B. Meier et al.
3
for 24 h under argon atmosphere 0.09 cm trimethyl
3
temperature and 0.26 cm benzyl bromide (2.22 mmol)
3
dissolved in 2 cm anhydrous THF was added dropwise
orthoformate (0.83 mmol) was admixed and the reaction
was stirred for further 24 h. After cooling to room
temperature the reaction mixture was neutralized with
over a period of about 10 min. The reaction mixture was
allowed to stir 30 min at ambient temperature and 24 h at
80 °C until TLC showed total consumption of the starting
material. After cooling to room temperature the reaction
1
N NaHCO3 solution and extracted three times with
EtOAc. The combined organic extracts were dried over
3
anhydrous Na SO and concentrated to obtain 4a or 4b as a
4
mixture was quenched with 10 cm saturated aqueous
2
pure yellowish oil which can be used without further
NH Cl solution and extracted three times with EtOAc. The
4
purification (L-isomer 4a: 0.241 g, 98 %; D-isomer 4b:
combined organic phases were dried over anhydrous
Na SO and evaporated. CC of the residue over silica with
0
.239 g, 97 %). R = 0.34 (EtOAc); IR data are in
f
2
4
1
accordance with those reported in Ref. [33]; H NMR data
agree with the data mentioned in Ref. [33], but we have
1
completed the given assignments of the H resonances and
CH/EtOAc (5:1) containing 1 % Et NH gave 6a or 6b as
2
pale yellow oil (L-isomer 6a: 0.67 g, 95 %; D-isomer 6b:
1
0.62 g, 88 %). R = 0.46 (CH/EtOAc = 5:1); H NMR
f
1
added those of the C: H NMR (400 MHz, CDCl3):
3
1
(400 MHz, CDCl ): d = 7.38–7.24 (m, 10H, aromatic H),
3
d = 4.75 (s, 2H, 2 9 CH–COO), 3.83 (s, 6H,
4.59 (d, J = 12.2 Hz, 2H, OCH Ph), 4.55 (d, J = 12.2 Hz,
2
2
9 CH OC=O), 1.73 (q, 4H, J = 7.5 Hz, 2 9 CH –CH ),
3
2H, OCH Ph), 4.00 (s, 2H, 2 9 OCH–CH ), 3.61 (s, 4H,
2
2
3
2
1
.94 (t, 6H, J = 7.5 Hz, 2 9 CH –CH ) ppm; C NMR
3
0
2 9 OCH –CH), 1.67 (q, J = 7.5 Hz, 4H, 2 9 CH –CH ),
2 2 3
3
2
1
3
(
(
100 MHz, CDCl ): d = 169.9 (2 9 COOCH ), 117.9
C(CH –CH ) ), 77.2 (2 9 CH–COO), 52.8 (2 9
2 3 2
0.91 (t, J = 7.5 Hz, 6H, 2 9 CH –CH ) ppm; C NMR
3 2
3
3
(100 MHz, CDCl ): d = 138.0 (aromatic C), 128.4 (aro-
3
CH OC=O), 29.5 (2 9 CH –CH ), 7.8 (2 9 CH –CH )
2
matic C), 127.6 (aromatic C), 113.5 (C(CH –CH ) ), 77.9
3 2
3
2
3
3
-3
2
-4
ppm; UV–Vis (CH Cl , c = 1.06 9 10 mol dm ): kmax
(2 9 OCH–CH ), 73.5 (2 9 OCH Ph), 70.8 (2 9 OCH –
2 2 2
2
2
-
1
3
-1
(
e) = 233.0 (2936.18) nm (mol dm cm ); HR-MS: m/z
CH), 30.5 (2 9 CH –CH ), 8.0 (2 9 CH –CH ) ppm; IR
2 3 3 2
?
%) = 269.0996 ([M ? Na] , 100), calc. for C H NaO :
(
(KBr): = 3431, 3030, 2973, 2939, 2880, 1749, 1454, 1203,
-1
1
-1
1
18
6
2
D
0
2
-4
-3
2
69.1001; [a] for L-isomer 4a: -18.8° cm g (c = 12.2,
CH Cl ), for D-isomer 4b: ?13.0° cm g
1092 cm ; UV–Vis (CH Cl , c = 0.68.10 mol dm ):
2 2
2
-1
-1
3
-1
(c = 12.2,
kmax (e) = 259.0 (676.27) nm (mol dm cm ); HR-MS:
m/z (%) = 393.2038 ([M ? Na] , 100), calc. for
2
2
?
CH Cl ).
2
2
2
D
0
C H NaO : 393.2042; [a] for L-isomer 6a: -8.2°
2
3
30
-1
4
(
2S,3S)-2,3-O-(3-Pentylidene)threitol (5a, C H O ) and
9 18 4
2
cm g
(c = 12.1, CH Cl ), for D-isomer 6b: ?7.1°
2
2
(
2R,3R)-2,3-O-(3-pentylidene)threitol (5b, C H O )
9
18
4
3
2 -1
cm g (c = 12.6, CH Cl ).
2
2
To a solution of 0.25 g 4a or 4b (1 mmol) in 3 cm MeOH
.082 g NaBH4 (2.18 mmol) was added at 0 °C. The
mixture was stirred for 40 min before it was quenched with
0
(2S,3S)-1,4-Di-O-benzylthreitol (1a, C H O ) and
18 22 4
(2R,3R)-1,4-di-O-benzylthreitol (1b, C H O )
1
8 22 4
3
1
2 cm H O/brine (1:3), extracted four times with EtOAc,
2
a. Deprotection with 1 N HCl: Ketal 6a or 6b (0.37 g,
3
3
and dried over anhydrous Na SO . Evaporation of the
2
1 mmol) was dissolved in 17 cm EtOH, 0.55 cm HCl
(1 N) was added, and the resulting mixture was refluxed for
about 2 h until TLC showed total consumption of the
starting material. After cooling to ambient temperature the
solvent was concentrated and the oily residue was
dissolved in Et O and washed once with 1 N NaHCO
4
organic solvent gave 5a or 5b as a white solid which can be
used for the next step without further purification (L-isomer
5
a: 0.184 g, 97 %; D-isomer 5b: 0.181 g, 95 %). R = 0.34
f
(
EtOAc); m.p. and NMR data as well as IR data were found
to be identical to the ones described in Ref. [34]; UV–Vis
2
3
-
4
-3
(
(
CH Cl , c = 1.40 9 10 mol dm ): kmax (e) = 349.0
solution. The water phase was re-extracted three times with
2
2
-
1
3
200.25) nm (mol dm cm ); HR-MS: m/z (%) =
-1
Et O. The ether extracts were combined, dried over
2
?
91.1278 ([M ? H] , 100), calc. for C H O : 191.1283;
1
anhydrous Na SO , filtered, and evaporated to dryness.
2
9
19
4
4
2
D
0
2
-1
[
a] for L-isomer 5a: -6.0° cm g (c = 12.4, CH Cl ),
The obtained residue was purified by CC on silica (CH/
2
2
2
-1
for D-isomer 5b: ?4.1° cm g (c = 12.3, CH Cl ).
EtOAc = 1:3) to afford 1 as a white solid (L-isomer 1a:
0.23 g, 75 %; D-isomer 1b: 0.24 g, 79 %). R = 0.41 (CH/
EtOAc = 1:3).
2
2
f
(
2S,3S)-1,4-Di-O-benzyl-2,3-O-(3-pentylidene)threitol (6a,
C H O ) and (2R,3R)-1,4-di-O-benzyl-2,3-O-(3-pentyli-
2
3
30
4
Ò
b. Deprotection with Dowex 50W X8: To 0.37 g ketal
3
a or 6b (1 mmol) dissolved in 8 cm EtOH were added
dene)threitol (6b, C H O )
2
3
30
4
6
3
A solution of 0.19 g 5a or 5b (1 mmol) in 5 cm anhydrous
THF was added dropwise to a stirred suspension of 0.12 g
Ò
3
.5 g Dowex 50W X8 and 0.80 cm H O. The resulting
0
2
mixture was heated to 70 °C and stirred for about 22 h.
When TLC showed consumption of the starting material
the reaction mixture was cooled to ambient temperature.
The insoluble ion exchanger was filtered off and washed
3
NaH (60 % in mineral oil, 3 mmol) in 5 cm anhydrous
THF under an argon atmosphere. The mixture was stirred
for 1 h at ambient temperature and then refluxed for an
additional hour. The suspension was cooled to room
1
23