Functionalized aryl-β-C-glycoside synthesis by Barbier-type reaction using 2,4,6-triisopropylphenyllithium

Article abstract of DOI:10.1016/j.tetlet.2015.01.054

We developed an efficient synthetic route for functionalized aryl-β-C-glycosides, which are difficult to prepare by conventional methods. An aryl halide having an ester, cyano, or carbonyl group was treated with 2,4,6-triisopropylphenyllithium in the pres

Full text of DOI:10.1016/j.tetlet.2015.01.054

Accepted Manuscript
Functionalized aryl-β-C-glycoside synthesis by Barbier-type reaction using
2,4,6-triisopropylphenyllithium
Kiyomi Ohba, Yuichi Koga, Sumihiro Nomura, Masaya Nakata
PII:
S0040-4039(15)00069-6
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.01.054
TETL 45724
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
10 November 2014
26 December 2014
7 January 2015
Please cite this article as: Ohba, K., Koga, Y., Nomura, S., Nakata, M., Functionalized aryl-β-C-glycoside synthesis
by Barbier-type reaction using 2,4,6-triisopropylphenyllithium, Tetrahedron Letters (2015), doi: http://dx.doi.org/
10.1016/j.tetlet.2015.01.054
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
To create your abstract, type over the instructions in the template box below.
Fonts or abstract dimensions should not be changed or altered.
Leave this area blank for abstract info.
Functionalized aryl-β-C-glycoside synthesis
by Barbier-type reaction using 2,4,6-
triisopropylphenyllithium
Kiyomi Ohba, Yuichi Koga, Sumihiro Nomura, Masaya Nakata
CO2R
Barbier-type reaction
(1)
-Pr
i
TIPPLi
-Pr
CO2R
O
H
OBn
OBn
OBn
OBn
-Pr
i
i
O
O
+
Li
BnO
BnO
I (or Br)
OBn
OBn
(2) -Pr3SiH, BF3•Et2
O
i

1
Tetrahedron Letters
journal homepage: www.els evier.com
Functionalized aryl-β-C-glycoside synthesis by Barbier-type reaction using 2,4,6-
triisopropylphenyllithium
Kiyomi Ohba a,b,∗, Yuichi Koga a, Sumihiro Nomura a, and Masaya Nakata b
a Medicinal Chemistry Research Laboratories, Mitsubishi Tanabe Pharma Corporation, 1000 Kamoshida-cho, Aoba-ku, Yokohama 227-0033, Japan
b Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
We developed an efficient synthetic route for functionalized aryl-β-C-glycosides, which are
difficult to prepare by conventional methods. An aryl halide having an ester, cyano, or carbonyl
group was treated with 2,4,6-triisopropylphenyllithium in the presence of a δ-lactone (Barbier-
type reaction conditions) to afford a coupling product. The following deoxygenation gave the
desired aryl-β-C-glycoside in good yield.
Available online
2014 Elsevier Ltd. All rights reserved.
Keywords:
C-Glycoside
Aldonolactone
Barbier-type reaction
Halogen–metal exchange reaction
2,4,6-Triisopropylphenyllithium
ing reagents or generated arylmetals. To address this limitation,
an indirect approach has been used by employing the correspond-
ing protected alcohols or acetals instead of ester groups on the
aromatic ring. This is followed by the required deprotection–
oxidation steps.11
Currently, a wide variety of chemoselective metalating rea-
gents for halogen–metal exchange reactions with electrophilic
functional groups have been studied and developed.12 We dis-
closed that a functionalized aryllithium generated by a halogen–
lithium exchange reaction using mesityllithium (MesLi) success-
fully reacted with a protected δ-gluconolactone.4d Another exam-
ple is a C-nucleoside synthesis using i-PrMgCl·LiCl as described
Aryl-C-glycosides are an important group of naturally occur-
ring products that exhibit various biological activities.1-3 Moreo-
ver, some synthetic aryl-C-glycosides have been exploited in
recent years as therapeutic agents for type 2 diabetes.4
For these reasons, aryl-C-glycosides have attracted much at-
tention and consequently, many preparation methods have been
developed.5 The main synthetic approaches reported in the litera-
ture thus far are Lewis acid promoted electrophilic reactions of
glycosyl donors,6 Fries-type reactions of phenols (O–C migra-
tion),7 nucleophilic additions of organometallic reagents to pro-
tected aldonolactones followed by reduction of the yielded
lactols,8 and transition metal-mediated C-glycosylations.9
by Pankiewicz, which is
a
Grignard reaction of 3-
Although these preparation methods are numerous, new and
complementary methodologies with higher efficiency are still
desired. As for the C-glycosides having electron-withdrawing
substituents on the aromatic ring, direct preparation methods are
limited; an electrophilic reaction of glycosyl donors with elec-
tron-deficient aromatic rings hardly proceeds because the
nucleophilicity of these rings decreases considerably. A catalytic
approach was thus adopted in an attempt to address this issue.9a-d
We turn next to a nucleophilic addition/reduction sequence us-
ing aldonolactones as glycosyl donors, which have been devel-
oped by Kishi and others.8 This methodology has been popularly
utilized for preparations of aryl C-glycosides because of its gen-
erality, high anomeric stereoselectivity, and scalability based on
the simple procedure.10 However, ester or cyano groups on the
aromatic ring react with highly reactive lithiating and magnesiat-
iodobenzonitrile with perbenzylated ribonolactone followed by
removal of the anomeric hydroxy group to afford 3-cyanophenyl-
C-riboside.13 Although these limited examples were reported,
there is no comprehensive study to date. Herein, we report a ro-
bust preparation method for functionalized aryl-β-C-glycosides
using 2,4,6-triisopropylphenyllithium (TIPPLi), which is a bulky
and efficient chemoselective lithiating agent.
Firstly, halogen–metal exchange reactions were examined be-
tween tert-butyl 4-iodobenzoate (1a) and various metalating rea-
gents (Table 1, entries 1–5). The reactions were quenched with
CD3OD to afford the corresponding deuterated product 3a in
good yields when using n-Bu3MgLi,14 i-PrMgCl·LiCl,15 and
MesLi16 (entries 3–5), in contrast to n-BuLi and t-BuLi (entries 1
and 2). These resulting arylmetals also reacted with
perbenzylated glucono δ-lactone 2 to give lactol 3b (entries 1–5).
———
∗ Corresponding author.
E-mail address: ohba.kiyomi@mf.mt-pharma.co.jp (K. Ohba)

2
Tetrahedron
Table 2
Barbier-type reactions with perbenzylated lactone 2
These coupling reactions afforded only C-β adduct (3b); however,
it remains unclear at present that the C-β stereoselectivity was
derived from the result of the stereoselective addition or from the
result of the isomerization to the thermodynamically stable C-β
isomer under the acidic quenching conditions. We next per-
formed this coupling with Barbier-type reaction conditions lead-
ing to the improved yield of 3b (entries 4 and 5). Based on our
observation of a small amount of adduct between MesLi and
lactone 2, TIPPLi16b was examined as a hindered halogen–lithium
exchange reagent that can be readily prepared from commercially
available 2,4,6-triisopropylphenylbromide (4, TIPPBr) and n-
BuLi at −78 °C. It was revealed that a Barbier-type reaction using
TIPPLi afforded adduct 3b in an excellent yield of 90% (entry 6).
i
-Pr
i
i
-Pr
-Pr
R
4
Br
(1.5 equiv)
n-
BuLi (1.5 equiv)
THF, –78 °C, 1 h
HO
O
R
OBn
OBn
TIPPLi
2
+
BnO
THF, –78 °C, 1 h
X
OBn
6
or
1
5
3
or
(1.0 equiv)
(1.0 equiv)
The
other
phenyllithiums
such
as
2,4,6-tri-tert-
O
O
butylphenyllithium, 2,3,4,5,6-pentamethylphenyllithium, and 4-
methoxy-2,6-dimethylphenyllithium were less effective than
TIPPLi (data not shown).
BnO
OBn
OBn
O
O
O
O
OBn
OBn
BnO
O
BnO
OBn
BnO
R1
Table 1
Halogen–metal exchange reactions and coupling reactions of resulting func-
tionalized arylmetals
OBn
7
R1
8
OBn
9
BnO
R2
O
R2
O
OBn
BnO
OBn
BnO
OBn
OBn
1
2
1
2
10a:
10b:
t
11a:
11b:
t
R =CO2 -Bu, R =OH
R =CO2 -Bu, R =OH (anomeric mixture)
1
2
1
2
C
R =CO2H, R =H
R =CO2H, R =H (
-
only)
Entry
R
X
Product
Yield (%)a
1
2
3
4
5
6
7
8
p-CO2t-Bu (1a)
p-CO2t-Bu (1b)
p-CO2Me (5a)
p-CO2Me (5b)
p-CN (5c)
p-CN (5d)
o-CO2Me (5e)
p-C(=O)Ph (5f)
I
Br
I
Br
I
Br
I
3b
3b
6a
6a
6b
6b
9
93
60
81
19
80b
75b
69c
52
Entry Reagent
3a (Yield, %)a 3b (Yield, %)a,b
1
n-BuLi
26
16
92
92
76
70
28 / N.T.c
12 / N.T.
49d / N.T.
55 / 71
68 / 76
62 / 90
I
6c
2
t-BuLi
3
4
5
n-Bu3MgLi
i-PrMgCl·LiCle
MesLi
9
6d
6e
79
(5g)
(5h)
6
TIPPLi
a Isolated yield.
10
0
b Grignard-type addition / Barbier-type addition.
c Not tested.
11
12
p-CO2t-Bu (1a)
p-CO2t-Bu (1a)
I
I
10a
11a
90d
63e
d
−
The reaction was performed at 78 °C, then allowed to warm to 0 °C.
e Performed at −60 °C.
a Isolated yield.
b 1.2 equiv of TIPPLi was used.
c An anomeric mixture of spiroketal 9 (C-α:β = 7:1).
The scope of this TIPPLi promoted Barbier-type reaction was
investigated (Table 2). The results indicated that the reactions
between perbenzylated lactone 2 and aryl iodides having an ester,
cyano, or carbonyl group proceeded smoothly to afford lactols
(entries 1, 3, 5, and 7–9). It should also be noted that the reaction
proceeded successfully not only with bulky tert-butyl 4-
iodobenzoate (1a) but also with methyl 4-iodobenzoate (5a) to
give lactols (3b and 6a) in excellent yield without any self-
condensation (entries 1 and 3). Methyl 2-iodobenzoate (5e) un-
derwent the reaction smoothly to produce spiroketal 9 in 69%
yield as an anomeric mixture (C-α:β = 7:1, entry 7), whereas
methyl 2-iodo-3,4,5-trimethoxybenzoate (5h) did not undergo
this reaction (entry 10). The coupling reactions between different
aldonolactones (perbenzylated mannolacton 7 or ribonolactone 8)
and tert-butyl 4-iodobenzoate (1a) were also studied and provid-
ed the corresponding lactols in 90% yield (10a, C-β only, entry
11) or in 63% yield (11a, an anomeric mixture, C-α:β = 1:2.7,
entry 12). In addition, aryl bromides were examined to give a
good to moderate yield of the products (entries 2, 4, and 6). In
d Tetra-O-benzyl-D-manno-1,5-lactone (7) was used instead of 2. The product
was C-β only.
e Tri-O-benzyl-D-ribo-1,4-lactone (8) was used and an anomeric mixture (C-
α:β = 1:2.7) was obtained.
these cases, tetra-O-benzyl-D-manno-1,5-lactone (7) was also
isolated in ca. 10% yield. It is presumed that a deprotonation
reaction at the α-position of lactone 2 occurred.
In order to avoid this side reaction, coupling reactions involv-
ing bulkier trimethylsilyl (TMS) protected glucono δ-lactone 124a
were investigated (Table 3). The coupling reaction mixture was
quenched with methanol/methanesulfonic acid to serve methyl
glycoside 13 in good yields (entry 1–6) with removal of the TMS
protecting groups. Notably, the coupling reaction of methyl 4-
bromobenzoate (5b) and the persilylated lactone 12 proceeded
smoothly (entry 3), contrary to the aforementioned reaction with
perbenzylated lactone 2 (entry 4, Table 2). Moreover, the reac-
tion with methyl 2-bromobenzoate (5j) afforded spiroketal 14 in
91% yield as an anomeric mixture (C-α:β = 9:1, entry 4). This C-

3
α stereoselectivity was observed similarly in the case of the cou-
pling reaction of methyl 2-iodobenzoate (5e) and perbenzylated
lactone 2 (C-α:β = 7:1, entry 7, Table 2), whereas the C-β prod-
ucts were obtained when using para- or meta- substituted aryl
halides.
conditions (entries 2–5). The reduction of spiroketal 9 did not
afford the
Table 4
Reduction of lactols
Table 3
Barbier-type reactions with persilylated δ-lactone 12a
Entry
R
R’ (Product)
Yield (%)a
1
2
3
p-CO2t-Bu (3b)
p-CN (6b)
p-CO2H (15a)
p-CN (15b)
81
63
Entry
R
Product Yield (%)b
83
1
2
3
4
5
6
p-CO2t-Bu (1b)
p-CO2i-Pr (5i)
p-CO2Me (5b)
o-CO2Me (5j)
p-Cl, m-CO2i-Pr (5k)
p-Me, m-CO2i-Pr (5l) 13e
13a
13b
13c
14
72
76
(6d)
p-CO2t-Bu (10a)
p-CO2t-Bu (11a)
(15c)
4
5
10b
11b
90
67
81
91c
76
a Isolated yield.
13d
74d
desired deoxgenated product as it yielded only an isomerized one
(see Supplementary Data).
a The coupling reaction mixture was quenched with MeOH/MeSO3H at rt for
64 h.
b Isolated yield.
Subsequently, methyl glucoside 13b was deoxygenated with
Et3SiH and BF3·Et2O in a stereoselective manner (Scheme 1).19
Reduction of spiroketal 14 was a little troublesome (Scheme 1).
Treatment of 14 with Et3SiH and BF3·Et2O did not produce the
desired deoxygenated product but yielded an isomerized product
(C-β) at the anomeric position instead. This was also the case for
the perbenzylated spiroketal 9. Therefore, 14 was isomerized to
the isochromanone derivative 17a by treating with metha-
nol/methanesulfonic acid. After acetylation of 17a, the resulting
17b was reduced with Et3SiH under the acidic conditions, fol-
lowed by hydrolysis of the acetyl groups to afford a bergenin-
type β-C-glucoside 17c in good yield. It is noted that protection
of the hydroxy groups of 17a was necessary to avoid the for-
mation of 1,5-anhydrate, and the usage of the acid combination
(BF3·Et2O/TFA) during silane reduction enhanced the reaction
rate markedly.20
c Treated with 2M HCl–MeOH for 30 min to afford an anomeric mixture of
spiroketal 14 (C-α:β = 9:1).
d2.0 equiv of TIPPLi was used.
From the observations in the cases of 5e (entry 7, Table 2) and
5j (entry 4, Table 3), it appears that an α-attack of aryllithium
compounds to the δ-lactone preferentially occurs under kinetic
control conditions. On the basis of the Felkin torsional strain
theory17a-c and the computational studies of the nucleophilic addi-
tions to cyclohexanone and related systems,17d-h it can be pre-
sumed that there is less torsional strain in the transition structure
of the axial attack than that of the equatorial attack (Figure 1). In
addition, there may be the influence of the electrostatic repulsion
between the negative nucleophile and lone pair of the ring oxy-
gen, favoring nucleophilic attack at the α face. In other cases,
however, it is difficult to definitively explain the stereoselectivity
at the coupling stage.17i,j
Figure 1. Stereoselectivity in nucleophilic addition to δ-lactone.
Next, we carried out reduction of lactols.8,18 As shown in Ta-
ble 4, reduction of lactol 3b in the presence of i-Pr3SiH8c and
BF3·Et2O was achieved to afford aryl-β-C-glycosides 15a (β
only, entry 1), whereas low selectivity was observed when treat-
ing with Et3SiH (α:β = 1:2.5, data not shown). The other lactols
6b, 6d, 10a, and 11a afforded the corresponding aryl-β-C-
glycosides in moderate to good isolated yields under the same
Scheme 1. Reduction of 13b and 14.
In conclusion, we have developed a practical and efficient
preparation method of functionalized aryl-β-C-glycosides. A
chemoselective halogen–lithium exchange reaction of functional-
ized aryl halides was accomplished through the use of the
TIPPLi, which has bulky isopropyl groups that rarely react with

4
Tetrahedron
11. (a) Tatsuta, K.; Ozeki, H.; Yamaguchi, M.; Tanaka, M.; Okui, T. Tetra-
hedron Lett. 1990, 31, 5495. (b) Krohn, K.; Heins, H.; Wielckens, K. J.
Med. Chem. 1992, 35, 511. (c) Herzner, H.; Palmacci, E. R.; Seeberger,
P. H. Org. Lett. 2002, 4, 2965. (d) Suzuki, T.; Imamura, M.; Iwasaki, F.;
Kurosaki, T.; Morimoto, A.; Moriguchi, H.; Yokono, M.; Tomiyama,
H.; Noda, A. PCT Int. Appl. WO2010/074219, 2010. (e) Prous, J. R.;
Serradell, N.; Muñoz, R.; Flores, R.; García-Delgado, N. PCT Int. Appl.
WO2013/045495, 2013. (f) Mavlan, M.; Ng, K.; Panesar, H.;
Yepremyan, A.; Minehan, T. G. Org. Lett. 2014, 16, 2212.
substrate sugar lactones. In addition, our study has given a new
bergenin-type β-C-glucoside synthesis.
Supplementary data
Supplementary data (experimental procedures and spectral da-
ta for all new compounds) associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/XXXX.
12. (a) Klatt, T.; Markiewicz, J. T.; Sämann, C.; Knochel, P. J. Org. Chem.
2014, 79, 4253. (b) Tilly, D.; Chevallier, F.; Mongin, F.; Gros, P. C.
Chem. Rev. 2014, 114, 1207.
References and notes
13. Bonnac, L.; Chen, L.; Pathak, R.; Gao, G.; Ming, Q.; Bennett, E.;
Felczak, K.; Kullberg, M.; Patterson, S. E.; Mazzola, F.; Magni, G.;
Pankiewicz, K. W. Bioorg. Med. Chem. Lett. 2007, 17, 1512.
14. (a) Yasuda, M.; Ide, M.; Matsumoto, Y.; Nakata, M. Bull. Chem. Soc.
Jpn. 1998, 71, 1417. (b) Ide, M.; Nakata, M. Bull. Chem. Soc. Jpn. 1999,
72, 2491. (c) Inoue, A.; Kitagawa, K.; Shinokubo, H.; Oshima, K. J.
Org. Chem. 2001, 66, 4333.
15. Krasovskiy, A.; Knochel, P. Angew. Chem. In. Ed. 2004, 43, 3333.
16. (a) Kondo, Y.; Asai, M.; Miura, T.; Uchiyama, M.; Sakamoto, T. Org.
Lett. 2001, 3, 13. (b) Beck, A. K.; Dahinden, R.; Seebach, D.; Kondo, Y.
Mesityllithium; e-EROS Encyclopedia of Reagents for Organic Synthe-
sis, 2004.
17. (a) Cherést, M.; Felkin, H.; Prudent, N. Tetrahedron Lett. 1968, 9, 2199.
(b) Cherést, M.; Felkin, H. Tetrahedron Lett. 1968, 9, 2205. (c) Anh, N.
T. Top. Curr. Chem. 1980, 88, 145. (d) Wu, Y.-D.; Houk, K. N. J. Am.
Chem. Soc. 1987, 109, 908. (e) Wu, Y.-D.; Tucker, J. A.; Houk, K. N. J.
Am. Chem. Soc. 1991, 113, 5018. (f) Wu, Y.-D.; Houk, K. N.; Paddon-
Row, M. N. Angew. Chem. Int. Ed. Engl. 1992, 31, 1019. (g) Gung, B.
W. Tetrahedron 1996, 52, 5263. (h) Ando, K.; Houk, K. N.; Busch, J.;
Menassé, A.; Séquin, U. J. Org. Chem. 1998, 63, 1761. (i) Comparable
findings of these C-α selectivities have been reported by Schweizer,
where the enolate of tert-butyl bromoacetate generated by LHMDS in
THF at −78 °C reacted with the perbenzylated δ-lactone 2 to give C-α
exocyclic epoxide in 81% yield: Schweizer, F.; Inazu, T. Org. Lett.
2001, 3, 4115. (j) The C-α addition of 2-lithiothiazole to the sugar lac-
tones under kinetic reaction conditions were reported by Dondoni and
Scherrmann: Dondoni, A.; Scherrmann, M.-C. J. Org. Chem. 1994, 59,
6404.
18. (a) Babirad, S. A.; Wang, Y.; Kishi, Y.; J. Org. Chem. 1987, 52, 1370.
(b) Czernecki, S.; Ville, G. J. Org. Chem. 1989, 54, 610. (c) Juaristi, E.;
Cuevas, G. Tetrahedron 1992, 48, 5019. (d) Abe, H.; Shuto, S.; Matsu-
da. A. J. Am. Chem. Soc. 2001, 123, 11870. (e) Tamura, S.; Abe, H.;
Matsuda, A.; Shuto, S. Angew. Chem. In. Ed. 2003, 42, 1021. (f) Abe,
H.; Terauchi, M.; Matsuda, A.; Shuto, S. J. Org. Chem. 2003, 68, 7439.
(g) Terauchi, M.; Abe, H.; Matsuda, A.; Shuto, S. Org. Lett. 2004, 6,
3751.
1.
2.
(a) Bililign, T.; Griffith, B. R.; Thorson, J. S. Nat. Prod. Rep. 2005, 22,
742. (b) Štambaský, J.; Hocek, M.; Kočovský, P. Chem. Rev. 2009, 109,
6729.
Bergenin, for instance, is a C-glucoside of 4-O-methyl gallic acid pos-
sessing anti-inflammatory and immunomodulatory properties: Patel, D.
K.; Patel, K.; Kumar, R.; Gadewar, M.; Tahilyani, V. Asian Pac. J. Trop.
Dis. 2012, 2, 163.
3.
4.
Salmochelin S4, which is a twofold β-C-glucosylated enterobactin
analogue, shows a very high affinity to Fe3+ ions: (a) Müller, S. I.;
Valdebenito, M.; Hantke, K. Biometals 2009, 22, 691. (b) Yu, X.; Dai,
Y.; Yang, T.; Gagné, M. R.; Gong, H. Tetrahedron 2011, 67, 144.
(a) Meng, W.; Ellsworth, B. A.; Nirschl, A. A.; McCann, P. J.; Patel,
M.; Girotra, R. N.; Wu, G.; Sher, P. M.; Morrison, E. P.; Biller, S. A.;
Zahler, R.; Deshpande, P. P.; Pullockaran, A.; Hagan, D. L.; Morgan,
N.; Taylor, J. R.; Obermeier, M. T.; Humphreys, W. G.; Khanna, A.;
Discenza, L.; Robertson, J. G.; Wang, A.; Han, S.; Wetterau, J. R.;
Janovitz, E. B.; Flint, O. P.; Whaley, J. M.; Washburn, W. N. J. Med.
Chem. 2008, 51, 1145. (b) Nomura, S.; Sakamaki, S.; Hongu, M.;
Kawanishi, E.; Koga, Y.; Sakamoto, T.; Yamamoto, Y.; Ueta, K.;
Kimata, H.; Nakayama, K.; Tsuda-Tsukimoto, M. J. Med. Chem. 2010,
53, 6355. (c) Knochel et al. recently reported a novel and practical tran-
sition-metal-free C-glycosylation method using arylzinc reagents and
successfully applied for the syntheses of canagliflozin and dapagliflozin
(sodium/glucose cotransporter-2 inhibitors): Lemaire, S.; Houpis, I. N.;
Xiao, T.; Li, J.; Digard, E.; Gozlan, C.; Liu, R.; Gavryushin, A.; Diène,
C.; Wang, Y.; Farina, V.; Knochel, P. Org. Lett. 2012, 14, 1480. (d)
Koga, Y.; Sakamaki, S.; Hongu, M.; Kawanishi, E.; Sakamoto, T.;
Yamamoto, Y.; Kimata, H.; Nakayama, K.; Kuriyama, C.; Matsushita,
Y.; Ueta, K.; Tsuda-Tsukimoto, M.; Nomura, S. Bioorg. Med. Chem.
2013, 21, 5561. (e) Bernhardson, D.; Brandt, T. A.; Hulford, C. A.;
Lehner, R. S.; Preston, B. R.; Price, K.; Sagal, J. F.; Pierre, M. J. S.;
Thompson, P. H.; Thuma, B. Org. Process Res. Dev. 2014, 18, 57. (f)
Bowles, P.; Brenek, S. J.; Caron, S.; Do, N. M.; Drexler, M. T.; Duan,
S.; Dubé, P.; Hansen, E. C.; Jones, B. P.; Jones, K. N.; Ljubicic, T. A.;
Makowski, T. W.; Mustakis, J.; Nelson, J. D.; Olivier, M.; Peng, Z.;
Perfect, H. H.; Place, D. W.; Ragan, J. A.; Salisbury, J. J.; Stanchina, C.
L.; Vanderplas, B. C.; Webster, M. E.; Weekly, R. M. Org. Process Res.
Dev. 2014, 18, 66.
19. Deshpande, P. P.; Ellsworth, B. A.; Buono, F. G.; Pullockaran, A.;
Singh, J.; Kissick, T. P.; Huang, M.-H.; Lobinger, H.; Denzel, T.;
Mueller, R. H. J. Org. Chem. 2007, 72, 9746.
20. Rolf, D.; Gray, G. R. J. Am. Chem. Soc. 1982, 104, 3539.
5.
(a) Jaramillo, C.; Knapp, S. Synthesis 1994, 1. (b) Du, Y.; Linhardt, R.
J. Tetrahedron 1998, 54, 9913. (c) Wu, Q.; Simons, C. Synthesis 2004,
1533. (d) Lee, D. Y. W.; He, M. Curr. Top. Med. Chem. 2005, 5, 1333.
Frick, W.; Schmidt, R. R. Carbohydr. Res. 1991, 209, 101.
6.
7.
8.
Suzuki, K. Pure & Appl. Chem. 1994, 66, 2175.
(a) Lewis, M. D.; Cha, J. K.; Kishi, Y. J. Am. Chem. Soc. 1982, 104,
4976. (b) Kraus, G. A.; Molina, M. T. J. Org. Chem. 1988, 53, 752. (c)
Ellsworth, B. A.; Doyle, A. G.; Patel, M.; Caceres-Cortes, J.; Meng, W.;
Deshpande, P. P.; Pullockaran, A.; Washburn, W. N. Tetrahedron:
Asymmetry 2003, 14, 3243.
9.
(a) Friesen, R. W.; Sturino, C. F. J. Org. Chem. 1990, 55, 2572. (b)
Dubois, E.; Beau, J.-M. Tetrahedron Lett. 1990, 31, 5165. (c) Gong, H.;
Gagné, M. R. J. Am. Chem. Soc. 2008, 130, 12177. (d) Sakamaki, S.;
Kawanishi, E.; Nomura, S.; Ishikawa, T.; Tetrahedron 2012, 68, 5744.
(e) Nicolas, L.; Angibaud, P.; Stansfield, I.; Bonnet, P.; Meerpoel, L.;
Reymond, S.; Cossy, J. Angew. Chem. In. Ed. 2012, 51, 11101. (f)
Parkan, K.; Pohl, R.; Kotora, M. Chem. Eur. J. 2014, 20, 4414.
10. (a) Deshpande, P. P.; Singh, J.; Pullockaran, A.; Kissick, T.; Ellsworth,
B. A.; Gougoutas, J. Z.; Dimarco, J.; Fakes, M.; Reyes, M.; Lai, C.;
Lobinger, H.; Denzel, T.; Ermann, P.; Crispino, G.; Randazzo, M.; Gao,
Z.; Randazzo, R.; Lindrud, M.; Rosso, V.; Buono, F.; Doubleday, W.
W.; Leung, S.; Richberg, P.; Hughes, D.; Washburn, W. N.; Meng, W.;
Volk, K. J.; Mueller, R. H. Org. Process Res. Dev. 2012, 16, 577. (b)
Wang, X.-J.; Zhang, L.; Byrne, D.; Nummy, L.; Weber, D.; Krishna-
murthy, D.; Yee, N.; Senanayake, C. H. Org. Lett. 2014, 16, 4090.