Szeged, Eötvös u. 6, Hungary and 2Stereochemistry Research Group
of the Hungarian Academy of Sciences, University of Szeged, H-6720
Szeged, Eötvös u. 6, Hungary
doi:10.3762/bjoc.11.66
Received: 17 February 2015
Accepted: 13 April 2015
Published: 30 April 2015
Email:
Ferenc Fülöp* - fulop@pharm.u-szeged.hu
Associate Editor: R. Sarpong
* Corresponding author
© 2015 Kiss et al; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
alkaloids; amino acids; ring closure; ring opening; stereocontrolled
synthesis
Abstract
A novel stereocontrolled approach has been developed for the syntheses of tashiromine and epitashiromine alkaloids from
cyclooctene β-amino acids. The synthetic concept is based on the azetidinone opening of a bicyclic β-lactam, followed by oxidative
ring opening through ring C–C double bond and reductive ring-closure reactions of the cis- or trans-cyclooctene β-amino acids.
Introduction
Indolizidine alkaloids are an important class of naturally occur-
ring compounds which have received considerable attention as a
result of their valuable physiological properties. A number of
representatives of this class exhibit glycosidase inhibitory
activity or antimetastatic, anticancer, antitumour or anti-HIV
properties [1-3]. A large number of natural products contain an
indolizidine framework, among them (−)-δ-coniceine,
(−)-swainsonine, indolizidine 167B [4-10], (+)-lentiginosine
[11-15], (+)-slaframine [16], (−)-elaeokanine C [17],
(+)-cyclizidine [18], lepadiformine [19], the highly oxygenated
(+)-castanospermine [20,21], or pumiliotoxin [22]. Figure 1
illustrates the structures of several such compounds.
Tashiromine is a natural indolizidine alkaloid isolated from
Figure 1: Some indolizidine alkaloids.
Maackia tashiroi (1990). Strategies for the synthesis of
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Beilstein J. Org. Chem. 2015, 11, 596–603.
indolizidine derivatives have received considerable interest (+)-Tashiromine has been synthetized from a pyrrolidinone
from synthetic and medicinal chemists (Figure 2). A number of derivative through chiral Lewis acid-catalysed cyclization to
synthetic approaches have been described earlier for construc- substituted pyrrolidinones [17], by the intramolecular cycliza-
tion of the indolizidine framework; access to tashiromine in tion of a chiral alkenylated pyrrolidinone, followed by hydrox-
racemic form can be achieved through the alkylation of succin- ylation [32], or by the intramolecular ring closure of chiral
imide, followed by ring closure via acyliminium intermediates pyrrolidine diesters followed by ester and oxo group reduction
[23,24], the reduction of cyclized pyridinium salts [25], [33], while the syntheses of (+)-epitashiromine starts from a
iminium cascade cyclization [26], alkyne-mediated hydro- chiral morpholine derivative, with nitrone 1,3-dipolar cycload-
formylation–cyclization [27], or electrophilic pyrolidinone dition and reduction [34] (Figure 3).
alkylation followed by ring closure [28,29]. Pyrrolidine alkyl-
ation and nucleophilic ring closure followed by C–C double
bond hydroboration [30] leads to racemic epitashiromine, as
does the N-alkylated succinimide transformation through the
corresponding indolizidinone [31].
Figure 3: Synthetic routes to (+)-tashiromine and (+)-epitashiromine.
(−)-Tashiromine has been accessed through the ring closure of
difunctionalized acyclic chiral sulfonamide-based β-amino
acids [35], the cyclization of pyrrole derivatives with a chiral
side-chain [36], or the enantioselective arylation of pyrrole, fol-
lowed by saturation [37]. The transformation of chiral function-
alized pyrrole or pyrrolidine derivatives has served as the basis
of the construction of (−)-epitashiromine [38,39] (Figure 4).
Figure 2: Approaches to racemic tashiromine and epitashiromine.
The oxidative functionalization of cyclic β-amino acid deriva-
tives has been reported to be a convenient route for the prepar-
Several synthetic procedures have also been developed for the ation of N-heterocyclic β-amino acid derivatives [40,41] or for
preparation of tashiromine or epitashiromine enantiomers.
the stereocontrolled synthesis of functionalized cispentacins
Figure 4: Synthetic routes to (−)-tashiromine and (−)-epitashiromine.
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Beilstein J. Org. Chem. 2015, 11, 596–603.
[42] and their acyclic counterparts [43,44] (Figure 5). The the formed β-amino esters and by reductive ring closure as key
oxidative ring cleavage of various vicinal diols and the transfor- steps.
mation of the resulting dialdehyde intermediates has been effi-
ciently applied in recent years for the synthesis of a series of Bicyclic β-lactam (±)-1 [53,54] was first transformed by
valuable organic molecules [45-52]. In particular, Davies and azetidinone opening to the corresponding amino ester
co-workers have utilized the oxidative ring opening of cyclic hydrochloride (±)-2 [53,54], N-protection of which with benzyl
vicinal diols followed by ring closure for access to pyrrolizidine chloroformate (Z-Cl) afforded protected amino ester (±)-3 in
alkaloids [45].
78% yield. In agreement with our earlier observations [40-42]
C–C double bond functionalization of the cyclooctene β-amino
ester via dihydroxylation with N-methyl morpholine N-oxide
Results and Discussion
We describe here a novel access route for the synthesis of (NMO) in the presence of OsO4 afforded the corresponding all-
tashiromine and epitashiromine by starting from an unsaturated cis dihydroxylated ethyl β-aminocyclooctanecarboxylate (±)-4
bicyclic β-lactam. The retrosynthetic concept of the synthesis is in 90% yield (for dihydroxylation, see also reference [54])
represented on Scheme 1 and was based on the lactam ring (Scheme 2). Amino ester (±)-4 was next subjected through its
opening, in continuation followed by oxidative ring opening of vicinal diol moiety to oxidative ring opening with NaIO4 in
Figure 5: Oxidative functionalizations of cyclic β-amino acids.
Scheme 1: Retrosynthesis of tashiromine and epitashiromine.
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Beilstein J. Org. Chem. 2015, 11, 596–603.
Scheme 2: Synthesis of (±)-tashiromine ((±)-6).
MeOH at 20 °C, which resulted (monitored by TLC) in the of 1H NMR data) failed, but the mixture could be applied in the
corresponding ring-opened unstable diformyl intermediate (I1), next ring-opening oxidation step, since it gave only one open-
which after work-up was immediately used without further chain diformyl intermediate I2.
purification (for several similar types of acyclic diformyl inter-
mediates, see references [40,41,43,44]). Thus, the crude ma- Similarly to the cis isomer, this unstable dialdehyde intermedi-
terial was submitted to catalytic hydrogenolysis and after ate was subjected without isolation to catalytic hydrogenolysis,
N-deprotection underwent double cyclization–reduction to followed by reductive cyclization, to give the corresponding
furnish indolizidine ester (±)-5 in 41% yield after purification indolizidine ester (±)-9 in 40% yield. Finally, ester reduction
by chromatography.
with LiAlH4 in THF resulted in epitashiromine (±)-10
[32,34,39] in 53% yield after isolation by chromatography
Reduction of the ester group of (±)-5 with an excess of LiAlH4 (Scheme 3). The stereochemistry of (±)-epitashiromine was
in THF at 20 °C gave the corresponding tashiromine (±)-6 [35- assigned by NMR data, which were in agreement with those
37], which was isolated in 48% yield after purification by reported [32,34,39].
column chromatography (Scheme 2). The stereochemistry of
(±)-6 was unequivocally assigned by NMR data, which were Conclusion
consistent with those reported [35-37].
In summary, a novel stereocontrolled efficient method has been
presented for the synthesis of tashiromine and epitashiromine
A similar strategy was applied for the synthesis of alkaloids in six or seven steps, based on the preparation of cis or
epitashiromine. On reaction with NaOEt in EtOH at 20 °C, trans cyclooctene β-amino esters, followed by their oxidative
ethyl cis-β-aminocyclooctenecarboxylate (±)-3 underwent ring cleavage and double reductive ring-closure reactions.
epimerization at C-1, leading after 18 h to an equilibrium mix-
Experimental
ture of cis and trans amino esters (1:1 ratio determined by
General procedure for the Z-protection of
amino esters
1H NMR on the crude mixture), the required trans isomer (±)-7
being separated from the cis counterpart and isolated in a yield
of 48% by means of column chromatography. Dihydroxylation
of (±)-7 with NMO/OsO4 next afforded an oily mixture of cis
and trans dihydroxylated cyclooctane β-amino esters (diastereo-
meric mixture of (±)-8) in 77% overall yield after column chro-
matography. Our attempts to separate this nearly 1:1 mixture of
the two dihydroxylated stereoisomers (determined on the basis
To a solution of amino ester hydrochloride ((±)-2 or (−)-2) [29]
(17.8 mmol) in THF (40 mL), Et3N (9 mL) was added at 0 °C,
followed by 7.8 mL (1 equivalent) of Z-Cl (a 50% solution in
toluene). The mixture was stirred for 14 h at 20 °C, and then
was diluted with EtOAc (120 mL). The organic layer was
washed with H2O (3 × 60 mL), dried (Na2SO4), and concen-
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Beilstein J. Org. Chem. 2015, 11, 596–603.
Scheme 3: Synthesis of (±)-epitashiromine ((±)-10).
trated under reduced pressure. The crude material was purified (3 × 20 mL). The organic layer was dried (Na2SO4) and
by column chromatography on silica gel (n-hexane/EtOAc 4:1), concentrated under reduced pressure. The crude mixture was
affording the amino ester.
dissolved in EtOAc (30 mL), Pd/C (150 mg) was added and the
mixture was stirred at 20 °C for 16 h. The catalyst was next
filtered off through Celite. The crude mixture was then purified
by column chromatography on silica gel (CH2Cl2/MeOH 95:5
General procedure for the dihydroxylation of
amino esters
To a solution of cis or trans Z-protected amino ester ((±)-3, or CH2Cl2/MeOH 9:1) to give the indolizidine derivative.
(−)-3 or (±)-7) (2.9 mmol) in acetone (30 mL) and H2O (1 mL),
NMO (1.5 equivalents) and 2% OsO4 in t-BuOH (0.7 mL) were General procedure for reduction of the ester
added and the mixture was stirred at 20 °C for 4 h. A saturated To a solution of indolizidine carboxylate ((±)-5, (±)-9 or (−)-9)
aqueous solution of Na2SO3 (40 mL) was then added, the mix- (1 mmol) in dry THF (15 mL), LiAlH4 (5 equivalents) was
ture was extracted with CH2Cl2 (3 × 30 mL), and the organic added at 0 °C and the mixture was stirred at 20 °C for 4 h. It
layer was dried (Na2SO4) and concentrated under reduced pres- was then cooled to 0 °C, H2O (2 mL) was added dropwise and
sure. The crude product was purified by column chromatog- the solid formed was filtered off through Celite. The filtrate was
raphy on silica gel (n-hexane/EtOAc 1:4) to give the dihydroxy- extracted with CH2Cl2 (3 × 15 mL), and the combined organic
lated amino ester.
layers were dried (Na2SO4) and concentrated under reduced
pressure. The crude oil was purified by column chromatog-
raphy on silica gel (CH2Cl2/MeOH/NH4OH 90:8:2 or CH2Cl2/
MeOH/NH4OH 90:5:5) to give the alkaloid.
General procedure for epimerization of the
cis-amino ester
To a solution of cis N-protected amino ester ((±)-3 or (−)-3)
(3.3 mmol) in EtOH (30 mL), EtONa (1.5 equivalents) was Ethyl (1R*,2S*)-2-(benzyloxycarbonylamino)cyclooct-5-
added at 0 °C and the mixture was stirred at 20 °C for 18 h. enecarboxylate ((±)-3)
H2O (70 mL) was then added, the mixture was extracted with
CH2Cl2 (3 × 30 mL), and the organic layer was dried over
Na2SO4 and concentrated under reduced pressure. The crude
material was purified by column chromatography on silica gel
(n-hexane/EtOAc 9:1) to give the trans isomer as a colourless
oil.
A colourless oil (Rf 0.6, n-hexane/EtOAc 4:1); yield: 78%;
General procedure for the oxidative ring
1H NMR (400 MHz, CDCl3) δ 1.28 (t, J = 7.1 Hz, 3H, CH3),
opening/reductive ring closure of
dihydroxylated amino esters
To a solution of dihydroxylated amino ester ((±)-4, (±)-8 or
(−)-8) (2.46 mmol) in MeOH (25 mL), NaIO4 (2 equivalents)
was added and the mixture was stirred at 20 °C for 45 min. It
was then diluted with H2O (50 mL) and extracted with CH2Cl2
1.76–1.87 (m, 2H, CH2), 1.88–1.97 (m, 1H, CH2), 1.98–2.07
(m, 1H, CH2), 2.09–2.18 (m, 2H, CH2), 2.22–2.31 (m, 1H,
CH2), 2.43–2.52 (m, 1H, CH2), 2.82–2.89 (m, 1H, H-1),
4.12–4.21 (m, 2H, OCH2), 4.22–4.30 (m, 1H, H-2), 5.08 (s, 2H,
OCH2), 5.30 (brs, 1H, N-H), 5.60–5.74 (m, 2H, H-5 and H-6),
7.33–7.48 (m, 5H, Ar-H); 13C NMR (100 MHz, DMSO) δ 14.9,
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Beilstein J. Org. Chem. 2015, 11, 596–603.
24.4, 25.1, 26.6, 32.3, 46.4, 52.1, 60.6, 66.1, 128.5, 128.6, N-CH), 3.41–3.46 (m, 1H, OCH2), 3.59–3.64 (m, 1H, OCH2);
129.2, 129.5, 130.7, 138.0, 156.3, 174.5; anal. calcd for 13C NMR (100 MHz, CDCl3) δ 21.1, 25.5, 28.0, 29.4, 44.9,
C19H25NO4: C, 68.86; H, 7.60; N, 4.23; found: C, 68.59; H, 53.1, 54.5, 66.0, 66.9; MS (ESI) m/z: 156.6 [M + 1]; anal. calcd
7.31; N, 3.93.
for C9H17NO: C, 69.63; H, 11.04; N, 9.02; found: C, 69.28; H,
10.70; N, 8.76.
Ethyl (1R*,2S*,5R*,6S*)-2-(benzyloxycarbonylamino)-5,6-
dihydroxycyclooctanecarboxylate ((±)-4)
Ethyl (1S*,2S*)-2-(benzyloxycarbonylamino)cyclooct-5-
enecarboxylate ((±)-7)
A colourless oil (Rf 0.4, n-hexane/EtOAc 1:4); yield: 90%;
1H NMR (400 MHz, CDCl3) δ 1.26 (t, J = 7.15 Hz, 3H, CH3), A colourless oil (Rf 0.55, n-hexane/EtOAc 4:1); yield: 48%;
1.62–1.94 (m, 4H, CH2), 1.97–2.28 (m, 4H, CH2), 2.77–2.82 1H NMR (400 MHz, DMSO) δ 1.18 (t, J = 7.10 Hz, 3H, CH3),
(m, 1H, H-1), 3.83–3.89 (m, 2H, H-5 and H-6), 4.02–4.10 (m, 1.55–1.64 (m, 2H, CH2), 1.73–1.97 (m, 2H, CH2), 2.04–2.19
1H, H-2), 4.11–4.19 (m, 2H, OCH2), 5.09 (m, 2H, OCH2), 5.49 (m, 2H, CH2), 2.33–2.47 (m, 2H, CH2), 2.68–2.75 (m, 1H,
(brs, 1H, N-H), 7.36–7.48 (m, 5H, Ar-H); 13C NMR (100 MHz, H-1), 3.88–4.02 (m, 3H, OCH2 and H-2), 4.96–5.02 (m, 2H,
DMSO) δ 14.8, 21.2, 26.9, 28.5, 29.0, 45.4, 51.6, 60.7, 65.9, OCH2), 5.53–5.60 (m, 2H, H-5 and H-6), 7.30–7.44 (m, 5H,
72.3, 72.4, 128.4, 128.5, 129.1, 138.1, 156.3, 174.6; anal. calcd Ar-H); 13C NMR (100 MHz, DMSO) δ 14.8, 24.5, 25.1, 29.2,
for C19H27NO6: C, 62.45; H, 7.45; N, 3.83; found: C, 62.19; H, 33.8, 49.2, 52.1, 60.4, 65.9, 128.0, 128.4, 129.0, 129.1, 130.7,
7.10; N, 4.13.
138.2, 156.9, 174.5; anal. calcd for C19H25NO4: C, 68.86; H,
7.60; N, 4.23; found: C, 68.57; H, 7.28; N, 3.97.
Ethyl (8R*,8aS*)-octahydroindolizine-8-carboxylate ((±)-5)
Ethyl (8S*,8aS*)-octahydroindolizine-8-carboxylate ((±)-9)
A yellow oil (Rf 0.55, CH2Cl2/MeOH 95:5); yield: 41%;
1H NMR (400 MHz, CDCl3) δ 1.27 (t, J = 7.15 Hz, 3H, CH3), A yellow oil (Rf 0.45, CH2Cl2/MeOH 4:1); yield: 40%;
1.46–1.53 (m, 2H, CH2), 1.57–1.92 (m, 5H, CH2), 1.99–2.10 1H NMR (400 MHz, CDCl3) δ 1.28 (t, J = 7.15 Hz, 3H, CH3),
(m, 3H, CH2), 2.13–2.20 (m, 1H, CH2), 2.25–2.31 (m, 1H, 1.28–1.33 (m, 1H, CH2), 1.42–1.55 (m, 2H, CH2), 1.58–1.64
H-8), 3.03–3.10 (m, 2H, CH2 and H-8a); 13C NMR (100 MHz, (m, 1H, CH2), 1.68–1.86 (m, 3H, CH2), 2.02–2.18 (m, 3H,
CDCl3) δ 14.6, 20.9, 25.1, 29.5, 30.1, 48.4, 52.6, 54.4, 60.6, CH2), 2.23–2.27 (m, 1H, CH2), 2.78–2.81 (m, 1H, H-8),
65.6, 174.6; MS (ESI) m/z: 198.5 [M + 1]; anal. calcd for 3.04–3.10 (m, 2H, CH2 and H-8a), 4.09–4.17 (m, 2H, OCH2);
C11H19NO2: C, 66.97; H, 9.71; N, 7.10; found: C, 66.60; H, 13C NMR (100 MHz, DMSO) δ 15.1, 21.2, 22.6, 26.8, 27.3,
10.02; N, 7.39.
42.0, 53.4, 55.0, 60.5, 64.9, 170.4; MS (ESI) m/z: 198.7 [M +
1]; anal. calcd for C11H19NO2: C, 66.97; H, 9.71; N, 7.10;
found: C, 67.28; H, 9.40; N, 6.78.
((8R*,8aS*)-Octahydroindolizin-8-yl)methanol;
((±)-tashiromine (±)-6) [35-37]
((8S*,8aS*)-Octahydroindolizin-8-yl)methanol; ((±)-
epitashiromine, (±)-10) [32,34,39]
A yellow oil (Rf 0.45, CH2Cl2/MeOH/NH4OH 90:8:2); yield:
48%; 1H NMR (400 MHz, CDCl3) δ 1.00–1.11 (m, 1H, CH2),
1.42–1.53 (m, 2H, CH2), 1.58–1.83 (m, 5H, CH2), 1.84–1.99 A yellow oil (Rf 0.45, CH2Cl2/MeOH/NH4OH 88:8:4); yield:
(m, 3H, CH2), 2.04–2.11 (m, 1H, CH2), 3.03–3.10 (m, 2H, 53%; 1H NMR (400 MHz, CDCl3) δ 1.56–1.62 (m, 2H, CH2),
601

Beilstein J. Org. Chem. 2015, 11, 596–603.
19.Han, M.-Y.; Jia, J.-Y.; Wang, W. Tetrahedron Lett. 2014, 55, 784–794.
doi:10.1016/j.tetlet.2013.11.048
1.65–1.74 (m, 4H, CH2), 1.97–2.12 (m, 5H, CH2), 2.20–2.28
(m, 1H, H-8), 2.94–3.00 (m, 1H, CH2), 3.08–3.14 (m, 1H,
N-CH), 3.70–3.75 (m, 1H, OCH2), 4.13–4.19 (m, 1H, OCH2);
13C NMR (100 MHz, CDCl3) δ 21.2, 23.7, 26.3, 30.1, 35.7,
54.0, 54.9, 66.0, 66.8; MS (ESI) m/z: 156.4 [M + 1]; anal. calcd
for C9H17NO: C, 69.63; H, 11.04; N 9.02; found: C, 69.30; H,
10.71; N, 8.79.
20.Singh, P.; Manna, S. K.; Panda, G. Tetrahedron 2014, 70, 1363–1374.
doi:10.1016/j.tet.2013.11.074
21.Tiwari, D. K.; Bharadwaj, K. C.; Puranik, V. G.; Tiwari, D. K.
Org. Biomol. Chem. 2014, 12, 7389–7396. doi:10.1039/C4OB00948G
22.Jouanno, L.-A.; Di Mascio, V.; Tognetti, V.; Joubert, L.; Sabot, C.;
Renard, P.-Y. J. Org. Chem. 2014, 79, 1303. doi:10.1021/jo402729a
23.McElhinney, A. D.; Marsden, S. P. Synlett 2005, 2528–2530.
doi:10.1055/s-2005-917072
Acknowledgements
24.Marsden, S. P.; McElhinney, A. D. Beilstein J. Org. Chem. 2008, 4,
No. 8. doi:10.1186/1860-5397-4-8
We are grateful to the Hungarian Research Foundation (OTKA
No. K100530 and NK81371) and TÁMOP-4.2.2.A-11/1/
KONV-2012-0035 for financial support. This paper was
supported by the János Bolyai Research Scholarship of the
Hungarian Academy of Sciences to L.K.
25.Bates, R. W.; Boonsombat, J. J. Chem. Soc., Perkin Trans. 1 2001,
654–656. doi:10.1039/b100407g
26.Amorde, S. M.; Jewett, I. T.; Martin, S. F. Tetrahedron 2009, 65,
3222–3231. doi:10.1016/j.tet.2008.10.074
27.Chiou, W.-H.; Lin, Y.-H.; Chen, G.-T.; Gao, Y.-K.; Tseng, Y.-C.;
Kao, C.-L.; Tsai, J.-C. Chem. Commun. 2011, 47, 3562–3564.
doi:10.1039/c0cc05646d
References
1. Michael, J. P. Nat. Prod. Rep. 2008, 25, 139–165.
28.Pohmakotr, M.; Prateeptongkum, S.; Chooprayoon, S.; Tuchinda, P.;
Reutrakul, V. Tetrahedron 2008, 64, 2339–2347.
doi:10.1039/B612166G
doi:10.1016/j.tet.2008.01.008
2. Brandi, A.; Cardona, F.; Cicchi, S.; Cordero, F. M.; Goti, A.
Chem. – Eur. J. 2009, 15, 7808. doi:10.1002/chem.200900707
3. Macchi, B.; Minutolo, A.; Grelli, S.; Cardona, F.; Cordero, F. M.;
Mastino, A.; Brandi, A. Glycobiology 2010, 20, 500–506.
doi:10.1093/glycob/cwp202
29.Bélanger, G.; Larouche-Gauthier, R.; Ménard, F.; Nantel, M.;
Barabé, F. J. Org. Chem. 2006, 71, 704–712. doi:10.1021/jo052141v
30.Dieter, R. K.; Watson, R. Tetrahedron Lett. 2002, 43, 7725–7728.
doi:10.1016/S0040-4039(02)01835-X
31.Kim, S.-H.; Kim, S.-I.; Lai, S.; Cha, J. K. J. Org. Chem. 1999, 64,
6771–6775. doi:10.1021/jo9907383
4. Felpin, F. X.; Lebreton, J. Eur. J. Org. Chem. 2003, 3693–3712.
doi:10.1002/ejoc.200300193
32.Dieter, R. K.; Chen, N.; Watson, R. T. Tetrahedron 2005, 61,
3221–3230. doi:10.1016/j.tet.2005.01.094
5. Hu, X.-G.; Hunter, L. Beilstein J. Org. Chem. 2013, 9, 2696–2708.
doi:10.3762/bjoc.9.306
33.David, O.; Blot, J.; Bellec, C.; Fargeau-Bellassoued, M.-C.; Haviari, G.;
Célérier, J.-P.; Lhommet, G.; Gramain, J.-C.; Gardette, D.
J. Org. Chem. 1999, 64, 3122–3131. doi:10.1021/jo982169p
34.Thorat, R. G.; Pansare, S. V. Eur. J. Org. Chem. 2013, 7282–7285.
doi:10.1002/ejoc.201301078
6. Faria, A. R.; Salvador, E. L.; Correia, C. R. D. J. Org. Chem. 2002, 67,
3651–3661. doi:10.1021/jo016189u
7. Jiang, X.-P.; Cheng, Y.; Shi, G.-F.; Kang, Z.-M. J. Org. Chem. 2007,
72, 2212–2215. doi:10.1021/jo0624290
8. Trajkovic, M.; Balanac, V.; Ferjancic, Z.; Saicic, R. N. RSC Adv. 2014,
4, 53722–53724. doi:10.1039/C4RA11978A
35.Cutter, A. C.; Miller, I. R.; Keily, J. F.; Bellingham, R. K.; Light, M. E.;
Brown, R. C. D. Org. Lett. 2011, 13, 3988–3991.
9. Davies, S. G.; Fletcher, A. M.; Foster, E. M.; Houlsby, I. T. T.;
Roberts, P. M.; Schofield, T. M.; Thomson, J. E. Org. Biomol. Chem.
2014, 12, 9223–9235. doi:10.1039/C4OB01737D
10.Rao, N. N.; Parida, B. B.; Cha, J. K. Org. Lett. 2014, 16, 6208–6211.
doi:10.1021/ol503136s
doi:10.1021/ol2015048
36.Gage, J. L.; Branchaud, B. P. Tetrahedron Lett. 1997, 38, 7007–7010.
doi:10.1016/S0040-4039(97)01638-9
37.Conrad, J. C.; Kong, J.; Laforteza, B. N.; MacMillan, D. W. C.
J. Am. Chem. Soc. 2009, 131, 11640–11641. doi:10.1021/ja9026902
38.Reddy, K. K. S.; Rao, B. V.; Raju, S. S. Tetrahedron: Asymmetry 2011,
22, 662–668. doi:10.1016/j.tetasy.2011.03.009
11.Kim, G.-W.; Jin, T.; Kim, J.-S.; Park, S.-H.; Lee, K.-H.; Kim, S.-S.;
Myeong, I.-S.; Ham, W.-H. Tetrahedron: Asymmetry 2014, 25, 87–91.
doi:10.1016/j.tetasy.2013.11.009
39.Banwell, M. G.; Beck, D. A. S.; Smith, J. A. Org. Biomol. Chem. 2004,
2, 157–159. doi:10.1039/b312552a
12.Du-a-man, S.; Soorukram, D.; Kuhakarn, C.; Tuchinda, P.;
Reutrakul, V.; Pohmakotr, M. Eur. J. Org. Chem. 2014, 1708–1715.
doi:10.1002/ejoc.201301671
40.Kazi, B.; Kiss, L.; Forró, E.; Fülöp, F. Tetrahedron Lett. 2010, 51,
82–85. doi:10.1016/j.tetlet.2009.10.072
13.Yoon, H.; Cho, K. S.; Sim, T. Tetrahedron: Asymmetry 2014, 25,
497–502. doi:10.1016/j.tetasy.2014.02.009
41.Kiss, L.; Kazi, B.; Forró, E.; Fülöp, F. Tetrahedron Lett. 2008, 49,
339–342. doi:10.1016/j.tetlet.2007.11.043
14.Kauloorkar, S. V.; Jha, V.; Jogdand, G.; Kumar, P. Org. Biomol. Chem.
2014, 12, 4454–4460. doi:10.1039/c4ob00461b
42.Kiss, L.; Cherepanova, M.; Forró, E.; Fülöp, F. Chem. – Eur. J. 2013,
19, 2102–2107. doi:10.1002/chem.201203183
15.Lingamurthy, M.; Rajander, A.; Rao, B. V. Tetrahedron: Asymmetry
2014, 25, 860–863. doi:10.1016/j.tetasy.2014.04.011
16.Ortiz, G. X., Jr.; Kang, B.; Wang, Q. J. Org. Chem. 2014, 79, 571–581.
doi:10.1021/jo4022666
43.Cherepanova, M.; Kiss, L.; Fülöp, F. Tetrahedron 2014, 70,
2515–2522. doi:10.1016/j.tet.2014.02.063
44.Cherepanova, M.; Kiss, L.; Forró, E.; Fülöp, F. Eur. J. Org. Chem.
2014, 403–409. doi:10.1002/ejoc.201301281
17.Suga, H.; Hashimoto, Y.; Yasumura, S.; Takezawa, R.; Itoh, K.;
Kakehi, A. J. Org. Chem. 2013, 78, 10840–10852.
doi:10.1021/jo401837d
45.Brambilla, M.; Davies, S. G.; Fletcher, A. M.; Roberts, P. M.;
Thomson, J. E. Tetrahedron 2014, 70, 204–211.
doi:10.1016/j.tet.2013.11.094
18.Hanessian, S.; Soma, U.; Dorich, S.; Deschênes-Simard, B. Org. Lett.
2011, 13, 1048–1051. doi:10.1021/ol103094j
602

Beilstein J. Org. Chem. 2015, 11, 596–603.
46.Lee, M.-r.; Stahl, S. S.; Gellman, S. H. Org. Lett. 2008, 10, 5317–5319.
doi:10.1021/ol802274x
47.Fricke, Y.; Kopp, N.; Wünsch, B. Synthesis 2010, 791–796.
doi:10.1055/s-0029-1218622
48.Malik, G.; Guinchard, X.; Crich, D. Org. Lett. 2012, 14, 596–599.
doi:10.1021/ol203213f
49.Sousa, C. A. D.; Rizzo-Aguiar, F.; Vale, M. L. C.; García-Mera, X.;
Caamaño, O.; Rodríguez-Borges, J. E. Tetrahedron Lett. 2012, 53,
1029–1032. doi:10.1016/j.tetlet.2011.12.037
50.Pérez-Bautista, J. A.; Sosa-Rivadeneyra, M.; Quintero, L.; Höpfl, H.;
Tejeda-Dominguez, F. A.; Sartillo-Piscil, F. Tetrahedron Lett. 2009, 50,
5572–5574. doi:10.1016/j.tetlet.2009.07.070
51.Caputo, F.; Cattaneo, C.; Clerici, F.; Gelmi, M. L.; Pellegrino, S.
J. Org. Chem. 2006, 71, 8467–8472. doi:10.1021/jo061391o
52.Robinson, A.; Thomas, G. L.; Spandl, R. J.; Welch, M.; Spring, D. R.
Org. Biomol. Chem. 2008, 6, 2978–2981. doi:10.1039/b809038f
53.Forró, E.; Árva, J.; Fülöp, F. Tetrahedron: Asymmetry 2001, 12,
643–649. doi:10.1016/S0957-4166(01)00100-8
54.Palkó, M.; Benedek, G.; Forró, E.; Wéber, E.; Hänninen, M.;
Sillanpää, R. Tetrahedron: Asymmetry 2010, 21, 957–961.
doi:10.1016/j.tetasy.2010.05.003
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