Kinetically controlled Ferrier rearrangement of 3-O-mesyl-d-glycal derivatives

Article abstract of DOI:10.1016/j.carres.2008.12.015

The Ferrier rearrangement, which is widely used in carbohydrate chemistry, is generally performed under acidic conditions to give an α anomer with high stereoselectivity. We have found that 3-O-mesyl-d-glycals 2-4 were smoothly reacted with alcohols in th

Full text of DOI:10.1016/j.carres.2008.12.015

Carbohydrate Research 344 (2009) 516–520
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Carbohydrate Research
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Note
Kinetically controlled Ferrier rearrangement of 3-O-mesyl-D-glycal derivatives
*
Yuhya Watanabe, Tsubasa Itoh, Tohru Sakakibara
Graduate School of Integrated Science, Yokohama City University, 22-2, Seto, Kanazawa-ku, Yokohama 236-0027, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 October 2008
Received in revised form 13 December 2008
Accepted 16 December 2008
Available online 25 December 2008
The Ferrier rearrangement, which is widely used in carbohydrate chemistry, is generally performed under
acidic conditions to give an
a anomer with high stereoselectivity. We have found that 3-O-mesyl-D-gly-
cals 2–4 were smoothly reacted with alcohols in the presence of triethylamine. The present reaction was
shown to proceed under kinetic control to give ꢀ1.3:1.0 mixture of
a and b anomers, indicating that a
kinetic anomeric effect does not operate.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Ferrier rearrangement
3-O-Mesyl-D-glycals
Kinetic control
Basic conditions
Reaction of glycals with nucleophiles in the presence of a Le-
wis acid or protic acid gives an allylic rearrangement product
having the double bond at the 2,3-position and new substituents
at the anomeric center. This reaction has been widely used and
is known as the Ferrier rearrangement.1 In general, the reaction
proceeds with high stereo- and regioselectivity.1b An acid cata-
lyst accelerates the departure of a leaving group at C-3 to gener-
ate the delocalized carbenium ion, followed by nucleophilic
addition reactions. The last step should be reversible to give
was neither isolated nor were the reaction conditions de-
scribed. In this paper, we report that the Ferrier rearrangement
of 3-O-mesyl derivatives 2–4 proceeds under slightly basic condi-
tions (pH ꢀ10), as judged from UNIV pH paper (ADVANTECÒ), to
give in good yield a mixture of
a and b anomers with the a ano-
mer predominating. Although the reaction of the mesylates with
methanol in the presence of triethylamine was shown to be kinet-
ically controlled, we found that anomerization occurs at least par-
tially in the presence of I2 or DDQ.
the thermodynamically more stable
a
anomer as a major prod-
Treatment of 3-O-acetyl-4,6-O-benzylidene-D-glucal (5) with
uct. For example, reaction of -glucal 1 (Fig. 1) and methanol
D
MeOH in the presence of BF3ꢁEt2O or I2 gave zones with low Rf val-
ues on TLC, suggesting partial debenzylidenation. Then, the leaving
group at C-3 was changed to the more reactive mesyloxy group, of
which isolation failed similar to its 3-epimer.7
in the presence of BF3ꢁOEt2 gave a 7:1 equilibrium mixture of
a
and b anomers.1b Even under kinetic control, C-glycosidation
3
is typical,2 and
a anomers predominate over b anomers. If I2,
DDQ,4 or iodonium dicolline perchlorate (IDCP)5 are used as
the catalyst, the reaction is thought to be mildly acidic or non-
After addition of 1.5 equiv of MsCl to a solution of 4,6-O-benzyl-
idene-
4 equiv of MeOH was added and warmed at 40 °C for 2 h to give a
1.3:1.0 mixture of and b anomers of the methyl 2-enopyranoside
D-glucal (6) in CH2Cl2 in the presence of 4 equiv of Et3N,
acidic, and the
Without catalyst, for example, reaction of 1 with methanol gave
the
anomer as the major product,6 probably as a result of ano-
a anomer again becomes the major product.
a
a
in 88% yield. On TLC, their spots completely overlapped, and their
merization due to the acetic acid generated during the reaction.
Thus the Ferrier rearrangement is performed under acidic, some-
times neutral conditions, but not under basic conditions.
However, there is one exception, in which treatment of 4,6-O-
separation was not achieved.à We isolated the b anomer by applica-
tion of the fact that LiAlH4 reductionof the aanomer to 3-deoxy-glycal
was much faster than that of the b anomer.8 As shown in Table 1,
ethanol, 2-propanol, and tert-butyl alcohol similarly reacted, from
benzylidene-3-O-mesyl-D-allal (4) with methanolic sodium meth-
oxide afforded methyl 4,6-O-benzylidene-b-D-2-enopyranoside 8a
in 91% yield.7 However, this reaction was carried out only to
confirm the generation of unstable mesylate 4, and the product
The following reaction gave a 3:2 mixture of methyl
Compound 7 (23.4 mg, 100 mol) was treated with MsCl (17.1 mg, 11.5
CH2Cl2 (3 mL) in the presence of Et3N (41 mg, 406 mol) for min at room
temperature. After addition of 0.1 M NaOMe (500 L), the mixture was warmed at 40
a
- and b-D-2-enopyranoside.
l
l
mol) in
l
5
l
°C for 2 h. These conditions, however, were not applied to acetate 10 because of
deacetylation.
* Corresponding author. Tel.: +81 45 787 2183; fax: +81 45 787 2413.
E-mail address: baratoru@yokohama-cu.ac.jp (T. Sakakibara).
à
Separation of both
a and b anomers was not achieved in the literature reports.
0008-6215/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2008.12.015

Y. Watanabe et al. / Carbohydrate Research 344 (2009) 516–520
517
OAc
OAc
OAc
O
R1
Ph
Ac
O
O
O
O
AcO
RO
O
O
R2
O
O
O
1
2
AcO
O
O
3
4
R = OMs, R = H
1
2
R = Ac
R = Ms
Me
1 =
R
H, R2 = OMs
Me
5 R1 = OAc, R2 = H
Figure 2. Possible intermediates of Ferrier rearrangement.
Figure 1.
use of 8 equiv of Et3N. Stereoselectivity was lower compared to
the conventional Ferrier rearrangement, and the ratios of and
b anomers generated from 2 were almost the same as those from
the benzylidene derivatives 3 (Table 2, entry 1). Mesylate 2
smoothly reacted with alcohols and thiols to give a mixture of
a
which
two alcohols were separated by column chromatography.
Similar reaction of 4,6-O-benzylidene- -allal (4) with methanol
gave the same results, indicating that the reaction proceeds via a
cationic intermediate similar to that of the Ferrier rearrangement.
a and b anomers of 2-enopyranosides generated by the latter
D
a
and b anomers in high yields, but stereoselectivities were again
low (Table 2). Although UNIV pH paper suggests that the reaction
medium was slightly basic (pH ꢀ10), distinct basicity is not clear
because of the nonaqueous solvent and the molar ratio of MsCl
(1.5 equiv) and Et3N (4 equiv). Anomerization of the 2-enopyrano-
side readily occurs under acidic conditions because a cationic
intermediate is stabilized by the oxygen atom (O-5) and the dou-
ble bond. However, if the reaction medium is neutral or basic, the
O- and S-glycosides are stable and avoid anomerization. When a
Di-O-acetyl-
available per-O-acetyl-
D
-glucal 10 is readily prepared from commercially
D
-glucal.9 Therefore, if the Ferrier rearrange-
ment of 2 proceeds under basic conditions, it would be useful be-
cause the reaction should be kinetically controlled and used for
acid-sensitive acceptors. It is noteworthy that the acetoxy group
is apparently able to stabilize a cationic intermediate via neighbor-
ing-group participation as shown in Figure 2, which serves to con-
trol the stereoselectivity.1,10
1.3:1.0 mixture of
a anomer 12a and b anomer 11a was treated
The Ferrier rearrangement of the diacetate 2 with methanol
was examined in the presence of several bases. When strong
bases (DMAP and DBU) and a large amount of Et3N were em-
ployed, the reactions became complicated because of the base
sensitivity of the acetoxy group. Four equivalents of Et3N gave
satisfactory results, and deacetylation was not observed by the
with Et3N in methanol, the ratio was unchanged. However, as
shown in Table 3, similar treatment of the mixture in the pres-
ence of the catalyst caused partial anomerization. Even in the
presence of DDQ, referred to as a nonacidic catalyst,4 anomeriza-
tion partially occurred.
Table 1
O-Glycosidation of 4,6-O-benzylidene-3-O-mesyl-D-glucal using triethylamine
O
R1
O
R1
Ph
Ph
O
O
R1
O
Ph
O
O
MsCl, Et3N
O
Acceptor
40 oC, 2 h.
O
CH2Cl2, 0 oC, 5 min.
R2
R2
R2
1
2
1
2
3
4
6
7
R = OMs, R = H
R = H, R = OMs
R = OH, R = H
R = H, R = OH
1
R = OR, R2 = H
8a~d
1
2
1
2
9a~d R1 = H, R2 = OR
Entry
1
Acceptora
Glycal
Products
Yieldb (%)
a
:b ratioc
O
O
O
O
Ph
Ph
O
O
O
O
O
O
O
MeOH
88
94
93
89
91
1.3:1.0
1.8:1.0
2.0:1.0
2.2:1.0
1.3:1.0
HO
OMe
OEt
6
8a, 9a
O
Ph
Ph
O
O
O
2
3
4
EtOH
HO
6
8b, 9b
O
Ph
Ph
O
O
2-PrOH
tert-BuOH
MeOH
HO
Oi-Pr
6
8c, 9c
O
O
O
Ph
Ph
O
O
O
O
O
O
HO
Ot-Bu
6
Ph
8d, 9d
Ph
O
O
O
5
OMe
7
8a, 9a
HO
a
4 equiv of acceptor was employed.
Isolated yield.
b
c
Determined by 1H NMR.

518
Y. Watanabe et al. / Carbohydrate Research 344 (2009) 516–520
Table 2
O- and S-glycosidation of 10
OAc
O
OAc
OAc
R1
MsCl, Et3N
CH2Cl2, 0 oC, 5 min.
O
AcO
HO
Acceptor
40 oC, 2 h.
O
AcO
MsO
AcO
R2
10
2
1
2
11a~k
12a~k
R = Nu, R = H
1
2
R = H, R = Nu
Entry
1
Acceptor
MeOH
Products
Basic conditionsa
Lit.b
AcO
AcO
O
O
O
O
1.3:1.0 (88%)
5.7:1.01a
OMe
OEt
11a, 12a
AcO
AcO
2
EtOH
1.4:1.0 (90%)
1.2:1.0 (89%)
0.8:1.0 (92%)
1.6:1.0 (94%)
1.2:1.0 (82%)
1.5:1.0 (93%)
1.2:1.0 (95%)
1.3:1.0 (90%)
1.2:1.0 (87%)
1.4:1.0 (93%)
9.0:1.011
8.0:1.03
11b, 12b
AcO
AcO
3
iso-PrOH
tert-BuOH
Oi-Pr
Ot-Bu
11c, 12c
AcO
AcO
4
10.0:1.011
10.0:1.012
10.5:1.011
7.0:1.012
6.7:1.013
8.0:1.014
6.7:1.015
8.0:1.011
11d, 12d
OH
AcO
AcO
O
O
5
O
O
11e, 12e
AcO
AcO
OH
6
11f, 12f
AcO
AcO
O
O
7
OH
OH
O
O
11g, 12g
AcO
AcO
8
11h, 12h
SH
AcO
AcO
O
O
9
S
S
11i, 12i
AcO
AcO
10
11
SH
11j, 12j
SH
AcO
AcO
O
S
11k, 12k
a
a
:b ratio and yield are shown in parentheses.
b
Examples:
a
:b ratio.
Low stereoselectivity observed under kinetically controlled con-
dition suggests that the kinetic anomeric effect does not operate
with these examples.
In conclusion, we found that 3-O-mesylates 2–4 were suitable
substrates for a kinetically controlled Ferrier rearrangement. The
present reactions apply, not only to acid-sensitive 4,6-O-

Y. Watanabe et al. / Carbohydrate Research 344 (2009) 516–520
519
benzylidene derivatives 3 and 4, but also to base-sensitive acetyl
derivative 2. This reaction should proceed via a cationic interme-
diate at least in the cases of 4,6-O-benzylidene derivatives 3 and
4. Neighboring-group participation of the acetoxy group should
5H, Ph), 6.10 (br d, 1H, J2,3 10.3 Hz, H-3), 5.66 (ddd, 1H, J1,2 1.4, J2,4
1.1 Hz, H-2), 5.60 (s, 1H, PhCH), 5.40 (dd, 1H, J1,2 1.3 Hz, H-1), 4.35
(dd, 1H, J4,5 10.2 Hz, H-4), 4.28 (dd, 1H, J6a,6e 10.2 Hz, J5,6e 4.5 Hz,
H-6e), 4.05–4.02 (m, 1H, 2-Pr), 4.02 (dd, 1H, J5,6a 10.3 Hz, H-6a),
3.77 (ddd, 1H, H-5), 1.26 (d, 3H, J 6.2 Hz, 2-Pr), 1.21 (d, 3H, J 6.2 Hz,
2-Pr). 13C NMR (CDCl3): d 137.8, 129.6, 128.8, 126.6(phenyl),
131.1(C-3), 129.6(C-2), 102.5 (PhCH), 97.7(C-1), 75.5(C-4), 71.4 (2-
Pr), 70.9(C-5), 69.6(C-6), 24.1, 22.6 (2-Pr). Anal. Calcd for C16H20O4:
C, 69.54, H, 7.30. Found: C, 69.75, H, 7.52.
not be operative, because the same
a/b ratios were obtained in
the reactions of 2 and 3. Thus, the high stereoselectivity ob-
served in conventional O- and S-Ferrier rearrangement should
be caused by anomerization. Low stereoselectivity observed
herewith is a drawback for a synthetic method, but should have
an advantage for using compounds 2–4 as substrates for combi-
natorial chemistry.
Compound 9c is known.19 1Y NMR (CDCl3): d 7.50–7.34 (m, 5H,
Ph), 6.10 (br d, 1H, J2,310.3 Hz, H-3), 5.68 (ddd, 1H, J1,2 2.5 Hz, J2,4
1.2 Hz, H-2), 5.56 (s, 1H, PhCH), 5.09 (m, 1H, H-1), 4.27 (dd, 1H,
J6a,6e 10.1 Hz, J5,6e 4.6, H-6e), 4.12 (dd, 1H, J4,5 10.0 Hz, H-4),
3.98–3.94 (m, 2H, H-5, 2-Pr), 4.02 (dd, 1H, J5,6a 10.3 Hz, H-6a),
1.24 (d, 3H, J 6.2 Hz, 2-Pr), 1.18 (d, 3H, J 6.2 Hz, 2-Pr).
1. Experimental
1.1. General methods
Melting points are uncorrected. Optical rotations were deter-
mined with a Horiba High Sensitive Polarimeter (SEPA-200). Most
of the reactions were monitored by TLC using silica gel coated on
glass. Products were purified by flash column chromatography
and recrystallized if necessary. NMR spectra were measured on a
Bruker AVANCE 400 instrument (400 MHz/1H, 100 MHz/13C) with
TMS as an internal standard. Some signals were assigned by the
use of COSY, HMQC, HMBC, and/or NOESY. IR spectra were re-
corded for KBr pellets on a Perkin–Elmer Spectrum One FTIR spec-
1.2.3. tert-Butyl 4,6-O-benzylidene-2,3-dideoxy-D-erythro-hex-
2-enopyranoside (8d and 9d)
Similar treatment of 6 (50 mg, 214 lmol) with tert-butanol gave
a 1.0:2.2 mixture of 8d and 9d (55 mg, 89%). The mixture was sep-
arated by column chromatography, eluting with toluene.
Physical data of b anomer 8d: 112–115 °C (EtOH); ½a D25
ꢂ
50.6 (c
1.1, CHCl3); IR:
m
2953, 2860, 1500, 1476, 1459. 1Y NMR (CDCl3):
d 7.50–7.34 (m, 5H, Ph), 6.07 (br d, 1H, J2,3 10.2 Hz, H-3), 5.59 (s,
1H, PhCH), 5.53 (dd, 1H, J1,2 1.2 Hz, H-2), 5.50 (dd, 1H, J1,3 1.3 Hz,
H-1), 4.37 (dd, 1H, J3,4 1.6 Hz, J4,5 8.4 Hz, H-4), 4.24 (dd, 1H, J6a,6e
10.2 Hz, J5,6e 4.5, H-6e), 3.96 (dd, 1H, J5,6a 10.3 Hz, H-6a), 3.96
(ddd, 1H, H-5), 1.30 (s, 9H, t-Bu). 13C NMR (CDCl3): d 137.8,
129.5, 128.7, 126.6 (phenyl), 130.8 (C-3), 130.6 (C-2), 102.5
(PhC), 94.0 (C-1), 76.4 (t-CMe3), 75.4 (C-4), 71.1 (C-5), 69.6 (C-6),
29.1 (t-C(CH3)3). Anal. Calcd for C17H22O4: C, 70.32, H, 7.64. Found:
C, 70.58, H, 7.79.
trometer. Silica gel {C-60 (Kanto) and 40–63
used for column chromatography.
lm (E. Merck)} was
1.2. Ferrier rearrangement of 4,6-O-benzylidene-
D
-glucal (6)
1.2.1. Methyl 4,6-O-benzylidene-2,3-dideoxy-
D-erythro-hex-2-
enopyranoside (8a and 9a)
Physical data of 9d: 55–57 °C (EtOH); ½a D25
ꢂ
86.4 (c 1.0, CHCl3);
To a solution of 6 (20 mg, 85
added Et3N (47 L, 342 mol) and MsCl (10
0 oC. After 5 min, MeOH (14
L, 342 mol) was added, and the
lmol) in 1 mL of CH2Cl2 were
IR:
m
2983, 2926, 1497, 1461, 1450. 1Y NMR (CDCl3): d 7.51–7.35
l
l
l
L, 128 mol) at
l
l
l
(m, 5H, Ph), 6.09 (br d, 1H, J2,3 10.2 Hz, H-3), 5.63 (ddd, 1H, J1,2
2.1 Hz, J2,4 1.3 Hz, H-2), 5.57 (s, 1H, PhCH), 5.30 (dd, 1H, J1,3
0.8 Hz, H-1), 4.25 (dd, 1H, J6a,6e 10.3 Hz, J5,6e 4.6, H-6e), 4.10
(ddd, 1H, J3,4 3.1 Hz, J4,5 8.9 Hz, H-4), 3.96 (ddd, 1H, J5,6a
10.3 Hz, H5), 3.96 (dd, 1H, H-6a), 1.29 (s, 9H, t-Bu). 13C NMR
solution was heated with stirring for 2 h at 40 oC. The reaction mix-
ture was washed with satd NH4Cl and satd NaCl, and dried. The fil-
trate was evaporated, and the residue was purified by column
chromatography with 4:1 n-hexane–acetone, to give a 1.0:1.3 mix-
ture of 8a and 9a18 (18.6 mg, 88%).
(CDCl3):
d 138.0, 128.9, 129.8, 126.8 (phenyl), 130.3(C-3),
Although ethyl b-glycoside 9b is a new compound, we could not
separate 8b and 9b.
129.6(C-2), 102.6 (PhC), 90.2 (C-1), 75.7 (t-CMe3), 75.6 (C-4),
70.0 (C-6), 64.0 (C-5), 29.3 (t-C(CH3)3). Anal. Calcd for
C17H22O4: C, 70.32, H, 7.64. Found: C, 70.53, H, 7.86.
1.2.2. 2-Propyl 4,6-O-benzylidene-2,3-dideoxy-D-erythro-hex-2-
enopyranoside (8c and 9c)
1.3. Typical procedure for Ferrier rearrangement of 4,6-di-O-
acetyl-D-glucal (10)
Compound 6 (20 mg, 85
conditions employed for the preparation of 8a and 9a using 2-
PrOH (26 L, 342 mol) instead of MeOH to give a 1.0:2.0 mix-
lmol) was treated under the same
l
l
To a solution of 10 (10 mg, 20 mg, 30 mg or 100 mg) in 1 M
CH2Cl2 were added Et3N (4 equiv) and MsCl (1.5 equiv) at 0 oC.
After 5 min, MeOH (4 equiv) was added, and the solution was
heated with stirring for 2 h at 40 oC. The reaction mixture was
washed with satd NH4Cl and satd NaCl, and dried. The filtrate
was evaporated, and a residue was purified by flash column chro-
matography with 4:1 hexane–acetone to give a 1.3:1.0 mixture of
11a and 12a. For details see Table 2.
ture of 8c and 9c (22 mg, 93%). This mixture was separated by
column chromatography, eluting with toluene.
Physical data for 8c: 100–102 °C (EtOH); ½a D25
ꢂ
41.7 (c 1.4, CHCl3);
IR: m
2980, 2872, 1458, 1400, 1379. 1Y NMR (CDCl3): d 7.51–7.34 (m,
Table 3
Anomerization of glycoside in the presence of catalyst
Entry
catalyst
a:b ratio
1a
2a
3a
4a
5a
6b
7b
Et3N
1.3:1.0
6.6:1.0
5.1:1.0
5.4:1.0
4.8:1.0
5.9:1.0
6.0:1.0
1.3.1. 4-Methylphenyl 4,6-di-O-acetyl-2,3-dideoxy-b-D-erythro-
1-thio-hex-2-enopyranoside (11i)
1b
BF3ꢁOEt2
16
FeCl3
1Y NMR (CDCl3): d 7.44, 7.13 (each d, 2H, J 8.1, –Ph), 5.96
(ddd, 1H, J1,2 1.8 Hz, J2,3 10.2 Hz, J2,4 0.7 Hz, H-2), 5.80 (dd, 1H,
J3,4 2.4 Hz, H-3), 5.59 (br d, 1H, H-1), 5.18 (ddd, 1H, J4,5 9.2 Hz,
H-4), 4.30–4.28(m, 2H, H-6), 4.10 (ddd, 1H, J5,6 4.7 Hz, 4.6, H-
5), 2.36 (s, 3H, -PhMe), 2.13, 2.11 (each s, 3H, OAc). For details
see Table 2.
3
I2
DDQ4a
6
BF3ꢁOEt2
17
BiCl3
a
Starting material is 1.3:1.0 mixture of 11a and 12a.
Starting material is 1.4:1.0 mixture of 11k and 12k.
b

520
Y. Watanabe et al. / Carbohydrate Research 344 (2009) 516–520
1.3.2. 4-Methylphenyl 4,6-di-O-acetyl-2,3-dideoxy-
1-thio-hex-2-enopyranoside (12i)
a
-
D
-erythro-
1.4. Anomerization of 11a and 12a by promoter used for the
Ferrier rearrangement
1Y NMR (CDCl3): d 7.46, 7.14 (each d, 2H, J 8.1 Hz, Ph), 6.07
(ddd, 1H, J1,2 1.9 Hz, J2,3 10.1 Hz, J2,4 1.2 Hz, H-2), 5.87 (dd, 1H,
J3,4 1.5 Hz, H-3), 5.70 (br d, 1H, H-1), 5.39 (ddd, 1H, J4,5 9.5 Hz,
H-4), 4.50 (m, 1H, H-5), 4.28–4.13 (m, 2H, H-6), 2.35 (s, 3H,
-PhCH3), 2.13, 2.11 (each s, 3H, –OAc). For details see Table 2.
A mixture of 11a and 12a (1.3:1.0) (30 mg, 130.3
lmol) in
MeCN (650 L)–MeOH (6 mg, 196 mol) was stirred in the pres-
l
l
ence of promoter (BF3ꢁEt2O, FeCl3, I2, DDQ, 0.1 equiv). After 1 h, a
product ratio was determined by 1H NMR spectroscopy. A 1.4:1.0
mixture of 11k and 12k (30 mg, 92 lmol) was treated similarly.
1.3.3. Ethyl 4,6-di-O-acetyl-2,3-dideoxy-b-D-erythro-1-thio-hex-
2-enopyranoside (11j)
References
1Y NMR (CDCl3): d 5.93 (dd, 1H, J1,2 1.3 Hz, J2,3 10.3 Hz, H-2),
5.88 (br d, 1H, H-3), 5.41 (d, 1H, H-1), 5.29 (dd, 1H, J4,5 6.6 Hz,
H-4), 4.27–4.19 (m, 2H, H-6), 3.87–3.83 (m, 1H, H-5), 2.71 (q, 2H,
J 4.2 Hz, –SCH2CH3) 2.15, 2.11 (each s, 3H, –OAc), 1.29 (t, 3H,
–SCH2CH3). For details see Table 2.
1. (a) Ferrier, R. J.; Prasad, N. J. J. Chem. Soc. 1969, 570–575; For a recent review on
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1.3.4. Ethyl 4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-1-thio-
hex-2-enopyranoside (12j)
1Y NMR (CDCl3): d 5.94 (br d, 1H, J2,3 10.1 Hz, H-2), 5.78 (br d,
1H, H-3), 5.58 (br s, 1H, H-1), 5.37 (d, 1H, J4,5 9.1 Hz, H-4), 4.32
0
(m, 1H, H-5), 4.27 (dd, 1H, J5,6 5.2 Hz, J6,6 11.9 Hz, H-6), 4.18 (d,
1H, H-60), 2.71 (q, 2H, J 4.2 Hz, –SCH2CH3), 2.12, 2.11 (each s, 3H,
–OAc), 1.34 (t, 3H, –SCH2CH3). For details see Table 2.
1.3.5. Phenyl 4,6-di-O-acetyl-2,3-dideoxy-b-D-erythro-1-thio-
hex-2-enopyranoside (11k)
1Y NMR (CDCl3): d 7.55–7.29 (m, 5H, -SPh), 5.96 (ddd, 1H, J1,2
1.8 Hz, J2,3 10.2 Hz, J2,4 2.4 Hz, H-2), 5.82 (dd, 1H, J3,4 2.4 Hz, H-3),
5.64 (br d, 1H, H-1), 5.20 (ddd, 1H, J4,5 7.5 Hz, H-4), 3.92 (m, 1H,
H-5), 4.28 (m, 2H, H-6), 2.10, 2.07 (each s, 3H, –OAc). For details
see Table 2.
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1.3.6. Phenyl 4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-1-thio-
hex-2-enopyranoside (12k)
1Y NMR (CDCl3): d 7.56–7.29 (m, 5H, -SPh), 6.06 (ddd, 1H, J1,2
1.2 Hz, J2,3 10.1 Hz, J2,4 1.9 Hz, H-2), 5.87 (dd, 1H, J3,4 1.9 Hz, H-3),
5.76 (br d, 1H, H-1), 5.38 (ddd, 1H, J4,5 9.4 Hz, H-4), 4.47 (m, 1H,
0
0
H-5), 4.29 (dd, 1H, J5,6 5.9 Hz, J6,6 12.1 Hz, H-6), 4.18 (d, 1H, J5,6
2.8 Hz, H-60), 2.11, 2.04 (each s, 3H, –OAc). For details see Table 2.