An efficient procedure for the synthesis of 2,3-unsaturated-O-glycosides: TiCl3(OTf) as the catalyst for type i Ferrier rearrangement

Article abstract of DOI:10.1016/j.tet.2013.04.051

An efficient type I Ferrier rearrangement reaction system for the synthesis of 2,3-unsaturated-O-glycosides has been established by using TiCl ₃(OTf) as the catalyst. A series of 2,3-unsaturated-O-glucosides were prepared from 3,4,6-tri-O-acetyl-d-glucal in good yield and high anomeric selectivity.

Full text of DOI:10.1016/j.tet.2013.04.051

Tetrahedron 69 (2013) 4524e4531
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Tetrahedron
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An efficient procedure for the synthesis of 2,3-unsaturated-O-
glycosides: TiCl3(OTf) as the catalyst for type I Ferrier rearrangement
,
b
,
a
Peiran Chen a , Lei Lin
*
a Key Lab of Eco-Textile, Ministry of Education, Donghua University, 2999 Renmin Road North, Songjiang District, Shanghai 201620, China
b Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, CAS, Shanghai 200032, China
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient type I Ferrier rearrangement reaction system for the synthesis of 2,3-unsaturated-O-glyco-
sides has been established by using TiCl3(OTf) as the catalyst. A series of 2,3-unsaturated-O-glucosides
Received 28 February 2013
Received in revised form 3 April 2013
Accepted 11 April 2013
were prepared from 3,4,6-tri-O-acetyl-D-glucal in good yield and high anomeric selectivity.
Ó 2013 Elsevier Ltd. All rights reserved.
Available online 17 April 2013
Keywords:
Type I Ferrier rearrangement
TiCl3(OTf)
Tri-O-acetyl-
2,3-Unsaturated-O-glycoside
3,4,6-Tri-O-acetyl- -glucal
D-glucal
D
1. Introduction
which leading to extensive work up. In view of that Ti(IV) catalysts
have been successfully used in many asymmetric synthesis,5 we
therefore have interest in investigating the catalytic behavior of
other Ti(IV) catalysts than TiCl4 for this reaction for milder and
more efficient synthetic process with good anomeric selectivity and
yield by using stoichiometric amount of nucleophile under low
catalyst load.
2,3-Unsaturated-O-glycosides are of great importance in syn-
thesis and have been widely used as chiral intermediates in the
preparation of biologically active compounds1 and functional ma-
terials2 because of the regio- and stereo-varieties that they could
provide for the subsequent reactions. One of the most useful pro-
cedures to achieve 2,3-unsaturated glycosides directly and effi-
ciently is type I Ferrier rearrangement, in which glycal is reacted
with nucleophile under the promotion of various Lewis acid cata-
lysts. This reaction is supposed to proceed through a highly
resonance-stabilized cyclic allylic oxocarbonium intermediate,
which is formed via removal of the leaving group at C-3 position of
the glycal promoted by catalyst, followed by the attack of a nucle-
ophile via quasi-equatorial orientation3 (Scheme 1).
Herein, we report our results using TiCl3(OTf) as a new highly
efficient catalyst for type I Ferrier rearrangement.
2. Results and discussion
2.1. Role of the counter-ion in the Ti(IV) catalysts
TiCl4 has been used as catalyst in type I Ferrier rearrangement to
prepare C-linked 2,3-unsaturates glycosides.4w For comparison of
the catalytic activity of different Ti(IV) catalysts, a comparative
study has been carried out in a model system by using tri-O-acetyl-
Lewis acids have been reported to be the major catalyst in type I
Ferrier Rearrangement besides some other type of catalysts. A wide
range of Lewis acid catalysts, such as BF3$Et2O, FeCl3, Fe2(SO4)3,
Fe(NO3)3, InCl3, BiCl3, CeCl3, ZnCl2, Pd(OAc)2, ZrCl4, K5CoW12
D-glucal (1) and EtOH as the nucleophile catalyzed by different
O
40$3H2O, Bi(OTf)3, Er(OTf)3, Yb(OTf)3, Fe(OTf)3,TiCl4, AuCl3,
HBF4eSiO2, ZnCl2/Al2O3 have been reported in the literature.4
However, some of those reaction systems suffered from the draw-
backs in terms of large excess of nucleophile, stoichiometric
amount of catalyst, harsh reaction conditions, and low yields,
Ti(IV) Lewis acid catalysts. Results are shown in Table 1.
Results shown in Table 1 demonstrate the remarkably different
catalytic activity of the Ti(IV) catalysts with different counter-ions
in this reaction. Among the tested Ti(IV) catalysts, TiCl3(OTf) is
the most efficient one in terms of conversion and selectivity, which
indicates that triflate anion might cause the Ti(IV) cation more
active in attracting the leaving group to form the intermediate
allyloxycarbenium ion (Scheme 1).
* Corresponding author. Tel.: þ86 21 67792594; e-mail address: prchen@dhu.
edu.cn (P. Chen).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.04.051

P. Chen, L. Lin / Tetrahedron 69 (2013) 4524e4531
4525
..
O
O
Nu
O
R2
R2
R2
..
1
:Nu
2
2
R1
allyloxycarbenium ion
R1
R1
3
3
LA
:
LG
LG = leaving group
LA = Lewis acid catalyst
Scheme 1. Mechanism of type I Ferrier rearrangement proposed by R. J. Ferrier.3b,f
Table 1
solvent, the Ferrier rearrangement was performed between 3,4,6-
A comparative study of the catalytic effect of different Ti(IV) Lewis acid catalysts in
the Ferrier rearrangement of glucal 1a
tri-O-acetyl-D-glucal (1 equiv) and various nucleophiles
(1.3 equiv) at 40 ꢀC. Results are summarized in Table 3. The struc-
ture and stereochemistry of all the glycosidation products were
characterized by 1H NMR, 13C NMR, IR, and MS data.
OAc
O
OAc
O
Ti(IV) Lewis acid
OAc
+
EtOH
OEt
Generally, by using 3,4,6-tri-O-acetyl-D-glucal as the starting
material, the reaction afforded 2,3-unsaturated-O-glycosides in
high yield with good anomeric selectivity.
o
40 C
AcO
AcO
1
Conversion (%)b
a
:
bc
The simple aliphatic alcohols (entries 1e5, Table 3) as the nu-
cleophile gave the products that were good both in yield and in
anomeric selectivity, while those with halogen or small alkyl-ring
substituents (entries 6e8, Table 3) gave the products with rela-
tively low anomeric selectivity. In the series of benzylic alcohols
(entries 9e11, Table 3), the nucleophiles gave satisfactory reaction
outcomes. As relatively weak nucleophiles, benzylic alcohols with
fluorine on the a-position (entries 12e14, Table 3) gave the corre-
sponding 2,3-unsaturated O-glycoside with relatively low anomeric
selectivity.
Entry
Lewis acid catalyst
Reaction time
1
2
3
4
TiCl4
4 h
24 h
120 min
10 h
Trace
N.R.
71
/
/
Ti(OiPr)4
TiCl3(OTf)
Ti(OiPr)3(OTf)
6:1
/
N.R.
a
Reaction conditions: tri-O-acetyl-D-glucal (1) (188 mg, 0.7 mmol), EtOH (5 mL),
catalyst (10 mol %), 40 ꢀC.
b
Determined by analysis of the 1H NMR spectra of the reaction mixture.
The anomeric ratio was determined by integration of the anomeric hydrogen in
c
the 1H NMR spectra.
2.2. Optimization of solvent
We have also explored the scope of this procedure for the
preparation of 2,3-unsaturated O-glycoside connected with various
biologically important natural products. Formation of two di-
saccharides (entries 17 and 18, Table 3), three steroid glycosides
Solvent played an important role in the reaction. Therefore, op-
timization of solvent has been carried out. Table 2 shows the results.
By comparison of the results in entry 3 with the others in Table 2,
DCM appeared to be the most proper solvent. When using THF,
diethyl ether or toluene as solvent, no product was detected (entries
4e6, Table 2). The solvents with high polarity hydrophilic character,
such as acetone or acetonitrile also led to relative low conversion
and much longer reaction time (entries 1 and 2, Table 2).
(entries 19, 20, and 21, Table 3) and two other natural product (L-
menthol and (1R)-endo-(þ)-fenchol) glycosides (entries 15 and 16,
Table 3) in good yield and high selectivity demonstrated the cata-
lytic capability of TiCl3(OTf) in the synthesis of natural product
analogs by the Ferrier rearrangement.
3. Conclusion
Table 2
Optimization of solventa for the TiCl3(OTf) catalyzed Ferrier rearrangement reaction
system
We have established a practical procedure for type I Ferrier
rearrangement with TiCl3(OTf) as the catalyst. By using this catalyst,
a series of alcohols were reacted with glucal donor affording 2,3-
unsaturated O-glycosides in high yield and good anomeric selec-
tivity. The influence of the inductive and the steric effects of
the nucleophiles on the reaction results have also been examined.
This reaction system has also demonstrated its applicability in the
synthesis of natural product analogs of biological interest by the
Ferrier rearrangement.
OAc
O
OAc
O
TiCl3(OTf)
(10mmol%)
OAc
AcO
+
EtOH
OEt
Solvent,
AcO
40oC
1
Entry
Solvent
Reaction time
Conversion (%)b
a
:
bc
1
2
3
4
5
6
Acetone
Acetonitrile
DCM
THF
Diethyl ether
Toluene
120 min
60 min
10 min
24 h
77
73
88
7:1
6:1
7:1
/
/
/
Trace
Trace
Trace
4. Experimental
24 h
24 h
4.1. Method and materials
a
Reaction conditions: tri-O-acetyl-D-glucal (1) (188 mg, 0.7 mmol), EtOH
(1.3 equiv), TiCl3(OTf) (10 mol %), solvent (5 mL), 40 ꢀC.
1H and 13C NMR spectra were recorded on a Bruker AV-400
(400 MHz) spectrometer with Me4Si as internal standard. 19F
NMR spectra were obtained on a Bruker AM-300 (282 M Hz)
spectrometer using CFCl3 as an external standard; downfield shifts
Determined by analysis of the 1H NMR spectra of the reaction mixture.
b
c
The anomeric ratio was determined by integration of the anomeric hydrogen in
the 1H NMR spectra.
2.3. Type I Ferrier rearrangement under the optimized
conditions
being designated as positive, all chemical shifts (d) were expressed
in parts per million and coupling constants (J) are in Hertz. Mass
spectra were recorded on a Finnigan-MAT-8430 instrument using
EI ionization at 70 eV. High-Resolution mass spectral (ESI) analyses
were performed on a Finnigan MAT 8430 spectrometer. IR spectra
After the optimization, we have established our reaction con-
ditions: with TiCl3(OTf) (10 mol %) as the catalyst and DCM as the

4526
P. Chen, L. Lin / Tetrahedron 69 (2013) 4524e4531
Table 3
Type I Ferrier rearrangement reaction of 3,4,6-tri-O-acetyl-
D
-glucal (1) with various nucleophiles (2aeu) catalyzed by TiCl3(OTf)a
OAc
OAc
O
TiCl3(OTf)
(10 mol%)
O
Nucleophile
(1.3eq)
OAc
+
Nu
DCM, 40oC
AcO
OAc
2a~u
1
3a~u
c
Entry
Nucleophile
Reaction time
10 min
Product
Yieldb (%)
(a:b)
OAc
O
1
EtOH
2a
88
7:1
OEt
AcO
3a
OAc
O
OH
O
2
3
180 min
150 min
84
83
10:1
2b
AcO
AcO
3b
OAc
O
n-C14H29OH
8:1
OC14H29-n
2c
3c
OAc
O
OH
4
5
195 min
77
90
a only
O
AcO
2d
3d
OAc
OH
OH
O
O
45 min
8:1
4:1
3:1
AcO
2e
3e
OAc
O
O
6
230 min
81
AcO
AcO
2f
3f
OAc
O
Cl
O
O
OH
O
7
80 min
86
Cl
2g
3g
OAc
O
Br
O
Br
Br
Br
Br
OH
Br
8
85 min
81
5:1
AcO
2h
3h

P. Chen, L. Lin / Tetrahedron 69 (2013) 4524e4531
4527
c
Table 3 (continued )
Entry
Nucleophile
Reaction time
18 min
Product
Yieldb (%)
(a:b)
OAc
O
OH
OH
O
9
76
a only
AcO
AcO
2i
2j
3i
OAc
O
10
40 min
72
8:1
O
CH3
3j
Br
OH
OAc
O
11
130 min
61
10:1
O
Br
AcO
AcO
2k
3k
CF3
OH
OAc
O
O
12
20 min
83
3:1
CF3
2l
3l
OMe
OH
CF
OAc
O
3
14
30 min
54
2:1
O
MeO
AcO
CF
3
2m
2m
OAc
O
OH
Ph
COOEt
C
O
F2
13
360 min
50
3:1
CF2
AcO
Ph
EtOOC
2n
3n
HO
OAc
O
O
15
125 min
61
a
only
AcO
2o
3o
OAc
O
O
16
12 min
70
10:1
OH
AcO
2p
(continued on next page)
3p

4528
P. Chen, L. Lin / Tetrahedron 69 (2013) 4524e4531
Table 3 (continued )
c
Entry
Nucleophile
Reaction time
Product
Yieldb (%)
(a:b)
O
O
O
OAc
O
O
O
O
17
115 min
42
a
only
O
O
HO
O
O
O
AcO
AcO
2q
3q
O
O
O
OAc
O
O
O
O
HO
18
19
20
190 min
70 min
40 min
100 min
52
70
58
72
6:1
O
O
O
O
O
2r
3r
O
O
H
H
OAc
H
H
H
O
10:1
H
H
H
HO
O
AcO
H
H
3s
2s
O
O
OAc
O
a
only
HO
O
AcO
3t
2t
O
O
OAc
O
21
a only
O
HO
AcO
2u
3u
a
Reaction conditions: tri-O-acetyl-D
-glucal (1) (188 mg, 0.7 mmol), nucleophile (2aeu) (1.3 equiv), TiCl3(OTf) (10 mol %), DCM (5 mL), 40 ꢀC.
b
c
Isolated yield.
The anomeric ratio was determined by integration of the anomeric hydrogen in the 1H NMR spectra.
were recorded on a Nicolet 380 spectrometer. Optical rotations
were measured by WZZ-2 polarimeter. Melting points were mea-
sured on a WRS-2A melting point apparatus. Glucal, epian-
(Table 3), and the extent of the reaction was monitored by TLC
analysis. The reaction mixture was diluted with cooled sodium
bicarbonate (satd, 20 mL) and extracted with DCM (3ꢁ10 mL). The
combined organics were dried over anhydrous Na2SO4. The solvent
was removed under vacuum. All the products were purified by
silica gel column chromatography (hexane/EtOAc¼6/1).
drosteron,
L
-menthol, (1R)-endo-(þ)-fenchol, and the protected
glucose were purchased from Energy-Chemical Company.
TiCl3(OTf) was prepared according to the known method.6 All the
solvents used in the reaction were purified by re-distillation.
4.2.1. Ethyl 4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-hex-2-
4.2. General procedure for preparation of 2,3-unsaturated
glycosides
enopyranoside (3a). Colorless oil; ½a D25
þ82.72 (c 0.83, CHCl3,
ꢂ
a:b
¼7:1) {lit.:4k
½
a 3D1:7
ꢂ
þ113.1 (c 1.0, CHCl3,
a
:b
¼9:1)}; 1H NMR
(400 MHz, CDCl3)
d
6.05e5.63 (m, 2H), 5.24 (d, J¼9.7 Hz, 1H), 4.97
To a stirred solution of tri-O-acetyl-
D
-glucal (188 mg, 0.7 mmol)
(s, 1H), 4.28e4.12 (m, 2H), 4.10e4.01 (m, 1H), 3.76 (m, 1H),
3.58e3.45 (m, 1H), 2.03 (s, 3H), 2.01 (s, 3H), 1.18 (t, J¼7.1 Hz, 3H)
ppm; IR (film, cmꢃ1): 2980, 2901, 1736, 1416, 1383, 1239, 1119, 1052,
889, 832, 737; MS (EI 70 eV) m/z:257 ([Mþꢃ1]), 213 ([MþꢃOEt], 6),
and the corresponding alcohol (1.3 equiv) in DCM (5 mL) were
added TiCl3(OTf) (10 mol %) at ambient temperature. The mixture
was stirred under 40 ꢀC for the appropriate amount of time

P. Chen, L. Lin / Tetrahedron 69 (2013) 4524e4531
4529
199 (1), 185 (1), 213 (7), 171 (2), 153 (9), 114 (100), 111 (24), 86 (13),
81 (5), 57 (9).
(film, cmꢃ1): 2959, 1743, 1420, 1230, 1041, 902, 844, 661, 607; MS
(ESI) m/z: 558.8 (100), 556.7 ([MþNa]þ, 40).
4.2.2. n-Butyl 4,6-di-O-acetyl-2,3-dideoxy-
a
-
D
-erythro-hex-2-
4.2.9. Benzyl 4,6-di-O-acetyl-2,3-dideoxy-
enopyranoside (3i). Colorless oil;
a 2D5
only) {lit.:4k
a 3D1:7
þ56.34 (c 1.0, CHCl3,
(400 MHz, CDCl3)
5.34 (d, J¼9.5 Hz, 1H), 5.14 (s, 1H), 4.81 (d, J¼11.7 Hz, 1H), 4.61 (d,
J¼11.7 Hz, 1H), 4.26 (dd, J¼11.6, 5.0 Hz, 1H), 4.15 (ddd, J¼17.7, 10.3,
1.8 Hz, 2H), 2.10 (s, 3H), 2.08 (s, 3H) ppm; IR (film, cmꢃ1): 3031,
2877, 1740, 1494, 1450, 1374, 1236, 1094, 1036, 909, 821, 740, 693;
MS (ESI) m/z; 338.0 ([MþNH4]þ, 100), 339.0 (18), 213.0 (14).
a-D-erythro-hex-2-
enopyranoside (3b). Colorless oil;
½
a 2D5
þ113.1 (c 1.0, CHCl3,
ꢂ
þ96.5 (c 0.73, CHCl3,
½
ꢂ
þ46.6 (c 0.64, CHCl3,
a
:
b
¼10:1) {lit.:4k
½
a 3D1:7
ꢂ
a
:b
¼9:1)}; 1H NMR
a
½
ꢂ
a
:
b
¼9:1)}; 1H NMR
(400 MHz, CDCl3)
d
5.79 (q, J¼10.4 Hz, 2H), 5.24 (d, J¼9.7 Hz, 1H),
d
7.37 (d, J¼4.2 Hz, 5H), 5.88 (d, J¼8.6 Hz, 2H),
4.96 (s, 1H), 4.25e4.00 (m, 3H), 3.72 (dd, J¼6.9, 2.6 Hz, 1H), 3.45 (dt,
J¼9.6, 6.4 Hz, 1H), 2.04 (s, 3H), 2.02 (s, 3H), 1.53 (dd, J¼7.6, 4.6 Hz,
2H), 1.39e1.28 (m, 2H), 0.87 (t, J¼7.3 Hz, 3H) ppm; IR (film, cmꢃ1):
2955, 2872, 1744, 1460, 1373, 1232, 1110, 1041, 904, 681, 607; MS
(ESI) m/z; 304.1 ([MþNH4]þ, 100), 305.1 (10), 212.9 (23).
2-enopyranoside (3c). White solid; mp¼37e38 ꢀC, ½aꢂDD25 þ73 (c 0.64,
2-enopyranoside (3j). Colorless oil; ½a D25
ꢂ
þ80.5 (c 1.67, CHCl3,
4.2.3. n-Tetradecyl
4,6-di-O-acetyl-2,3-dideoxy-
a
-
-erythro-hex-
4.2.10. 1-Phenyl ethyl 4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-hex-
CHCl3,
(400 MHz, CDCl3)
a
:
b
¼8:1) {lit.:7a
½
a 2D5
ꢂ
þ59 (c 0.59, CHCl3,
a
:b
¼20:1)}; 1H NMR
a:
b
¼4:1) {lit.7d}; 1H NMR (400 MHz, CDCl3); 1H NMR (400 MHz,
d
6.00e5.79 (m, 2H), 5.32 (d, J¼9.5 Hz, 1H), 5.03
CDCl3): d a-anomer 7.31 (t, J¼13.6 Hz, 5H), 5.86 (s, 1H), 5.75 (dd,
J¼10.2, 1.4 Hz, 1H), 5.29 (d, J¼9.9 Hz, 1H), 4.87 (d, J¼6.8 Hz,1H), 4.79
(q, J¼6.2 Hz, 1H), 4.28 (dt, J¼18.3, 10.0 Hz, 3H), 2.12 (s, 3H), 2.08 (s,
(s, 1H), 4.23 (dt, J¼28.4, 8.7 Hz, 2H), 4.12 (d, J¼8.1 Hz, 1H), 3.77 (dd,
J¼15.1, 7.4 Hz, 1H), 3.51 (dd, J¼14.9, 7.4 Hz, 1H), 2.10 (s, 3H), 2.09 (s,
3H), 1.64e1.57 (m, 2H), 1.26 (m, 22H), 0.88 (t, J¼6.1 Hz, 3H) ppm; IR
(film, cmꢃ1): 2924, 2856,1745,1468,1373,1237,1044, 899, 832, 730,
603; MS (ESI) m/z:449.2 ([MþNa]þ, 100), 450.2 (30), 213.0 (13).
3H), 1.50 (d, J¼6.1 Hz, 3H) ppm; -anomer 7.37 (d, J¼7.5 Hz, 1.5H),
b
5.91 (d, J¼21.5 Hz, 0.3H), 5.18 (s, 0.3H), 4.79 (q, J¼6.2 Hz, 0.3H), 4.00
(dd, J¼11.8, 3.0 Hz, 0.3H), 3.83 (d, J¼9.4 Hz, 0.3H), 3.41 (d, J¼12.2 Hz,
0.3H), 2.03 (s, 1H), 1.97 (s, 1H); IR (film, cmꢃ1): 2924, 1746, 1494,
1374, 1234, 1132, 909, 858, 754, 701, 632, 609; MS (ESI) m/z: 357.0
([MþNa]þ, 100), 212.9 (10).
4.2.4. tert-Butyl
4,6-di-O-acetyl-2,3-dideoxy-
a-
D-erythro-hex-2-
enopyranoside (3d). Colorless oil; ½a D25
ꢂ
þ98.8 (c 0.65, CHCl3,
a
only)
{lit.:7b
d
½
a 3D1:7
ꢂ
þ100.69 (c 0.75, CHCl3)}; 1H NMR (400 MHz, CDCl3)
5.87e5.69 (m, 2H), 5.33e5.27 (m, 1H), 5.23 (dd, J¼9.3, 1.3 Hz, 1H),
4.2.11. 1-(p-Bromo-phenyl)prop-2-ynyl 4,6-di-O-acetyl-2,3-dideoxy-
4.25e4.07 (m, 3H), 2.05 (s, 3H), 2.04 (s, 3H), 1.25 (s, 9H) ppm; IR
(film, cmꢃ1): 3047, 2974, 2925, 1744, 1445, 1373, 1235, 1039, 897,
774, 608; MS (ESI) m/z: 309 ([MþNa]þ, 100), 212.9 (68), 153.0 (42).
a
-
D
-erythro-hex-2-enopyranoside (3k). Colorless oil; ½a D25
þ3.5 (c
ꢂ
1.61, CHCl3,
a:b
¼10:1), 1H NMR (400 MHz, CDCl3)
7.54 (d, J¼8.2 Hz,
d
2H), 7.44 (d, J¼8.2 Hz, 2H), 5.92 (dd, J¼23.5, 10.3 Hz, 2H), 5.56 (s,1H),
5.53 (s, 1H), 4.35e3.90 (m, 3H), 2.70 (s, 1H), 2.10 (s, 3H), 2.09 (s, 3H),
13C NMR (101 MHz, CDCl3): 170.85, 170.18, 136.67, 131.73, 129.75,
129.17, 128.28, 127.26, 122.76, 91.80, 80.16, 76.56, 67.46, 65.28, 63.06,
20.93, 20.78. IR (film, cmꢃ1): 3499, 2207,1740,1639,1560,1478,1412,
1372,1235,1139,1098,1015, 642; MS (ESI) m/z: 445.0 ([MþNa]þ,100).
HR-ESI C19H19O6Br1Na1 [MþNa]þ, calcd 445.02572, found 445.02605.
4.2.5. Cyclohexyl
4,6-di-O-acetyl-2,3-dideoxy-
a 2D5
þ110.7 (c 1.0, CHCl3,
a-D-erythro-hex-2-
enopyranoside (3e). Colorless oil;
½
ꢂ
þ65.3 (c 0.60, CHCl3,
a
:b
¼8:1) {lit.:4k
½
a 3D1:7
(400 MHz, CDCl3)
ꢂ
a
:
b
¼9:1)}; 1H NMR
d 5.84e5.71 (m, 2H), 5.29e5.21 (m, 1H), 5.11 (s,
1H), 4.20e4.13 (m, 2H), 4.10 (t, J¼4.5 Hz, 1H), 3.66e3.53 (m, 1H),
2.03 (s, 3H), 2.02 (s, 3H), 1.87 (dd, J¼20.1, 11.2 Hz, 2H), 1.69 (d,
J¼5.1 Hz, 2H), 1.53e1.45 (m, 1H), 1.29 (d, J¼2.6 Hz, 5H) ppm; IR
(film, cmꢃ1): 3047, 2933, 2859, 1744, 1446, 1372, 1232, 1037, 739,
608; MS (ESI) m/z; 330.1 ([MþNH4]þ, 100), 212.9 (65), 153 (27).
4.2.12. 2,2,2-Trifluoro-1-phenyl ethyl 4,6-di-O-acetyl-2,3-dideoxy-a-
D
-erythro-hex-2-enopyranoside (3l). Colorless oil; ½a D25
þ72 (c 0.63,
ꢂ
CHCl3,
a
:b
¼3:1) {lit.:7e
½
a 2D5
ꢂ
þ61 (c 0.58, CHCl3,
a
:b
¼3:1); 1H NMR
(400 MHz, CDCl3): d a-anomer: 7.40 (d, J¼5.4 Hz, 5H), 5.94 (s, 1H),
5.79 (d, J¼10.2 Hz, 1H), 5.31 (dd, J¼14.7, 9.8 Hz, 1H), 5.10 (q,
J¼6.9 Hz, 1H), 4.92 (s, 1H), 4.34e4.19 (m, 3H), 2.11 (s, 3H), 2.10 (s,
4.2.6. Cyclopropylmethyl 4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-
hex-2-enopyranoside (3f). Colorless oil; ½a D25
þ82.72 (c 0.83, CHCl3,
ꢂ
a
:b
¼4:1) {lit.:7c
½
a 3D1:7
(400 MHz, CDCl3)
ꢂ
þ113.1 (c 1.0, CHCl3,
a
:b
¼9:1)}; 1H NMR
3H).
b
-anomer: 7.45 (d, J¼7.7 Hz, 1.5H), 5.38 (s, 0.3H), 5.03e4.98 (m,
d
5.88 (d, J¼38.3 Hz, 2H), 5.26 (d, J¼9.7 Hz, 1H),
0.3H), 3.91 (dd, J¼12.2, 3.4 Hz, 0.3H), 3.71 (d, J¼8.3 Hz, 0.3H), 3.47
5.03 (s, 1H), 4.28e4.03 (m, 3H), 3.43 (ddd, J¼31.0, 10.3, 7.2 Hz, 2H),
2.04 (s, 3H), 2.04 (s, 3H), 1.07 (s, 1H), 0.52 (d, J¼7.9 Hz, 2H), 0.19 (t,
J¼5.5 Hz, 2H) ppm; IR (film, cmꢃ1): 2998, 2903, 1741, 1584, 1373,
1231, 1038, 907, 830, 736, 608; MS (ESI) m/z; 302.0 ([MþNH4]þ,
100), 303.0 (20), 212.9 (23).
(d, J¼12.3 Hz, 0.3H), 2.03 (s, 1H), 1.88 (s, 1H). 19F NMR (377 MHz,
CDCl3)
d
ꢃ76.35 (d, J¼6.9 Hz), ꢃ76.72 (d, J¼6.7 Hz); IR (film, cmꢃ1):
2924, 1746, 1447, 1374, 1234, 1132, 990, 909, 868, 754, 701, 602; MS
(ESI) m/z; 406.0 ([MþNH4]þ, 100), 213.0 (15).
4.2.13. 1-Trifluoromethyl 3-(p-methoxy-phenyl) prop-2-enyl 4,6-di-
4.2.7. 2-(2-Chloroethoxyl)-ethoxyl 4,6-di-O-acetyl-2,3-dideoxy-
a
-
D
-
O-acetyl-2,3-dideoxy-a-D -erythro-hex-2-enopyranoside
erythro-hex-2-enopyranoside (3g). Colorless oil; ½a D25
ꢂ
þ55.6 (c 0.56,
(3m). Colorless oil; ½a D25
ꢂ
128.7 (c 1.52, CHCl3,
(400 MHz, CDCl3) d 7.40e7.30 (m, 2H), 6.93e6.82 (m, 2H),
a
:
b
¼2:1), 1H NMR
CHCl3,
(400 MHz, CDCl3)
a
:
b
¼6:1) {lit.7e
½
a 2D5
ꢂ
þ75.8 (c 0.86, CHCl3,
a
:b
¼8:1)}; 1H NMR
d
5.90e5.78 (m, 2H), 5.29 (d, J¼9.6 Hz, 1H), 5.06
5.99e5.74 (m, 4H), 5.36e5.29 (m, 1H), 5.12 (s, 1H), 4.72e4.56 (m,
1H), 4.26e4.08 (m, 3H), 3.80 (s, 3H), 2.10 (s, 3H), 2.09 (s, 3H). 13C
NMR (101 MHz, CDCl3): 170.72, 170.27, 160.25, 138.59, 135.87,
130.39, 128.34, 128.15, 127.72, 126.61, 115.91, 114.12, 90.95, 67.56,
65.04, 62.65, 55.30, 20.92, 20.68.19F NMR (376 MHz, CDCl3)
(s, 1H), 4.24e4.07 (m, 3H), 3.97e3.83 (m, 1H), 3.75e3.67 (m, 5H),
3.61 (d, J¼4.3 Hz, 2H), 2.07 (s, 3H), 2.05 (s, 3H) ppm; IR (film, cmꢃ1):
2883, 1741, 1442, 1372, 1232, 1122, 1044, 903, 832, 738, 663, 608,
485; MS (ESI) m/z: 354.1 ([MþNH4]þ, 100), 213.0 (18), 153.1 (10).
d
ꢃ76.68 (d, J¼6.7 Hz), ꢃ77.11 (d, J¼6.6 Hz). IR (film, cmꢃ1): 2939,
4.2.8. 2,2,2-Tribromomethyl ethoxyl 4,6-di-O-acetyl-2,3-dideoxy-
a
-
1744, 1641, 1559, 1514, 1416, 1246, 1176, 1129, 1037; MS (ESI) m/z:
467.1 ([MþNa]þ, 100). HR-ESI C21H23O7F3Na1 [MþNa]þ, calcd
467.12774, found 467.12652.
D
-erythro-hex-2-enopyranoside (3h). Colorless oil; ½a D25
ꢂ
þ73 (c 0.65,
CHCl3,
(400 MHz, CDCl3)
(s, 1H), 4.28e4.18 (m, 2H), 4.07 (ddd, J¼9.3, 4.2, 2.6 Hz, 1H), 3.93 (d,
J¼9.4 Hz, 1H), 3.57e3.45 (m, 7H), 2.09 (s, 3H), 2.09 (s, 3H) ppm; IR
a:b
¼10:1); {lit.:7e
½
a 2D5
ꢂ
þ88 (c 0.75, CHCl3,
a
only)}; 1H NMR
d
5.98e5.74 (m, 2H), 5.32 (d, J¼9.7 Hz, 1H), 5.04
4.2.14. Ethyl 2,2-difluoro-3-O-(4,6-Di-O-acetyl-2,3-dideoxy-
a-D-er-
ythro-hex-2-enopyranosyl)-3-(4-phenylphenylpropanoate)

4530
P. Chen, L. Lin / Tetrahedron 69 (2013) 4524e4531
(3n). Colorless oil; ½a D25
ꢂ
0.6 (c 1.39, CHCl3,
a
:
b
¼3:1), 1H NMR
2.10 (s, 3H), 2.08 (s, 3H), 1.97e1.78 (m, 4H), 1.67 (s, 2H), 1.57e1.40
(400 MHz, CDCl3): d a-anomer 7.68e7.35 (m, 9H), 5.96 (d,
J¼10.2 Hz, 1H), 5.85 (t, J¼13.3 Hz, 1H), 5.37 (dd, J¼17.3, 9.6 Hz, 2H),
4.98 (s, 1H), 4.44e4.24 (m, 3H), 4.18e4.06 (m, 1H), 2.18 (s, 3H), 2.13
(m, 6H), 1.37e1.24 (m, 5H), 1.16 (d, J¼12.4 Hz, 1H), 0.96 (s, 2H), 0.86
(s, 3H), 0.83 (s, 3H), 0.73e0.65 (m, 1H) ppm. IR (film, cmꢃ1): 3048,
2933, 2851,1744,1641,1373,1229,1037, 898, 828, 744, 600; MS (ESI)
m/z: 525.2 ([MþNa]þ, 100), 213 (18).
(s, 3H), 1.34 (t, J¼6.9 Hz, 3H). -anomer: 3.92 (dd, J¼12.3, 3.7 Hz,
b
0.3H), 3.74 (d, J¼9.7 Hz, 0.3H), 3.34 (d, J¼12.1 Hz, 0.3H), 2.07 (s, 1H),
1.89 (s,1H),1.28 (t, J¼7.0 Hz,1H). 13C NMR (101 MHz, CDCl3): 170.86,
170.49, 170.20, 142.63, 141.98, 140.34, 130.12, 129.53, 128.85, 127.69,
127.33, 127.15, 126.96, 125.79, 96.72, 91.17, 67.72, 64.99, 63.66,
4.2.20. (5,6-Dihydro-16-dehydropregnenolonyl)-4,6-di-O-acetyl-2,3-
dideoxy-
a
-
D
-erythro-hex-2-enopyranoside
(3t). White
þ76 (c 0.53, CHCl3,
only); 1H NMR
(400 MHz, CDCl3) d 6.66 (s, 1H), 5.90e5.72 (m, 2H), 5.27 (d,
solid;
mp¼124e126 ꢀC; ½a D25
ꢂ
a
62.53, 20.95, 20.79, 13.44. 19F NMR (376 MHz, CDCl3)
d
ꢃ118.56 (d,
J¼15.3 Hz), ꢃ118.94 (d, J¼16.1 Hz). IR (film, cmꢃ1): 2985.66, 1744.81,
1437.30, 1372.86, 1302.43, 1228.20, 1044.41, 983.65, 751.96, 696.6;
MS (ESI) m/z: 541.0 ([MþNa]þ, 100). HR-ESI C27H28O8F2Na1
[MþNa]þ, calcd 541.16430, found 541.16445.
J¼9.1 Hz, 1H), 5.14 (s, 1H), 4.19 (ddd, J¼18.5, 10.9, 5.0 Hz, 3H),
3.66e3.53 (m, 1H), 2.33 (d, J¼11.8 Hz, 1H), 2.22 (s, 3H), 2.07 (s, 3H),
2.05 (s, 3H), 1.96e1.62 (m, 4H), 1.56 (d, J¼11.2 Hz, 2H), 1.48e1.05 (m,
10H),1.04e0.91 (m, 2H), 0.85 (s, 3H), 0.82 (s, 3H), 0.75e0.64 (m,1H)
ppm. 13C NMR (101 MHz, CDCl3): 196.66, 170.66, 170.21, 155.44,
144.32,128.73,128.47, 93.00, 77.84, 66.75, 65.36, 63.19, 56.27, 54.78,
46.27, 45.29, 36.72, 36.29, 35.75, 34.72, 33.73, 32.14, 31.90, 28.69,
28.09, 27.07, 20.98, 20.92, 20.75, 15.86, 12.17. IR (film, cmꢃ1): 2933,
2855, 1744, 1641, 1665, 1586, 1443, 1372, 1235, 1036, 913, 820, 735,
606; MS (ESI) m/z: 551.3 ([MþNa]þ, 100). HR-ESI C31H44O7Na1
[MþNa]þ, calcd 551.29792, found 551.29820.
4.2.15.
L
-Menthyl
4,6-di-O-acetyl-2,3-dideoxy-
a
-
D
-erythro-hex-2-
enopyranoside (3o). Colorless oil; ½a D25
ꢂ
þ141 (c 0.53, CHCl3, only)
a
{lit.:4s
½
a 2D5
ꢂ
þ142.5 (c 0.5, CHCl3,
a
only)}; 1H NMR (400 MHz, CDCl3)
d
5.93e5.76 (m, 2H), 5.28 (t, J¼8.0 Hz, 1H), 5.09 (s, 1H), 4.27e4.12
(m, 3H), 3.42 (td, J¼10.6, 4.4 Hz, 1H), 2.20 (t, J¼10.8 Hz, 1H), 2.10 (s,
3H), 2.07 (s, 3H), 1.68e1.58 (m, 2H), 1.41 (ddd, J¼13.1, 12.4, 9.1 Hz,
1H), 1.33e0.94 (m, 5H), 0.91 (d, J¼1.6 Hz, 3H), 0.90 (d, J¼2.2 Hz, 3H),
0.77 (d, J¼6.9 Hz, 3H). IR (film, cmꢃ1): 2952, 2921, 2865, 1745, 1580,
1455, 1373, 1233, 1098, 1037, 913, 844, 740; MS (ESI) m/z: 391.0
([MþNa]þ, 100), 212.9 (8).
4.2.21. 16-Dehydropregnenolonyl-4,6-di-O-acetyl-2,3-dideoxy-a- -
erythro-hex-2-enopyranoside (3u). White solid; mp 71e73 ꢀC; ½aꢂD2D5
þ134 (c 0.51, CHCl3,
a
only) {lit.:4v
½
a 2D5
ꢂ
þ174 (c 0.60, CHCl3,
a
only),
70e72 ꢀC}; 1H NMR (400 MHz, CDCl3)
d 6.73 (s, 1H), 5.87 (dd,
4.2.16. (þ)-endo-Fenacholyl
4,6-di-O-acetyl-2,3-dideoxy-
a
-
D
-er-
ꢂ
J¼23.6,10.4 Hz, 2H), 5.38 (s,1H), 5.32 (d, J¼10.2 Hz,1H), 5.20 (s, 1H),
4.24 (dt, J¼19.3, 8.1 Hz, 3H), 3.67e3.48 (m, 1H), 2.41 (dd, J¼14.1,
10.3 Hz, 3H), 2.28 (s, 3H), 2.12 (s, 3H), 2.10 (s, 3H), 1.89 (d, J¼9.9 Hz,
2H), 1.78e1.25 (m, 12H), 1.05 (d, J¼8.9 Hz, 3H), 0.94 (s, 3H) ppm; IR
(film, cmꢃ1): 2939, 2855, 1744, 1662, 1434, 1372, 1232, 1037, 904,
807, 747, 652; MS (ESI) m/z: 549.3 ([MþNa]þ, 100).
ythro-hex-2-enopyranoside (3p). White solid; mp¼74e76 ꢀC; ½a D25
þ55.1 (c 0.54, CHCl3,
a
only), {lit.:4s
½
a 2D4
ꢂ
þ48.7 (c 0.5, CHCl3,
a
only)}; 1H NMR (400 MHz, CDCl3)
d 6.00e5.80 (m, 2H), 5.31 (d,
J¼9.4 Hz, 1H), 5.00 (s, 1H), 4.33e4.12 (m, 3H), 3.47 (s, 1H), 2.11 (s,
6H), 1.80e1.60 (m, 3H), 1.50 (d, J¼10.4 Hz, 1H), 1.46e1.38 (m, 1H),
1.28 (s, 1H), 1.14 (s, 3H), 1.07 (s, 3H), 0.99 (d, J¼11.0 Hz, 1H), 0.90 (s,
3H) ppm; IR (film, cmꢃ1): 3043, 2951, 2875, 1741, 1416, 1373, 1261,
1098, 972, 908, 832, 747, 611; MS (ESI) m/z: 389.0 ([MþNa]þ, 100),
212.9 (15).
Acknowledgements
This work is financially supported by a grant of the National
Natural Science Foundation of China (NSFC, Grant No. 21272305),
The Natural Science Foundation of Shanghai Municipality (Grant
No. 12ZR1400200) and The Fundamental Research Funds for the
Central Universities.
4.2.17. 3-O-(4,6-Di-O-acetyl-2,3-dideoxy-
enopyranosyl)-1,2:5,6-di-O-isopropylidene-
a
-
D
-erythro-hex-2-
a
-
D-glucofuranose
(3q). Colorless oil; ½a D25
ꢂ
þ77 (c 0.56, CHCl3,
a
:
b
¼5:1), {lit.:7g
½ ꢂ
a 2D1
þ47.0 (c 0.8, CHCl3,
a d 5.94e5.87
only)}; 1H NMR (400 MHz, CDCl3)
(m, 2H), 5.83 (d, J¼10.2 Hz,1H), 5.27 (s,1H), 4.63 (s,1H), 4.32 (s,1H),
4.25e4.05 (m, 6H), 3.98 (dd, J¼8.3, 5.3 Hz, 1H), 2.12 (s, 3H), 2.09 (s,
3H), 1.49 (s, 3H), 1.40 (s, 3H), 1.32 (s, 6H) ppm; IR (film, cmꢃ1): 2991,
1746, 1638, 1555, 1379, 1232, 1066, 847, 599; MS (ESI) m/z: 495.0
([MþNa]þ, 100), 511.0 (10).
Supplementary data
Supplementary data include 1H NMR, 19F NMR spectra of all the
products; 13C NMR, HRMS of the new compounds. Supplementary
data related to this article can be found at http://dx.doi.org/10.1016/
j.tet.2013.04.051.
4.2.18. 6-O-(4,6-Di-O-acetyl-2,3-dideoxy-
a
-
D
-erythreo-hex-2-
enopyranosyl)-1,2:3,4-di-O-isopropylidene-a-D-galactopyranose
References and notes
(3r). White solid; mp¼132e133 ꢀC; ½a D25
þ24.2 (c 0.73, CHCl3,
ꢂ
¼6:1), {lit.:7f
½
a 2D5
d
ꢂ
þ16.8 (c 1.0, CHCl3,
a
:b
¼5:1)}; 1H NMR
1. For examples, see: (a) Durham, T. B.; Miller, M. J. Org. Lett. 2002, 4, 135; (b)
Williams, D. R.; Heidebrecht, R. W., Jr. J. Am. Chem. Soc. 2003, 125, 1843; (c)
Domon, D.; Fujiwara, K.; Ohtaniuchi, Y.; Takezawa, A.; Takeda, S.; Kawasaki, H.;
Murai, A.; Kawai, H.; Suzuki, T. Tetrahedron Lett. 2005, 46, 8279; (d) Panarese, J.
D.; Waters, S. P. Org. Lett. 2009, 11, 5086; (e) Rusin, A.; Zawisza-Puchalka, J.;
Kujawa, K.; Gogler-Piglowska, A.; Wietrzyk, J.; Switalska, M.; Glowala-Kosinska,
M.; Gruca, A.; Szeja, W.; Krawczyk, Z.; Grynkiewicz, G. Bioorg. Med. Chem. 2011,
19, 295.
a
:
b
(400 MHz, CDCl3)
5.88 (q, J¼10.7 Hz, 2H), 5.54 (d, J¼5.0 Hz, 1H),
5.34 (d, J¼9.6 Hz, 1H), 5.11 (s, 1H), 4.66e4.59 (m, 1H), 4.32 (ddd,
J¼20.3, 9.0, 5.1 Hz, 3H), 4.17 (d, J¼10.2 Hz, 2H), 4.02 (t, J¼6.7 Hz,1H),
3.89 (dd, J¼10.0, 6.4 Hz, 1H), 3.77 (dd, J¼10.0, 7.2 Hz, 1H), 2.13
(s, 3H), 2.10 (s, 3H), 1.55 (s, 3H), 1.46 (s, 3H), 1.36 (s, 3H), 1.35
(s, 3H) ppm; IR (film, cmꢃ1): 2996, 1742, 1640, 1417, 1379, 1242,
1068, 1006, 902, 806, 687, 605; MS (ESI) m/z: 495.2 ([MþNa]þ, 72),
511.2 (8).
2. For example, see: Bozell, J. J.; Tice, N. C.; Sanyal, N.; Thompson, D.; Kim, J.-M.;
Vidal, S. J. Org. Chem. 2008, 73, 8763.
3. (a) Ferrier, R. J.; Sankey, G. H. J. Chem. Soc. C 1966, 2345; (b) Ferrier, R. J.; Prasad,
N. J. Chem. Soc. C 1969, 570; (c) Wieczorek, B.; Thiem, J. J. Carbohydr. Chem. 1998,
17, 785; (d) Csuk, R.; Shaad, M.; Krieger, C. Tetrahedron 1996, 52, 6397; (e) Ferrier,
R. J. Top. Curr. Chem. 2001, 215, 153; (f) Ferrier, R. J. Org. React. 2003, 62, 174; (g)
Ferrier, R. J.; Zubkov, O. A. Org. React. 2004, 62, 569.
4. (a) Babu, B. S.; Balasubramanian, K. K. Tetrahedron Lett. 2000, 41, 1271; (b)
Masson, C.; Soto, J.; Bessodes, M. Synlett 2000, 1281; (c) Takhi, M.; Rahman, A.;
Adel, A. H.; Schmidt, R. R. Tetrahedron Lett. 2001, 42, 4053; (d) Swamy, N. R.;
Venkateswarlu, Y. Synthesis 2002, 598; (e) Yadav, J. S.; Reddy, B. V. S.; Reddy, K.
B.; Satyanarayana, M. Tetrahedron Lett. 2002, 43, 7009; (f) Bettadaiah, B. K.;
Srinivas, P. Tetrahedron Lett. 2003, 44, 7257; (g) Kim, H.; Men, H.; Lee, C. J. Am.
4.2.19. Epiandrosteronyl-4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-
hex-2-enopyranoside (3s). White solid; mp¼124e126 ꢀC; ½a D25
ꢂ
þ106 (c 0.61, CHCl3,
a
:b
¼10:1) {lit.:4v
½
a 2D5
ꢂ
þ105 (c 0.53, CHCl3,
a
:b
¼9:1), mp¼124e126 ꢀC}; 1H NMR (400 MHz, CDCl3)
d 5.83 (ddd,
J¼13.2, 10.2, 6.4 Hz, 2H), 5.33e5.29 (m, 1H), 5.18 (s, 1H), 4.26e4.15
(m, 3H), 3.63 (td, J¼11.2, 5.4 Hz, 1H), 2.44 (dd, J¼19.1, 8.6 Hz, 1H),

P. Chen, L. Lin / Tetrahedron 69 (2013) 4524e4531
4531
Chem. Soc. 2004, 126, 1336; (h) Swamy, N. R.; Srinivasulu, M.; Reddy, T. S.; Goud,
T. V.; Venkateswarlu, Y. J. Carbohydr. Chem. 2004, 23, 435; (i) Rafiee, E.;
Tangestaninejad, S.; Habibi, M. H.; Mirkhani, V. Bioorg. Med. Chem. Lett. 2004, 14,
3611; (j) Babu, J. L.; Khare, A.; Vankar, Y. D. Molecules 2005, 10, 884; (k) Naik, P.
U.; Nara, J. S.; Harjani, J. R.; Salunkhe, M. M. J. Mol. Catal. A: Chem. 2005, 234, 35;
(l) Procopio, A.; Dalposso, R.; De Nino, A.; Nardi, M.; Oliverio, M.; Russo, B.
Synthesis 2006, 2608; (m) Procopio, A.; Dalpozzo, R.; Nino, A. D.; Maiuolo, L.;
Nardi, M.; Oliverio, M.; Russo, B. Carbohydr. Res. 2007, 342, 2125; (n) Zhang, G.;
Shi, L.; Liu, Q.; Wang, J.; Li, L.; Liu, X. Tetrahedron 2007, 63, 9705; (o) Zhang, G.;
Liu, Q. Synth. Commun. 2007, 37, 3485; (p) Tayama, E.; Otoyama, S.; Isaka, W.
Chem. Commun. 2008, 4216; (q) Baramulugan, R.; Kopollu, S. R. Tetrahedron 2009,
65, 8139; (r) Rodriguez, O. M.; Colinas, P. A.; Bravo, R. D. Synlett 2009, 1154; (s)
Gorityala, B. K.; Lorpitthaya, R.; Bai, Y.; Liu, X.-W. Tetrahedron 2009, 65, 5844; (t)
Nagaraj, P.; Ramesh, N. G. Tetrahedron Lett. 2009, 50, 3970; (u) Ding, F.; William,
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6. Noftle, R. E.; Cady, G. H. Inorg. Chem. 1966, 5, 2182.
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Chem. Soc. 2001, 66, 499; (b) Yadav, J. S.; Srinivas, C. Tetrahedron 2003, 59, 10325;
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