The synthesis of higher carbon sugars: A study on the rearrangement of higher sugar allylic alcohols

Article abstract of DOI:10.1016/j.tetasy.2011.04.021

The C12 higher sugar enone 15 (prepared from the corresponding phosphonate and aldehyde) was highly stereoselectively reduced to the d-glycero-allylic alcohol. The epimeric l-glycero-isomer was obtained by the non-selective reduction of the higher enone under Luche conditions. The separate treatment of both allylic alcohols with triflic anhydride provided the corresponding triflates, which in situ underwent allylic rearrangement with the elimination of one of the benzyl groups (from the aldehyde part of the molecule). The stereochemical aspects of this transformation are also discussed.

Full text of DOI:10.1016/j.tetasy.2011.04.021

Tetrahedron: Asymmetry 22 (2011) 780–786
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
The synthesis of higher carbon sugars: a study on the rearrangement
of higher sugar allylic alcohols
⇑
Mykhaylo A. Potopnyk, Piotr Cmoch, Maciej Cieplak, Agnieszka Gajewska, 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:
Received 22 March 2011
Accepted 20 April 2011
The C12 higher sugar enone 15 (prepared from the corresponding phosphonate and aldehyde) was highly
stereoselectively reduced to the D-glycero-allylic alcohol. The epimeric L-glycero-isomer was obtained by
the non-selective reduction of the higher enone under Luche conditions. The separate treatment of both
allylic alcohols with triflic anhydride provided the corresponding triflates, which in situ underwent allylic
rearrangement with the elimination of one of the benzyl groups (from the aldehyde part of the molecule).
The stereochemical aspects of this transformation are also discussed.
Dedicated to Professor Janusz Jurczak on the
occasion of his 70th birthday
Ó 2011 Elsevier Ltd. All rights reserved.
activation
1. Introduction
(C)n
Higher carbon sugars containing more than 10 carbon atoms in
the chain, because of their structural complexity, are interesting
synthetic targets. Their synthesis can be realized by iterative
homologation of a parent monosaccharide by a small unit (e.g.,
C1–C31), but a much more convenient method consists of the elon-
gation of a parent sugar with a longer sub-unit. This fragment may
be represented by an achiral unit (such as for example highly acti-
vated dienes, which upon reaction with sugar-derived aldehydes
afford the precursors of these targets2) or more conveniently by al-
ready functionalized block.3
OH
O
OH
O
n = 0,1,2
Sug2
Sug1
R
R
O
O
We have previously reported on a convenient methodology for
the coupling of two sugar sub-units via their terminal C-atoms,
which allowed us to connect two sugars either directly or via a
Cn-carbon bridge3e,4 (Fig. 1).
Sug1
Sug2
Figure 1. Synthesis of higher sugars by coupling of two properly activated subunits.
One of the most useful methods for such a coupling is repre-
sented by the reaction of stabilized Wittig reagents such as 1 or,
more conveniently, phosphonates 2 with sugar aldehydes; this al-
lows for the facile preparation of enones of type 3 (Fig. 2).5
The reduction of the carbonyl group with zinc borohydride af-
O
OH
O
O
P
OMe
OMe
O
ref. 5
Sug
Sug1-CHO
K2CO3 / 18-crown-6
2
fords the higher sugar allylic alcohols with the D-glycero-configura-
ref. 4
tion at the newly created stereogenic center with very high
stereoselectivity. Such results can be explained by the complexa-
tion of the carbonyl and the ring oxygen atoms of the sugar moiety
with the zinc cation, which allows the attack of the hydride ion to
occur from the less hindered side of the molecule (Fig. 3).6
However, a problem occurs in the synthesis of the opposite
O
Sug1
O
Sug1-CHO
PPh3
Sug
heat
3
Sug
1
L
-glycero-isomer. The SN2 inversion (either under Mitsunobu7 or
Figure 2. Synthesis of higher carbon sugars via phosphorane and phosphonate
methodology.
‘classical’ conditions) in many cases is not applicable to such com-
plex derivatives.
⇑
Corresponding author. Tel.: +48 22 343 23 22; fax: +48 22 632 66 81.
E-mail addresses: slawomir.jarosz@icho.edu.pl, sljar@icho.edu.pl (S. Jarosz).
0957-4166/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2011.04.021

M. A. Potopnyk et al. / Tetrahedron: Asymmetry 22 (2011) 780–786
781
OBn
Sug1
Sug1
D-glycero
O
O
P
H(-)
BnO
5
OH
O
O
OH
5
i.
H
OMe
OBn
Zn2+
Zn(BH4)2
O
MeO
BnO
O
1
O
OMe
11
10
OBn OBn
iv.
ii.
Figure 3. Stereoselective reduction of higher sugar enones with zinc borohydride.
O
1
OBn
OBn OBn
14
Recently we have reported that attempts to invert the configu-
ration in such alcohols 5 and 8 do not result in an SN2 product, but
provide the compound arising from the rearrangement of the mol-
ecule. This process was highly stereoselective (see Fig. 4) which al-
lowed us to propose an SN20 mechanism to this transformation.8
Herein a more detailed study on such a transformation is provided.
5
OR
1
HO
v.
L-xylose
OH OBn
12: R = H
iii.
13: R = Bn
Scheme 1. Preparation of phosphonate 11 and aldehyde 14. Reagents and
conditions: (i) (1) CrO3/H2SO4/acetone, rt, 75%; (2) MeOH/H2SO4, rt, 92%; (3)
MeP(O)(OMe)2/BuLi, THF, ꢀ78 °C, 90% (Ref. 5); (ii) (1) Ac2O/H2SO4, rt, 92%; (2)
LiAlH4, THF, ꢀ78 °C, 95%; (iii) (1) TsOH/acetone, rt, 72%; (2) BnBr/NaH, DMF, rt, 73%;
(3) TsOH, MeOH/THF, rt, 80%; (iv) NaIO4, Et2O/H2O, rt, 92%; (v) (1) EtSH, HCl, 0 °C,
45%; (2) BnBr, NaH, DMF, rt, 70%; (3) HgCl2, CdCO3, acetone/H2O, reflux, 73% (Ref. 9).
BnO BnO
8
11
6
O
Glu
O
BnO
BnO
6
8
BnO
O
HO
O
5
4
was more suitable and afforded both stereoisomers 16 and 17 in the
ratio 37:63 (Scheme 2).
BnO
MeO
1
Tf2O
O
O
BnO BnO
OBn
H
O
OBn
Gluc
8
12
6
BnO
BnO
O
O
11
6
H
O
11
OBn
6
11
+
8
i.
TfO
BnO
O
OBn
Gluc
O
OBn OBn
8
14
6
7
1
BnO
OMe
'Glu'
15
ii.
iii.
Glu
HO
6
6
H
11
OH
OH
8
8
Tf2O
8
OBn
8
Glu
+ 16
Glu
6
6
8
9
BnO
OBn
H
OH
17
ratio 16 : 17 = 37 : 63
16
Figure 4. The SN20 rearrangement of higher sugar allylic alcohols 5 and 8 induced
BnO
BnO
6
iv.
with triflic anhydride.
O
OH
1
18
2. Results and discussion
OMe
Scheme 2. Preparation of 15, 16 and 17. Reagents and conditions: (i) K2CO3,
toluene, 18-crown-6, rt, 63%; (ii) Zn(BH4)2, Et2O, 0 °C, 94%; (iii) NaBH4/CeCl3,
CH2Cl2/MeOH (1:1), rt, 94%; (iv) (1) O3, CH2Cl2, ꢀ78 °C, then NaBH 89%.
For our studies, the readily available glucose phosphonate 115a
and 2,3,4,5-tetra-O-benzyl-
sis of both sub-units was initiated from the common precursor,
methyl 2,3,4-tri-O-benzyl- -glucopyranoside (Scheme 1, see also
L-xylose 13 were selected. The synthe-
D
A study on the rearrangement of the allylic alcohols was per-
Section 4). Alternatively, aldehyde 14 can be prepared from L-xy-
formed on both allylic alcohols 16 and 17. The treatment of the
lose according to the known methodology.9
L-glycero allylic alcohol 17 with triflic anhydride provided an insep-
Reaction of both units 11 and 14 under mild PTC conditions10
arable mixture of two stereoisomeric compounds in a ratio 2.8:1,12
to which structures 19 and 20 were assigned (Scheme 3) on the ba-
sis of the spectroscopic data. The molecular ion (m/z = 885.2) indi-
cated the loss of the benzyl group, which strongly suggested the
rearrangement of the molecule with the formation of the tetrahy-
drofuran ring. The confirmation of the tetrahydrofuran structure of
both products of the cyclization (the 5-exo-trig mode13) was deter-
mined from the NMR experiments. In the 1H NMR spectrum of the
mixture two sets of olefinic signals were observed. The first one
(main stereoisomer) was seen at d = 5.81 and 6.07 ppm, whereas
a second set for the minor isomer was centered at d = 5.72 and
6.03 ppm, respectively.
provided the expected
a,b-unsaturated ketone 15 in good yield
(Scheme 2). The reduction of the carbonyl group with zinc borohy-
dride afforded, as expected,3e,6 allylic alcohol 16.
The (R)-configuration at the newly created stereogenic center
was proven by chemical correlations. Ozonolytic cleavage of the
double bond followed by reduction of the crude ozonide with so-
dium borohydride furnished the known8
D-glycero-D-gluco-heptose
18 (Scheme 2).
As already mentioned, there is no direct method for the stereose-
lective reduction of the higher sugar enones of type 15 to the -glycero
L
isomers; we decided, therefore, to use the classical (non-selective)
process, that is, reduction with sodium borohydride. However, treat-
ment of enone 15 with NaBH4 provided a complicated mixture of at
least four compounds resulting from 1,2- and 1,4-additions of the
Further proof of the structure came from the chemical correla-
tions, which also enabled the precise assignment of the configura-
tion at the newly created stereogenic centers (at C-8) in these new
products. Ozonolytic cleavage of the double bond in both stereo-
isomers followed by reduction of the resulting ozonides and
hydride ion to the
a,b-unsaturated enone system. On the other hand,
the reduction of enone 15 under the conditions described by Luche11

782
M. A. Potopnyk et al. / Tetrahedron: Asymmetry 22 (2011) 780–786
carbon signals. For instance: protons at d = 4.51 and 4.57 ppm cor-
OBn
H
OH
OBn
12
relate with carbon at d = 70.42 ppm, whereas protons at d = 4.38
and 4.48 ppm with carbon at d = 82.63 ppm. An opposite relation-
ship (protons at 3.52 and 3.63 ppm correlate with carbon at
d = 72.23 ppm) was also observed. These 3J(C–H) couplings seem
to be of significant importance in the structure assignment.
BnO
BnO
11
OBn
6
O
OBn OBn
17
1
i.
Glu
OMe
The reaction of the D-glycero-isomer 16 under the same condi-
tions was more complex. In addition to tetrahydrofurans 19 and
20 (present in the ratio 3:1 as assigned by integration of the 1H
NMR signals at d = 5.81 and 5.72 ppm, respectively) another iso-
meric compound with the same (by MS) formula was formed.
The structure of this unexpected compound can be deduced on
the basis of the spectroscopic data recorded for the (inseparable)
mixture of the products formed in this rearrangement. This un-
known product also had a double bond (signals at d = 5.86 and
5.96 ppm), which suggested that a similar rearrangement occurred,
but another benzyloxy group was involved in the process
(Scheme 4).
OTf
6
OBn
OBn
OBn OBn
17a
5-exo-trig
Glu
6
Glu
O
11
8
O
OBn
+
OBn
BnO
OBn
BnO
OBn
20
19
ratio 19 : 20 = 2.8 : 1
i.
ii.
16
OBn
BnO
O
OBn
OTf
OBn
11
OBn
Glu
23
O
OBn
9
+
19 + 20
+
OBn
Gluc
OBn
12
6
10
(ratio 3.4 : 1)
OBn
OBn OBn
BnO
OBn
5-exo-trig
22
21
ratio 21 : 22 = 3.3 : 1
+
12
Scheme 3. Rearrangement of the
L-glycero stereoisomer 17 induced by triflic
BnO
OBn
OBn
O
anhydride. Reagents and conditions: (i) Tf2O, 2,6-lutidine, CH2Cl2, ꢀ78 °C to rt; (ii)
12
11
O3, MeOH, then NaBH4, then benzylation.
O
Gluc
OBn
OBn
or
OBn
protection of the hydroxyl group as benzyl ether should provide
24a
Gluc
24b
either the C2- or C1-symmetrical derivatives 21 and 22 and methyl
6-exo-trig
2,3,4,6-tetra-O-benzyl-a-D
-glucoside14 23.
4-exo-trig
Gluc
OBn
12
Indeed, such a sequence of reactions yielded three (chromato-
graphically isolable) compounds: 23 and two others (easily distin-
guished by the 13C NMR spectra: d = 81.3, 79.0, 73.4, 72.2, 68.4 and
83.7 for the main isomer and 82.7, 82.6, 80.1, 73.4, 73.2, 71.5, 71.4,
70.4, 68.3 for the ‘non-symmetrical’ derivative) with tetrahydrofu-
ran structures 21 and 22 in the ratio: 3.3:1. These structures were
proposed on the basis of the spectroscopic data (1D and 2D NMR
experiments). The C2 symmetry of 21 caused crucial simplification
of the 1H and 13C NMR spectra, whereas in case of its diastereoiso-
meric form 22 all individual 1H/13C NMR signals were present for
each unique 1H/13C nucleus of the unsymmetrical structure. The
assignment of the 1H/13C signals of the non-symmetrical isomer
(based on the 2D spectra) is presented in Figure 5.
or
OBn
O
OBn
3-exo-trig
24c
Scheme 4. Triflation of alcohol 16. Reagents and conditions: (i) Tf2O, 2,6-lutidine,
CH2Cl2, ꢀ78 °C to rt.
Three eventual structures (in agreement with Baldwin’s rules13
)
arising from the 6-exo-trig 24a, or 4-exo-trig 24b, or 3-exo-trig 24c
cyclizations might be considered. The detailed analysis of the
1H–13C g-HSQC and g-HMBC, as well as the 13C NMR spectra, ex-
cluded the three- and six-membered rings. Oxirane rings are well
featured by the position of the carbon nuclei in the 13C NMR spec-
tra, which are ca. 55–60 ppm15; the 13C NMR spectrum of the reac-
tion mixture contained no oxirane carbon resonances.
4.51
4.50
4.60
3.72
3.77
3.52
3.63
4.57
The 3J(C–H) couplings, which play an important role in the
1H–13C g-HMBC experiments, allowed the determination of the
structure of the compounds studied. The methylene protons of
the ‘last’ benzyl group in the six-membered derivative 24a (located
at the C11) should correlate to the methine carbon C11 and not to
methylene carbon C12. On the other hand, in the four-membered
compound 24b the correlation of the ‘last’ OBn group (this time lo-
cated at the C12) should be visible to the methylene carbon C12
and not to the methine carbon.
(72.23)
(73.37)
(68.27)
(70.42)
O
Ph
Ph
4.25
4.11
O
O
(80.09)
(82.71)
3.97
(82.63)
4.49
4.38
4.48
(72.23)
3.94
(83.70)
O
(71.46)
O
Ph
Ph
The detailed analysis of the 1H–13C g-HMBC spectrum for the
Figure 5. The NMR signals of the unsymmetrical isomer 22.
reaction mixture after rearrangement of the D-glycero alcohol 16
Careful analysis of the 2D g-HMBC spectrum of 22 led to the fol-
lowing observation; the methylene protons of all benzyl groups
correlate with appropriate neighboring methylene or methine
indicated that the methylene protons of this benzyl group (at
d = 4.46 and 4.57 ppm) in this unknown structure correlate with
the methylene carbon at d = 68.35 ppm instead of the methine

M. A. Potopnyk et al. / Tetrahedron: Asymmetry 22 (2011) 780–786
783
carbon at 80.16 ppm. This excluded the structure containing the
16
anti
six-membered ring. Since the third (besides 19 and 20) five-mem-
bered structure is not possible, we should expect the four-mem-
bered ring as in 24b. As reported in the literature,15a,16 the 13C
Ph
H
H
NMR chemical shifts for the
an/furan and oxetane rings are very similar and do not allow us to
distinguish between the possible forms.
a
carbons to the oxygen atom for pyr-
OTf
O
OBn
OBn
Sug
O
Sug
OBn
OBn
Although the formation of a tetrahydrofuran derivative was
expected under these conditions, the stereochemical outcome, that
is, the presence of both stereoisomers, was surprising, especially in
the light of our recent results8 shown in Figure 4. Two mecha-
nisms: SN10 or SN20 may be considered; both are observed in nucle-
ophilic substitution at the allylic carbon atom. The SN10 process
proceeding via a planar allylic cation should give the same mixture
of the products regardless of the configuration of the higher sugar
allylic alcohols 16 and 17. This is not the case; although the pro-
portion of tetrahydrofuran derivatives 19 and 20 is similar for both
rearrangements, we observed an ‘additional’ product, olefin 24, in
26a
BnO
OBn
20
syn
Ph
OBn
H
Sug
O
O
H
OTf
OBn
Sug
OBn
BnO
OBn
OBn
reaction of the D-glycero-isomer 16 with triflic anhydride.
19
26b
The SN20 substitution at the allylic carbon can occur either via
syn- or anti-addition.17 The stereochemical outcome of the rear-
rangement of the L-glycero-alcohol 17 is presented in Figure 6.
The syn-attack of the benzyloxy group located at the C-11 position
provides the ‘unsymmetrical’ tetrahydrofuran 20, while the anti-
attack leads to a ‘symmetrical’ derivative 19. No attack leading to
olefin 24 was noted.
anti or syn
Ph
BnO
O
H
H
OTf
17
24
Bn
Sug
O
OBn
syn
26c
Sug
Ph
H
O
O
Figure 7. The SN20 mechanism of allylic substitution in 16.
TfO
Sug
OBn
H
OBn
11
OBn
OBn
BnO
20
OBn
derivatives can be highly stereoselectively converted into the
glycero-allylic alcohols by reduction of the carbonyl group with
zinc borohydride. The -glycero-isomers can be prepared in low
D-
25a
L
yield by a non-selective reduction of the enones under Luche con-
ditions. Direct inversion of the configuration at the allylic carbinol
center was not possible. Instead of the expected SN2 product, com-
pounds arising from the allylic rearrangement with elimination of
the benzyl group were formed as a mixture of stereoisomers.
anti
Ph
OBn
H
Sug
O
TfO
Sug
H
O
OBn
OBn
4. Experimental
4.1. General
OBn
BnO
OBn
25b
19
Figure 6. The SN20 mechanism of allylic substitution in 17.
The NMR spectra of all compounds/mixtures were measured in
CDCl3 solutions (unless otherwise stated) with the following spec-
trometers: Bruker DRX 500 (at temperature 303 K) equipped with
a TBI 500SB HC/BB-D-05 Z-G probehead, Varian-NMR-vnmrs500
On the other hand, a similar reaction performed on the D-glyce-
ro-isomer was more complex. In addition to the formation of both
tetrahydrofuran derivatives 19 and 20 (in the ratio: 3:1), another
product 24 was also formed (Fig. 7). However, we do not have an
explanation of this phenomenon.
Cyclizations arising from the attack of the benzyloxy group
(although proceeding via a simple SN2 process) and subsequent re-
moval of the benzyl moiety are known.18 The process observed by
us resembles similar reactions, in which the double bond is acti-
vated by iodine and then attacked by an oxygen atom bearing
the benzyl group (5-exo-trig; Fig. 7).19
(at temperature 298 K) equipped with
a PFG Auto XDB
(1H–19F/15N–31
P
5 mm) direct probehead and Varian-NMR-
vnmrs600 (at temperature 298 K) equipped with a PFG Auto XID
(1H/15N–31P 5 mm) indirect probehead. The concentration of all
solutions containing pure compounds used for NMR measurements
was about 20–30 mg in 0.6 cm3 of solvent, whereas in case of mix-
tures 40–60 mg of sample in 0.6 cm3 of solvent. Standard experi-
mental 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 opti-
mized for 1J(C–H) = 146 Hz and nJ(C–H) = 8 Hz, respectively. The 1H
and 13C NMR spectroscopic data are given relative to the TMS signal
at 0.0 ppm. The 1H and 13C NMR signals of phenyl in benzyl groups
3. Conclusion
Reaction of sugar phosphonates with sugar aldehydes offers a
convenient and attractive route to higher sugar enones. Such useful

784
M. A. Potopnyk et al. / Tetrahedron: Asymmetry 22 (2011) 780–786
occurring at the typical d values were omitted for simplicity. Mass
spectra were recorded with an ESI/MS Mariner (PerSeptive Biosys-
tem) 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. Column chromatography was per-
formed on silica gel (Merck, 70–230 or 230–400 mesh); HPLC anal-
565.2561, found [M+Na]+ 565.2576. Anal. Calcd for C34H38O6
(542.66): C, 75.25; H, 7.06. Found: C, 75.03; H, 7.05.
To a solution of diol 13 (1.05 g, 1.93 mmol) in Et2O/H2O (40/
20 mL) NaIO4 (455 mg, 2.13 mmol) was added and the reaction
mixture was stirred at rt for 24 h. Then the organic phase was sep-
arated and the aqueous one extracted with AcOEt (2 ꢁ 50 mL). The
combined organic solutions were washed with water (30 mL),
brine (20 mL), dried, and concentrated. The crude aldehyde 14
(918 mg, 92 %) (identical with the prepared from xylose9) was used
in the next step without further purification.
yses were conducted with
a 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.
4.3. Synthesis of enone 15
4.2. The preparation of 2,3:4,5-tetra-O-benzyl-L-xylose 14 from
methyl 2,3,4-tri-O-benzyl- -glucoside 10
a
-D
To a solution of aldehyde 14 (817 mg, 1.6 mmol) and phospho-
nate 115a (910 mg, 1.6 mmol) in dry toluene (100 mL), anhydrous
potassium carbonate (300 mg) was added followed by 18-crown-
6 (50 mg) and stirred for 12 h at room temperature. Water
(100 mL) was added, the organic phase was separated and the
aqueous one extracted with AcOEt (150 mL). The combined organic
solutions were washed with water (2 ꢁ 50 mL), brine (50 mL),
dried, concentrated, and the product was isolated by column chro-
matography (hexane–ethyl acetate, 7:1 to 5:1) to afford 15
To a solution of 10 (3.0 g, 6.5 mmol) in acetic anhydride
(50 mL), sulfuric acid (1 mL) was added. The mixture was stirred
at rt for 2 h and then diluted with CH2Cl2 (200 mL) and poured into
H2O–ice (200 mL). The mixture was carefully neutralized with
NaHCO3, the phases were separated, and the aqueous was ex-
tracted with CH2Cl2 (3 ꢁ 200 mL). The combined organic solutions
were washed with brine (100 mL), dried, filtered, concentrated,
and the crude product was reduced with LiAlH4 under the standard
(979 mg, 1.0 mmol, 63%) as an oil. [a]
D = +3.9 (c 1, CHCl3); 1H
conditions to afford the known20 triol 12. [
a]D = +12.8 (c 1, CHCl3);
NMR (600 MHz) d: 6.96 (1H, dd, J8,7 16.0 Hz, J8,9 5.5 Hz, H-8),
6.55 (1H, dd, J7,8 16.0 Hz, J7,9 1.4 Hz, H-7), 4.96 (1H, d, J 10.9 Hz,
benzylic H), 4.82 (1H, d, J 10.9 Hz, benzylic H), 4.79 (1H, d, J
12.1 Hz, benzylic H), 4.75 (1H, d, J 10.8 Hz, benzylic H), 4.64 (1H,
d, J 11.1 Hz, benzylic H), 4.63 (2H, d, J 11.6 Hz, 2 ꢁ benzylic H),
4.57 (2H, d, J 11.0 Hz, 2 ꢁ benzylic H), 4.56 (1H, d, J1,2 3.5 Hz, H-
1), 4.50 (1H, d, J 11.8 Hz, benzylic H), 4.44 (1H, d, J 11.7 Hz, benzylic
H), 4.38 (1H, d, J 11.6 Hz, benzylic H), 4.37 (1H, d, J 11.6 Hz, ben-
zylic H), 4.34 (1H, d, J5,4 9.9 Hz, H-5), 4.27 (1H, d, J 11.7 Hz, benzylic
H), 4.23 (1H, ddd, J9,10 5.5 Hz, H-9), 4.03 (1H, dd, J3,4 9.3 Hz, J3,2
9.4 Hz, H-3), 3.71 (1H, m, H-11), 3.63–3.69 (2H, m, H-10, H-4),
1H NMR (400 MHz) d: 4.67 (1H, d, J 2.6 Hz), 4.65 (s, OH), 4.59 (1H,
d, J 1.6 Hz), 3.90–3.78 (5H, m), 3.77–370 (4H, m), 3.68–3.61 (3H,
dd, J 7.2 Hz, 4.2 Hz + t, J 3.5 Hz), 2.80–2.40 (4H, wide, OH); 13C
NMR (100 MHz) d: 137.8, 137.5, 137.4, (3 ꢁ Cquat), 79.2, 79.1,
76.7 (C-2, C-3, C-4), 74.2, 73.6, 73.1 (PhCH2O), 71.1 (C-5), 63.5,
61.7 (C-1, C-6). Anal. Calcd for C27H32O6ꢂ1/2H2O (452.55 + 1/
2 18.02): C, 70.26; H, 7.21. Found: C, 70.59; H, 7.08.
To a solution of triol 12 (2.35 g, 5.2 mmol) in acetone (30 mL), p-
toluenesulfonic acid (17 mg, 0.1 mmol) was added and the mixture
was stirred at room temperature for 24 h.
Then it was diluted with CH2Cl2 (100 mL) and solid NaHCO3
(150 mg) was added. The mixture was stirred vigorously at rt for
1 h, the precipitates were removed by filtration and the filtrate
was concentrated under reduced pressure to afford 2,3,4-tri-O-
0
3.56 (1H, dd, J12,11 4.6 Hz, J12,12 10.0 Hz, H-12), 3.52 (1H, dd, H-
2), 3.47 (1H, dd, J12 ,11 5.3 Hz, H-120), 3.31 (3H, s, OCH3); 13C NMR
0
(125 MHz) d: 194.8 (C-6), 145.6 (C-8), 138.6, 138.4, 138.10,
138.07, 138.05, 138.0, 137.7 (Cquat, 6 ꢁ Ph), 128.1 (C-7), 98.8 (C-
1), 81.7 (C-3), 80.7 (C-10), 79.4 (C-2), 79.1 (C-9), 79.0 (C-4), 78.2
(C-11), 75.9, 75.0, 74.8, 73.6, 73.3, 72.9, 71.9, (7 ꢁ OCH2Ph), 72.5
(C-5), 69.6 (C-12), 55.8 (CH3); HR-MS (ESI) m/z calcd for
benzyl-5,6-O-isopropylidene-a-D-glucitol. This compound (1.72 g,
3.5 mmol) was dissolved in DMF (25 mL) to which sodium hydride
(60% dispersion in mineral oil; 160 mg, 4 mmol) was carefully
added and the mixture was stirred vigorously for 30 min. Benzyl
bromide (0.48 mL, 4 mmol) was then added and the mixture was
stirred at rt for another 5 h. The excess hydride was decomposed
by the careful addition of water and the mixture was partitioned
between water (50 mL) and ether (100 mL). The organic layer
was separated and the aqueous one extracted with ether
(2 ꢁ 100 mL). Combined organic solutions were washed with
water (50 mL) and brine (30 mL), dried, and concentrated to yield
C
62H64O10Na 991.4392, found [M+Na]+ 991.4398. Anal. Calcd for
C62H64O10 (969.17): C, 76.84; H, 6.66. Found: C, 76.83; H, 6.62.
4.4. Reduction of the enone 15
Method 1: To a cooled (to 0 °C) solution of enone 15 (194 mg,
0.2 mmol) in dry ether (10 mL), zinc borohydride (0.7 mL of a
0.5 M solution in dry ether) was added, and the mixture was stir-
red at 0 °C for 30 min. The excess hydride was decomposed with
water (10 mL), the organic phase was separated, washed with di-
luted (5%) sulfuric acid (10 mL), water (10 mL), dried, concentrated,
and the product 16 (183 mg; 94 %) was isolated by column chro-
matography (hexane–ethyl acetate, 7:1 to 2:1) as oil. Data for 16:
1,2,3,4-tetra-O-benzyl-5,6-O-isopropylidene-
mixture was used in the next step without further purification.
To solution of the above obtained derivative (1.48 g,
D-glucitol. The crude
a
2.54 mmol) in MeOH/THF (30/30 mL), p-toluenesulfonic acid
(17 mg, 0.1 mmol) was added, the mixture was stirred at rt for
24 h and partitioned between water (100 mL) and ethyl acetate
(150 mL). The organic phase was separated, washed with 10% NaH-
CO3 (20 mL), dried, concentrated, and the product was isolated by
column chromatography (hexane–ethyl acetate, 3:1 to 1:2) to af-
[a]
D = +23.6 (c 1, CHCl3); 1H NMR (600 MHz) d: 5.82 (1H, dd, J7,8
15.8 Hz, J7,6 6.8 Hz, H-7), 5.68 (1H, ddd, J8,7 15.8 Hz, J8,9 7.2 Hz,
J8,6 0.9 Hz, H-8), 4.99 (1H, d, J 10.8 Hz, benzylic H), 4.89 (1H, d, J
11.0 Hz, benzylic H), 4.77 (1H, d, J 11.0 Hz, benzylic H), 4.73 (1H,
d, J 11.6 Hz, benzylic H), 4.70 (1H, d, J 12.1 Hz, benzylic H), 4.65
(1H, d, J 11.7 Hz, benzylic H), 4.63 (1H, d, J 11.4 Hz, benzylic H),
4.56 (1H, d, J 12.1 Hz, benzylic H), 4.56 (1H, d, J 10.3 Hz, benzylic
H), 4.54 (1H, d, J 11.6 Hz, benzylic H), 4.52 (1H, d, J 11.2 Hz, ben-
zylic H), 4.52 (1H, d, J1,2 3.8 Hz, H-1), 4.37 (1H, d, J 12.8 Hz, benzylic
H), 4.34 (1H, d, J 12.8 Hz, benzylic H), 4.32 (1H, m, H-6), 4.31 (1H, d,
J 11.7 Hz, benzylic H), 4.10 (1H, dd, J9,10 5.6 Hz, H-9), 4.01 (1H, dd,
J3,4 9.2 Hz, H-3), 3.80 (1H, ddd, H-11), 3.75 (1H, dd, J5,6 3.9 Hz, H-5),
ford 1,2,3,4-tetra-O-benzyl-
[a]
D-glucitol (13; 1.1 g, 80 %) as an oil.
D = +14.4 (c 1, CHCl3); 1H NMR (500 MHz) d: 4.73 (1H, d, J
11.6 Hz, benzylic H), 4.54–4.65 (5H, m, 5 ꢁ benzylic H), 4.40–
4.46 (2H, m, 2 ꢁ benzylic H), 3.95 (1H, dd, J 9.2 Hz, 5.2 Hz), 3.79–
3.85 (2H, m), 3.68–3.73 (2H, m), 3.59–3.67 (2H, m), 3.39 (1H, d, J
4.0 Hz, OH), 2.14 (1H, t, J 6.1 Hz, OH); 13C NMR (125 MHz) d:
138.1, 137.9, 137.8, 137.7 (4 ꢁ Cquat), 78.2, 77.3, 77.0, 73.9, 73.6,
73.3, 73.1, 71.8, 69.4, 63.7; HR-MS (ESI) m/z calcd for C34H38O6Na

M. A. Potopnyk et al. / Tetrahedron: Asymmetry 22 (2011) 780–786
785
0
3.60 (1H, dd, J10,11 4.6 Hz, H-10), 3.56 (1H, dd, J11,12 4.6 Hz, J12,12
at 0 °C. Then it was partitioned between CH2Cl2 (10 mL) and water
(5 mL), the organic phase was separated, washed with 10% NaHCO3
(3 ꢁ 3 mL), dried, concentrated, and the product was isolated by
column chromatography (hexane–ethyl acetate, 4:1) to afford
(161 mg; 78 %) an inseparable mixture compounds 19 and 20 in
the ratio: 2.8:1 as determined by the integration of the signals at
d = 5.81 and 5.72 ppm, respectively. HR MS (ESI) m/z calcd for
9.6 Hz, H-12), 3.49 (1H, dd, J11,12 5.5 Hz, J 9.6 Hz, H-120), 3.40
0
(1H, dd, J2,3 9.5 Hz, H-2), 3.39 (1H, dd, J4,5 9.7 Hz, H-4), 3.33 (3H,
s, CH3); 13C NMR (125 MHz, CDCl3) d: 138.74, 138.67, 138.62,
138.4, 138.2, 138.0, 137.8 (Cquat, 7 ꢁ Ph), 131.9 (C-7), 130.9 (C-8),
97.7 (C-1), 82.1 (C-3), 81.6 (C-10), 80.3 (C-2), 79.9 (C-9), 79.5 (C-
4), 78.6 (C-11), 75.6, 75.0, 74.6, 73.3, 73.2, 72.9, 70.7 (7 ꢁ OCH2Ph),
72.3 (C-5), 72.1 (C-6), 70.0 (C-12), 55.2 (CH3). Anal. Calcd for
C
55H58O9Na 885.3973, fund [M+Na]+ 885.3963.
C62H66O10 (971.18): C, 76.68; H, 6.85. Found: C, 76.46; H, 6.80.
Data for 19: 1H NMR (600 MHz) d: 6.07 (1H, ddd, J7,6 15.6 Hz, J7,8
Method 2: To a solution of enone 15 (678 mg, 0.7 mmol) in
7.8 Hz, J7,5 1.2 Hz, H-7), 5.81 (1H, ddd, J6,5 6.0 Hz, J6,8 0.6 Hz, H-6).
Data for 20: 1H NMR (600 MHz) d: 6.04 (1H, ddd, J7,6 15.6 Hz, J7,8
7.8 Hz, J7,5 1.2 Hz, H-7), 5.72 (1H, ddd, J6,5 6.0 Hz, J6,8 0.6 Hz, H-6).
CH2Cl2/MeOH (1:1 v/v ratio: 20/20 mL), CeCl3ꢂ7H2O (339 mg,
0.91 mmol, 1.3 equiv) was added. The mixture was stirred for
5 min, then NaBH4 (32 mg, 0.84 mmol, 1.2 equiv) was added in
small portions over a period of 15 min and stirring was continued
for another 1 h. The mixture was partitioned between water
(40 mL) and CH2Cl2 (30 mL), the phases were separated, and the
aqueous one extracted with CH2Cl2 (3 ꢁ 40 mL). The combined or-
ganic solutions were washed with brine, dried, concentrated, and
the products were isolated by column chromatography (hexane–
ethyl acetate, 7:1 to 2:1) to afford alcohol 16 (236 mg, 35%) and
4.7. Determination of the structures of 19 and 20
A stream of ozone was passed through a cooled (to ꢀ78 °C)
solution of a mixture of 19 and 20 (147 mg, 0.17 mmol, 1.0 equiv)
in dichloromethane/methanol (25/5 mL), until the distinctive blue
color was observed. The excess ozone was removed by passing a
stream of nitrogen through the solution. Then NaBH4 (51.5 mg,
1.36 mmol, 8 equiv) was added at ꢀ78 °C, and the mixture was al-
lowed to reach rt. Water (50 mL) was added and the mixture was
stirred overnight. The layers were separated and the aqueous one
extracted with CH2Cl2 (3 ꢁ 30 mL). The combined organic solutions
were washed with saturated NaHCO3 (20 mL) and brine (20 mL),
dried, concentrated, and the mixture of crude products was used
in the next step (benzylation) without further purification.
its diastereoisomer 17 (403 mg, 59%). Data for 17: [a]D = +4.4 (c
1, CHCl3); 1H NMR (600 MHz) d: 5.77 (1H, dd, J7,8 15.6 Hz, J7,6
5.5 Hz, H-7), 5.65 (1H, ddd, J8,7 15.6 Hz, J8,9 7.3 Hz, J8,6 1.3 Hz, H-
8), 4.98 (1H, d, J 10.9 Hz, benzylic H), 4.93 (1H, d, J 10.8 Hz, benzylic
H), 4.84 (1H, d, J 10.9 Hz, benzylic H), 4.79 (1H, d, J 12.2 Hz, ben-
zylic H), 4.67–4.72 (4H, m, 4 ꢁ benzylic H), 4.63 (1H, d, 12.2 Hz,
benzylic H), 4.57 (1H, d, J 11.9 Hz, benzylic H), 4.51 (1H, d, J
11.7 Hz, benzylic H), 4.48 (1H, d, J1,2 3.5 Hz, H-1), 4.38 (1H, d, J
11.9 Hz, benzylic H), 4.32 (2H, m, H-6 + benzylic H), 4.24 (1H, d, J
11.7 Hz, benzylic H), 4.05 (1H, dd, J9,8 7.0 Hz, J9,10 5.3 Hz, H-9),
3.98 (1H, dd, J3,4 9.2 Hz, J3,2 9.4 Hz, H-3), 3.80 (1H, m, H-11), 3.67
(1H, dd, J4,5 9.7 Hz, J4,3 9.2 Hz, H-4), 3.58 (1H, dd, J10,9 5.3 Hz,
J10,11 5.2 Hz, H-10), 3.53–3.57 (2H, m, H-5 + H-12), 3.46 (1H, dd,
To a stirred solution of the above products in DMF (10 mL), so-
dium hydride (60% dispersion in mineral oil; 20 mg, 0.5 mmol) was
added and the mixture was stirred for 30 min at rt. Benzyl bromide
(0.07 mL, 0.6 mmol) was then added, the mixture was stirred at rt
for another 4 h and the reaction was partitioned between water
(25 mL) and ether (50 mL). The layers were separated and the
aqueous phase was extracted with Et2O (3 ꢁ 50 mL). The combined
organic solutions were washed with water (50 mL), brine (30 mL),
dried, concentrated, and the products were isolated by column
chromatography (hexane–ethyl acetate, 15:1 to 10:1) to afford
0
J2,1 3.5 Hz, J2,3 9.4 Hz, H-2), 3.44 (1H, dd, J12,11 5.2 Hz, J12,12
10.1 Hz, H-120), 3.17 (3H, s, CH3); 13C NMR (125 MHz, CDCl3) d:
138.76, 138.73, 138.72, 139.22, 138.20, 138.17, 138.09 (Cquat
,
7 ꢁ Ph), 133.72 (C-7), 129.28 (C-8), 98.27 (C-1), 81.94 (C-3),
81.63 (C-10), 79.77 (C-2), 79.65 (C-9), 78.68 (C-11), 77.52 (C-4),
75.71, 75.22, 75.03, 73.48, 73.29, 72.88, 70.62 (7 ꢁ OCH2Ph),
72.44 (C-5), 69.83 (C-12), 69.29 (C-6), 55.11 (CH3); HR-MS (ESI)
m/z calcd for C62H66O10Na 993.4548, found [M+Na]+ 993.4585.
Anal. Calcd for C62H66O10 (971.18): C, 76.68; H, 6.85. Found: C,
76.61; H, 6.64.
methyl 2,3,4,6-tetra-O-benzyl-a-D
-glucoside16 (23; 71.5 mg;
76 %), and two tetrahydrofuran derivatives: 21 (53 mg, 59 %) and
22 (16 mg, 18 %).
Data for 23: 1H NMR (600 MHz) d: 4.97 (1H, d, J 10.9 Hz, ben-
zylic H), 4.82 (1H, d, J 10.9 Hz, benzylic H), 4.81 (1H, d, J 10.9 Hz,
benzylic H), 4.79 (1H, d, J 12.2 Hz, benzylic H), 4.66 (1H, d, J
12.2 Hz, benzylic H), 4.63 (1H, d, J1,2 3.6 Hz, H-1), 4.59 (1H, d, J
11.9 Hz, benzylic H), 4.47 (1H, d, J 12.2 Hz, benzylic H), 4.46 (1H,
d, J 10.6 Hz, benzylic H), 3.98 (1H, dd, J3,4 9.3 Hz, J3,2 9.6 Hz, H-3),
3.70–3.96 (2H, m, H-5, H-6), 3.63–3.65 (1H, m, H-60), 3.62 (1H,
dd, J4,5 9.6 Hz, H-4), 3.56 (1H, dd, H-2), 3.37 (3H, s, CH3); 13C
NMR (125 MHz, CDCl3) d: 138.8, 138.3, 138.2, 137.9 (Cquat, 4 ꢁ C-
Ph), 98.2 (C-1), 82.1, 79.8, 77.7, 75.7, 75.0, 73.5, 73.4, 70.0, 68.5
(C-2, 3, 4, 5, 6, 4 ꢁ OCH2Ph), 55.2 (CH3).
4.5. Determination of the configuration of alcohol 16
Through a cooled (ꢀ78 °C) solution of alcohol 16 (100 mg,
0.1 mmol) in dry CH2Cl2 (20 mL), ozone was bubbled until the blue
color persisted (5 min). Then methyl disulfide (0.3 mL) was added
to decompose the ozonide and the mixture was stirred overnight at
rt. Sodium borohydride (10 mg) was then added and stirring was
prolonged for another 24 h. The mixture was partitioned between
water (20 mL) and AcOEt (10 mL), the phases were separated, and
the aqueous one extracted with AcOEt (3 ꢁ 10 mL). The combined
organic solutions were washed with water, brine, dried, concen-
trated, and products were isolated by column chromatography
(hexane–ethyl acetate, 9:1 to 6:1) to afford the known diol8 18
Data for 21: [a]
D = +31.7 (c 1, CHCl3); 1H NMR (600 MHz) d: 4.59
(2H, d, J 12.0, benzylic H), 4.51 (2H, d, J 12.1, benzylic H), 4.50 (2H,
d, J 11.9, benzylic H), 4.44 (2H, d, J 12.0, benzylic H), 4.35 (2H, m, H-
2, H-5), 4.01 (2H, d, J 3.4, H-3, H-4), 3.72 (2H, dd, J1,2 = J5,6 = 6.4,
J1,1 = J6,6 = 9.7, H-1, H-6), 3.68 (2H, dd, J 6.3, J1,1 = J6,6 = 9.7, H-10,
H-60); 13C NMR (125 MHz, CDCl3) d: 138.3, 137.9 (Cquat, 4 ꢁ C-
Ph), 128.4, 128.3, 127.79, 127.55 (double intensity, 16 ꢁ C-Ph),
127.75, 127.53 (4 ꢁ C-Ph), 81.3, 79.0, 73.4, 72.2, 68.4 (C-1, 2, 3, 4,
5, 6, 4 ꢁ OCH2Ph). Anal. Calcd for C34H36O5 (524.65): C, 77.84; H,
6.92. Found: C, 78.07; H, 7.03.
0
0
0
0
(45.5 mg, 0.09 mmol, 89%) and 2,3,4,5-tetra-O-benzyl-
L-xylitol.
4.6. Reaction of the -glycero-alcohol 17 with triflic anhydride
L
This reaction was performed under an argon atmosphere. To a
cooled (0 °C) solution of allyl alcohol 17 (233 mg, 0.24 mmol) in
dry CH2Cl2 (10 mL), containing dry 2,6-lutidine (0.084 mL,
0.72 mmol) triflic anhydride (0.060 mL, 0.36 mmol, 1.5 equiv)
was added in one portion and the mixture was stirred for 50 min
Data for 22: [a]
D = +24.6 (c 1, CHCl3); 1H NMR (500 MHz) d: 4.60
(1H, d, J 12.0 Hz, benzylic H), 4.57 (1H, d, J 12.0 Hz, benzylic H),
4.46–4.52 (5H, m, 5 ꢁ benzylic H), 4.25 (1H, ddd, J5,4 3.9 Hz, J5,6
5.7 Hz, J 1.0 Hz, H-5), 4.11 (1H, ddd, J2,3 3.0 Hz, J 5.8 Hz, J 1.0 Hz,
H-2), 3.97 (1H, dd, J 3.8 Hz, J 1.0 Hz, H-4), 3.94 (1H, dd, J 3.1 Hz, J

786
M. A. Potopnyk et al. / Tetrahedron: Asymmetry 22 (2011) 780–786
4. Jarosz, S. J. Carbohydr. Chem. 2001, 20, 93–107.
0
1.0 Hz, H-3), 3.77 (1H, dd, J6,6 9.5 Hz, H-6), 3.72 (1H, dd, J 6.5 Hz, H-
5. (a) Jarosz, S.; Mach, M. J. Chem. Soc., Perkin Trans. 1 1998, 3943–3948; (b) Jarosz,
S.; Sałan´ ski, P.; Mach, M. Tetrahedron 1998, 54, 2583–2594.
6. Jarosz, S. Carbohydr. Res. 1988, 183, 201–207.
7. (a) Mitsunobu, O. Synthesis 1981, 1–28; (b) Castro, B. R. Org. React. 1983, 29, 1–
162; (c) Lipshutz, B. H.; Chung, D. W.; Rich, B.; Corral, R. Org. Lett. 2006, 8,
5069–5072; (d) Green, J. E.; Bender, D. M.; Jackson, S.; O’Donnell, M. J.;
McCarthy, J. R. Org. Lett. 2009, 11, 807–810.
60), 3.63 (1H, dd, J1,2 5.5 Hz, J1,1 10.0 Hz, H-1), 3.52 (1H, dd, J1 ,2
6.5 Hz, H-10); 13C NMR (150 MHz, CHCl3) d: 138.20, 138.18,
137.87, 137.79 (Cquat, 4 ꢁ Ph), 83.7 (C-3), 82.7 (C-2), 82.6 (C-4),
80.1 (C-5), 73.4, 73.2, 71.5, 71.4 (4 ꢁ OCH2Ph), 70.4 (C-1), 68.3
(C-6). Anal. Calcd for C34H36O5 (524.65): C, 77.84; H, 6.92. Found:
C, 77.67; H, 7.01.
0
0
8. Jarosz, S.; Gajewska, A.; Luboradzki, R. Tetrahedron: Asymmetry 2008, 19, 1385–
1391.
9. Park, H. M.; Piatak, D. M.; Peterson, J. R.; Clark, A. M. Can. J. Chem. 1992, 70,
1662–1665.
10. (a) Makosza, M. Pure Appl. Chem. 2000, 72, 1399–1403; (b) Makosza, M.;
Fedorynski, M. Advances in Catalysis 1987, 35, 375–422; (c) Makosza, M.;
Fedorynski, M. Catal. Rev. 2003, 45, 321–367.
11. Gemal, A. L.; Luche, J. L. J. Am. Chem. Soc. 1981, 103, 5454–5459.
12. This proportion was assigned by integration of the signals of 19 at d = 6.07
(ddd) and 5.81 (ddd) and 20 at 6.04 (ddd) and 5.72 (ddd) ppm respectively (see
Section 4).
13. (a) Baldwin, J. E. J. Chem. Soc., Chem. Commun. 1976, 734–736.; (b) Baldwin, J. E.;
Cutting, J.; Dupont, W.; Kruse, L.; Silberman, L.; Thomas, R. C. J. Chem. Soc.,
Chem. Commun. 1976, 736–738.; (c) Johnson, C. D. Acc. Chem. Res. 1993, 26,
476–482.
4.8. Reaction of the
D
-glycero-alcohol 16 with triflic anhydride
-glycero-
This reaction was performed analogously as for the
L
isomer 17 starting from 230 mg of 16. Chromatographic purifica-
tion afforded an inseparable mixture of three products, which were
identified on the basis of the NMR data. HR-MS (ESI) m/z calcd for
C
55H58O9Na 885.3973, found [M+Na]+ 885.3968. Ratio
19:20:24 = 3.4:1:1.5 as determined by the integration of the sig-
nals at d = 5.81, 5.72 and 5.97 ppm, respectively. Data for 24: 1H
NMR (600 MHz) d: 5.97 (1H, ddd, J7,6 15.6 Hz, J7,8 7.8 Hz, J7,5
1.2 Hz, H-7), 5.87 (1H, ddd, J6,5 6.6 Hz, J6,8 0.6 Hz, H-6).
14. Glaudemans, C. P. J.; Fletcher, H. G., Jr. Methods in Carbohydrate Chemistry 1971,
6, 373–376.
15. (a) Mordini, A.; Bindi, S.; Pecchi, S.; Capperucci, A.; Degl’Innocenti, A.; Reginato,
G. J. Org. Chem. 1996, 61, 4466–4468; (b) Burke, C. P.; Shi, Y. Org. Lett. 2009, 11,
5150–5153.
Acknowledgments
16. (a) Galatsis, P.; Millan, S. D.; Ferguson, G. J. Org. Chem. 1997, 62, 5048–5056; (b)
Johnson, S. W.; Jenkinson, S. F.; Angus, D.; Jones, J. H.; Watkin, D. J.; Fleet, G. W.
J. Tetrahedron: Asymmetry 2004, 15, 3263–3273; (c) Malmberg, J.; Mani, K.;
Säwén, E.; Wirén, A.; Ellervik, U. Bioorg. Med. Chem. 2006, 14, 6659–6665.
17. (a) Kantner, S. S.; Humski, K.; Goering, H. L. J. Am. Chem. Soc. 1982, 104, 1693–
1697; (b) Magid, R. M. Tetrahedron 1980, 36, 1901–1930.
This work was financed by the Ministry of Science and Higher
Education, Grant No. N N204 092635.
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