Synthesis of long-chain monosaccharides via the coupling of three 'normal' sugar units via Wittig type methodology: Unusual removal of the benzyl group under basic conditions

Article abstract of DOI:10.1016/j.tetasy.2011.10.001

The reaction of diacetonogalactose phosphonate 6 with 2,3:4,5-di-O- isopropylidene-d-arabinose (7) afforded C₁₂-higher sugar enone with an E-geometry across the double bond, which was converted into the fully protected C₁₁-aldehyde 16. This compound was very unreactive and resistant toward the Wittig type and Tebbe reagents, but under PTC conditions, underwent a reaction with stabilized sugar phosphonate to afford C ₁₈-enone 17. Very surprisingly unusual removal of the benzyl blocks under these conditions was observed.

Full text of DOI:10.1016/j.tetasy.2011.10.001

Tetrahedron: Asymmetry 22 (2011) 1757–1762
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Synthesis of long-chain monosaccharides via the coupling of three ‘normal’
sugar units via Wittig type methodology: unusual removal of the benzyl
group under basic conditions
⇑
Maciej Cieplak, Sławomir Jarosz
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warszawa, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of diacetonogalactose phosphonate 6 with 2,3:4,5-di-O-isopropylidene-D-arabinose (7)
Received 8 September 2011
Accepted 14 October 2011
Available online 16 November 2011
afforded C12-higher sugar enone with an E-geometry across the double bond, which was converted into
the fully protected C11-aldehyde 16. This compound was very unreactive and resistant toward the Wittig
type and Tebbe reagents, but under PTC conditions, underwent a reaction with stabilized sugar phospho-
nate to afford C18-enone 17. Very surprisingly unusual removal of the benzyl blocks under these condi-
tions was observed.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Bu3SnH / heat
CHO
Br
SnBu3
BuLi
O
PPh3 / CBr4
The term ‘higher carbon’ is assigned to heptoses, octoses, and
nonoses, which play an important role in the biology of living cells;
many synthetic methods have been developed to prepare these
important compounds.1 Much less is known about sugars contain-
ing more than 10 carbon atoms in the chain,2 which are very
demanding synthetic targets and might possess interesting confor-
mational and complexing properties. Their synthesis can be real-
ized by iterative homologation of a parent monosaccharide by a
small unit (e.g. C1–C33).
A more economic method is represented by an elongation of a
parent sugar with a longer sub-unit, either an achiral molecule4
or, more conveniently, an already functionalized unit. One of the
first examples of the latter approach was presented by Secrist in
his synthesis of hikozamine, in which an unstabilized sugar phos-
phorane reacted with sugar aldehydes to afford unsaturated higher
monosaccharides.5 Soon after, other syntheses proposing conve-
nient routes to such complicated molecules appeared in the
literature.6,7
Br
Sug
Sug
Sug
1. BuLi
2. Sug1-CHO
1. BuLi
2. Sug1-CHO
OH
3. H2 / Lindlar
OH
Sug
Sug1
Sug
*
Sug1
*
Figure 1. Synthesis of higher sugar allylic alcohols via acetylenic methodology.
or phosphonates 4 with sugar aldehydes, which provided higher
sugar enones 5. The highly stereoselective reduction of the car-
bonyl group with zinc borohydride to give 3,7,10,11 followed by
the oxidation of the double bond afforded the higher sugars 1
(Fig. 2).7,10,12
Functionalization at both terminal positions of 1 (having 12–15
carbon atoms) should afford much higher analogues. Elongation at
either end requires orthogonal protecting groups enabling the
facile deprotection at both terminal positions.
Herein we report a methodology, which allows for the conve-
nient coupling of two sugar sub-units via their terminal positions.
The first route involves conversion of the parent monosaccharide
into an acetylene (according to the method reported by Corey8)
which was then transformed into the E- or Z-higher sugar allylic
alcohols (Fig. 1).7,9 The second route was based on the coupling
of two units via the reaction of stabilized sugar phosphoranes 2
The easily available ‘diacetono-galactose’ phoshonate 613 and
2,3:4,5-di-O-isopropylidene-D
-arabinose 714 were chosen as the
starting materials. The reaction of both units under mild PTC con-
ditions provided higher sugar enone 8 in almost quantitative yield
(Scheme 1). Reduction of the carbonyl group with zinc borohydride
afforded, as expected,11 single stereoisomer 9. The
D
-glycero-con-
⇑
Corresponding author. Tel.: +48 22 632 32 21; fax: +48 22 632 66 81.
E-mail address: sljar@icho.edu.pl (S. Jarosz).
figuration at the newly created stereogenic center was proven by
0957-4166/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2011.10.001

1758
M. Cieplak, S. Jarosz / Tetrahedron: Asymmetry 22 (2011) 1757–1762
OH
with Mo2(OAc)4; the positive Cotton effect indicated unambigu-
(R)
pentose
or
Sug1
ously at the (7R,8R)-configuration for the newly created stereogen-
ic centers.
When such a cis-dihydroxylation reaction was performed on the
free allylic alcohol 9, much lower stereoselectivity (2:1) was
observed but with the same (R,R)-stereoisomer predominating
(see Section 3).
The protection of both hydroxyl groups in 12 gave compound
13, which was then subjected to selective hydrolysis. The terminal
C11–C12-isopropylidene group was removed out preferentially to
Sug
hexose
OH OH
1
O
(R)
Sug1
HO
PPh3
Sug
3
2
Sug
key-step
Zn(BH4)2
or
O
OMe
OMe
Sug1-CHO
O
Sug1
O
P
O
O
H
BnO BnO
11
Sug
O
O
9
4
Sug
i
OH
5
12
5
13
OH
O
OBn
O
Figure 2. Synthesis of higher carbon sugars via phosphorane and phosphonate
methodology.
1
14
O
its conversion into the known15 1,2:3,4-di-O-isopropyli-dene-
glycero- -galacto-heptose 11.
D
-
ii
a-D
O
O
Functionalization of the three carbon bridge connecting the su-
gar parts followed a route already reported7,10 (Scheme 1). Osmy-
lation of the double bond in 9 should lead to products whose
configuration can be assigned on the basis of Kishi’s rule.16 This
assignment, however, should always be verified by proof. It is
known that the CD spectra of the molybdenum complexes of opti-
cally active threo-diols, allow us to connect the sign of the Cotton
effect with their absolute configuration.17 This methodology was
used in our synthesis.
OH
9
iii
O
9
O
11
15
O
16
Scheme 2. Selective deprotection of the terminal position in higher carbon sugar.
Reagents and conditions: (i) H2SO4 (c 0.46), H2O/THF 3:1; (ii) NaIO4; (iii) NaBH4.
O
16
O
H
O
O
O
P
OMe
OMe
O
O
6, K2CO3, toluene, 18-crown-6, rt
O
O
then Jones' oxid.
O
O
O
+
O
6
Ara
O
O
O
H
O
BnO BnO
OBn
O
O
7
11
O
O
DAGA
9
5
O
i
OR
O
O
O
O
O
ii
O
1
DAGA
DAGA
Ara
17
O
8
+
iii
18
OH
9. R = H
iv
O
O
O
H
O
BnO BnO
10. R = Bn
O
O
OH
6
7
14
11
O
13
9
v
8
5
12
10
11
O
O
O
O
O
O
H
BnO OR O
O
1
11
(
)
R
O
O
5
18
O
(
)
R
CD for 12
lmax (De')
320
12
O
positive
Cotton
effect
O
OR
O
removal of the benzyl group (followed by oxidation under work-up
conditions)
1 O
(+0.8069)
COSY: H11-H10, H10-H9, H9-H8; no cross peaks H7, 8 and H6, 7
12.
R = H
vi
13. R = Bn
O
Scheme 1. Preparation of fully protected higher sugar. Reagents and conditions: (i)
K2CO3, toluene, 18-crown-6, rt; (ii) Zn(BH4)2 ether; (iii) O3, MeOH, then NaBH4; (iv)
BnBr, NaH, DMF; (v) (from 10) OsO4, NMO (cat.), 77%; (vi) BnCl, toluol, NaOH (50%),
TEBACl.
+
O
O
O
H
O
BnO O
O
O
7
O
O
9
10
O
OBn
O
O
O
1
19
Protection of the free hydroxyl group in 9 provided ether 10,
which was treated with OsO4 to afford the single stereoisomeric
diol in good yield. The structure of 12 is proposed on the basis of
Kishi’s rule, and was verified by the CD spectrum of its complex
Scheme 3. Synthesis of a 18-carbon sugar. Unexpected removal of the benzyl block
under basic conditions.

M. Cieplak, S. Jarosz / Tetrahedron: Asymmetry 22 (2011) 1757–1762
1759
afford diol 14 (Scheme 2), which was then converted into aldehyde
16 (characterized as alcohol 15) by periodate cleavage.
The most plausible explanation of this phenomenon is shown in
Figure 3. Normal decomposition of intermediate 20 led to the ex-
pected higher sugar enone 17. However, since this expected rear-
rangement may not be quick enough, other processes are
possible including the attack of the benzyloxy-oxygen functional-
ity from the C-7 or C-8 positions with elimination of the anion of
6 and cyclization to a hemiacetal (6-exo-tet and 5-exo-tet, respec-
tively). The resulting hemiacetals react with phosphonate 6 to af-
ford the products lacking the benzyl group.
The reaction of various nucleophiles with 16 should allow easy
access to highly functionalized long-chain polyhydroxylated com-
pounds. However, this aldehyde was very resistant toward simple
Wittig reagents as well as Tebbe reagents. The low reactivity of
other (similar) higher sugar aldehydes toward such species was
also previously observed, although we found that they did react
with stabilized phosphoranes under high pressure or with sugar
phosphonates under PTC conditions.7
The reaction of aldehyde 16 with phosphonate 6 was successful
and afforded the desired enone (in low yield), which was contam-
inated with two side-products, which were identified ‘indirectly’.
In order to remove the excess aldehyde from the post-reaction
mixture we used an oxidative work-up; thus, the crude product
was treated first with the Jones’ reagent and then subjected to col-
umn chromatography (Scheme 3).
Three compounds were isolated: the desired enone 17 and two
more products whose molecular mass was lower by 92 Daltons, to
which structures 18 and 19 were assigned on the basis of the NMR
data. The 13C NMR spectrum of 18 indicated the absence of one
benzyl group (only two signals of the quaternary C-atoms at d:
138.06 and 138.01 ppm were seen) and the presence of two signals
of the carbonyl group (d: 210.38 and 195.86 ppm). This indicated
the removal of one benzyl group leading to an alcohol which was
oxidized to a ketone under the work-up conditions.
2. Conclusion
The most important result of this study was the observation of
the deprotection of the benzyl ethers under basic conditions. To
the best of our knowledge this is the first example of the removal
of such a group in basic media. Also important is the selective
hydrolysis of one out of four isopropylidene groups in a C-12 high-
er sugar, which opens up the possibility of the preparation of poly-
hydroxylated systems with long chains.
3. Experimental
3.1. General
The NMR spectra of all compounds/mixtures were measured in
CDCl3 solutions (unless otherwise stated) with the following spec-
trometers: Bruker DRX 500 (at 303 K) equipped with a TBI 500SB
HC/BB-D-05 Z-G probehead, Varian-NMR-vnmrs 500 (at 298 K)
equipped with a PFG Auto XDB (1H–19F/15N–31P 5 mm) direct pro-
behead and Varian-NMR-vnmrs 600 (at 298 K) equipped with a
PFG Auto XID (1H/15N–31P 5 mm) indirect probehead. The concen-
tration of all solutions containing pure compounds used for NMR
measurements was about 20–30 mg in 0.6 cm3 of solvent, whereas
in the case of mixtures 40–60 mg of sample in 0.6 cm3 of solvent.
Standard experimental conditions and standard Bruker and Varian
(Chempack 4.1) programs were used. To assign the structures, the
following 1D and 2D experiments were employed: 1H selective
NOESY/TOCSY, 2D COSY/NOESY, 2D 1H–13C gradient selected HSQC
and HMBC optimized for 1J(C–H) = 146 Hz and nJ(C–H) = 8 Hz,
respectively. The 1H and 13C NMR spectroscopic data are given rel-
ative to the TMS signal at 0.0 ppm. The 1H and 13C NMR signals of
the phenyl in the benzyl groups occurring at the typical d values
are omitted for simplicity. Mass spectra were recorded with an
ESI/MS Mariner (PerSeptive Biosystem) mass spectrometer. Optical
rotations were measured with a Digital Jasco polarimeter DIP-360
(k = 589 nm) for solutions in CHCl3 (c 1) at room temperature. Col-
umn chromatography was performed on silica gel (Merck, 70–230
The precise assignment of the structure of this di-ketone was
carried out on the basis of its COSY spectrum. The H8 signal in
the spectrum of 18 showed a cross peak only to H9; alternatively
the H6 correlated only to H5, which indicated that the initial hy-
droxyl located at the C7-position was oxidized to a ketone
(Scheme 3). Similarly, structure 19 was also proven.
The hypothesis that compounds 18 and 19 are secondary prod-
ucts resulting from the decomposition of enone 17 should be ex-
cluded, since this enone was stable under the reaction conditions
for at least 5 days, which means that removal of the benzyl group
occurred directly from the aldehyde during the reaction. Moreover,
aldehyde 16 by itself was also resistant under PTC in the absence of
phosphonate 6.
DAGA
O
13
PTC
O
10
16 +
6
17
O-
P
O
O
RO
OR
20
5-exo-tet
BnO
or 230–400 mesh); HPLC analyses were conducted with
a
6
O
Shimadzu Preparative Liquid Chromatograph LC-8A equipped with
UV detector SPD-6A. Organic solutions were dried over anhydrous
magnesium sulfate. THF was distilled from potassium prior
to use.
7
8
O
BnO
10
O
BnO
O
10
8
6
BnO
7
(MeO)2P(O)
O
BnO
O-
O-
20'
19
DAGA
3.2. Synthesis of the enone 8: 1,2,3,4,9,10,11,12-tetra-O-isopro-
pylidene-7,8-dideoxy-7,8-didehydro-D-arabino–D-galacto-
dodec-7(E)-ene-1,5-pyranos-6-ulose
O
PTC, 6 then [O]
6-exo-tet
18
OBn
BnO
O
To a solution of aldehyde 7 (0.58 g, 2 mmol) and phosphonate 6
(0.8 g, 2.1 mmol) in dry toluene (60 mL) anhydrous potassium
carbonate (0.59 g) was added followed by a catalytic amount of
18-crown-6 (10 mg). After vigorous stirring at room temperature
(until disappearance of the aldehyde; 48 h), water (100 mL) and
AcOEt (100 mL) were added. The organic phase was separated
and the aqueous one extracted with ethyl acetate (2 ꢀ 50 mL).
The combined organic solutions were washed with water (2 ꢀ 50
7
6
O
BnO
8
O
8
10
BnO
10
6
(MeO)2P(O)
7
O
O-
O
O-
BnO
20''
DAGA
O
Figure 3. Proposed mechanism for the removal of the benzyl group under the PTC
conditions.

1760
M. Cieplak, S. Jarosz / Tetrahedron: Asymmetry 22 (2011) 1757–1762
mL), brine (50 mL), dried and concentrated, and the product was
isolated by column chromatography (hexane–ethyl acetate, 9:1
3.5. Benzylation of the allylic alcohol 9 to give 1,2,3,4,
9,10,11,12-tetra-O-isopropylidene-6-O-benzyl-7,8-dideoxy-7,8-
to 4:1) as a colorless oil (980 mg, 2 mmol, 98%). [
a
]
D = ꢁ90.1 (c 1,
didehydro-D-gluco–D-galacto-dodec-7(E)-ene-1,5-pyranose 10
CHCl3); 1H NMR (500 MHz) d: 7.02 (dd, J7,8 = 15.8, J8,9 = 4.4 Hz, H-
8), 6.90 (dd, J7,9 = 1.6 Hz, H-7), 5.67 (d, J1,2 = 5.0 Hz, H-1), 4.65
(dd, J3,4 = 7.8 Hz, J2,3 = 2.3 Hz, H-3), 4.62 (dd, J4,5 = 2.0 Hz, H-4),
4.58 (ddd, J9,10 = 7.6 Hz, H-9), 4.37 (dd, H-2), 4.33 (d, H-5), 4.15–
4.05 (m, 1H, H-11), 3.97–3.91 (m, 2H, H-120, 12), 3.72 (dd,
J9,10 = J10,11 = 7.6 Hz, H-10), 1.57–1.30 (8 ꢀ s, CMe2); 13C NMR d:
196.4 (C-6), 144.0 (C-8), 124.8 (C-7), 110.3, 109.8, 109.7, 108.9
(4 ꢀ CMe2), 96.5 (C-1), 81.1, (C-10), 79.3 (C-9), 73.3 (C-5), 72.4
(C-4), 70.7 (C-3), 70.4 (C-2), 67.4 (C-11 + 12), 27.0, 26.7, 26.3,
26.0, 25.9, 25.2, 24.8, 24.3 (8 ꢀ CMe2). Anal. Calcd for
C24H36O10 + ½H2O: C, 58.41; H, 7.56. Found: C, 58.51; H, 7.62.
To a solution of alcohol 9 (11.35 g, 23 mmol) in DMF (500 mL)
containing imidazole (100 mg), excess sodium hydride (2 g of a
60% solution in mineral oil) was added and the mixture was stirred
at room temperature for 30 min. After cooling to 0 °C, benzyl bro-
mide (5 mL, 42 mmol) was added and stirring was continued for
two days. The mixture was diluted with ether (500 mL) and the ex-
cess hydride decomposed with methanol (100 mL). Water
(250 mL) was then added. The organic phase was separated, and
the aqueous one extracted with ether (3 ꢀ 100 mL). The combined
organic layers were washed with water (100 mL) and brine
(100 mL), dried, and concentrated. Product 10 was isolated by col-
umn chromatography (hexane–ethyl acetate, 9:1 to 4:1) as a
3.3. Reduction of enone 8 to give 1,2,3,4,9,10,11,12-tetra-O-
isopropylidene-7,8-dideoxy-7,8-didehydro-D-gluco–D-galacto-
dodec-7(E)-eno-1,5-pyranose 9
brownish oil (8.56 g, 15 mmol, 63.5%). [
a]D = ꢁ23.8 (c 1, CHCl3);
1H NMR d: 5.9–5.81 (m, 2H, H-7, 8), 5.46 (d, J1,2 = 4.9 Hz, H-1),
4.63 (d, J = 11.2 Hz,1H, PhCH2O), 4.57 (dd, J3,4 = 8 Hz, J2,3 = 2.2 Hz,
H-3), 4.51 (dd, J4,5 = 1.7 Hz, H-4), 4.45 (d, J = 11.2 Hz, 1H, PhCH2O),
4.41 (dd, J5,6 = 7.7 Hz, J6,7 = 5.0 Hz, H-6), 4.25 (dd, H-2), 4.18 (dd,
J11,12 = 6.1 Hz, H-11), 4.05 (m, 2H, H-9, 120), 3.93 (dd,
To a cooled (to 0 °C) solution of enone 8 (11.68 g, 24 mmol) in
dry ether (500 mL), zinc borohydride (30 mL of a 0.5 M solution
in dry ether) was added. The mixture was stirred at 0 °C for
2.5 h, and then diluted with diethyl ether (250 mL). The excess zinc
borohydride was decomposed with water (100 mL). Dilute (5%)
sulfuric acid (50 mL) was then added. The organic phase was sep-
arated, washed with water (3 ꢀ 50 mL), brine (50 ml), dried, and
concentrated. Product 9 was isolated by column chromatography
(hexane–ethyl acetate, 9:1 to 5:1) as an oil (11.35 g, 23 mmol,
0
J12,12 = 8.5 Hz, H-12), 3.77 (dd, H-5), 3.69 (dd, J10,11 = 9.2 Hz, H-
10), 1.47–1.29 (8s, CMe2); 13C NMR d: 131.9, 131.4 (C-8 + C-7),
109.5, 108.8, 108.4 (4 ꢀ CMe2), 96.3 (C-1), 81.3 (C-5), 79.1 (C-6),
77.2 (C-9), 76.0 (C-11), 71.3, 70.9 (C-2), 70.7 (C-3), 70.4 (C-4),
69.52 (C-5), 68.1, 66.3 (C-12), 38.7, 30.6, 30.4, 28.9, and 26.99,
26.95, 26.5, 26.1, 26.0, 25.2, 25, 24.3 (8 ꢀ CMe2). Anal. Calcd for
C31H44O10: C, 64.57; H, 7.69. Found: C, 64.47; H, 7.72.
96.7%). [
a
]
D = ꢁ29.4 (c 1, CHCl3); 1H NMR (500 MHz) d: 6.01
(ddd, J7,8 = 15.6, J6,7 = 5.0, J7,9 = 0,9 Hz, H-7), 6.93 (ddd, J8,9 = 6.0,
J6,8 = 1.4 Hz, H-8), 5.56 (d, J1,2 = 5.0 Hz, H-1), 4.61 (dd, J3,4 = 8.0,
J2,3 = 2,4 Hz, H-3), 4.47 (dd, J4,5 = 2.0 Hz, H-4), 4.42 (m, 1H, H-9),
4.38 (m, 1H, H-6), 4.31 (dd, 1H, H-2), 4.16–4.05 (m, 2H, H-11,
3.6. The cis-dihydroxylation of the protected allylic alcohol 10
to give 1,2,3,4,9,10,11,12-tetra-O-isopropylidene-6-O-benzyl-
7,8-dihydroxy-D-manno-D-erytro–D-galacto–dodec-1,5-
pyranose 12
120), 3.93 (dd, J12,12 = 8.5, J11,12 = 5.4 Hz, H-12), 3.76 (dd,
0
J10,11 = 7.7 Hz, H-10), 3.7 (dd, J5,6 = 6.7 Hz, H-5), 1.74 (1H, OH)
1.50–1.32 (8 ꢀ s, CMe2); 13C NMR d: 132.6 (C-7), 129.6 (C-8),
109.6, 109.5, 109.4, 108.6 (4 ꢀ CMe2), 96.5 (C-1), 81.1 (C-10),
79.5 (C-9), 76.5 (C-11), 71.4 (C-6), 71.3 (C-4), 70.8 (C-3), 70.5 (C-
2), 69.2 (C-5), 66.82 (C-12), 26.98, 26.94, 26.6, 26.0, 25.9, 25.3,
24.9, 24.3 (8 ꢀ CMe2). Anal. Calcd for C24H38O10: C, 59.49; H,
7.87. Found: C, 59.32; H, 8.15.
To a solution of 10 (152 mg, 0.26 mmol) in THF (5 mL), water
(0.5 mL), tert-butanol, and 4-N-morpholine oxide (100 mg) were
added followed by osmium tetraoxide (0.5 mL of a 2% solution in
tert-BuOH) and the mixture was stirred in room temperature for
ten days. Aqueous NaHSO3 (1 mL) was added to decompose
OsO4. The mixture was stirred for 30 min, diluted with toluene
(15 mL), filtered, and concentrated. The residue was dissolved in
ethyl acetate (25 mL), washed with brine (2 ꢀ 10 mL), dried, and
concentrated to give product 12, which was isolated by column
chromatography (hexane–ethyl acetate, 9:1 to 4:1) as an oil
(70 mg). The unreacted starting material (80 mg) was recovered
and oxidized again with OsO4 to afford another crop of 12 (the
overall yield: 125 mg, 0.22 mmol, 78%). Anal. Calcd for
3.4. Determination of the configuration at the newly created
stereogenic center (C-6) in allylic alcohol 9
Allylic alcohol 9 (101 mg, 0.2 mmol) was dissolved in methy-
lene chloride (20 mL) containing small amounts of methanol
(1 mL). The mixture was cooled to ꢁ78 °C and ozone (ca. 3% in
oxygen) was bubbled through the solution until blue color per-
sisted (5 min.). Dimethyl sulfide (4 equiv) was added and the
mixture was left at rt for 24 h. Then sodium borohydride was
added, the mixture stirred at rt for another 24 h, and partitioned
between water (20 mL) and ethyl acetate (10 mL). The organic
phase was separated and the aqueous one extracted with ethyl
acetate (3 ꢀ 10 mL). The combined organic solutions were
washed with water (10 mL), brine (2 ꢀ 10 mL), dried, and con-
centrated. Chromatographic purification (hexane–EtOAc, 9:1 to
4:1) of the residue afforded the desired heptose (36 mg,
0.12 mmol, 59%), which was acetylated under the standard
conditions (Py–Ac2O–DMAP) to afford the known heptose 11.
1H NMR (200 MHz) d: 5.58 (d, 1H, J1,2 = 4.8 Hz, H-1), 5.26–5.19
(m, 1H, H-6), 4.71 (dd, 1H, J3,4 = 9,6 Hz, J2,3 = 2,6 Hz, H-3), 4.65
(dd, 1H, J4,5 = 2,2 Hz, H-4), 4.41 (dd, 1H, H-2), 4.35 (dd, 1H,
C31H46O12: C, 60.97; H, 7.59. Found: C, 60.91; H, 7.71.
The configuration at the newly created stereogenic centers (C7,
C8) was assigned by the CD spectroscopy of the complex of the diol
with di-molybdenum tetracetate (Table 1). The positive Cotton ef-
fect indicated a (7R,8R)-configuration for diol 12.
3.7. The cis-dihydroxylation of the free allylic alcohol 9
Allylic alcohol 9 (150 mg, 0.31 mmol) was oxidized according to
the same procedure as for 10. The product was isolated by column
chromatography (hexane–ethyl acetate, 9:1 to 4:1) as a yellowish
Table 1
Assignment of the configuration of diol 12 by CD
kmax
(
D
e0
)
kmax
(
D
e0
)
Cotton effect
+
Configuration
J7,7 = 4 Hz, J6,7 = 2 Hz, H-7), 4.29 (dd, 1H, J6,7 = 10,6 Hz, H-70),
4.1 (dd, 1H, J5,6 = 9 Hz, H-5).
0
0
271 (ꢁ0.4106)
320 (+0.8069)
(7R,8R)

M. Cieplak, S. Jarosz / Tetrahedron: Asymmetry 22 (2011) 1757–1762
1761
oil (127 mg; 79%). The crude product was benzylated under stan-
dard conditions to afford a mixture of two diastereoisomeric prod-
ucts in a 2:1 ratio (as determined by the integration of the signal of
H-1 at d: 5.30 and 5.14 ppm). The main isomer was identical in all
respects to compound 13 prepared below.
added, and the slurry was stirred vigorously at room temperature.
After 15 min, a solution of diol 14 (157 mg, 0.21 mmol) in methy-
lene chloride (0.4 mL) was added and the mixture was stirred at
30 °C for 4 days. Next, it was filtered and concentrated to afford
aldehyde 16 as a colorless oil (68.5 mg, 0.09 mmol, 45%). This prod-
uct was used for further transformations without purification.
3.8. Benzylation of the diol 12 to give 1,2,3,4,9,10,11,12-tetra-O-
isopropylidene-6,7,8-tri-O-benzyl-
D
-manno-
D
-erythro–
D-
3.11. Reduction of the aldehyde 16 to give 1,2,3,4,9,10-tri-O-
galacto–dodec-1,5-pyranose 13
isopropylidene-6,7,8-tri-O-benzyl-11-hydroxy-
D-xylo-D-
erythro– -galacto–undec-1,5-pyranose 15
D
To a solution of 12 (2.6 g, 4.5 mmol) in toluene (180 mL), 50%
aqueous NaOH (140 mL), benzyl chloride (4.8 mL, 42 mmol), and
Bu4NCl were added, and the mixture was stirred vigorously at
room temperature for two days. Then it was partitioned between
toluene (500 mL) and water (250 ml); the layers were separated,
and the aqueous one extracted with ether (3 ꢀ 50 mL). The com-
bined organic solutions were washed with water (2 ꢀ 50 mL),
brine (50 mL), dried, concentrated, and the crude product 13
(8.5 g) was used for hydrolysis without further purification.
A small amount of the crude product was purified by column
chromatography (hexane–EtOAc, 9:1 to 5:1) for analytical pur-
To a solution of crude 16 (65 mg, 0.09 mmol) in dry ether
(10 mL), NaBH4 (30 mg) was added, and the mixture was stirred
at room temperature overnight; then it was partitioned between
water (5 mL) and AcOEt (5 mL). The organic layer was separated,
and the aqueous one extracted with ether (2 ꢀ 5 mL). The com-
bined organic solutions were washed with water (2 ꢀ 5 mL), brine
(5 mL), dried, and concentrated to afford product 15 as colorless oil
(57.9 mg, 0.08 mmol, 89%). [
a
]
D = ꢁ35 (c 1, CHCl3); 1H NMR
(600 MHz) d: 5.5 (d, J1,2 = 4.8 Hz, H-1), 4.98 (d, J = 11.3 Hz, 1H,
PhCH2O), 4.81 (d, J = 11.1 Hz, 1H, PhCH2O), 4.75 (d, J = 11.1 Hz,
1H, PhCH2O), 4.7–4.57 (m, 4H, H-3 + 3 ꢀ PhCH2O), 4.5 (dd,
J4,5 = 1.5 Hz, J3,4 = 8.1 Hz, H-4), 4.28 (dd, J5,6 = 9.8 Hz, H-5), 4.26
(dd, J2,3 = 2.3 Hz, H-2), 4.18 (dd, J6,7 = J7,8 = 7.1 Hz, H-7), 4.12 (dd,
H-6), 4.04 (m, 1H, H-10), 3.97 (dd, J8,9 = 7.2 Hz, H-8), 3.92 (dd,
poses. [a]
D = ꢁ26.3 (c 1, CHCl3); 1H NMR (500 MHz) d: 5.49 (d,
1H, J1,2 = 4.8 Hz, H-1), 4.95 (d, J = 11.3 Hz, 1H, PhCH2O), 4.82–4.66
(m, 4H, PhCH2O), 4.62–4.58 (2H, H-3 + PhCH2O), 4.51 (dd,
J = 1.6 Hz, J = 8.14 Hz, H-4), 4.35–4.23 (m, 3H, H-2, 5, 8), 4.18 (dd,
J = 6.5 Hz, J = 13.0 Hz, H-9), 4.14-3.93 (m, 6H, H-6, 7, 9, 10, 12,
120), 1.46–1.26 (8s, CMe2); 13C NMR d: 109.5, 109.2, 108.8, 108.7
(4 ꢀ CMe2), 96.2 (C-1), 81.4 (C-7), 80.1 (C-9), 79.4 (C-10), 78.2,
77.7, 77.2 (C-6, 8, 11), 75.5, 74.9, 72.8 (3 ꢀ PhCH2O), 71.1 (C-4),
70.9 (C-2), 70.7 (C-3), 66.5 (C-5), 66.3 (C-12), 27.3, 27.2, 26.6,
0
J9,10 = 7.2 Hz, H-9), 3.72 (dd, J10,11 = 1.8 Hz, J11,11 = 11.7 Hz, H-11),
3.61 (dd, J10,11 = 4.8 Hz, H-110), 1.44–1.27 (6s, CMe2); 13C NMR d:
0
109.1, 108.8, 108.7 (3 ꢀ CMe2), 96.1 (C-1), 82.0 (C-8), 79.9 (C-10),
78.8 (C-7 + C-9), 77.7 (C-6), 75.3, 74.7, 72.9 (3 ꢀ PhCH2O), 71.0
(C-4), 70.8 (C-7), 70.7 (C-3), 66.6 (C-2), 63.4 (C-11), 27.2, 26.8,
26.1, 25.8, 25.1, 24.4 (6 ꢀ CMe2). m/z Calcd for C41H52O11Na:
743.34018. Found: 743.33829.
26.1, 25.8, 25.5, 25.2, 24.4 (8 ꢀ CMe2). Anal. Calcd for C45H58O12
:
C, 68.34; H, 7.39. Found: C, 68.45; H, 7.49.
3.9. Hydrolysis of 13 to give 1,2,3,4,9,10-tri-O-isopropylidene-
3.12. Reaction of aldehyde 16 with phosphonate 6 to give
6,7,8-tri-O-benzyl-11,12-dihydroxy-
D
-manno-
D
-erytro–
D-
1,2,3,4,9,10,15,16,17,18-penta-O-isopropylidene-6,7,8-tri-O-
galacto–dodec-1,5-pyranose 14
benzyl-11,12-dideoxy-11,12-didehydro–D-galacto-D-xylo-D-
erythro– -galacto–octadeka-1,5;14,18-dipyranos-13-ulose 17
D
To a solution of crude 13 (8.5 g) in THF (600 mL) and water
(200 mL), sulfuric acid (1.9 mL) was added and the mixture was
stirred at room temperature for 12 days. Toluene (400 mL) was
then added, after which the organic layer was separated and the
aqueous one extracted with ether (3 ꢀ 50 mL). The combined or-
ganic layers were washed with concd aq NaHCO3, water
(3 ꢀ 50 mL), dried, concentrated, and the product was isolated by
column chromatography (hexane–ethyl acetate, 9:1 to 4:1) as a
yellow oil (1.61 g, 49%). The recovered substrate was subjected
again to hydrolysis to give, after chromatography, another crop
of product (overall yield of 14: 2.31 g, 3.08 mmol, 70%).
To a solution of aldehyde 16 (50 mg, 0.07 mmol) and phospho-
nate 6 (30.7 mg, 0.08 mmol) in dry toluene (2 mL) anhydrous
potassium carbonate (20 mg) was added followed by catalytic
amounts of 18-crown-6 (5 mg). The mixture was then stirred for
two days at room temperature. Next, it was partitioned between
water (5 mL) and AcOEt (5 mL). The organic phase was separated
and the aqueous one extracted with ethyl acetate (2 ꢀ 5 mL). The
combined organic solutions were washed with water (2 ꢀ 5 mL),
brine (5 mL), dried, and concentrated.
The residue was dissolved in acetone (15 mL) to which Jones’
reagent was added (0.3 mL) and the mixture was stirred for 3 h.
The excess oxidant was decomposed with iso-propanol (1 mL).
After the addition of toluene (20 mL), the solution was concen-
trated under vacuum (to remove acetone), washed with aqueous
NaHCO3 (3 ꢀ 5 mL), brine (5 mL), dried, and concentrated. The
crude material was purified by column chromatography (hex-
ane–ethyl acetate, 9:1 to 4:1) to afford enone 17 as a colorless oil
[
a]
D = ꢁ55.9 (c 1, CHCl3); 1H NMR (500 MHz) d: 5.53 (d,
J1,2 = 4.8 Hz, H-1), 5.12 (d, J = 11.1 Hz, 1H, PhCH2O), 4.86 (d,
J = 11.3 Hz, 1H, PhCH2O), 4.78 (d, J = 11.3 Hz, 1H, PhCH2O), 4.71–
4.52 (m, 5H, H-3, 4 and 3 ꢀ PhCH2O), 4.35 (dd, J4,5 = 1.1 Hz,
J5,6 = 9.4 Hz, H-5), 4.29 (dd, J2,3 = 2.3 Hz, H-2), 4.23–4.18 (m, 2H,
H-6, 8), 4.04 (d, J6,7 = J7,8 = 7.8 Hz, H-7), 3.96–3.86 (m, 2H, H-9,
0
0
10), 3.71 (dd, J12,12 = 3.6 Hz, J12,12 = 11.4 Hz, H-12), 3.65–3.55 (m,
3H, H-11, 120), 2.38–2.23 (m), 1.7 (–OH) 1.47–1.27 (6s, CMe2);
13C NMR d: 109.8, 108.8, 108.6 (3 ꢀ CMe2), 96.1 (C-1), 82.6 (C-7),
81.4 (C-9), 80.2 (C-10), 77.8 and 76.0 (C-6, 8), 75.5, 75.2, 72.8
(3 ꢀ PhCH2O), 73.0 (C-11), 71.0 (C-4), 70.8 (C-2), 70.6 (C-3), 66.8
(C-5), 63.2 (C-12), 27.1, 26.5, 26.1, 25.8, 25.1, 24.3 (6 ꢀ CMe2). Anal.
Calcd for C42H54O12: C, 67.18; H, 7.25. Found: C, 67.33; H, 7.57.
(14.2 mg, 0.015 mmol, 21%). [
(500 MHz) d: 6.94 (dd, J10,11 = 5.5 Hz, J11,12 = 15.7 Hz, H-11), 6.9
a
]
D = ꢁ47.2 (c 1, CHCl3); 1H NMR
(d, H-12), 5.65 (d, J1,2 = 4.95 Hz, H-1), 5.1 (d, J1 ,2 = 4.95 Hz, H-10),
4.87 (d, J = 11.3 Hz, 1H, PhCH2O), 4.78 (d, J = 10.8 Hz, 1H, PhCH2O),
4.76 (d, J = 10.5 Hz, 1H, PhCH2O), 4.72–4.65 (m, 2H, H-10, PhCH2O),
4.64–4.55 (m, 4H, H-3, H-16, H-15, PhCH2O) 4.52 (d, J = 11.1 Hz,
1H, PhCH2O), 4.48 (dd, 1H, J4,5 = 1.6 Hz, J3,4 = 8 Hz, H-4), 4.35 (dd,
J2,3 = 2.6 Hz, H-2), 4.31–4.28 (m, 3H, H-5, H-8, H-14), 4.26 (dd,
0
0
3.10. Synthesis of aldehyde 16
J2 ,3 = 2.3 Hz, H-20), 4.0 (dd, 1H, J9,10 = 4.5 Hz, J8,9 = 8 Hz, H-9), 3.96
(dd, 1H, J5,6 = J6.7 = 9.3 Hz, H-6), 3.93 (dd, 1H, J7,8 = 8.4 Hz, H-7),
1.48–1.28 (10s, CMe2); 13C NMR d: 196.0 (C-13), 144.1 (C-11),
0
0
To a suspension of silica gel (400 mg) in methylene chloride
(3.2 mL), sodium periodate (55.6 mg), and water (0.4 mL) were

1762
M. Cieplak, S. Jarosz / Tetrahedron: Asymmetry 22 (2011) 1757–1762
139.1 (PhCH2 quat. C-atom), 139 (2 ꢀ PhCH2 quat. C-atom), 126.0
(C-12), 109.7, 109.5, 108.9, 108.8, 108.7 (5 ꢀ CMe2), 96.4 (C-1),
96.2 (C-10), 81.9 (C-9), 81.5 (C-7), 78.6 (C-8), 77.6 (C-6), 77 (C-
10), 75.6, 74.9 (2 ꢀ PhCH2O), 73.3 (C-14), 72.8 (PhCH2O), 72.2 (C-
15), 71.1 (C-4), 70.8 (C-17), 70.68, 70.65 (C-3, C-16), 70.4 (C-2),
66.3 (C-5), 26.95, 26.78, 26.07, 25.98, 25.79, 25.7, 25.1, 24.8, 24.4,
24.1 (10 ꢀ CMe2). m/z Calcd for C54H68O16Na: 995.43996. Found:
995.44143.
J3,4 = 10.2 Hz, H-4), 1.49–1.26 (10s, CMe2); 13C NMR d: 212.2 (C-
8), 196.1 (C-13), 145.8 (C-11), 138.5 (PhCH2 quat. C-atom), 138.0
(PhCH2 quat. C-atom), 123.2 (C-12), 110.0, 109.8, 109.1, 108.8,
108.7 (5 ꢀ CMe2), 96.5 (C-1), 96.3 (C-18), 80.2, 80.0, 79.5, 79.0,
75.5, 73.7, 73.2, 72.3, 70.7, 70.6, 70.5, 70.4, 70.3, 66.7, 27.1, 27.0,
26.05, 25.97, 25.89, 25.85, 24.9, 24.8, 24.5, 24.3 (10 ꢀ CMe2).
Acknowledgement
When the reaction of 16 (100 mg, 0.14 mmol) and phosphonate
6 (61 mg, 0.16 mmol) was prolonged for 4 days, three products
were obtained: the desired enone 17 (18.9 mg, 0.019 mmol, 14%),
and two isomeric side products 18 and 19 in a 37% yield
(45.3 mg, 0.051 mmol). Integration of the anomeric protons (at d:
5.63 and 5.67) allowed us to assign a 1:1 ratio of 18 and 19. HRMS
for the mixture 18/19; m/z Calcd for C47H60O16Na: 903.37736.
Found: 903.38171. This mixture was separated by preparative
TLC (Silica Gel 60 F254, 0.5 mm, hexane–ethyl acetate, 9:1) into
pure isomers, which were characterized separately.
This work was financed by the Ministry of Science and Higher
Education, Grant No. N N204 092635.
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3.13. 1,2,3,4,9,10,15,16,17,18-Penta-O-isopropylidene-6,8-di-O-
benzyl-11,12-dideoxy-11,12-didehydro–
D
-galacto-
D-xylo-D-
glycero–D-galacto–octadeca-1,5:14,18-dipyranose-7,13-diulose
18
[a
]
D = ꢁ13.6 (c 1, CHCl3); 1H NMR (500 MHz) d: 7.0 (dd,
J10,11 = 4.3 Hz, J11,12 = 15.8 Hz, H-11), 6.82 (dd, J10,12 = 1.6 Hz, H-
12), 5.63 (d, J1,2 = 4.7 Hz, H-1), 5.49 (d, J17,18 = 5 Hz, H-18), 4.75
(d, J5,6 = 9.4 Hz, H-6), 4.72–4.68 (m, 1H, H-10), 4.65–4.6 (m, 3H,
H-3, 16, 1 ꢀ PhCH2O), 4.59 (d, 1H, H8), 4.58–4.55 (m, 2H, H-15,
1 ꢀ PhCH2O), 4.47 (dd, J4,5 = 1.3 Hz, J3,4 = 8.1 Hz, H-4), 4.42–4.39
(m, 2H, 2 ꢀ PhCH2O) 4.36 (dd, J2,3 = 2.3 Hz, H-2), 4.33 (d,
J14,15 = 2.2 Hz, H-14), 4.3 (dd, J16,17 = 2.4 Hz, H-17), 4.09 (dd, H-5),
3.87 (dd, J = 6.6 Hz, J = 8 Hz, H-9), 1.49–1.28 (10s, CMe2); 13C
NMR d: 210.4 (C-7), 195.9 (C-13), 144.3 (C-11), 138.06 (PhCH2
quat. C-atom), 138.01 (PhCH2 quat. C-atom), 124.8 (C-12), 111.1,
109.8, 109.2, 109.1, 108.9 (5 ꢀ CMe2), 96.4 (C-1), 96.0 (C-18),
84.2, 80.2, 80.0, 79.2, 73.4 (PhCH2O), 72.4 (PhCH2O), 72.2, 72.0,
70.7, 70.7, 70.41, 70.38, 70.32, 69.8, 26.90, 26.88, 26.03, 26.02,
25.98, 25.8, 25.0, 24.8, 24.4, 24.3 (10 ꢀ CMe2).
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benzyl-11,12-dideoxy-11,12-didehydro–
D-galacto-D-threo-L-
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[
a
]
D = ꢁ17.8 (c 1, CHCl3); 1H NMR (500 MHz) d: 7.1 (dd,
J10,11 = 4.3 Hz, J11,12 = 15.8, H-11), 6.84 (dd, J10,12 = 1.6 Hz, H-12),
5.67 (d, J1,2 = 5.1 Hz, H-1), 5.48 (d, J17,18 = 5.1 Hz, H-18), 4.88 (d,
J = 10.2 Hz, 1H, PhCH2O), 4.75 (m, J9,10 = 9.5 Hz, H-10), 4.72 (d,
J = 11.5 Hz, 1H, PhCH2O), 4.68–4.56 (m, 5H, H-3, H-16, H-7,
2 ꢀ PhCH2O), 4.43 (dd, 1H, J15,16 = 1.7 Hz, J14,15 = 8.2 Hz, H-15),
4.38–4.35 (m, 2H, J2,3 = 2.2 Hz, H-14, H-2), 4.33–4.28 (m,
J16,17 = 2.4 Hz, H-17), 4.14 (dd, 1H, J4,5 = 2 Hz, J5,6 = 9.7 Hz, H-5),
4.03–3.97 (m, 2H, J6,7 = 7.1 Hz, H-9, H-6) 3.89 (dd, 1H,
15. Jarosz, S. Pol. J. Chem. 1992, 66, 1853–1858.
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