Synthesis of - C -glycosides by samarium diiodide mediated coupling of glycosyl pyridyl sulfones with alkenes

Article abstract of DOI:10.1055/s-0030-1261230

A mild method for the synthesis of -C-glycosides by the samarium diiodide mediated coupling reactions of glycosyl 2-pyridyl sulfones with different ,-unsaturated carbonyl compounds has been developed. This method allows the use of less amount of substrates. Georg Thieme Verlag Stuttgart - New York.

Full text of DOI:10.1055/s-0030-1261230

2410
LETTER
Synthesis of a-C-Glycosides by Samarium Diiodide Mediated Coupling of
Glycosyl Pyridyl Sulfones with Alkenes
Synthesis of
a-
C
-G
e
lycosides n Li, De-Cai Xiong, Xin-Shan Ye*
State Key Laboratory of Natural and Biomimetic Drugs and School of Pharmaceutical Sciences, Peking University,
Xue Yuan Road 38, Beijing 100191, P. R. of China
Fax +86(10)82802724; E-mail: xinshan@bjmu.edu.cn
Received 7 June 2011
SmI2 could be further reduced by SmI2 to form glycosyl
Abstract: A mild method for the synthesis of a-C-glycosides by the
samarium diiodide mediated coupling reactions of glycosyl 2-py-
ridyl sulfones with different a,b-unsaturated carbonyl compounds
has been developed. This method allows the use of less amount of
substrates.
anomeric samarium(III) species, which would couple
with carbonyl substrates to afford 1,2-trans-C-glycosides
under Barbier conditions, that is to say, to obtain a-C-gly-
cosides, the C2-substituents have to be axially oriented
just like in the mannopyranoside case. Moreover, a few
examples have shown that the anomeric radical induced
by SmI2 can be trapped by the intramolecular alkene or
alkyne to produce a-C-glycosides.9 Although the reac-
tions of glycosyl anomeric samarium(III) with carbonyl
substrates have been successfully realized, and some
examples of intramolecular anomeric radical addition to
alkenes have been reported, the SmI2-mediated intermo-
lecular coupling reaction of glycosyl pyridyl sulfones
with alkenes for the synthesis of a-C-glycosides has never
been disclosed.
Key words: C-glycosides, samarium diiodide, glycosyl 2-pyridyl
sulfones, coupling reaction
C-Glycosides as stabilized isosteres of O-glycosides play
an important role in pharmaceutical or biological re-
search. They exist in some biologically active natural
products, and they have also been used as useful chiral
building blocks for the synthesis of complex molecules.1
Toward the synthesis of C-glycosides, a variety of syn-
thetic methods have been developed.2 Among the C-gly-
cosides, the C-alkyl glycosides are very important, and
their synthesis has drawn much attention in recent years.
For instance, the preparation of C-alkyl glycosides was
achieved by the coupling of glycosyl donors with
nucleophiles3 or the Ni-catalyzed Negishi cross-coupling
reaction.4 In particular, radical chemistry was used for the
formation of C-alkyl glycosides by the coupling of glyco-
syl anomeric carbons and alkenes,5 but usually a signifi-
cant excess (6–20 equiv) of alkenes was needed. Very
recently, the Gagné group developed efficient methods for
the synthesis of C-alkyl glycosides by the reductive cou-
pling of glycosyl bromides with 2 equivalents of alkenes.6
Although the methods were well-behaved for acetate- or
benzoate-protected glycosyl bromides, they were not
well-applied to the benzyl-protected glycosyl halide sub-
strates.
In this work, we tried to prepare a-C-glycosides by the
SmI2-induced reductive coupling of glycosyl 2-pyridyl
sulfones with a,b-unsaturated esters, amides, and acids. It
seemed to be difficult, because glycosyl anomeric radical
could dimerize and also abstract a hydrogen atom from
the solvent. Meanwhile, anomeric radicals could be re-
duced by SmI2 to form glycosyl anomeric samarium(III)
which would tend to elimination.10 Moreover, a,b-unsat-
urated esters, amides, and acids could probably be re-
duced by SmI2.11 In spite of these difficulties, we decided
to tackle this problem. First, the coupling of glucosyl 2-
pyridyl sulfone 1 with 1.2 equivalents of methyl acrylate
was induced by 0.1 M SmI2 in THF at room temperature
under Barbier conditions (Table 1). The a-C-glycoside 2
was isolated in only 10% yield when SmI2 in THF was
added dropwise in less than 10 s (Table 1, entry 1), 1-
deoxy-2,3,4,6-tetra-O-benzyl-D-glucopyranose and glu-
cal were produced as the major byproducts. However, the
C-glycoside 2 was obtained in 26% yield when SmI2 was
added at a speed of 1.5 mL/h by a syringe pump (Table 1,
entry 2), meaning that it is favorable for the reaction when
the addition of SmI2 is slow enough. To improve the re-
ductive ability of SmI2, HMPA9a,10,12 as a generally uti-
lized co-solvent was used, encouragingly leading to an
increased yield (34%) of the desired C-glucoside product
In order to overcome some shortages of coupling reac-
tions of glycosyl anomeric radicals with alkenes, we pos-
tulated that SmI2 would be competent for it. Since SmI2
was pioneered by Kagan, it has become one of the most
important reagents in organic chemistry.7 SmI2 is com-
mercially available and easy to handle. In fact, this re-
agent has been employed for the stereoselective synthesis
of C-glycosides.8 In the SmI2-mediated synthesis of C-
glycosides, more reactive glycosyl 2-pyridyl sulfones
were used. The glycosyl anomeric radical induced by
2 (Table 1, entry 3). In an effort to avoid the use of toxic
8e,13
HMPA, when a catalytic amount of NiI2
(1%) was
added instead of HMPA, compound 2 was obtained in
39% yield (Table 1, entry 4). Since proton sources have a
considerable impact on the efficiency of SmI2-mediated
reactions,14 several proton sources were tested for the re-
SYNLETT 2011, No. 16, pp 2410–2414
Advanced online publication: 13.09.2011
DOI: 10.1055/s-0030-1261230; Art ID: W13311ST
© Georg Thieme Verlag Stuttgart · New York
x
x
.x
x
.2
0
1
1

LETTER
Synthesis of a-C-Glycosides
2411
common approaches to produce glycosyl propionic ac-
ids.15 The synthesis of glycosyl propionic acids from gly-
cosyl halides was reported by Somsák’s group,16 who
used a significant excess (18 equiv) of acrylic acid pro-
ducing the glycosyl propionic acid in 52% yield. In our
approach, the glycosyl propionic acid 7 was obtained in
47% yield when only 1.2 equivalents of acrylic acid were
used (Table 2, entry 5). The optimized conditions were
also applied to disubstituted alkenes.
Table 1 Optimization of the Coupling Reaction of Glucosyl 2-Py-
ridyl Sulfone with Methyl Acrylatea
O
O
S
N
BnO
BnO
O
OBn
OBn
O
CO2Me
1
BnO
BnO
SmI2
+
As can be seen, the coupling reaction of 1 and methyl
methacrylate afforded a-C-glucoside 9 in 91% yield
(Table 2, entry 7, dr = 3.2:1). 2-Acetamidoacrylate and
methacrylamide also underwent the reaction successfully
to gain 10 and 11 in 59% (dr = 1.3:1) and 68% (dr = 2.5:1)
yields, respectively (Table 2, entries 8 and 9).
OBn
additive
COOMe
OBn
2
(1.2 equiv)
Entry
Additive
Product 2 (%)b
1
2
–
–
10c
26
34
39
52
55
71
80
84
84
In addition to glucosyl 2-pyridyl sulfone 1, the SmI2-me-
diated reaction was extended to the coupling of galactosyl
and mannosyl 2-pyridyl sulfones with methyl acrylate
(Table 3). As shown, the a-C-glycosides were smoothly
isolated in 74% and 65% yields, respectively (Table 3, en-
tries 1 and 2). Glycosyl halides are usually used to pro-
duce anomeric radicals for the preparation of C-
glycosides. However, when 2-acetamido-3,4,6-tri-O-
acetyl-2-deoxy-D-glucopyranosyl bromide was used, no
coupling product (only oxazoline side-product) was
achieved.17 Gallagher’s group18 developed a method for
the synthesis of C-2-amino-2-deoxyglycosides by using
anomeric selenides as radical precursors, but toxic
Bu3SnH was needed. In our approach, when N-acetyl-glu-
cosyl 2-pyridyl sulfone was used, the desired a-coupling
product 14 was gained in 55% isolated yield when four
equivalents of methyl acrylate were employed.
3
HMPA (5 mol%)
NiI2 (1 mol%)
4
5
NiI2 (1 mol%), H2O (2 equiv)
6
NiI2 (1 mol%), MeOH (2 equiv)
NiI2 (1 mol%), n-PrOH (2 equiv)
NiI2 (1 mol%), t-BuOH (2 equiv)
NiI2 (1 mol%), i-PrOH (2 equiv)
NiI2 (1 mol%), i-PrOH (4 equiv)
7
8
9
10
a 0.1 M solution of SmI2 was added at a speed of 1.5 mL/h by a syringe
pump.
b Isolated yield.
c 0.1 M solution of SmI2 was added in less than 10 s.
The anomeric configuration of the coupling product was
1
determined by H NMR analysis. The coupling constant
action. Fortunately, the yield of 2 was increased signifi-
cantly when two equivalents of H2O were added (Table 1,
entry 5, 52%). Other solvents such as MeOH, n-PrOH,
and t-BuOH also worked well and product 2 was afforded
in 80% yield when two equivalents of t-BuOH were used
(Table 1, entry 8). Interestingly, i-PrOH proved to be most
effective, the C-glycoside 2 was generated in 84% yield
after the addition of two equivalents of i-PrOH (Table 1,
entry 9). The addition of more i-PrOH did not improve the
yield (Table 1, entry 10).
J1,2 = 5.6–6.0 Hz indicates that the anomeric configura-
tion of C-glucosides is a type. For example, the stereo-
chemsitry of C-glycosides 4–6, which adopt a 4C1
conformation, was established by their 1H NMR spectra:
3
for compound 4, H(2) d = 3.72 (dd, J2,3 = 9.2 Hz,
3J1,2 = 5.6 Hz); for compound 5, H(2) d = 3.74 (dd,
3
3J2,3 = 9.6 Hz, J1,2 = 5.6 Hz); for compound 6, H(2) d =
3.75 (dd, 3J2,3 = 9.2 Hz, 3J1,2 = 5.6 Hz). In order to further
confirm the anomeric configuration, the C-glycoside 12
was deprotected by hydrogenolysis which was followed
by acetylation to yield the product 15 (Scheme 1, a), its
spectroscopic data coincide with those described in the lit-
erature.19 The protective groups of C-glycoside 14 were
also manipulated to form compound 16 (Scheme 1, b).
For C-glycoside 16, the a-configuration of the predomi-
Under the optimized reaction conditions, the scope of al-
kene substrates was examined (Table 2). The coupling re-
action with acrylate derivatives such as tert-butyl acrylate
produced the desired product 3 in good yield (Table 2, en-
try 1). The a,b-unsaturated amides such as acrylamide, N-
phenylacrylamide, and 2-acrylamidoacetate reacted with
glucosyl 2-pyridyl sulfone 1 under the same conditions to
give the corresponding products in good or moderate
yields (Table 2, entries 2–4). As anticipated, 1-(vinylsul-
fonyl)benzene worked well, the coupling product 8 was
4
1
nant C1 conformation was again assigned by using H
3
NMR analysis: H(2) d = 4.28 (td, J2,NH = 8.4 Hz,
3J2,3 = 8.0 Hz, J1,2 = 3.6 Hz). Using our method, only a-
3
C-glycosides were provided, and b-isomers were not de-
tected by the 1H NMR analysis of the crude mixtures. Our
obtained in 62% yield, and no sulfone reduction product results are different from the previous reports.8a–g In the
previous approach, 1,2-trans-C-glycosides were obtained
by the coupling reaction of glycosyl 2-pyridyl sulfones
with alkyl ketones and aldehydes. That is because the C1
was isolated (Table 2, entry 6). Glycosyl propionic acids
are useful synthetic intermediates, and the hydroboration–
oxidation or Jones’ oxidation of C-allyl glycosides are
Synlett 2011, No. 16, 2410–2414 © Thieme Stuttgart · New York

2412
G. Li et al.
LETTER
radicals were reduced by SmI2 to produce glycosyl samar- cals were trapped with alkenes to result in a-C-glyco-
iums that could be trapped with alkyl ketones and alde- sides.20
hydes, affording 1,2-trans-C-glycosides.4a In our
procedure, the thermodynamically stable a-glycosyl radi-
Table 2 Coupling Reactions of Alkenes with Glucosyl 2-Pyridyl Sulfonea
R1
O
O
R2
SmI2
BnO
BnO
O
S
N
BnO
BnO
R2
OBn
O
+
R1
NiI2, i-PrOH
OBn
OBn
(1.2 equiv)
OBn
3–11
1
Entry
1
Alkene
Product
Yield (%, dr)b,c
CO2t-Bu
CONH2
CONHPh
O
O
BnO
BnO
80
CO2t-Bu
OBn
OBn
OBn
OBn
O
3
BnO
BnO
2
3
80
67
CONH2
OBn
O
4
BnO
BnO
CONHPh
OBn
O
5
H
N
N
H
CO2Et
BnO
BnO
CO2Et
4
51
OBn
OBn
OBn
OBn
O
OBn
O
6
CO2H
BnO
BnO
5
6
7
47
CO2H
OBn
O
7
SO2Ph
CO2Me
BnO
BnO
62
SO2Ph
CO2Me
OBn
O
8
BnO
BnO
91 (3.2:1)
OBn
O
9
CO2Me
BnO
BnO
CO2Me
NHAc
NHAc
OBn
8
59 (1.3:1)
OBn
10
Synlett 2011, No. 16, 2410–2414 © Thieme Stuttgart · New York

LETTER
Synthesis of a-C-Glycosides
2413
Table 2 Coupling Reactions of Alkenes with Glucosyl 2-Pyridyl Sulfonea (continued)
R1
O
O
R2
SmI2
BnO
BnO
O
S
N
BnO
BnO
R2
OBn
O
+
R1
NiI2, i-PrOH
OBn
OBn
(1.2 equiv)
OBn
3–11
1
Entry
9
Alkene
Product
Yield (%, dr)b,c
CONH2
O
BnO
BnO
CONH2
68 (2.5:1)
OBn
OBn
11
a Reaction conditions: NiI2 (1 mol%), i-PrOH (2.0 equiv), SmI2 (0.1 M in THF, 2.0–5.0 equiv), r.t., 0.7–1.7 h.
b Isolated yield.
c An inseparable mixture of diastereomers was observed, the dr value was determined by NMR.
Table 3 Coupling Reactions of Glycosyl 2-Pyridyl Sulfones with Methyl Acrylatea
O
O
CO2Me
O
S
N
SmI2, NiI2
i-PrOH
CO2Me
+
O
glycosyl 2-pyridyl sulfone
(1.2 equiv)
12–14
Entry
Glycosyl 2-pyridyl sulfone
Product
Yield (%)b
O
CO2Me
O
BnO
BnO
O
S
N
1
74
BnO
BnO
OBn
O
OBn
OBn
12
OBn
O
CO2Me
O
BnO
BnO
O
S
N
2
3
65
BnO
BnO
OBn
O
OBn
O
OBn
13
OBn
O
O
S
CO2Me
O
55c
O
N
O
Ph
O
NHAc
Ph
O
NHAc
OTBS
OTBS
14
a Reaction conditions: NiI2 (1 mol%), i-PrOH (2.0 equiv), SmI2 (0.1 M in THF, 2.0–5.0 equiv), r.t., 0.7–1.7 h.
b Isolated yield.
c Methyl acrylate (4 equiv) was used.
In summary, we have developed a mild method for the as a proton source. This method can be also applied to the
synthesis of a-C-glycosides by the SmI2-mediated cou- preparation of a-C-N-acetyl-2-amino-2-deoxyglucosides.
pling of glycosyl 2-pyridyl sulfones with a,b-unsaturated
esters, amides, and acids. This approach enjoys the use of
low amounts of alkene substrates. The yields of C-glyco-
sides can be significantly improved by the use of i-PrOH
Supporting Information for this article is available online at
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Synlett 2011, No. 16, 2410–2414 © Thieme Stuttgart · New York

2414
G. Li et al.
LETTER
Jarreton, O.; Mazéas, D.; Urban, D.; Beau, J.-M. Chem. Eur.
J. 1998, 4, 655. (d) Miquel, N.; Doisneau, G.; Beau, J.-M.
Chem. Commun. 2000, 2347. (e) Miquel, N.; Doisneau, G.;
Beau, J.-M. Angew. Chem. Int. Ed. 2000, 39, 4111.
(f) Chiara, J. L.; Sesmilo, E. Angew. Chem. Int. Ed. 2002, 41,
3242. (g) Mikkelsen, L. M.; Skrydstrup, T. J. Org. Chem.
2003, 68, 2123. For C-glycosides of 2-amino-2-deoxy
sugars, see: (h) Andersen, L.; Mikkelsen, L. M.; Beau,
J.-M.; Skrydstrup, T. Synlett 1998, 1393. (i) Urban, D.;
Skrydstrup, T.; Beau, J.-M. Chem. Commun. 1998, 955.
(j) Ren, Z.-X.; Yang, Q.; Price, K. N.; Chen, T.; Nygren, C.;
Turner, J. F. C.; Baker, D. C. Carbohydr. Res. 2007, 342,
1668. For C-glycosides of neuraminic acids, see:
(k) Vlahov, I. R.; Vlahova, P. I.; Linhardt, R. J. J. Am. Chem.
Soc. 1997, 119, 1480. (l) Polat, T.; Du, Y.; Linhardt, R. J.
Synlett 1998, 1195. (m) Du, Y.; Linhardt, R. J. Carbohydr.
Res. 1998, 308, 161. (n) Bazin, H. G.; Du, Y.; Polat, T.;
Linhardt, R. J. J. Org. Chem. 1999, 64, 7254. (o) Wang, Q.;
Linhardt, R. J. J. Org. Chem. 2003, 68, 2668. (p) Abdallah,
Z.; Doisneau, G.; Beau, J.-M. Angew. Chem. Int. Ed. 2003,
42, 5209. (q) Malapelle, A.; Abdallah, Z.; Doisneau, G.;
Beau, J.-M. Angew. Chem. Int. Ed. 2006, 45, 6016.
(r) Malapelle, A.; Coslovi, A.; Doisneau, G.; Beau, J.-M.
Eur. J. Org. Chem. 2007, 3145. (s) Papin, C.; Doisneau, G.;
Beau, J.-M. Chem. Eur. J. 2009, 15, 53.
(a)
O
CO2Me
i) Pd/C, H2
O
CO2Me
BnO
AcO
AcO
ii) Ac2O, py
85%
BnO
OBn
OAc
OBn
12
OAc
15
(b)
Ph
O
CO2Me
O
CO2Me
AcO
O
i) CSA, MeOH
ii) Ac2O, py
NHAc
AcO
NHAc
O
80%
OAc
16
OTBS
14
Scheme 1 The protective group manipulations of C-glycosides 12
and 14
Acknowledgment
This work was financially supported by the National Natural Sci-
ence Foundation of China (20732001).
References
(1) (a) Compain, P.; Martin, O. R. Bioorg. Med. Chem. 2001, 9,
3077. (b) Bililign, T.; Griffith, B. R.; Thorson, J. S. Nat.
Prod. Rep. 2005, 22, 742. (c) Nicolaou, K. C.; Mitchell,
H. J. Angew. Chem. Int. Ed. 2001, 40, 1576.
(2) (a) Levy, D. E.; Tang, C. The Chemistry of C-Glycosides;
Pergamon: Tarrytown (NY), 1995. (b) Du, Y.; Linhardt, R.
J.; Vlahov, I. R. Tetrahedron 1998, 54, 9913. (c) Dondoni,
A.; Marra, A. Chem. Rev. 2000, 100, 4395. (d) Somsák, L.
Chem. Rev. 2001, 101, 81. (e) Koester, D. C.; Holkenbrink,
A.; Werz, D. B. Synthesis 2010, 3217.
(3) (a) McGarvey, G. J.; LeClair, C. A.; Schmidtmann, B. A.
Org. Lett. 2008, 10, 4727. (b) Crich, D.; Sharma, I. Org.
Lett. 2008, 10, 4731.
(4) (a) Gong, H.; Gagné, M. R. J. Am. Chem. Soc. 2008, 130,
12177. (b) Gong, H.; Sinisi, R.; Gagné, M. R. J. Am. Chem.
Soc. 2007, 129, 1908.
(5) (a) Adlington, R. M.; Baldwin, J. E.; Basak, A.; Kozyrod, R.
P. J. Chem. Soc., Chem. Commun. 1983, 944. (b) Dupuis,
J.; Giese, B.; Hartung, J.; Leising, M.; Korth, H.-G.;
Sustmann, R. J. Am. Chem. Soc. 1985, 107, 4332. (c) Praly,
J.-P.; Ardakani, A. S.; Bruyère, I.; Marie-Luce, C.; Qin,
B. B. Carbohydr. Res. 2002, 337, 1623. (d) DeShong, P.;
Slough, G. A.; Elango, V. Carbohydr. Res. 1987, 171, 342.
(e) Parrish, J. D.; Little, R. D. Org. Lett. 2002, 4, 1439.
(f) Readman, S. K.; Marsden, S. P.; Hodgson, A. Synlett
2000, 1628. (g) Micskei, K.; Juhász, Z.; Ratković, Z. R.;
Somsák, L. Tetrahedron Lett. 2006, 47, 6117.
(6) (a) Gong, H.; Andrews, R. S.; Zuccarello, J. L.; Lee, S. J.;
Gagné, M. R. Org. Lett. 2009, 11, 879. (b) Andrews, R. S.;
Becker, J. J.; Gagné, M. R. Angew. Chem. Int. Ed. 2010, 49,
7274.
(7) For reviews on SmI2 chemistry, see: (a) Kagan, H. B.
Tetrahedron 2003, 59, 10351. (b) Steel, P. G. J. Chem. Soc.,
Perkin Trans. 1 2001, 2727. (c) Molander, G. A. Chem. Rev.
1992, 92, 29.
(9) (a) Chénedé, A.; Perrin, E.; Rekaï, E. D.; Sinaÿ, P. Synlett
1994, 420. (b) Mazéas, D.; Skrydstrup, T.; Doumeix, O.;
Beau, J.-M. Angew. Chem., Int. Ed. Engl. 1994, 33, 1383.
(c) Skrydstrup, T.; Mazéas, D.; Elmouchir, M.; Doisneau,
G.; Riche, C.; Chiaroni, A.; Beau, J.-M. Chem. Eur. J. 1997,
3, 1342.
(10) Doisneau, G.; Beau, J.-M. Tetrahedron Lett. 1998, 39, 3477.
(11) (a) Inanaga, J.; Handa, Y.; Tabuchi, T.; Otsubo, K.;
Yamaguchi, M.; Hanamoto, T. Tetrahedron Lett. 1991, 32,
6557. (b) Cabrera, A.; Alper, H. Tetrahedron Lett. 1992, 33,
5007.
(12) (a) Inanaga, J.; Ishikawa, M.; Yamaguchi, M. Chem. Lett.
1987, 1485. (b) Krief, A.; Laval, A. M. Chem. Rev. 1999, 99,
745.
(13) Machrouhi, F.; Hamman, B.; Namy, J.-L.; Kagan, H. B.
Synlett 1996, 633.
(14) (a) Keck, G. E.; Wager, C. A.; Sell, T.; Wager, T. T. J. Org.
Chem. 1999, 64, 2172. (b) Tarnopolsky, A.; Hoz, S. J. Am.
Chem. Soc. 2007, 129, 3402.
(15) (a) Cook, B. N.; Bhakta, S.; Biegel, T.; Bowman, K. G.;
Armstrong, J. I.; Hemmerich, S.; Bertozzi, C. R. J. Am.
Chem. Soc. 2000, 122, 8612. (b) Miller, G. J.; Gardiner,
J. M. Org. Lett. 2010, 12, 5262.
(16) Juhász, Z.; Micskei, K.; Gál, E.; Somsák, L. Tetrahedron
Lett. 2007, 48, 7351.
(17) Cui, J.; Horton, D. Carbohydr. Res. 1998, 309, 319.
(18) (a) SanMartin, R.; Tavassoli, B.; Walsh, K. E.; Walter, D. S.;
Gallagher, T. Org. Lett. 2000, 2, 4051. (b) Grant, L.; Liu,
Y.; Walsh, K. E.; Walter, D. S.; Gallagher, T. Org. Lett.
2002, 4, 4623. (c) Liu, Y.; Gallagher, T. Org. Lett. 2004, 6,
2445.
(19) Gotanda, K.; Matsugi, M.; Suemure, M.; Sano, A.; Oka, M.;
Kita, Y. Tetrahedron 1999, 55, 10315.
(20) Procter, D. J.; Flowers, R. A. II; Skrydstrup, T. Organic
Synthesis Using Samarium Diiodide; RSC: Cambridge,
2009, 188–189.
(8) (a) Hung, S.-C.; Wong, C.-H. Angew. Chem., Int. Ed. Engl.
1996, 35, 2671. (b) Jarreton, O.; Skrydstrup, T.; Beau, J.-M.
Tetrahedron Lett. 1997, 38, 1767. (c) Skrydstrup, T.;
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