Efficient activation of glycosyl N-(phenyl)trifluoroacetimidate donors with ytterbium(III) triflate in the glycosylation reaction

Article abstract of DOI:10.1016/S0040-4039(02)01124-3

The mild, moisture-stable and cheap catalyst Yb(OTf)₃ activates glycosyl N-(phenyl)trifluoroacetimidates in the stereoselective synthesis of 1,2-trans and 1,2-cis glycosides. A suitable choice of the reaction solvent led to good yields and stereoselectivity ratios. The protocol was successfully applied to acceptors and donors both exhibiting a wide range of reactivity.

Full text of DOI:10.1016/S0040-4039(02)01124-3

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 5573–5577
Efficient activation of glycosyl N-(phenyl)trifluoroacetimidate
donors with ytterbium(III) triflate in the glycosylation reaction†
Matteo Adinolfi, Gaspare Barone, Alfonso Iadonisi* and Marialuisa Schiattarella
Dipartimento di Chimica Organica e Biochimica, Universita` degli Studi di Napoli Federico II, Via Cynthia 4, I-80126 Napoli,
Italy
Received 8 May 2002; revised 31 May 2002; accepted 13 June 2002
Abstract—The mild, moisture-stable and cheap catalyst Yb(OTf)3 activates glycosyl N-(phenyl)trifluoroacetimidates in the
stereoselective synthesis of 1,2-trans and 1,2-cis glycosides. A suitable choice of the reaction solvent led to good yields and
stereoselectivity ratios. The protocol was successfully applied to acceptors and donors both exhibiting a wide range of reactivity.
© 2002 Published by Elsevier Science Ltd.
We have very recently described1,2 the feasible use of
moisture-stable lanthanide triflates in the activation of
the widely used glycosyl trichloroacetimidate3 donors.
In the course of this research we disclosed that some
lanthanide triflates were efficient even in catalytic
amounts, although with the less reactive disarmed
donors heating was required for glycosidations to be
performed.2 On the other hand, good yields were
gained using 2-O-alkoxycarbonyl protected donors, the
undesired formation of orthoester-like coupling prod-
ucts being minimized.
was attempted with trichloro- and trifluoroacetimidate
2-O-alkoxycarbonylated donors 52 and 65 in the pres-
,
ence of catalytic Yb(OTf)3 (0.15 equiv.) and 4 A MS.
The glycosidation of 1 with donor 5 in toluene at 50°C2
1
afforded 7 in average yield (45–50%, H NMR), while
the coupling involving donor 6 furnished an improved
result (55–60%) albeit a slightly higher temperature
(60°C) was required. Interesting results were also
obtained by coupling trifluoroacetimidate donor 6 with
other secondary more reactive acceptors such as 2 and
3 at 60°C (yields 70 and 90% for 8 and 9, respectively)
(Chart 1).
In this paper we report the improvement and the conve-
nient extension of the use of a cheap lanthanide triflate,
Yb(OTf)3, to the activation of the recently reported4
glycosyl N-(phenyl) trifluoroacetimidates, that we have
recently observed to provide better results than the
corresponding trichloroacetimidates in an investigation
which allowed us to develop another moisture-stable
activation system (stoichiometric iodine/catalytic tri-
ethylsilane) for glycosyl imidates.5 Furthermore, tri-
fluoroacetimidate donors offer the advantages of an
increased stability6 which can be useful for their purifi-
cation as well as for their storage.
At this stage, in order to avoid the recourse to high
temperatures to effect the reactions, several solvent
mixtures were tested in addition to the use of acid
washed molecular sieves (AW 300). The utilization of
these latter was found decisive to drive to completion
glycosidations promoted by I2/Et3SiH,5 supposedly
because of the ability of ordinary molecular sieves to
function as proton scavengers. This property could also
be deleterious in the glycosidations promoted by
Yb(OTf)3, where triflic acid is reasonably generated in
small amounts as a transient species apt to regenerate
the lanthanide catalyst (or act itself as a promoter).
Accordingly, the model acceptor 2 was coupled with
trifluoroacetimidate donor 6 (1.3 equiv.) under the acti-
vation of Yb(OTf)3 (0.15 equiv.) in the presence of AW
300 MS.7 The results, reported in Table 1 (entries 1–4),
showed that in all cases the reactions proceeded in a
satisfactory or even good yields at room temperature or
below 40°C with a variety of solvent mixtures.8 The
mixture 4:1 dichloroethane/propionitrile furnished the
In a preliminary comparative experiment the glycosyla-
tion of the acceptor 1, carrying a poorly reactive 4-OH,
Keywords: carbohydrates; glycosylation; glycosyl N-(phenyl)-
trifluoroacetimidates; lanthanides.
* Corresponding author. Fax: +39 081 674393; e-mail: iadonisi@
unina.it
† Dedicated to Professor L. Mangoni on the occasion of his 70th
birthday.
0040-4039/02/$ - see front matter © 2002 Published by Elsevier Science Ltd.
PII: S0040-4039(02)01124-3

5574
M. Adinolfi et al. / Tetrahedron Letters 43 (2002) 5573–5577
O
OH
O
Ph
O
BnO
HO
BnO
AcO
AcO
CH3O2CO
CH3O2CO
O
O
O
O
R1O
O
R2O
O
R
BnO
OCH3
OCH3
O
4
R1 = Bn; R2 = H
R1 = H; R2 = Bn
1
5 R = α-OC(=NH)CCl3
6 R = -OC(=NPh)CF3
2
3
18 R1 = H; R2 = Ac
19 R1 = Ac; R2 = H
Ph
O
Ph
O
O
O
AcO
O
O
BnO
O
AcO
AcO
CH3O2CO
OCH3
O
O
O
O
AcO
BnO
O
CH3O2CO
AcO
AcO
CH3O2CO
CH3O2CO
BnO
O
CH3O2CO
BnO
BnO
OCH3
CH3O2CO
OCH3
7
8
9
O
Ph
OBn
O
O
BnO
BnO
BnO
OBn
O
Ph
AcO
AcO
CH3O2CO
CH3O2CO
O
O
O
O
O
O
O
O
O
O
B
B
A
A
O
BnO
O
TrocHN
N3
OAll
O
CH3O2CO
O
CH3O2CO
SePh
11
12
10
Ph
O
BnO
BnO
OBn
O
Ph
O
BnO
BnO
BnO
O
O
O
O
HO
HO
N3
R
CH3O2CO
BnO
OC(=NPh)CF3
TrocHN
OAll
SePh
13
14
16 R = -OC(=NPh)CF3
17 R = α-OC(=NH)CCl3
15
Ph
O
O
O
O
O
BnO
BnO
BnO
RO
O
BnO
O
O
O
O
BnO
OCH3
BnO
O
O
BnO
BnO
20 R = Bn
24 R = Ac
21
Ph
O
BnO
O
BnO
BnO
BnO
BnO
O
O
O
O
BnO
O
BnO
O
BnO
BnO
AcO
BnO
OCH3
OCH3
OBn
23
22
Chart 1.
Table 1. Glycosylation of saccharidic acceptors (1 equiv.) with disarmed imidates 5, 6 and 13 (1.3 equiv.) in the presence of
,
Yb(OTf)3 (0.15 equiv.) and AW 4 A MS
Entry
Donor
Acceptor
Solvent
Temperature, time
Product
Yielda
1
2
3
4
5
6
7
6
6
6
6
6
5
6
6
2
2
2
2
1
1
3
4
4:1 toluene/dioxane
4:1 toluene/MeCN
4:1 toluene/EtCN
4:1 (ClCH2)2/EtCN
4:1 (ClCH2)2/EtCN
4:1 (ClCH2)2/EtCN
4:1 (ClCH2)2/EtCN
4:1 MeCN/EtCN
4:1 (ClCH2)2/EtCN
4:1 CH2Cl2/EtCN
rt, 4 h
rt, 4 h
8
8
8
8
7
7
9
10
11
12
70
66
75
80
65
60
87
77
71
51
rt, 2 h+40°C, 1 h
rt, 4 h
rt, 2 h+40°C, 2 h
rt, 3 h+35°C, 2 h
rt, 1 h+40°C, 2 h
rt, 4 h
8
9b
10
13
13
14
15
0°C, 2 h+rt, 1 h
−15°C, 1 h
a Isolated yield.
b 0.1 equiv. of promoter were used.
best results (Table 1, entry 4), so that it was used for
the coupling of donor 6 with the secondary saccharidic
acceptors 1 and 3 to furnish the desired disaccharides in
good yields (Table 1, entries 5 and 7).10
Also under these milder conditions the coupling of
acceptor 1 with trifluoroacetimidate 6 proceeded in
better yield than with the corresponding trichloroace-
timidate 5 (entries 5 and 6).

M. Adinolfi et al. / Tetrahedron Letters 43 (2002) 5573–5577
5575
phenylselenyl transfer from the acceptor to the
donor14,15 was minimized, while with the use of the
corresponding less reactive 3,4,6-tri-O-acetylated donor
this undesired aglycon transfer was the preponderant
process.
The coupling of acceptor 4 with trifluoroacetimidate 6
(Table 1, entry 8) required a more polar solvent mixture
(4:1 CH3CN/propionitrile) to reduce the formation of
an 1,2-orthocarbonate as an undesired coupling
product.11 Encouraged by these results, we tested the
efficiency of this activation protocol in the synthesis of
the biologically interesting disaccharide building blocks
11 and 12, precursors of the Lewis A trisaccharide and
the antigen T disaccharide,12 respectively, and poten-
tially elongable through the position 2 of the galactose
residue. For this purpose the tri-O-benzylated galactose
imidate 13 was easily prepared from acetobromogalac-
tose in 7 steps (Scheme 1). Donor 13 was then coupled
with the readily obtained acceptors 1413 and 1514,15 to
furnish the b-linked disaccharides 11 and 12 (Table 1,
entries 9 and 10).16 Activation of 13 was expectedly
achieved under milder conditions (low reaction temper-
ature and minor amounts of catalyst) than 6. Interest-
ingly, in the coupling of 13 with 15 the undesired
The activation of armed trifluoroacetimidates was next
investigated using 2,3,4,6-tetra-O-benzyl N-(phenyl)-
trifluoroacetimidate 16 as a model donor. As 16 was
prevailingly obtained as b anomer,17 the exploitation of
a SN2 based glycosidation was considered in order to
achieve stereoselective synthesis of a-glucosides (not
attainable through vicinal participation strategy).
Model acceptors 3 and 4 were thus coupled with 16 in
a solvent of low polarity such as toluene in the presence
catalytic Yb(OTf)3 (0.1 equiv.) at low temperature
(−10°C). In both cases the stereoselectivity result was
quite disappointing, but the overall glycosidation yields
were impressively high (Table 2, entries 1 and 2). Hav-
ing previously established that a mixture of ethyl ether
and dioxane afforded the best a-selectivity in the
Sm(OTf)3 promoted glycosidation with armed glucosyl
trichloroacetimidates1 (e.g. 2,3,4,6-tetra-O-benzyl tri-
chloroacetimidate 17) we examined the behaviour of
the ternary solvent mixture toluene/ethyl ether/dioxane
in order to reconcile the achievement of high yields with
a good control of a-stereoselectivity.
OAc
O
OAc
AcO
OBn
O
OBn
BnO
a, b, c
AcO
O
Br
O
H3C
OEt
d, e
OBn
O
OBn
BnO
BnO
Adopting the solvent mixture 1:1:1 toluene/ethyl ether/
dioxane (entry 3, Table 2), the best a-selectivity was
achieved, but with the mixture 4:1:1 toluene/ethyl ether/
dioxane the highest yield for the a-linked disaccharide
could be obtained due to a marked increase of the
overall glycosidation yield (entry 4). Consequently, this
latter solvent was adopted in the following experiments
in which the reactivity of poorly reactive secondary
acceptors 1, 18 and 19 was examined. In all cases a very
good yield was achieved along with a good control of
stereoselectivity (entries 8, 9, 11). In contrast, a disap-
pointing a-selectivity was attained with the more reac-
tive primary acceptor 4, even in the absence of toluene
OBn
O
f, g
OC(=NPh)CF3
BnO
CH3O2CO
CH3O2CO
OAc
13
Scheme 1. Synthesis of donor 13. (a) EtOH (2 equiv.), TBABr
(0.5 equiv.), lutidine (1.3 equiv.), DCM, reflux, 5 h; (b)
NaOMe, MeOH, rt, 1 h; (c) BnBr (5 equiv.), DMF, then NaH
(4 equiv.), 62% over three steps; (d) 95:5 AcOH/H2O, rt, 30
min; (e) ClCO2CH3 (1.5 equiv.), TMEDA (1 equiv.), DCM,
0°C, 30 min; (f) BnNH2 (1.3 equiv.), THF, rt, 16 h, 65% over
three steps; (g) DIPEA (3.5 equiv.), N-(phenyl)-trifluoroace-
timidoyl chloride (3.0 equiv.), DCM, rt, 16 h, 70%.
Table 2. Activation of donor 16 (1.3 equiv.) for the synthesis of 1,2-cis glycosides promoted by Yb(OTf)3 (0.10 equiv.)
,
(−10°C for 2–4 h, 4 A AW 300 MS)
Entry
Acceptor
Solvent
Producta
Yieldb
a/b
1
2
3
4
5
3
4
3
3
4
4
4
1
toluene
toluene
1:1:1 toluene/Et2O/dioxane
4:1:1 toluene/Et2O/dioxane
4:1:1 toluene/Et2O/dioxane
4:1 Et2O/dioxane
20
21
20
20
21
21
21
22
23
23
24
97
97
76
97
93
86
81
75
93
76
80
1.7:1
1.3:1
3.8:1
3.1:1
1.1:1
1.7:1
1:1
3.5:1
4:1
1.8:1
3.5:1
6
7c
8
4:1 Et2O/dioxane
4:1:1 toluene/Et2O/dioxane
4:1:1 toluene/Et2O/dioxane
dichloromethane
9
18
18
19
10d
11
4:1:1 toluene/Et2O/dioxane
a All disaccharides were identified by 1H and 13C NMR.
b Isolated yield.
c Donor 17 was used with 0.03 equiv. of promoter.
TMSOTf (0.05 equiv.) was used as the promoter (from 0°C to rt) in the presence of 4 A MS.
d
4
,

5576
M. Adinolfi et al. / Tetrahedron Letters 43 (2002) 5573–5577
Table 3. Activation of donor 16 (1.3 equiv.) for the synthesis of 1,2-trans glycosides promoted by Yb(OTf)3 (0.1 equiv.) in
,
the presence of 4 A AW MS
Entry
Acceptor
Solvent
Temperature, time
Producta
Yieldb
b/a
1
2c
3
4
5
6
7
8
9
18
18
18
18
18
18
18
1
MeCN
MeCN
−10°C, 2 h
23
23
23
23
23
23
23
22
21
24
82
78
97
85
84
93
90
77
93
86
1.4:1
1.4:1
1:1.1
1.4:1
1.4:1
1.3:1
1.5:1
3.3:1
6:1
−25 to 0°C, 2 h
−10°C to rt, 6 h
−10°C, 6 h
−10°C, 12 h
−10°C to rt, 7 h
−10°C, 3 h
−10°C to rt, 5 h
−10°C, 1 h
−10°C, 2 h
3:2 toluene/MeCN
1:4 toluene/MeCN
EtCN
4:1 EtCN/MeCN
1:4 EtCN/MeCN
1:4 EtCN/MeCN
1:4 EtCN/MeCN
1:4 EtCN/MeCN
4
19
10
3.8:1
a All disaccharides were identified by 1H and 13C NMR.
b Isolated yield.
c Donor 17 was used with 0.03 equiv. of promoter.
(entries 5–7). It should be noted that in the case of the
secondary model acceptor 18, lower yield and stereose-
lectivity were obtained when the described4 glycosida-
tion conditions were adopted (compare entries 9 and
10).
sita` Federico II di Napoli (Progetto Giovani
Ricercatori).
References
The Yb(OTf)3 promoted glycosidation was also investi-
gated in nitrile solvents that are known18 to favour
b-selectivity even in the absence of a participating
group at the donor C-2. Several mixtures were tested in
the glucosidation of acceptor 18 (which had provided
low yields and b-selectivities in our previous investiga-
tion concerning the Sm(OTf)3 activation of armed gly-
cosyl trichloroacetimidate 17)1 (Table 3, entries 1–7).
Although the selectivity was always modest, very high
yields could be obtained with a wide range of solvents.
The 4:1 acetonitrile/propionitrile mixture (entry 7) fur-
nished the best compromise in terms of yields, selectiv-
ity and rapidity. Use of this mixture with other
acceptors turned out to be quite satisfying even in the
stereoselectivity (entries 8–10).
1. Adinolfi, M.; Barone, G.; Guariniello, L.; Iadonisi, A.
Tetrahedron Lett. 2000, 41, 9005–9008.
2. Adinolfi, M.; Barone, G.; Iadonisi, A.; Mangoni, L.;
Schiattarella, M. Tetrahedron Lett. 2001, 42, 5967–5969.
3. Schmidt, R. R.; Kinzy, W. Adv. Carbohydr. Chem.
Biochem. 1994, 50, 21–123.
4. Yu, B.; Tao, H. Tetrahedron Lett. 2001, 42, 2405–2407.
5. Adinolfi, M.; Barone, G.; Iadonisi, A.; Schiattarella, M.
Synlett 2002, 269–270.
6. Nakajima, N.; Saito, M.; Kudo, M.; Ubukata, M. Tetra-
hedron 2002, 58, 3579–3588.
7. The use of acid washed molecular sieves in glycosidations
has been explicitly reported in few examples: (a) Wilster-
mann, M.; Magnusson, G. Carbohydr. Res. 1995, 272,
1–7; (b) Kornilov, A. V.; Kononov, L. O.; Zatonskii, G.
V.; Shashkov, A. S.; Nifant’ev, N. E. Bioorg. Khim. 1997,
23, 655–666; (c) Wilstermann, M.; Balogh, J.; Magnus-
son, G. J. Org. Chem. 1997, 62, 3659–3665; (d) Wilster-
mann, M.; Magnusson, G. J. Org. Chem. 1997, 62,
7961–7971.
8. The use of polar cosolvents avoided the necessity to add
the donor and the acceptor by cannula to the promoter,
that is sparingly soluble in the reaction solvent (toluene).
Actually, this procedure was time consuming as it implied
the drying of the weighed amount of lanthanide catalyst
(overnight heating at 200°C under vacuum)9 every time a
reaction had to be performed. On the other hand, it
should be noted that every attempt to glycosylate sec-
ondary acceptors at 50°C with trichloroacetimidate
donors adopting cosolvents useful for the addition of the
catalyst as a solution resulted in a sensible decrease in
yields.2
In conclusion, the results reported here complement our
previous findings well in the development of a general
glycosidation protocol based on the use of mild, mois-
ture-stable and cheap catalysts. We have shown that
both armed and disarmed N-(phenyl)-glycosyl tri-
fluoroacetimidates can be conveniently adopted for the
glycosylation of several saccharidic acceptors under the
catalytic action of Yb(OTf)3. Use of acid washed
molecular sieves also allows the reactions with disarmed
donors to be performed at lower temperature than
previously reported.2 Furthermore, a suitable choice of
the reaction solvents allows a simplification of the
procedure being the catalyst added as a solution.8,10,19
Both yields and stereoselectivities were gratifying in all
cases, with only few exceptions being observed as for as
the latter issue.
9. Forsberg, J. H.; Spaziano, V. T.; Balasubramanian, T.
M.; Liu, G. K.; Kinsley, S. A.; Duckworth, C. A.;
Poteruca, J. J.; Bown, P. S.; Miller, J. L. J. Org. Chem.
1987, 52, 1017–1021.
Acknowledgements
This work was supported by MIUR (Progetti di Inter-
esse Nazionale) and by a grant (to M.S.) from Univer-
10. Solutions of freshly dried Yb(OTf)3 in propionitrile or
dioxane, stored in an essicator in the presence of P2O5,

M. Adinolfi et al. / Tetrahedron Letters 43 (2002) 5573–5577
5577
turned out to be efficient in promoting glycosidations
even after 1 week from their preparation.
Selected 13C NMR signals of 12: l 155.0 (-CO-OMe),
138.3, 137.7, 137.7, 137.6 and 133.8 (aromatic quaternary
carbons), 129.1–126.1 (aromatic CH), 102.3 and 100.5
(benzylidene CH and C-1 residue A), 85.4 (C-1 residue
B), 54.9 (-CO-OCH3).
11. This reaction in less polar mixtures afforded appreciable
amounts of a dimeric side product whose NMR spectrum
(CDCl3) displays the anomeric proton of the glucose
residue at l=5.75 (doublet, J1,2=5.4 Hz) and an upfield
shift for one of the two methoxy protons signals (l=3.81
and 3.54, singlets). Other significative signals at l 5.52
(1H, d, J1,2=5.2 Hz, H-1 Gal), 5.19 (1H, dd, H-3 Glc),
5.01 (1H, dd, H-4 Glc), 4.45 (1H, dd, H-2 Glc), 2.07 (6H,
overlapped singlets, 2×COCH3), 1.52, 1.44, 1.32, 1.32
(12H, 4×s, acetonides CH3).
12. Ernst, B.; Hart, G. W.; Sinay, P. Carbohydrates in Chem-
istry and Biology; Wiley-VCH, 2000.
13. Oikawa, M.; Wada, A.; Yoshizaki, H.; Fukase, K.;
Kusumoto, S. Bull. Chem. Soc. Jpn. 1997, 70, 1435–1440.
14. Jiang, W.-T.; Chang, M.-Y.; Tseng, P.-H.; Chen, S.-T.
Tetrahedron Lett. 2000, 41, 3127–3130.
17. The preparation of 16 was achieved by reacting 2,3,4,6-
tetra-O-benzyl glucopyranose with trifluoroacetimmidoyl
chloride in the presence of sodium hydride
(dichloromethane, 0°C, 2 h, 90% yield) to furnish an
anomeric mixture largely enriched of the b-anomer (b/a
5:1). In our hands milder bases were found quite ineffi-
cient.4 The synthesis of glycosyl trichlororacetimidates
promoted by strong bases generally yields the nearly
exclusive formation of thermodynamically favoured a-
anomers due to the reversibility of the addition to the
electron deficient nitrile.3 In the case of N-
(phenyl)trifluoroacetimidates the presence of a phenyl
group on the nitrogen atom in place of a hydrogen
prevents the reversibility of the addition (via base-
induced b-elimination) and the kinetically favoured b-
anomer can be preponderantly formed.
15. Tseng, P.-H.; Jiang, W.-T.; Chang, M.-Y.; Chen, S.-T.
Chem. Eur. J. 2001, 7, 585–590.
16. Selected 1H NMR (CDCl3, 400 MHz) signals of 11: l
5.52 (1H, s, benzylidene CH), 5.11 (1H, dd, J1,2=7.8 Hz,
18. Schmidt, R. R.; Behrendt, M.; Toepfer, A. Synlett 1990,
694–696.
J
2,3=10.0 Hz, H-2 A), 4.92 (1H, d, J1,2=3.6 Hz, H-1 B),
4.55 (1H, d, H-1 A), 3.81 (3H, s, -OCH3), 3.44 (1H, dd,
2,3=9.8 Hz, J3,4=2.6 Hz, H-3 A). Selected 13C NMR
19. Typical procedure: donor 6 (23 mg, 0.042 mmol) and
acceptor 2 (12 mg, 0.032 mmol) were dissolved in
dichloroethane (480 mL) in the presence of acid washed 4
J
signals of 11: l 155.0 and 154.1 (CO), 138.5, 137.8, 137.8,
137.4 (aromatic quaternary carbons), 133.2 (-OCH2-
CHꢀCH2), 128.8–126.0 (aromatic CH), 118.3 (-OCH2-
CHꢀCH2), 101.4, 101.0 and 97.1 (benzylidene CH and
,
A molecular sieves (Fluka Chemie AG, AW 300 MS)
under argon. A solution of freshly dried Yb(OTf)3 in
EtCN (0.04 M, 120 mL, 4.8 mmol) was then added at
room temperature. After 4 h Et3N was added and the
mixture was diluted with dichloromethane and washed
with water. The organic phase was concentrated and the
residue was chromatographed on a short silica gel
column eluted with 7:3 hexane/ethyl acetate to afford
disaccharide 82 (19 mg, yield 80%).
1
anomeric carbons), 54.7 (-CO-OCH3). Selected H NMR
(CDCl3, 400 MHz) signals of 12: l 6.05 (1H, d, J1,2=5.2
Hz, H-1 B), 5.47 (1H, s, benzylidene CH), 5.23 (1H, dd,
J1,2=7.6 Hz, J2,3=10.0 Hz, H-2 A), 5.05–4.54 (4H, 2×
-CH2Ph), 4.72 (1H, d, H-1 A), 4.42 (2H, s, -CH2Ph), 4.35
(1H, dd, J2,3=10.0 Hz, H-2 B), 3.73 (3H, s, -OCH3).