(c 1, CHCl3)]; 1H NMR (250 MHz, CDCl3) δ 1.43-1.57 (m, 1 H),
1.78-1.91 (m, 1 H), 1.92-2.27 (m, 2 H), 3.14 (td, 1 H, J ) 2.5,
9.3 Hz), 3.39-3.63 (m, 5 H), 3.89 (d, 1 H, J ) 2.5 Hz), 4.33 and
4.40 (2d, 2 H, J ) 11.8 Hz), 4.53-4.69 (m, 4 H), 4.83-4.94 (m,
4 H), 5.65-5.82 (m, 1 H), 7.14-7.31 (m, 20 H). 13C NMR (62.9
MHz, CDCl3) δ 29.9, 31.1, 69.2, 72.3, 73.6; 73.8, 74.5, 75.6, 77.2,
79.1, 79.3, 85.0, 114.7, 127.7, 127.8, 128.0, 128.2, 128.3, 128.5,
138.1, 138.5, 138.6, 138.9.
optimized to prepare the per-benzylated glycosylethenes
1 and 5. The second method explored, through an
alternative approach to the intermediate hemiketals 11
and 13, afforded a better result only for compound 5 (65%
total yield instead of 50%). The observed side reaction
with vinylmagnesium bromide has been successfully
explored to prepare the â-C-but-3-enyl glycosides and
other â-C-glycosides.
2-Meth yl-1-(2′,3′,4′,6′-tetr a -O-ben zyl-â-D-glu cop yr a n osyl)-
3-p en ten e (9): 51% of a mixture of four diastereoisomers.
Further purification by preparative thin-layer chromatography
(3:2 CH2Cl2/cyclohexane) allowed the separation into two major
isomers 9a and 9b. 9a : Rf 0.32 (3:2 CH2Cl2/cyclohexane), mp
78-80 °C; 1H NMR (250 MHz, CDCl3) δ 0.91 (d, 3 H, J ) 6.8
Hz), 1.35-1.61 (m, 2 H), 1.51 (dd, 3 H, J ) 1.8, 6.8 Hz), 2.80-
2.90 (m, 1 H), 3.13-3.28 (m, 3 H), 3.58-3.66 (m, 4 H), 4.45-
5.06 (m, 8 H), 4.97-5.06 (m, 1 H), 5.34-5.41 (m, 1 H), 7.21-
7.29 (m, 20 H). 13C NMR (62.9 MHz, CDCl3) δ 13.0, 21.9, 27.5,
39.3, 69.0, 73.6, 75.0, 75.3, 75.7, 78.7, 78.9, 82.8, 87.5, 123.7,
127.8, 128.0, 128.1, 128.6, 136.1, 138.4, 138.8, 159.4. 9b: Rf 0.27
(3:2 CH2Cl2/cyclohexane), mp 58-60 °C; 1H NMR (250 MHz,
CDCl3) δ 0.94 (d, 3 H, J ) 6.5 Hz), 1.33-1.70 (m, 2 H), 1.56 (dd,
3 H, J ) 1.0, 6.3 Hz), 2.72-2.88 (m, 1 H), 3.20-3.40 (m, 3 H),
3.58-3.68 (m, 4 H), 4.53-4.62 (m, 4 H), 4.77-4.85 (m, 4 H),
5.13-5.38 (m, 2 H), 7.21-7.31 (m, 20 H). 13C NMR (62.9 MHz,
CDCl3) δ 13.1, 20.1, 27.6, 39.3, 69.2, 73.6, 75.1, 75.4, 75.7, 77.3,
78.8, 79.2, 83.0, 87.6, 122.1, 127.8, 127.9, 128.1, 128.6, 137.4,
138.4, 138.8, 159.2. Anal. Calcd for C40H46O5: C, 77.18; H, 7.64.
Found: C, 77.36; H, 7.55.
Exp er im en ta l Section
Gen er a l Com m en ts. 1H and 13C NMR spectra were recorded
in CDCl3 solution. All assignments were confirmed by 1H/1H,
1H/13C correlations, and Dept 135. Column chromatography was
performed on E. Merck Silica Gel 60 (230-400 mesh). Analytical
thin-layer chromatography was performed on E. Merck alumi-
num percolated plates of Silica Gel 60F-254 with detection by
UV and by spraying with 6 N H2SO4 and heating about 2 min
at 300 °C. Dichloromethane was distilled over CaH2. THF was
distilled over sodium and benzophenone prior to use.
Gen er a l P r oced u r e for th e P r ep a r a tion of â-C-Alk en yl
Glycosid es (1, 3, 5, 6, a n d 9) by Ad d ition of Or ga n om a g-
n esiu m Rea gen t on th e La cton e. To a cold (-78 °C) solution
of lactone 2 or 4 (0.25 mmol) in THF (2.5 mL) under an argon
atmosphere was added dropwise the corresponding commercially
available organomagnesium reagent. After 2.5 h of stirring at
-78 °C, the reaction mixture was quenched with saturated NH4-
Cl and extracted with EtOAc. The combined organic layers were
washed with brine, dried (MgSO4), and concentrated to give the
corresponding hemiketal. To a cooled (-40 °C) solution of the
hemiketal in anhydrous acetonitrile (or dichloromethane when
TMSOTf was used) (1 mL) were added triethylsilane (3 equiv)
and boron trifluoride-diethyl ether (1 equiv) or TMSOTf (0.2
equiv). The solution was stirred 10 to 30 min at -40 °C
(monitoring by TLC), then quenched with saturated K2CO3 and
extracted with CH2Cl2. The combined organic layers were
washed with brine, dried (MgSO4), and concentrated. Purifica-
tion by preparative thin-layer chromatography (1:4 Et2O/cyclo-
hexane) afforded the corresponding â-C-glycoside.
(2,3,4,6-Tet r a -O-b en zyl-â-D-glu cop yr a n osyl)et h en e (1):
mp 72-73 °C, [R]D +33 (c 1, CH2Cl2) [lit.1 mp 68-69 °C, [R]D
+28 (c 0.2, CHCl3)].
1-(2′,3′,4′,6′-T e t r a -O -b e n zy l-â-D -g lu c o p y r a n o s y l)-3-
bu ten e (3): mp 83-84 °C, [R]D +6.2 (c 1, CH2Cl2) [lit.7 mp 83-
84 °C, [R]D +3 (c 1.2, CHCl3)].
(2,3,4,6-Te t r a -O-b e n zyl-â-D-ga la ct op yr a n osyl)e t h e n e
(5): oil, [R]D +19.2 (c 1.3, CHCl3); 1H NMR (250 MHz, CDCl3) δ
3.52-3.64 (m, 3 H), 3.70-3.74 (m, 2 H), 3.96 (d, 1 H, J ) 2.8
Hz), 4.41 (dd, 2 H, J ) 11.8, 15.5 Hz), 4.60-4.96 (m, 6 H), 5.25
(dd, 1 H, J ) 1.5, 10.5 Hz), 5.40 (dd, 1 H, J ) 1.5, 17.3 Hz),
5.89-5.95 (m, 1 H), 7.21-7.36 (m, 20 H); 13C NMR (62.9 MHz,
CDCl3) δ 67.0, 72.6, 73.6, 74.0, 74.6, 75.4, 76.9, 79.0, 80.8, 84.4,
118.4, 127.6, 127.7, 127.8, 128.3, 128.4, 128.5, 135.5, 138.0, 138.4,
138.6, 138.9. Anal. Calcd for C36H38O5: C, 78.51; H, 6.97.
Found: C, 78.42; H, 7.06.
1-(2,3,4,6-Tetr a -O-ben zyl-â-D-glu cop yr a n osyl)-2-p h en yl-
eth a n e (8). To a cold (-78 °C) solution of lactone 2 (135 mg,
0.25 mmol) in THF (2.5 mL) under an argon atmosphere was
added dropwise vinylmagnesium bromide (1 M solution in THF,
300 µL, 0.3 mmol). After 2.5 h of stirring at -78 °C, phenyl-
magnesium bromide (1 M solution in THF, 1 mL, 1 mmol) was
added and the reaction was continued over 2.5 h at -78 °C. The
reaction mixture was then quenched with saturated NH4Cl and
treated as described in the general procedure. The corresponding
hemiketal was reduced with 3 equiv of Et3SiH and 0.6 equiv of
TMSOTf as described in the general procedure to afford, after
purification by preparative thin-layer chromatography (1:4 Et2O/
cyclohexane), 110 mg of a white solid: 70%, mp 90-91 °C, [R]D
-8.3 (c 0.7, CHCl3); 1H NMR (250 MHz, CDCl3) δ 1.83-1.93 (m,
1 H), 2.16-2.26 (m, 1 H), 2.72-2.85 (m, 1 H), 2.91-3.00 (m, 1
H), 3.28-3.50 (m, 3 H), 3.69-3.88 (m, 4 H), 4.64-4.78 (m, 4 H),
4.90-4.97 (m, 4 H), 7.22-7.45 (m, 25 H). 13C NMR (62.9 MHz,
CDCl3) δ 31.8, 33.5, 69.2, 73.6, 75.1, 75.4, 75.7, 78.4, 78.8, 79.0,
82.6, 87.4, 125.9, 127.7, 127.9, 128.0, 128.1, 128.5, 128.6, 128.7,
138.2, 138.3, 138.7, 142.2. Anal. Calcd for C42H44O5: C, 80.23;
H, 7.05. Found: C, 80.08; H, 7.19.
Ack n ow led gm en t. The authors thank Drs Se´bas-
tien Comesse, Luc Dechoux, and Louis Hamon for
fruitful discussions.
1-(2′,3′,4′,6′-Te t r a -O-b e n zyl-â-D -ga la ct op yr a n osyl)-3-
bu ten e (6): mp 54-56 °C, [R]D +2.2 (c 1, CHCl3) [lit.10 [R]D -2.0
J O034795E
7898 J . Org. Chem., Vol. 68, No. 20, 2003