An abnormal deallylation reaction of an L-fucopyranoside

Article abstract of DOI:10.1016/S0008-6215(99)00055-5

Deallylation of allyl 2,3,4-tri-O-benzyl-L-fucopyranoside in the presence of palladium chloride and cuprous chloride led to an unexpected result. Instead of the expected deallylated product, (2-oxopropyl)-2,3,4-tri-O-benzyl-L-fucopyranoside was obtained.

Full text of DOI:10.1016/S0008-6215(99)00055-5

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Carbohydrate Research 317 (1999) 191–192
Note
An abnormal deallylation reaction of an
L-fucopyranoside
Zhong-Jun Li *, Hui Li, Yi-Ping Lu, Xu-Ling Shi, Meng-Shen Cai
Department of Bioorganic Chemistry, School of Pharmaceutical Sciences, Beijing Medical Uni6ersity,
Beijing 100083, People’s Republic of China
Received 9 September 1998; accepted 9 February 1999
Abstract
Deallylation of allyl 2,3,4-tri-O-benzyl-
L
-fucopyranoside in the presence of palladium chloride and cuprous
chloride led to an unexpected result. Instead of the expected deallylated product, (2-oxopropyl)-2,3,4-tri-O-benzyl-L-
fucopyranoside was obtained. © 1999 Elsevier Science Ltd. All rights reserved.
Keywords: Allyl fucoside; Deallylation; Wacker–Hoechst reaction
sodium hydride to give compound 3 (also an
a,b mixture). To compound 3 in 10:1 (v/v)
tetrahydrofuran–water, were added the equiv-
alent amount of palladium chloride and
cuprous chloride to effect the modified
Mereyala deallylation process [7]. The reac-
tion mixture was exposed to air and stirred
vigorously instead of oxygen bubbling accord-
ing to Mereyala. This modification had
proved effective in our previous work [9,10].
An unexpected compound 5 was obtained
in 46% overall yield and some material de-
composed (the a, b anomers, 5a and 5b, could
be isolated by column chromatography with
8:1 cyclohexane–EtOAc as eluent, a:bꢀ2:1).
No deallylated compound 4 was detected in
these experiments even when the reaction time
was extended.
The allyl group is a useful protective group
for the synthesis of oligosaccharides because it
can be readily introduced and removed. There
are various methods for deallylation under
different conditions [1–7]. In an attempt to
prepare 2,3,4-tri-O-benzyl- -fucopyranose (4),
L
the allyl group was chosen to protect the
hydroxyl group at the anomeric position of
L
-fucose, based on the consideration that the
allyl group could be removed under very mild
conditions as described by Mereyala et al. [7],
whereas the common procedure for prepara-
tion of compound 4 via the methyl glycoside
needs relatively more drastic conditions to
remove the methyl group [8].
Allylation of L-fucose with acidified allyl
alcohol under reflux for 1 h gave a mixture of
the allyl a- and b-fucosides (2a, 2b) in ꢀ4:1
a/b ratio, detected by TLC, which was directly
O-benzylated with benzyl bromide and
The mechanism of the reaction seems to
involve the addition of a water molecule to the
carbon–carbon double bond, followed by oxi-
dation by palladium chloride, a mechanism
similar to the Wacker–Hoechst reaction [11].
* Corresponding author. Fax: +86-10-6201-5584.
0008-6215/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(99)00055-5

192
Z.-J. Li et al. / Carbohydrate Research 317 (1999) 191–192
Physical and spectroscopic data are
7.26–7.39 (m, 15 H, aromatic H); 13C NMR
(500 MHz, CDCl3): lC (ppm) 16.87 (C-6),
27.07 (CH3CO), 70.71, 73.28, 74.31, 74.75,
75.30, 76.20, 79.27, 82.52 (C-2,3,4,5, 3×
recorded for compounds 5a and 5b. The a and
b anomers could be discriminated by the
3
chemical shifts and JC–H of C-1.
3
PhCH2, CH2COCH3), 103.51 (C-1, JC–H
2-Oxopropyl 2,3,4-tri-O-benzyl-h-
L
-fucopyr-
158.9 Hz), 127.69–138.77 (aromatic C),
207.31 (CH3CO). Anal. Calcd for C30H34O6:
C, 73.45; H, 6.99. Found: C, 73.51; H, 6.77.
anoside (5a).—Colorless syrup, [h]D−7.8° (c
0.51, CHCl3); IR: 3058, 3026, 2948, 1719,
1449, 1168 cm−1; FABMS: m/z 497 [M+
1
Li]+, 513 [M+Na]+; H NMR (500 MHz,
CDCl3): lH (ppm) 1.10 (d, 3 H, J 6.4 Hz,
H-6), 2.11 (s, 3 H, COCH3), 3.66–5.00 (m, 13
H, H-1,2,3,4,5, 3×PhCH2–, CH2COCH3),
7.21–7.42 (m, 15 H, aromatic H); 13C NMR
(500 MHz, CDCl3): lC (ppm) 16.72 (C-6),
26.53 (CH3CO), 67.05, 72.10, 73.24, 73.42,
75.00, 76.21, 77.84, 79.09 (C-2,3,4,5, 3×
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