Regioselective benzylation of pentitols, tetritols, and some hexitols via their stannyl ether derivatives: Versatile synthesis of monobenzylalditols

Article abstract of DOI:10.1081/CAR-100106930

The xylitol, ribitol and D-arabinitol were transformed into their tributylstannyl ether derivatives by reaction with bis-tributyltin oxide [(nBu₃Sn)₂O I] and azeotropic removal of water. Subsequent benzyl etherification, using BnBr with solvent or under free solvent conditions, led regioselectively to primary mono-O-benzylalditol derivatives in satisfactory yields for a direct regioselective synthesis (~ 52%). This etherification when applied to tetritols and some hexitols exhibits similar behaviour. With pentitols, an analogous study carried out with the n-dibutyltin oxide [nBu₂SnO (II)] as the activating reagent showed contrasting results as regards regioselectivity.

Full text of DOI:10.1081/CAR-100106930

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REGIOSELECTIVE BENZYLATION OF PENTITOLS,
TETRITOLS, AND SOME HEXITOLS VIA THEIR STANNYL
ETHER DERIVATIVES: VERSATILE SYNTHESIS OF
MONOBENZYLALDITOLS
Sami Halila a , Mohammed Benazza b & Gilles Demailly a
a Université de Picardie Jules Verne , Laboratoire de Chimie Organique, 33 rue Saint-
Leu, Amiens, F-80039, France
b Université de Picardie Jules Verne , Laboratoire de Chimie Organique, 33 rue Saint-
Leu, Amiens, F-80039, France
Published online: 19 Aug 2006.
To cite this article: Sami Halila , Mohammed Benazza & Gilles Demailly (2001) REGIOSELECTIVE BENZYLATION OF
PENTITOLS, TETRITOLS, AND SOME HEXITOLS VIA THEIR STANNYL ETHER DERIVATIVES: VERSATILE SYNTHESIS OF
MONOBENZYLALDITOLS, Journal of Carbohydrate Chemistry, 20:6, 467-483, DOI: 10.1081/CAR-100106930
To link to this article: http://dx.doi.org/10.1081/CAR-100106930
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J. CARBOHYDRATE CHEMISTRY, 20(6), 467–483 (2001)
REGIOSELECTIVE BENZYLATION OF
PENTITOLS, TETRITOLS, AND SOME HEXITOLS
VIA THEIR STANNYL ETHER DERIVATIVES:
VERSATILE SYNTHESIS OF
MONOBENZYLALDITOLS
Sami Halila, Mohammed Benazza,* and Gilles Demailly
Laboratoire de Chimie Organique, Université de Picardie Jules Verne,
33 rue Saint-Leu F-80039 Amiens, France
ABSTRACT
The xylitol, ribitol and D-arabinitol were transformed into their tributylstannyl
ether derivatives by reaction with bis-tributyltin oxide [(nBu3Sn)2O I] and
azeotropic removal of water. Subsequent benzyl etherification, using BnBr
with solvent or under free solvent conditions, led regioselectively to primary
mono-O-benzylalditol derivatives in satisfactory yields for a direct regioselec-
tive synthesis (ꢀ 52%). This etherification when applied to tetritols and some
hexitols exhibits similar behaviour. With pentitols, an analogous study carried
out with the n-dibutyltin oxide [nBu2SnO (II)] as the activating reagent showed
contrasting results as regards regioselectivity.
INTRODUCTION
The regioselective etherification and esterification of unprotected polyols is
a useful transformation in organic synthesis.1,2 A range of conditions for the re-
gioselective introduction of a benzyl moiety has been described in the literature.3–5
With alditols which contain more than three hydroxyl groups, the direct re-
gioselective etherification of the primary alcohol functions are drastically limited,
*Corresponding author. Fax ꢀ33(3)22827562; E-mail: mohammed.benazza@sc.u-picardie.fr
467
Copyright © 2001 by Marcel Dekker, Inc.
www.dekker.com

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468
HALILA, BENAZZA, AND DEMAILLY
Scheme 1.
due to random etherification also occurring at the secondary hydroxyl goups. To
avoid this difficulty with xylitol, a prior acetal protection step enables one free pri-
mary hydroxyl group to be conserved,6 and this can subsequently be esterified,
etherified or thioetherified.7
More recently, efficient direct regioselective monoalkylation of symmetric
l,n-alkanediols (n ꢁ 2 to 10) via their dibutylstannylene acetal derivatives (using
Table 1. Benzylation of Pentitols via Their
Conditions
BnBr
Entry
Substrate
Xylitol (1)
Tin-reagent
(eq.)
(eq.)
Salt(eq)
Solvent
1
2
3
4
5
6
7
8
9
(n-Bu3Sn)2O (I)
(2.5)
“
“
“
“
(1)
“
(2.5)
(1)
“
(4)
“
“
“
-
-
-
-
-
-
HCCl3
without
“
“
“
“
“
“
“
“
Ribitol (5)
D-Arabinitol (9)
Xylitol (1)
“
HCCl3
n-Bu2SnO (II)
(2.5)
“
“
“
“
“
“
“
“
“
“
“
“
“
“
“
“
CsF(2)
-
NBu4Br (2)
10
Ribitol (5)
-
11
12
13
14
“
“
“
“
“
(2.5)
“
(4)
“
-
-
-
-
“
“
“
“
“
D-Arabinitol (9)
(2)
(2.5)
(4)
“
(2.5)
pp ꢁ primaryꢂprimary; ps ꢁ primaryꢂsecondary; *With complex mixture; **peracetylated alditols

ORDER
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VERSATILE SYNTHESIS OF MONOBENZYLALDITOLS
469
nBu2SnO (II) as the activating reagent) has been reported.8a For example, ribose
diethyl dithioacetal has been converted into its 5-O-alkyl ether in good yield (68%)
via the dibutylstannylene acetal.8b
We have required some monobenzylated pentitols for use in recent thia and
aza heterocyclic synthesis,9 the stannylene acetal complexes of pentitols being
used as intermediates. Unfortunately, the only targeted primary monobenzyl
derivative obtained was from xylitol.10
Herein, we report the regioselective primary mono benzylation of the penti-
tols, xylitol, ribitol and D-arabinitol, via their stannyl ether complexes (using
(Bu3Sn)2O (I) as activating reagent). Next, this reaction was applied to tetritols,
erythritol and D,L-threitol, and some hexitols, D-mannitol with C2-symmetry, D-
glucitol and galactitol. The alditol stannyl ether derivatives were prepared by re-
fluxing a mixture of bis-(tributyltin) oxide and alditols in toluene with azeotropic
removal of the water formed.3
RESULTS AND DISCUSSION
The first regioselective pentitol O-benzylation attempt was carried out with
xylitol (1) (Scheme 1) and (nBu3Sn)2O (I) under the conditions reported in the
Table 1 (entry 1). The expected 2,3,4,5-tetra-O-acetyl-1-O-benzyl-DL-xylitol (3)
was obtained as the main product (45% yield) after acetylation and chromatogra-
Stannyl Ether or Stannylene Acetal Derivatives
Isolated yields (%)
Substrate
T(°C)
Time(h)
Mono-(%)
di-(%)
tri-(%)
(%)**
reflux
80
90
80
reflux
“
rt
reflux
rt
120
10
20
“
65
“
3
“
“
(45)
2pp
(3)
(10)
(52)
(16)
(4)
-
-
-
-
-
-
-
-
-
-
4 (50)
(50)
(20)
(52)
(50)
(60)
(53)
(28)
(10)
(17)
“
“
“
“
(30)
(5)
7
11/12
3
6pp
8
13
4
(23)
(36)
(33)
(9)
10pp
2pp
(5)
“
-
5
“
“
“
“
(23)
(52)
-
141,2,5
(8)
(17)
-
“
65
10
65
“
“
“
(0)
“
7
“
8
(85)
(47)
(15)
(16)
65
6pp
(10)
mixture
15ps (1,4)
“
50
65
“
“
40
65
“
“
“
(26)
(31)
(25)
(20)
6pp
15ps (1,4)
6pp
15ps (1:4)
10pp
17p,s;(4:5)
10pp
17p,s;(4:5)
(11) (20)
(8) (17)
(4) (13)
(0) (25)
“
“
“
“
16(1:4:5)
“
(32)
(51)
(13)
11/12
“
(3)
13
13
(33)

ORDER
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470
HALILA, BENAZZA, AND DEMAILLY
phy on silica gel. The 1,5-di-O-benzylxylitol derivative 2 was isolated in only a
small amount (3%). The yield of monobenzylated derivative 3 reached 50% in a
short time using solvent free conditions (entry 2). Increasing both reaction temper-
ature (90 °C) and time (20 h) led to the 1,5-di-O-benzyl derivative 2 in good yield
(52%, entry 3).
With the solvent free conditions reported in entry 4, ribitol (5) and the organ-
otin reagent I gave the mono-O-benzylated and di-O-benzylated derivatives 7 and
6 in yields of 52 and 16%, respectively (Scheme 2). The monobenzylation of ribitol
was slower than that of xylitol (entry 2), as 20 h were needed to complete the re-
action. On the other hand, the attempt to favour the dibenzylated derivative 6 at a
higher temperature and a long time (90 °C, 20 h) led to a complex mixture.
The stannyl ether complex of D-arabinitol (9) was submitted to both solvent-
free conditions and using solvent. The solvent-free conditions appear to be drastic
since compound 9 led mainly to a mixture of unidentified benzylated by-products.
However, with chloroform as solvent, the D-arabinitol tin complex refluxed with
BnBr for 65 h (entry 5) led, after acetylation (Scheme 3), to an equimolar mixture
of regioisomeric 1-O-benzyl and 5-O-benzyl-D-arabinitol (or 1-O-benzyl-D-lyxi-
tol) derivatives 11 and 12 in 50% overall yield (ratio determined by 13C NMR spec-
troscopy). The further O-benzylation of the second terminal primary alcohol group
in the corresponding monoprotected tin complexes is slower. Only a 20% yield of
the 2,3,4-tri-O-acetyl-1,5-di-O-benzyl-D-arabinitol (10) was obtained after 5 days
in refluxing HCCl3.
Compared with previous results obtained with the stannylene acetal interme-
diate (obtained with organotin oxide II as the activating reagent), xylitol appears
to follow the same behaviour. Both the primary-primary di-O-benzylated and the
primary mono-O-benzylated derivatives 2 and 3 were obtained mainly under con-
ditions shown in entries 6 to 8, respectively.10 The use of only 1 equivalent of
nBu2SnO favoured a selective formation of targeted mono-O-benzyl xylitol 3 in
Scheme 2.

ORDER
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VERSATILE SYNTHESIS OF MONOBENZYLALDITOLS
471
Scheme 3.
good yield (60%, entry 6); the benzylation of secondary hydroxyl groups was ex-
cluded. Furthermore, under the same conditions, but in the presence of added ce-
sium fluoride (2 equiv, entry 7), the benzylation occurred much faster (5 h instead
of 65 h for complete reaction) without heating and with approximately the same re-
giochemistry. This salt effect was previously reported by Naguashima et al.11 Sur-
prisingly, tetrabutylammonium bromide (entry 9), which was conveniently used
under nonpolar conditions, led to an unexpected decrease in reaction rate, and to a
complex mixture when DMF was used as the aprotic polar solvent. Finally, the
complete benzylation of both primary positions seems to depend on the organ-
otin/substrate ratio used. Thus, 2.5 equiv of II (entry 8) instead of 1 equiv led to
1,5-di-O-benzylated derivative in 52% yield.
It should be emphasized, that use of added salt or base to the xylitol stannyl
ether and benzyl bromide led to complex mixtures.
In comparison to xylitol, ribitol and D-arabinitol O-benzylation via the stan-
nylene acetal (obtained with organotin reagent II) led, in addition to normally
formed primary O-benzylated derivatives (6, 7, 10, 11 and 12), to some unexpected
primary-secondary di-O-benzylated by-products (15, 16 and 17). The amount of
secondary O-benzyl substitution seems to depend on the pentitol substrate; under
moderate conditions, unsymmetrical D-arabinitol (9) gave, after acetylation of the
crude product, a regioisomeric mixture of primary mono-O-benzyl derivatives 11
and 12 in 25% overall yield (one of them is in twofold majority) plus 1,2,3-tri-O-
acetyl-4,5-di-O-benzyl-D-arabinitol (17) in a yield of 13% (entry 13). Only traces
of primary di-O-benzyl derivative 10 (4%) and 1,4,5-tri-O-benzyl derivative 16
(3%) were isolated. With a large excess of BnBr (4 equiv, entry 14) the obtained
yields of 4,5-di-O-benzylated and 1,4,5-tri-O-benzylated derivatives 17 and 16
were, respectively, 25 and 33%. Only a small amount of substrate remained (13%).

ORDER
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472
HALILA, BENAZZA, AND DEMAILLY
This result suggests that D-arabinitol was first transformed primarily into a mixture
of regioisomeric mono-O-benzyl derivatives, 5-O-benzyl-D-arabinitol as major
product and 1-O-benzyl-D-arabinitol as minor product, the former then undergoing
regioselective O-benzylation of the secondary hydroxyl group at C-4. Further
etherification took place subsequently at the primary C-1 alcohol.
It is of interest to note that a different regioselectivity behaviour was adopted
by the stannylene acetal complex of ribitol (obtained with organotin complex II).
While the vicinal 4,5-di-O-benzyl derivative 17 was formed from D-arabinitol, un-
der the same conditions ribitol stannylene acetal as intermediate led to primary-
secondary 1,4-di-O-benzyl derivative 15 (entry 11 to 13). No tri-O-benzylated
derivative was detected.
In compound 17, the secondary and the primary benzyl groups at C-4 and C-
5 positions, respectively, were located by NMR spectroscopy (Table 2, 3 and 4).
1
The H NMR spectrum showed a large coupling constant of 6.9 Hz for anti-3,4-
methine and a weak coupling constant of 3.7 Hz for syn-2,3-methine. These values
Table 2. 1H Chemical Shifts (ꢃ) for Peracetylated Mono,
H-1
H-1ꢄ
H-2
H-3
H-4
H-4ꢄ
H-5
2 (xylo)
3.49(dd) 3.55(dd) 5.22(dd) 5.57(t)
5.22 (dd)
3.49 (dd)
3 “
4 “
2.40(dd) 2.36(dd) 5.13(m)
3.80(dd
5.44(dd) 5.22(m)
5.10(dd)
4.24(dd)
3.80(dd)
4.13(dd) 5.10(dd) 5.20(t)
6 (ribo)
3.52(dd) 3.62(dd) 5.27(dd) 5.38(t)
5.27(dd)
3.52(dd)
7 “
8 “
3.48(dd) 3.58(dd) 5.25(m)
4.40(dd) 4.63(dd) 5.66(dd) 5.80(t)
5.33(dd) 5.20(m)
4.09(dd)
4.40(dd)
5.66(dd)
10 (arabino) 3.53(dd) 3.55(dd) 5.46(m)
5.43(dd) 5.16(m)
5.88(dd) 5.57(m)
3.48(dd)
4.41(dd)
13 “
4.29(dd) 4.59(dd) 5.77(m)
14 (xylo)
15 (ribo)
3.61(d)
3.61(d)
3.77(m)
5.50(dd) 5.34(m)
3.38(dd)
4.10(dd)
3.59(dd)
3.50(dd)
3.55(dd) 3.62(dd) 5.40(m
5.40(m)
5.20(m)
16 (arabino) 3.55(dd) 3.59(dd) 5.48(m)
17 “
19 (threo)
20 “
21 “
25 (erythro)
26 “
27 “
31(manno)
32 “
35
5.43(dd) 3.73(m)
5.34(dd) 3.70(m)
4.00(dd) 4.23(dd) 5.50(m)
3.42(dd) 3.44(dd) 5.13(m)
3.55(m)
3.70(m)
3.50(dd) 3.55(dd) 5.18(m)
3.51(dd) 3.56(dd) 5.24(m)
3.68(dd) 3.75(dd) 5.42(m)
3.43(dd) 3.52(dd) 5.07(m)
3.43(dd) 3.52(dd) 5.05(m)
3.41(dd) 3.45(dd) 5.06(m)
4.36(dd) 4.55(dd) 5.50(m)
5.28(m)
3.83(m)
4.00(m)
5.25(m)
3.70(m)
3.99(m)
5.46(d)
5.46(s)
3.92(dd)
4.02(dd)
3.7(m)
4.15(dd)
4.18(dd)
3.80(dd)
5.46(d)
5.41(s)
4.21(dd)
4.15(dd)
3.70(m)
4.27(dd)
4.30(dd)
3.83(dd)
3.55(m)
3,70(m)
5.14(m)
5.40(m)
5.07(m)
5.03(m)
5.19(m)
5.50(dd)
5.17(t)
5.41(dd) 5.59(dd)
38
5.88(d)
5.33(s)
5.88(d)
5.33(s)
40 (galacto)
41
3.38(d)
3.38(d)
3.38(d)
3.38(d)
5.17(t)
5.21(m)
5.35(dd) 5.30(dd)
5.19(m)

ORDER
REPRINTS
VERSATILE SYNTHESIS OF MONOBENZYLALDITOLS
473
are consistent with the planar zig-zag conformation previously proposed for per-
acetylated12 and 1,5-dihalogenated D-arabinitol derivatives.13 Subsequently, the
vicinal 4,5-di-O-benzyl positions were indicated by 13C NMR shift correlation.
The same study was carried out for the tribenzylated and dibenzylated derivatives
16 and 10; these produced the same J3,4-J2,3 anti-syn methine sequence.
The synthesis in satisfactory yields of primary monobenzylated pentitols via
their stannyl ether derivatives, allowed us to expand this reaction to tetritols and
some hexitols (Tables 5 and 6). Thus, we showed that with tetritol stannyl ether
complexes, the monobenzylation occurred in good yields using solvent-free con-
ditions. Furthermore, we observed that the rate of primary regioselective O-benzy-
lation of D,L-threitol (18) was faster than of erythritol (24). In fact, while only 5 h
were needed to obtain the 1-O-benzyl-D,L-threitol derivative 19 in 54% yield (en-
try 1, Table 6), 20 h were required to obtain 1-O-benzyl-D,L-erythritol derivative
25 in 50% yield (entry 3). On the other hand, in both cases, 1,3-di-O-benzylated
derivatives were isolated as by-product in minor yields. With erythritol, the yield
Di, and Tri-O-benzylated Alditol Derivatives (in CDCl3)
H-5ꢄ
H-6
H-6ꢄ
CH3
CH2(Bn)
Ph(Bn)
3.55 (dd)
2.02(s) (6H);
1.99(s, 3H)
2; 1.98; 1.93
1.84(s, 6H);
1.89(s, 3H)
1.92(s, 6H);
1.99(s, 3H)
2.03; 1.98; 1.95
2(s, 6H);
4.45(s)(4H)
7.29(m)(10H)
3.92(dd)
4.13(dd)
3.62(dd)
4.46(s, 4H)
7.29(m, 10H)
4.29(dd)
4.63(dd)
4.44(s, 2H)
-
7.24 (m, 5H)
-
2.1(s,9H)
3.60(dd)
4.54(dd)
2.05; 1.98; 1.92
2.07(m, 12H)
4.45(m,4H)
7.20(m, 10H)
3.49(dd)
4.30(dd)
3.61(dd)
3.62(dd)
2.10(s, 6H)
2.02; 2; 1.96
2; 1.96
2.01; 1.98; 1.91
1.89; 1.91; 1.95
1.29; 1.98
4.49(s, 6H)
4.38(s, 4H)
4.48(m, 6H)
4.55(m, 4H)
4.36(dd, 2H)
4.47(d); 4.40(d)
4.81(dd); 4.68(dd)
4.45(dd)
4.50(dd); 4.12(dd)
4.74(dd); 4.78(dd)
4.47(d); 4.40(d)
4.47(dd)
7.30(m, 15H)
7.24(m, 5H)
7.27(m, 15H)
7.26(m, 10H)
7.19(m, 5H)
7.25(m, 10H)
7.3(m)
7.24(m)
7.25(m)
7.39(m)
7.24(m)
2.08
1.94; 1.96; 2.00
1.98(s, 6H)
2.07
2.10(m, 12H)
2.03(m, 15H)
1.98(m, 12H)
2.13; 2.11; 2.03
2.01; 1.96
3.43(dd)
4.01(dd)
3.58(dd)
4.36(dd)
3.38(d)
3.52(dd)
4.17(dd)
3.62(dd)
4.55(dd)
3.38(d)
7.25(m)
7.23(m)
4.43(m, 4H)
4.34(dd); 4.42(dd)
4.34(dd); 4.42(dd)
7.23(m)
7.24(m)
3.77(dd)
4.20(dd)
2.01; 1.94

ORDER
REPRINTS
474
HALILA, BENAZZA, AND DEMAILLY
Table 3. Coupling Constants (Hz) for Peracetylated Mono, Di, and Tri-O-benzylated Alditol
Derivatives (in CDCl3)
Coupling constants (Hz)
Compd.
J1,1ꢄ J1,2 J1ꢄ,2 J2,3 J3,4 J3,4ꢄ J4,4ꢄ J4,5 J4,5ꢄ J5,5ꢄ J5,6 J5,6ꢄ J6,6ꢄ
2(xylo)
3 “
4 “
10.6 4.6 5.2 5.4 5.4
10.7 4.8 4.7 5.4 5.4
4.6 5.2
4.6 6.2
6.2 4.3
10.6
11.9
12
12
6.2 4.3 5.3 5.3
6(ribo)
7 “
8 “
12.6 6.2 3.7 5.4 5.4
10.7 5.8 4.0 5.2 5.2
12.3 3.3 6.1 5.7 5.7
6.2 3.7
6.4 3.0
3.3 6.1
12.6
12.2
12.3
10(arabino) 10.3 7.3 3.8 3.1 7.9
7.4 5.7
5.1 2.6
10.8
12.4
13 “
11.9 6.9 4.6 2.3 8.6
14(xylo)
15(ribo)
-
5.0 5.0 6.2 4.4
5.2 4.0
5.3 3.4
6.0 4.2
5.0 4.2
10.8
12.2
10.3
10.3
10.5 5.7 3.2
-
-
16(arabino) 10.7 7.5 3.5 4.4 5.8
17 “
19(threo)
20 “
21 “
11.8 6.3 5.0 3.7 6.9
4.0 4.0 0.0 5.3 3.1 12.1
10.5 5.9 3.9 0.0 6.1 4.5 11.6
10.2 5.7 4.4 5.0 10.4
-
-
-
25(erythro) 10.7 5.4 4.3 5.8 6.2
3
12.5
26 “
27 “
10.8 5.5 4.3 5.6 6.6 2.7 12.7
10.7 5.4 4.3 5.8 5.7 4.2 11.0
31(manno) 10.8 5.4 3.9 8.3
-
8.3
8.8
5.4 3.9 10.8
5.2 2.5 12.5
32 “
10.7 5.1 3.8 9.3 2.0
35(glu)
38 “
8.6 5.6 3.1 4.2 6.1
4.5
5.9
5.2 2.5 12.5
5.1 2.8 12.4
12.4 5.1 2.8 5.9
-
40(galacto)
41 “
-
-
6
5
6
5
0
9.9
-
-
0
10.5
6
6
-
8.1 4.2 11.1
of 1,3 primary-secondary di-O-benzyl derivative 26 reached 50% using a large ex-
cess of BnBr (entry 4). Furthermore, with both D,L-threitol and erythritol, simulta-
neous use of a large excess of BnBr and a long reaction time (20 h) led mainly to
the tribenzylated derivatives 21 (62%, entry 2) and 27 (60%, entry 5), respectively.
Finally the more complex hexitols namely, D-mannitol (30), D-glucitol (34)
and galactitol (39), transformed to their stannyl ether derivatives, led after benzy-
lation, to the corresponding monobenzyl ethers 32, 36/37 and 41 in reasonable
yields (45 to 48%) (entries 6 to 9, Table 6).
In conclusion, from a synthetic point of view, the most interesting result to
note in this work is the generalized regioselective benzylation (via the tributyl-
stannyl ether complex) at only one primary position of alditols, and often under

ORDER
REPRINTS
VERSATILE SYNTHESIS OF MONOBENZYLALDITOLS
475
solvent-free conditions. The monobenzylated derivatives were obtained in satis-
factory yields for a direct regioselective synthesis (47 to 54%). Current work is di-
rected towards studying the reactivity of alditols organotin complexes towards
other electrophiles.
EXPERIMENTAL
General methods. Melting points were determined with a Buchi 535 ap-
paratus and are uncorrected. 1H and 13C NMR spectra were recorded in CDCl3 on
Bruker 300 WB spectrometer; chemical shifts are reported in ꢃ (ppm) relative to
Me4Si. Coupling constants, assigned by double irradiation, are in Hz. All 13C NMR
signals were assigned though C,H-correlated spectra. TLC was performed on sil-
ica Gel 60 F254 230 mesh (E. Merck) with hexane-EtOAc as eluent, and zones were
detected by vanillin-H2SO4 reagent. The silica gel used in column chromatography
was 35–70 m (Amicon). Mass spectroscopy analyses were performed by the “Ser-
vice d’Analyse de la Faculté de Pharmacie, Laboratoire de Chimie Thérapeutique
U.R.A. au CNRS, (Université de Reims Champagne Ardenne)”. Elemental analy-
ses were performed by the “Service de Microanalyse du CNRS” (Laboratoire de
Bioorganique, Université de Reims Champagne Ardenne”.
General procedure for O-benzylation via the stannyl ether complex.
The alditol (0.2 g) was allowed to react with the (nBu3Sn)2O (I) in refluxing
toluene (20 mL). After azeotropic removal of water over 5 h the solvent was evap-
orated under vacuum. The syrup obtained was dried and submitted to O-benzyla-
tion under conditions reported in Tables 1 and 2. The crude product was dried and
peracetylated with excess of acetic anhydride in pyridine at room temperature. Af-
ter extraction following the usual procedure, the syrup obtained was treated with
aqueous KF14 (20%) overnight. The organotin residue was filtered and the crude
product was chromatographed on silica gel with a mixture of hexane-ethyl acetate
as eluent. From the alditols studied, the following products were isolated in the re-
ported yields under optimal conditions of monobenzylated derivatives (see Tables
1 and 2).
From xylitol (1) (for conditions see entry 2, Table 1):
2,3,4-Tri-O-acetyl-1,5-di-O-benzylxylitol (2). Syrup; Yield 60 mg (10%);
Rf 0.49 in 5:2 hexane-EtOAc; MS: m/z 459, M (C25H30O8) 458.50;
Anal. Calcd for C25H30O8: C, 65.49; H, 6.60; O, 27.92. Found: C, 65.77; H,
6.68.
2,3,4,5-Tetra-O-acetyl-1-O-benzyl-D,L-xylitol (3). Syrup; Yield 270 mg
(50%); Rf 0.37 in 5:2 hexane-EtOAc; MS: m/z 411 [M ꢀ 1], M (C20H26O9) 410.42.
Anal. Calcd for C20H26O9: C, 58.53; H, 6.39; O, 35.09. Found: C, 58.90; H,
6.42.
The di-O-benzyl derivative 2 was obtained in major part (50%) in conditions
reported in entry 4.

ORDER
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476
HALILA, BENAZZA, AND DEMAILLY
Table 4. 13C Chemical Shifts (ꢃ) for Peracetylated Mono,
Compd
C-1
C-2
C-3
C-4
C-5
C-6
CO(Ac)
2
3
68.1
67.7
70.5
69.3
69.9
70.3
70.5
69.3
68.1
61.8
169.4; 170.1
169.6; 169.8;
170; 170.2
168.5; 168.7;
169
169.4; 169.9;
170.6
169.3; 169.7;
169.8; 170.5
169.8; 169.5;
170.2
4
60.9
67.9
67.7
61.8
68.3
68.2
69.4
69.7
69.8
69.0
68.2
70.2
70.3
69.3
70.3
68.2
69.4
69.7
69.8
69.3
60.9
67.9
61.9
61.8
61.8
6
7
8
10
169.6; 169.8;
170; 170.2
169.51; 169.77;
170.34
11/ 12
67.90, 67.72,
62.02 or
61.62
68.71 68.18 68.71 67.90, 67.72,
62.02 or
61.62
13
14
15
16
17
62.9
68.2
76.2
70.7
70.2
69.2
70.0
69.4
71.2
71.8
70.5
70.0
69.4
68.7
71.1
73.9
76.0
75.6
61.9
62.5
68.2
61.2
68.7
69.0
170.4; 170.6;
170.7
170.1
69.7
66.9
64.4
62.7
169.5; 168.7;
168.3
169.9; 170.1
169.7; 169.9;
170.3
169.85; 169.74
170.29; 170.62
19
20
67.6
67.68
71.49 77.46 62.87
21
68.72
71.26 75.85 67.36
169.48
25
26
27
60.97
62.67
68.42
68.81 69.19 66.63
75.18 71.18 67.86
76.91 72.08 69.75
168.88; 169.59
169.04
169.5
29
68.39
68.32 68.56 68.56 68.32
68.5 68.9 68.9 68.5
68.39
169.68; 169.93
31
32
62.7
68.21
62.7
61.84
170.9; 170.4
169.65; 169.92;
170.53
68.49 68.04 67.56 67.84
33
67.64
68.99 69.75 70.48 68.99
67.92
169.77; 170.23
36/37
67.21 or 67.72
-
-
-
-
60.49 or 169.20
60.77
40
41
68.3
67.6
68.4
67.9
67.9
68.4
68.3
62.21
169.37; 168.82
170.24; 169.74
67.63 67.63 67.63 67.63
* In mixture with 12; ** In mixture with 11

ORDER
REPRINTS
VERSATILE SYNTHESIS OF MONOBENZYLALDITOLS
477
Di, and Tri-O-benzylated Alditol Derivatives (in CDCl3)
Me(Ac)
CH2 (Bn)
73.2
Ph (Bn)
C-ipso
137.5
20.5; 20.7
20.5; 20.6;
20.7
128.3; 127.7
128.3; 127.7
73.3
137.4
19.3; 19.4;
19.5
20.9; 20.7
-
-
128.3; 128; 127.7
128
-
73.1
73.1
137.6
137.5
20.6; 20.7;
20.9
20.2; 20.4
-
-
-
20.5; 20.9;
20.7
20.49
73.3
128.3; 127.7
128.30; 127.73
137.4
73.25
137.32
-
20.8; 20.9;
21
-
-
20.9; 20.8
73.5; 73.1;
72.5
69.6; 69.0
128.3; 127.9;
127.7
127.1; 126.8
137.9; 137.7
136.5; 136.2
137.9
19.7; 19.5
20.9; 20.7
20.6
73.4; 73.2;
72.4
73.5; 72.5
128.3; 128.1;
127.7
128.3; 128.1;
127.8
137.7; 137.4
20.59; 20.51
20.76; 20.94
73.1
73.21
127.62; 128.29
127.65; 127.83;
127.95; 128.35
126.88; 127.11;
127.24; 127.56
137.45
137.68
20.20
72.27; 72.42;
72.58
137.18;
137.30;
137.58
137.53
19.67; 19.79
20.90
21.13
72.22
127.39; 126.71
128.2
73.13; 73.39;
73.43
137.3
20.60; 20.91
73.22
127.66; 127.78;
128.28
137.53
21.2; 20.9
20.55; 20.77;
20.89
73.26
127.82; 128.29
137.43
20.77; 20.63
20.58
73.07; 73.29
73.20
127.8
127.27
137.61
136.37;
136.58
136.61
137.48
19.88; 19.66
20.55
72.35
73.32
127.36; 126.79
128.31; 127.73

ORDER
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478
HALILA, BENAZZA, AND DEMAILLY
Table 5. Summary of Benzylated Tetritol and Hexitol Derivatives Obtained via the
Corresponding Stannyl Ether Complexes
Substrate
Isolated Products*
19 R1 ꢁ Bn; R ꢁ R2 ꢁ R3 ꢁ Ac
OH
OR1
HO
RO
20 R1 ꢁ R3 ꢁ Bn; R ꢁ R2 ꢁ Ac
21 R1 ꢁ R2 ꢁ R3 ꢁ Bn; R ꢁ Ac
23 R1 ꢁ R2 ꢁ R3 ꢁ R ꢁ Ac
OH
OH
OR3
OR2
D,L-Threitol (18)
OH
OH
OH
OH
OR1
OR
OR3
OR2
25 R1 ꢁ Bn; R ꢁ R2 ꢁ R3 ꢁ Ac
26 R1 ꢁ R3 ꢁ Bn; R ꢁ R2 ꢁ Ac
27 R1 ꢁ R2 ꢁ R3 ꢁ Bn; R ꢁ Ac
29 R1 ꢁ R2 ꢁ R3 ꢁ R ꢁ Ac
Erythritol (24)
OR1
OR1
RO
RO
RO
RO
31 R1 ꢁ R2 ꢁ Bn; R ꢁ Ac
32 R1 ꢁ Bn; R2 ꢁ R ꢁ Ac
33 R1 ꢁ R2 ꢁ R ꢁ Ac
OR
OR
OR2
OR
OR
OR2
D-Malnnitol (30)
OR1
OR
OR1
OR
35 R1 ꢁ R2 ꢁ Bn; R ꢁ Ac
36 R1 ꢁ Bn; R2 ꢁ R ꢁ Ac
37 R1 ꢁ R ꢁ Ac; R ꢁ Bn
38 R1 ꢁ R2 ꢁ R ꢁ Ac
RO
RO
OR
OR
OR2
OR
OR
OR2
D-Glucitol (34)
OR1
OR
OR1
OR
40 R ꢁ R2 ꢁ Bn; R ꢁ Ac
41 R1 ꢁ Bn; R2 ꢁ R ꢁ Ac
42 R1 ꢁ R2 ꢁ R ꢁ Ac
RO
RO
RO
RO
OR
OR2
OR
OR2
Galactitol (39)
* After acetylation of crude product
Table 6. Benzylation of Tetritols and Some
Conditions
BnBr
Entry
Substrate
Tin-reagent
(eq)
(eq)
Solvent
T(°C)
Time(h)
1
2
3
4
5
6
7
8
9
D,L-Threitol (18)
(n-Bu3Sn)2O
(1)
(2.5)
(1)
(2.5)
“
“
“
“
(4)
(1.2)
(4)
(1.2)
(4)
“
“
“
“
“
without
80
“
“
“
“
“
“
70
“
5
20
“
“
“
“
“
“
“
“
“
“
“
“
“
“
Erythritol (24)
“
“
5
20
240
20
25
30
D-Mannitol (30)
“
D-Glucitol (34)
Galactitol (39)
HCCl3
without
“
“
pp ꢁ primary-primary; ps ꢁ primary-secondary; *With complex mixture; **peracetylated alditols

ORDER
REPRINTS
VERSATILE SYNTHESIS OF MONOBENZYLALDITOLS
479
From ribitol (5) (for conditions see entry 4, Table 1) :
2,3,4-Tri-O-acetyl-1,5-di-O-benzylribitol (6). Syrup; Yield 96 mg (16%);
Rf 0.67 in 5:3 hexane-EtOAc; MS: m/z 459, M (C25H30O8) 458.50.
Anal. Calcd for C25H30O8: C, 65.49; H, 6.60; O, 27.92. Found: C, 65.56; H,
6.65.
2,3,4,5-Tetra-O-acetyl-1-O-benzyl-D,L-ribitol (7). Syrup; Yield 280 mg
(52%); Rf 0.55 in 5:2 hexane-EtOAc; MS: m/z 411 [M ꢀ 1], M (C20H26O9) 410.42.
Anal. Calcd for C20H26O9: C, 58.53; H, 6.39; O, 35.09. Found: C, 58.72; H,
6.50.
From D-arabinitol (9) (for conditions see entry 5, Table 1) :
2,3,4-Tri-O-acetyl-1,5-di-O-benzyl-D-arabinitol (10). Syrup; Yield 24
mg (4%); Rf 0.67 in 5:3 hexane-EtOAc; MS: m/z 459, M (C25H30O8) 458.50.
Anal. Calcd for C25H30O8: C, 65.49; H, 6.60; O, 27.92. Found: C, 65.82; H,
6.63.
2,3,4,5-Tetra-O-acetyl-1-O-benzyl-D-arabinitol (11) and 1,2,3,4-tetra-O-
acetyl-5-O-benzyl-D-arabinitol (12). Syrup; Yield 270 mg (50%); Rf 0.52 in
5:3 hexane-EtOAc; MS: m/z 411 [M ꢀ 1], M (C20H26O9) 410.42.
Anal. Calcd C20H26O9: C, 58.53; H, 6.39; O, 35.09. Found: C, 58.80; H, 6.52.
From D,L-threitol (18) (for conditions see entry 1, Table 6) :
2,3,4-Tri-O-acetyl-1-O-benzyl-D,L-threitol (19). Syrup Yield 299 mg
(54%); Rf 0.38 in 6:2 hexane-EtOAc; MS: m/z 339 [M ꢀ 1], M (C17H22O7) 338.35.
Anal. Calcd for C17H22O7: C, 60.35; H, 6.55; O, 33.10. Found: C, 60.41; H,
6.63.
2,4-Di-O-acetyl-1,3-di-O-benzyl-D,L-threitol (20). Syrup; Yield 95 mg
(15%); Rf 0.41 in 6:2 hexane-EtOAc; MS: m/z 387 [M ꢀ 1], M (C22H26O6) 386.44.
Hexitols via Their Stannyl Ether Derivatives
Isolated yields (%)
Substrate
Mono-(%)
19
di-(%)
20ps (1:3)
“
26ps (1:3)
“
tri-(%)
(%)**
(54)
(0)
(15)
(17)
(13)
(50)
(15)
(0)
(5)
(23)
(21)
211,3,4
(0)
(62)
(0)
(10)
(60)
-
-
-
-
23
“
29
“
“
33
“
(27)*
“
25
“
“
27
“
“
-
-
-
-
(0)*
(36)*
(3)*
(50)
(30)
(5)
“
“
(0)*
32
“
36/37
41
(45)
(36)
(48)
(47)
31pp
“
(31)*
(49)*
(29)
35pp
40pp
38
42
(25)

ORDER
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480
HALILA, BENAZZA, AND DEMAILLY
Anal. Calcd for C22H26O6: C, 68.38; H, 6.78; O, 24.84. Found: C, 68.75; H,
6.81.
From D,L-threitol (18) (for conditions see entry 2, Table 5) : The di-O-ben-
zyl derivative 20 was obtained in 17% yield plus:
2-O-acetyl-1,3,4-tri-O-benzyl-D,L-threitol (21). Syrup; Yield 441 mg
(62%); Rf 0.56 in 6:2 hexane-EtOAc; MS: m/z 435 [M ꢀ 1], M (C27H30O5) 434.21.
From erythritol (24) (three sets of conditions):
Entry 3, Table 6: Optimal conditions for primary monobenzylated derivative:
2,3,4-Tri-O-acetyl-1-O-benzyl-D,L-erythritol (25). Syrup; Yield 277 mg
(50%); Rf 0.30 in 6:2 hexane-EtOAc; MS: m/z 339[M ꢀ 1], M (C17H22O7) 338.35.
Anal. Calcd for C17H22O7: C, 60.35; H, 6.55; O, 33.10. Found: C, 60.83; H,
6.57.
2,4-Di-O-acetyl-1,3-di-O-benzyl-D,L-erythritol (26). Syrup; Yield 82 mg
(13%); Syrup; Rf 0.41 in 6:2 hexane-EtOAc; MS: m/z 387 [M ꢀ 1], M (C22H26O6)
386.44.
Anal. Calcd for C22H26O6: C, 68.38; H, 6.78; O, 24.84. Found: C, 68.88; H,
6.90.
Entry 4, Table 6: Optimal conditions for 1,3-dibenzylated derivative 26
(50%).
Entry 5, Table 6: Optimal conditions for 1,3,4-tribenzylated derivative 27:
2-O-Acetyl-1,3,4-tri-O-benzyl-D,L-erythritol (27). Syrup; Yield 427 mg
(60%); Syrup; Rf 0.58 in 6:2 hexane-EtOAc; MS: m/z 435 [M ꢀ 1], M (C27H30O5)
434.21.
From D-mannitol (30) (for conditions see entry 6, Table 6):
2,3,4,5,6-Penta-O-acetyl-1-O-benzyl-D-mannitol (32). Syrup; Yield 238
mg (45%); Rf 0.44 in 5:3 hexane-EtOAc; MS: m/z 483 [M ꢀ 1], M (C23H30O11)
482.48.
Anal. Calcd for C23H30O11: C, 57.26; H, 6.27; O, 36.48. Found: C, 57.68; H,
6.35.
Under conditions reported in entry 7, the 1,6-dibenzylated derivative was ob-
tained as minor product :
2,3,4,5-Tetra-O-acetyl-1,6-di-O-benzyl-D-mannitol (31). Syrup; Yield
29 mg (5%); Rf 0.52 in 5:3 hexane-EtOAc; MS: m/z 531 [M ꢀ 1], M (C28H34O10)
530.56.
Anal. Calcd for C28H34O10: C, 63.39; H, 6.46; O, 30.16. Found: C, 63.45; H,
6.49.
From D-glucitol (34) (for conditions see entry 8, Table 5) :
2,3,4,5,6-Penta-O-acetyl-1-O-benzyl-D-glucitol (36) and 1,2,3,4,5-penta-
O-acetyl-6-O-benzyl-D-glucitol (37). Syrup; Yield 254 mg (48%); Rf 0.34 in 5:3
hexane-EtOAc; MS: m/z 483 [M ꢀ 1], M (C23H30O11) 482.48.

ORDER
REPRINTS
VERSATILE SYNTHESIS OF MONOBENZYLALDITOLS
481
Anal. Calcd for C23H30O11: C, 57.26; H, 6.27; O, 36.48. Found: C, 57.73; H,
6.38.
2,3,4,5-Tetra-O-acetyl-1,6-di-O-benzyl-D-glucitol (35). Syrup; Yield 134
mg (23%); Rf 0.47 in 5:3 hexane-EtOAc; MS: m/z 531 [M ꢀ 1], M (C28H34O10)
530.56.
Anal. Calcd for C28H34O10: C, 63.39; H, 6.46; O, 30.16. Found: C, 63.72; H,
6.49.
From galactitol (39) (for conditions see entry 9, Table 5):
2,3,4,5-Tetra-O-acetyl-1,6-O-benzylgalactitol (40). Yield 122 mg (21%);
mp 149–151 °C; Rf 0.55 in 5:3 hexane-EtOAc; MS: m/z 531 [M ꢀ 1], M
(C28H34O10) 530.56.
Anal. Calcd for C28H34O10: C, 63.39; H, 6.46; O, 30.16. Found: C, 63.68; H,
6.52.
2,3,4,5,6-Penta-O-acetyl-1-O-benzyl-D,L-galactitol (41). Yield 249 mg
(47%); mp 138 °C; Rf 0.39 in 5:3 hexane-EtOAc; MS: m/z 483 [M ꢀ 1], M
(C23H30O11) 482.48.
Anal. Calcd for C23H30O11: C, 57.26; H, 6.27; O, 36.48. Found: C, 57.33; H,
6.27.
General procedure for benzyl etherification of pentitols via the stanny-
lene acetal complex. A mixture of pentitols (0.2 g) and dibutyltin oxide in
toluene was refluxed for 16 h with azeotropic removal of water. The white powder
obtained after removal of the solvent was dried under vacuum and treated with ben-
zyl bromide under the conditions reported in Table 1. The crude product obtained
was subsequently acetylated (Ac2O in pyridine overnight at room temperature).
The syrup obtained after concentration of the solution was dissolved in ethyl ether
and treated with 2,2ꢄ-bipyridyl to precipitate organotin compounds. The filtrate
was concentrated to dryness to give a residue which was processed by column
chromatography on silica gel using a mixture of hexane-AcOEt as eluant.
From xylitol (1): for optimal conditions in monobenzylated derivative 3 see
entry 6, Table 1. The previously described mono and dibenzylated derivatives 3
and 2 were obtained, respectively, in 60 and 5% yields plus:
3,4-Di-O-acetyl-1,2,5-tri-O-benzyl-D,L-xylitol (14). Syrup; Yield 20 mg
(3%); Rf 0.65 in 5:2 hexane-EtOAc.
Anal. Calcd for C30H34O7: C,71.15; H, 6.72; O, 22.13. Found: C,71.02;
H,.6.68.
For optimal conditions in dibenzylated derivative 2 see entry 8, Table 1. The
previously described mono, di and tribenzylated derivatives 3, 2 and 14 were ob-
tained in 28, 52 and 17% yields respectively.
From ribitol (5): for conditions see entry 4, Table 1. The previously described
mono and dibenzylated derivatives 7 and 6 were obtained, respectively, in 31 and

ORDER
REPRINTS
482
HALILA, BENAZZA, AND DEMAILLY
8% yields plus:
2,3,5-Tri-O-acetyl-1,4-di-O-benzyl-D,L-ribitol (15). Syrup; Yield 102
mg (17%); Rf 0.62 in 5:3 hexane-EtOAc; MS: m/z 459 [M ꢀ 1], M(C25H30O8)
458.50.
Anal. Calcd for C25H30O8: C, 65.49; H, 6.60; O, 27.92. Found: C, 65.67; H,
6.63.
From D-arabinitol (9): for conditions see entry 14, Table 1. The previously
described monobenzylated derivatives 11 and 12 were obtained in 20% overall
yields plus:
2,3-Di-O-acetyl-1,4,5-tri-O-benzyl-D-arabinitol (16). Syrup; Yield 220
mg (33%); Rf 0.60 in 5:2 hexane-EtOAc; MS: m/z 507 [M ꢀ 1] M(C30H24O7)
506.6.
Anal. Calcd for C30H24O7: C,71.15; H, 6.72; O, 22.13. Found: C,71.23;
H,.6.75.
1,2,3-Tri-O-acetyl-4,5-di-O-benzyl-D-arabinitol (17). Syrup; Yield 151
mg (25%); Syrup; Rf 0.47 in 5:2 hexane-EtOAc; MS: m/z 459 [M ꢀ 1]
M(C25H30O8) 458.5.
ACKNOWLEDGMENTS
The authors thank the Conseil Regional de Picardie for its financial support.
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Received January 29, 2001
Accepted May 14, 2001

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