(R)-2,3-O-Cyclohexylideneglyceraldehyde: A useful template for a simple entry into carbafuranose stereoisomers

Article abstract of DOI:10.1016/j.tetasy.2012.09.007

(R)-2,3-O-Cyclohexylideneglyceraldehyde 1 provides a simple route for the preparation of carbafuranoses. This has been exemplified by the preparation of 10c and 10d, the derivatives of carba d-xylofuranose and carba-l-arabinofuranose respectively, starting from homoallylic alcohol 2a derived from 1. The key step in this protocol was the intramolecular allylation of 9 promoted by several metals under wet conditions that resulted in the construction of the carbafuranose skeleton of 10. The potential of several metals regarding the efficacy and stereoselectivity of this crucial intramolecular allylation reaction has been studied. The moderate stereoselectivity in all of the successful intramolecular allylations of 9 yielding both d-10c and l-10d as the major products contributed significantly in attaining stereo-divergence in this route. The utility of this route was due to the easy availability of 1, and the operational simplicity as well as scalability of all of the reactions involved.

Full text of DOI:10.1016/j.tetasy.2012.09.007

Tetrahedron: Asymmetry 23 (2012) 1423–1429
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
(R)-2,3-O-Cyclohexylideneglyceraldehyde: a useful template for a simple
entry into carbafuranose stereoisomers
⇑
Sibanarayan Tripathy, Angshuman Chattopadhyay
Bio-Organic Division, Bhabha Atomic Research Center, Mumbai 400085, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 August 2012
Accepted 12 September 2012
(R)-2,3-O-Cyclohexylideneglyceraldehyde 1 provides a simple route for the preparation of carbafuranos-
es. This has been exemplified by the preparation of 10c and 10d, the derivatives of carba
D-xylofuranose
and carba- -arabinofuranose respectively, starting from homoallylic alcohol 2a derived from 1. The key
L
step in this protocol was the intramolecular allylation of 9 promoted by several metals under wet con-
ditions that resulted in the construction of the carbafuranose skeleton of 10. The potential of several met-
als regarding the efficacy and stereoselectivity of this crucial intramolecular allylation reaction has been
studied. The moderate stereoselectivity in all of the successful intramolecular allylations of 9 yielding
both D-10c and L-10d as the major products contributed significantly in attaining stereo-divergence in
this route. The utility of this route was due to the easy availability of 1, and the operational simplicity
as well as scalability of all of the reactions involved.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
metric construction of several structural units7 that are present
in our target molecules. Included among them was our recent
Chiral polyoxygenated cyclopentanes are constituents of many
bioactive compounds, such as glycosidase inhibitors,1 carbocyclic
nucleosides,2 and prostaglandins.3 They are also referred to as car-
bafuranoses and treated as analogues of monosaccharides in which
the ring oxygen of a furanose has been replaced by a methylene (–
CH2–) group. This modification transforms the (hemi-) acetal ano-
meric center of a natural sugar unit into an ether (alcohol) group in
the resulting carbasugar. The lack of an acetal moiety preserves the
carbafuranoses from hydrolysis as compared to sugar derivatives.
In addition, this modification has a positive effect on the conforma-
tional changes in their structures. Over the last few decades, the
chemistry of carbafuranoses and other carbasugars has emerged
as a topic of intense investigation in bioorganic research.4 Interest-
ingly, two carbafuranose nucleosides were identified in natural
sources, neplanocin A5a and aristeromycin,5b which display antibi-
otic and antitumor activities but so far no carbafuranose sugar has
been isolated as such in Nature. In view of this, since the first syn-
thesis reported by Wilcox et al.6a,b considerable attention has been
focused on the synthesis6 of carbafuranoses and analogues in their
different stereochemical forms in order to make them amenable
for varied applications.
work7i related to the synthesis of carbocycles. Herein we report an-
other application of 1 to develop a simple and efficient route for
the preparation of carbafuranose sugars in their different stereo-
chemical forms. This is shown here by the synthesis of 10c and
10d, derivatives of two carbafuranose sugars.
2. Results and discussion
Retrosynthetic analysis (Fig. 1) of carbafuranose sugar skeleton,
X suggested that it could be obtained from its olefinic precursor Y.
Consequently, the C-3 and C-4 stereocenters of Y could simulta-
neously be constructed via intramolecular allylation of intermedi-
ate Z, which are accessible starting from either of the two
homoallylic alcohols 2a,b derived from 1. For the present work
we chose anti-2a7b to start with (Scheme 1). Silylation of both hy-
droxyl of groups diol 3a, which was obtained from 2a,8 using
2 equiv of TBDMS chloride and imidazole produced 3b in good
overall yield. Ozonolysis of the olefin of 3b, followed by PPh3
reduction of the resulting ozonide in one-pot afforded aldehyde
4. This was found to be unstable on standing, and so without fur-
ther purification was quickly subjected to Wittig Horner olefin-
ation to obtain 5 in good yield. The DIBAL reduction of 5 afforded
allylic alcohol 6 which was transformed into bromide 7b in two
steps [(a) mesylation; (b) treatment of mesylate 7a with NaBr in
acetone] in good overall yield. Next, the regioselective desilylation
of 7b was accomplished by stirring it in acidified CHCl3 solution to
afford 8 in good yield. The free hydroxyl of 8 was oxidized with
In our ongoing program on the synthesis of biologically active
molecules, we have been exploiting easily accessible and highly
stable (R)-2,3-O-cyclohexylideneglyceraldehyde 17a for the asym-
⇑
Corresponding author.
E-mail address: achat@barc.gov.in (A. Chattopadhyay).
0957-4166/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetasy.2012.09.007

1424
S. Tripathy, A. Chattopadhyay / Tetrahedron: Asymmetry 23 (2012) 1423–1429
5
5
R1O
OR1
4
1
4
1
BASE
HO
2
O
O
2
3
O
3
OR2
O
OR2
OH
R3O
HO
O
O
Br
X
Y
Z
2a,b
1
OH
Figure 1. Retrosynthesis of carbafuranose.
OR
O
O
O
ref 7e
ref 7b
i
RO
ii
O
O
H
O
1
OBn
3a, R = H
OH
2b
O
2a OH
3b, R = TBDMS
OR
OR
OR
OTBDMS
R1
O
RO
RO
RO
v
R1
iv
R1
iii
viii
vi
OBn
OBn
OBn
OBn
Br
4
, R1 = CO2Et
, R1 = CH2OMs
5
6
7a
7b
1
8
, R = CH2OH
vii
ix
1
1
R = TBDMS
9, R1 = CHO
, R = CH2OH
, R = CH2Br
OBn
OBn
+
OBn
OBn
x
+
+
HO
OTBDMS
HO
xii
OTBDMS
HO
OTBDMS
HO
OTBDMS
10a
10b
10c
10d
OH
OBn
HO
HO
HO
iii, xi
10c
HO
HO
OH
HO
HO
OH
I
11
12
OBn
OH
HO
xii
iii, xi
10d
OH
OH
II
Scheme 1. Synthesis of carbafuranose. Reagents and conditions: (i) Ref. 8; (ii) TBDMSCl, imidazole, DMAP, DMF, 94%; (iii) O3, PPh3, CH2Cl2, ꢀ78 °C, 86%; (iv) NaH,
C2H5COOCH2P(O)(OC2H5)2, THF, 25 °C, 81%; (v) DIBAL-H, THF, ꢀ78 °C, 91%; (vi) MsCl, Et3N, CH2Cl2, 0 °C; (vii) NaBr, NaHCO3, Acetone, 25 °C, 90% (in two steps); (viii) CHCl3 aq
HCl, 91%; (ix) Dess Martin Periodinane, CH2Cl2, 91%; (x) (a) Zn/aq NH4Cl, moist THF, 74%, (b) Zn/Fecl3, moist THF, 68%, (c) Zn/Sncl2ꢁ2H2O, moist THF, 88%, (d) Zn/CuCl2ꢁ2H2O
moist THF, no reaction, (e) In/H2O, no reaction; (xi) LiAlH4, Et2O; (xii) 10% Pd/C, H2, EtOH, 94% from 11 to I, 90% from 12 to II.
Dess Martin periodinane to obtain aldehyde 9, which was equiva-
lent to Z in Figure 1. Since Compound 9 was relatively unstable on
long standing, it was quickly subjected to intramolecular allylation
resulting in construction of the carbafuranose unit of 10 (equiva-
lent to intermediate Y in Fig. 1) with simultaneous generation of
its two stereocenters at C-3 and C-4. With a view to determine
its practical viability, this allylation reaction was performed under
wet conditions in the presence of five different metal mediators viz
Luche’s zinc9 and three low valent metals iron, copper, and tin,10
and indium.11 In order to ensure smooth progress, all of the heter-
ogeneous metal mediated allylation reactions were performed
using an excess of metal/metal salts. The efficacies of all these ally-
lation reactions (step xi, Scheme 1) are summarized in Table 1.
Luche’s allylation9 of 9 produced 10 in good yield (74.7%, Ta-
ble 1, entry a) containing a mixture of its all four possible diaste-
reomers 10a–d. Among them, 10c and 10d were obtained as the
major products of which 10d was produced with better selectivity.
Both 10c and 10d could easily be isolated by column chromatogra-
phy of the reaction product to obtain each in pure form. The other
two stereoisomers 10a and 10b were obtained in much smaller
amounts and could be isolated as a mixture of chromatographically
inseparable compounds.12
The low valent iron mediated reaction10a produced 10, albeit in
a lower yield (68.2%, Table 1, entry b) compared to Luche’s reac-
tion. This reaction also afforded 10c and 10d as the major products
and the mixture of 10a/b as the minor product. Similar to Luche’s
allylation, the iron mediated reaction produced 10d with better
stereoselectivity than that of 10c. The low valent tin mediated10c
reaction was found to be more efficient compared to the previous
ones that was evident from the improved yield of 10 (87.5%,

S. Tripathy, A. Chattopadhyay / Tetrahedron: Asymmetry 23 (2012) 1423–1429
1425
Table 1
Intramolecular allylation of aldehyde 9
Entry
Metal/salt or metal salt/metal
Solvent
Time (h)
Overall yield of 10 (%)
10a and 10b:10c:10da
a
b
c
d
e
Zn/NH4Cl
FeCl3/Zn
SnCl2, 2H2O/Zn
CuCl2, 2H2O/Zn
In
THF
THF
THF
THF
18
18
18
18
48
74.7
68.2
87.5
NR
8.7: 20.8: 70.5
10.2: 23.2: 66.6
11.4: 62.7: 25.9
—
—
H2O/THF
NR
NR: No reaction.
a
The relative ratio of the chromatographically separable components of the reaction product.
Table 1, entry c). In this case, the reaction yielded 10a,b in a minor
amount while the other two were obtained as the major products.
However, contrary to the previous two cases, this reaction yielded
10c with better stereoselectivity than that of 10d. However, our at-
tempts to perform the same intramolecular allylation of 9, in the
presence of either low valent copper10a or indium12 as mediators
were unsuccessful, as no reaction took place in either case even
when stirring the reaction mixture for longer (Table 1, entries d
and e). The stereochemical differentiations of the aforementioned
successful allylation reactions could be assessed from the isolable
amount of all of the chromatographically separable components
of 10 and the results are summarized in Table 1.
3. Conclusion
In conclusion, compound 1 has been exploited as a useful chiral
template to develop a simple route to obtain carbafuranose sugars.
This has been shown by the preparation of 10c and 10d, derivatives
of carba
a-D-xylofuranose and carba-b-L-arabinofuranose respec-
tively, from 2a in turn obtained from 1. The efficacy of this protocol
was due to the easy availability of 2a from 1 on a multigram sca-
le,7a the low cost and operational simplicity of all of the reactions
involved. Due to all of these advantages, the overall route could
be scalable. The novel feature in the structures of both 10c,d was
due to the presence of differently hydroxyl protected substituents
at three centers (C-1, C-2, and C-3), which could allow selective
chemical and stereo chemical manipulation. Understandably, the
presence of a vinyl unit at the C-4 position in both compounds
could be advantageous because of its amenability to be converted
into different functionalities through suitable chemical transfor-
mation. It is worth mentioning that there is precedent for the prep-
aration of 4-vinyl substituted carbafuranoses that are relevant to
the synthesis of modified carbocycles.6d,t The availability of homo-
chiral 10c and 10d in substantial amounts could provide an oppor-
tunity for their versatile applications in different synthetic
The stereochemistry of 10c could be established by transform-
ing it into the known carba
a-D
-xylofuranose I6d following
Scheme 1, which involves only functional manipulation and so
does not affect any of its stereocenters. Accordingly, 10c was sub-
jected to a series of reactions viz (a) ozololysis, (b) in situ PPh3
reduction of the resulting ozonide; and (c) LiAlH4 reduction of
the crude aldehyde thus obtained (this took place with concomi-
tant desilylation) to afford 11. This upon catalytic hydrogenation
afforded I whose specific rotation and spectroscopic data were in
good agreement with the reported values.6d Following the same
reaction protocol, 10d was transformed into carba-b-L-arabinof-
objectives. The formation of both D- and L-carbasugars 10c and
uranose II via intermediate 12. The specific rotation and spectro-
scopic data of synthetic II were in good agreement with the
reported values.6k
10d respectively as the major products in all of these successful
metal mediated intramolecular allylation (Table 1) reactions of 9
could be of considerable importance with regard to achieving ste-
reo divergence ivian this route. This was facilitated by the moder-
ate stereoselectivity that is found in all of these allylation
The preferential formation of 10c,d in the three successful intra-
molecular metal mediated allylations (Table 1, entries a–c) sug-
gested that all of these reactions took place via a Felkin-Anh
model13 (Fig. 2). Simultaneously, the formation of the same two
major products with a reversal in stereochemistry at the C-4 posi-
tion [(4R) in 10c and (4S) in 10d] in the intramolecular addition
reactions of E-allylic bromide 9 suggested that there could be an
isomerization between the initially formed E-crotylmetal E-M
(from 9) and Z-crotylmetal Z-M (step (i) Fig. 3).10c This was fol-
lowed by the intramolecular allylation of the aldehyde functional-
ity through the corresponding Zimmerman–Traxler transition
states (steps (ii) and (iii), Fig. 3).14 Thus, the relative ratio between
the two Felkin-Anh products 10c and 10d obtained in each of the
successful reactions (Table 1, entries a–c) largely depended on
the degree of isomerization between the corresponding E-M and
Z-M of the crotylmetal.
reactions. The preparation of
L-10d could be relevant due to the re-
cent interest in the application of
L
-carbanucleosides in anti viral
chemotherapy.15 There is also scope to apply the present protocol
with 2b,7e or the homoallylic alcohols corresponding to 2a,b, which
could be derived from (ꢀ)-1,16 and explore their efficacies as well
as stereoselectivities to gain access to other stereoisomers of 10,
the derivatives of the corresponding carbafuranoses.
4. Experimental
4.1. General
Chemicals used as starting materials were commercially avail-
able and used without further purification. All solvents used for
extraction and chromatography were distilled twice at atmo-
spheric pressure prior to use. The organic extracts were desiccated
over dry Na2SO4.
BnO
M
4.2. (4S,5R)-4-O-Benzyl-5,6-O-tert-butyldimethylsilyl-4,5,6-
trihydroxy-hex-1-ene 3b
O
M = Metal
To a cooled (0 °C) solution of 3a9 (1.77 g, 8 mmol) in dry DMF
(30 ml) containing DMAP (100 mg) was added imidazole (1.4 g,
20.5 mol), followed by the addition of tert-butyldimethylsilyl chlo-
ride (2.5 g, 16.6 mmol). The solution was stirred at room tempera-
ture overnight until completion of the reaction (confirmed by TLC).
10c,d
OTBDMS
H
H
Figure 2. Felkin-Anh model for metal mediated intramolecular allylation of 9.

1426
S. Tripathy, A. Chattopadhyay / Tetrahedron: Asymmetry 23 (2012) 1423–1429
OR1
OR1
OR1
M
MBr
MBr (i)
9
OHC
OHC
OHC
OR2 MBr
OR2
OR2
E-crotyl metal
E-M
Z-crotyl metal
Z-M
H
M
O
10b,c
(ii)
M
E-
H
R
OTBDMS
OBn
R =
H
M
H
10a,d
M
(iii)
Z-
O
R
Figure 3. Zimmermann–Traxler model for the metal mediated intramolecular allylation of 9.
The mixture was treated with water and extracted with EtOAc. The
combined organic extract was washed with water, brine and dried
over Na2SO4. Solvent removal under reduced pressure, and column
chromatography (silica gel, 0–10% EtOAc in hexane) of the residue
afforded pure 3b (3.38 g, 93.8%) as a colorless oil. ½aꢂ2D6 ¼ ꢀ17:9 (c
1.06, CHCl3); 1H NMR (200 MHz CDCl3): d 0.05 (2s, 6H each), 0.90
(br s, 18H), 2.34 (t, J = 6.8 Hz, 2H), 3.55–3.64 (m, 3H), 3.79–3.82
(m, 1H), 4.52, 4.64 (AB q, J = 11.6 Hz, 2H), 5.05 (m, 2H), 5.7–5.9
(m, 1H), 7.2–7.4 (m, 5H). 13C NMR (50 MHz CDCl3): ꢀ5.38, ꢀ5.35,
ꢀ4.7, ꢀ4.4, 18.1, 18.3, 25.92, 25.98, 34.9, 64.6, 72.3, 74.8, 80.2,
116.5, 127.4, 127.8, 128.2, 135.9, 138.9. Anal. Calcd for
an argon atmosphere. After the addition, the reaction mixture was
gradually brought to room temperature and stirred until the reac-
tion mixture became clear. The mixture was again cooled to 0 °C
and to it a solution of 4 (4.06 g, 8.97 mmol) in dry THF (20 ml)
was added dropwise over a period of 45 min. The mixture was
gradually brought to room temperature and stirred for 4 h until
completion of reaction (confirmed from TLC). After cooling the
reaction mixture to 0 °C, it was treated with water and with 2%
aqueous dilute HCl to make it neutral. The mixture was then ex-
tracted with EtOAc. The combined organic layer was washed with
water, brine and dried over Na2SO4. Solvent removal under re-
duced pressure and column chromatography (silica gel, 0–15%
EtOAc in hexane) of the residue afforded pure 5 (3.79 g, 80.8%) as
C25H46O3Si2: C, 66.61; H, 10.29. Found: C, 66.48; H, 10.52.
4.3. (3S,4R)-3-O-Benzyl-4,5-O-di tert-butyldimethylsilyl-3,4,5-
trihydroxypent-1-al 4
a colorless oil. ½a D27
ꢂ
¼ ꢀ25:0 (c 1.24, CHCl3); 1H NMR (200 MHz
CDCl3): d 0.04, 0.09 (2s, 6H each), 0.88 (br s, 18H), 1.28 (t,
J = 7.1 Hz 3H), 2.46 (t, J = 6.5 Hz 2H), 3.56–3.68 (m, 3H), 3.80–
3.84 (m, 1H), 4.17 (q, J = 7.1 Hz, 2H), 4.47, 4.62 (ABq, J = 11.5 Hz,
2H), 5.86 (d, J = 15.6 Hz, 1H), 7.02(dt, J = 15.6 Hz, 7.2 Hz, 1H)
7.25–7.32 (m, 5H); 13C NMR (50 MHz CDCl3): ꢀ5.4, ꢀ4.8, ꢀ4.5,
14.2, 18.1, 18.2, 25.8, 25.9, 32.9, 60.0, 64.4, 72.1, 74.3, 78.8,
122.9, 127.5, 127.8, 128.2, 138.3, 146.7, 166.4; Anal. Calcd for
Ozone was bubbled through a cooled (ꢀ78 °C) solution of 3b
(4.8 g, 10.65 mmol) in CH2Cl2 (40 ml) until the solution turned
blue. After stirring the reaction mixture for another 10 min, Ph3P
(4.2 g, 15.97 mmol) was added in portions and the mixture was
gradually brought to room temperature and stirred for 1 h, after
which it was concentrated under reduced pressure to afford an oily
residue, which was quickly purified by passing through a short pad
of silica gel, eluting with 10% hexane: in EtOAc to obtain aldehyde
4 (4.14 g, 85.9%) as a colorless oil. The aldehyde was found to be
unstable on long standing and hence a major portion of it was
immediately used for the next step. A small portion was used for
spectroscopic characterization. 1H NMR (200 MHz CDCl3): d 0.04,
0.08 (2s, 6H each), 0.88 (s, 18H), 2.59–2.67 (m, 2H), 3.49–3.58
(m, 2H), 3.91–3.95 (m, 1H), 4.08–4.11 (m, 1H), 4.53, 4.66 (ABq,
J = 11.5 Hz, 2H), 7.17–7.40 (m, 5H), 9.77 (t, J = 1.9 Hz, 1H); 13C
NMR (50 MHz CDCl3): ꢀ5.5, ꢀ4.7, 18.1, 18.2, 25.8, 25.9, 43.9,
64.4, 71.9, 74.0, 75.6, 127.6, 127.3 128.8, 138.2, 201.5.
C28H50O5Si2: C, 64.32; H, 9.64. Found: C, 64.48; H, 9.55.
4.5. (5S,6R)-5-O-Benzyl-6,7-O-di-tert-butyl-dimethylsilyl-
1,5,6,7-tetrahydroxy-hept-2E-ene 6
To a cooled (ꢀ78 °C) solution of 5 (3.7 g, 7.07 mmol) in THF, DI-
BAL-H (14.3 ml, 1.0 M solution in hexane, 14.3 mmol) was added
dropwise over a period of 30 min. The mixture was then stirred for
another hour at the same temperature until completion of the reac-
tion (confirmed from TLC). To the mixture, methanol (15 ml) was
added. The mixture was stirred at room temperature for 2 h and
the resulting solid was filtered through a Celite pad. Solvent removal
under reduced pressure and column chromatography (silica gel, 0–
20% EtOAc in hexane) of the residue afforded pure 6 (3.1 g, 91.1%) as
4.4. (5S,6R)-Ethyl-5-O-benzyl-6,7-O-di tert-butyl-dimethylsilyl-
5,6,7-trihydroxy-hept-2E-enoate 5
a colorless oil. ½a D24
ꢂ
¼ ꢀ21:7 (c 0.92, CHCl3); 1H NMR (200 MHz
CDCl3): d 0.04, 0.07 (2s, 12H), 0.89 (br s, 18H), 1.44 (br s, 1H), 2.31
(t, J = 5.6 Hz, 2H), 3.50–3.65 (m, 3H), 3.80(dd, J = 9.1 Hz, 5.1 Hz
1H), 4.04 (d, J = 3.5 Hz, 2H), 4.52, 4.64 (AB q, J = 5.6 Hz, 2H), 5.66–
5.75 (m, 2H), 7.25–7.32 (m, 5H); 13C NMR (50 MHz CDCl3): ꢀ5.4,
ꢀ4.7, ꢀ4.4, 18.1, 18.3, 26.0, 25.9, 33.0, 63.5, 64.5, 72.2, 74.6, 79.9,
To a cooled (0 °C) suspension of sodium hydride (0.47 g, 50%
suspension in oil, 9.8 mmol, washed twice with dry hexane) and
dry THF (20 ml), triethyl phosphonoacetate (2.21 g, 9.86 mmol) in
dry THF (10 ml) was added dropwise over a period of 30 min under

S. Tripathy, A. Chattopadhyay / Tetrahedron: Asymmetry 23 (2012) 1423–1429
1427
127.4, 127.9, 128.1, 129.8, 131.0, 138.7; Anal. Calcd for C26H48O4Si2;
C, 64.95; H, 10.06; Found: C, 65.08; H, 10.19.
ganic layer was separated and the aqueous layer was extracted
with chloroform. The combined organic layer was washed with
water, brine and dried over Na2SO4. Solvent removal under re-
duced pressure gave an oily residue which was passed through a
short pad of silica gel eluting with 10% EtOAc in hexane to obtain
pure 9 (1.36 g, 91.4%) as a colorless oil. This was found to be unsta-
ble on long standing and hence a major part of it was immediately
used for the next step. A small portion was used for tentative char-
4.6. (5S,6R)-1-Bromo-5-O-benzyl-6,7-O-di tert-butyl-
dimethylsilyl-5,6,7-trihydroxy-hept-2E-ene 7b
To the cooled (0 °C) solution of 6 (3.0 g, 6.24 mmol) in dry DCM
(25 ml), triethylamine (1.07 g, 10.60 mmol) was added dropwise
over a period of 15 min followed by the addition of methylsulfonyl
chloride (0.93 g, 8.11 mmol) dropwise at the same temperature.
The mixture was slowly brought to room temperature and stirred
for 3 h until completion of the reaction (confirmed from TLC). The
mixture was washed with water for neutrality and extracted with
chloroform. The combined organic layer was washed with brine
and dried over Na2SO4. Solvent removal under reduced pressure
afforded a yellow oily liquid containing the crude mesylate 7a
product, which was used in the next reaction without further
purification.
acterization. ½a D25
ꢂ
¼ ꢀ25:0 (c 0.92, CHCl3); 1H NMR (200 MHz
CDCl3): d 0.07 (s, 6H), 0.94 (br s, 9H), 2.35–2.41 (m, 2H), 3.69–
3.75 (m, 1H), 4.00 (d, J = 5.4 Hz, 2H), 4.12 (dd, J1 = 3.6 Hz,
J2 = 1.5 Hz, 1H), 4.54, 4.64 (AB q, J = 11.72 Hz 2H), 5.65–5.72 (m,
2H), 7.25–7.35 (m, 5H), 9.6 (d, J = 1.5 Hz, 1H); 13C NMR (50 MHz
CDCl3): ꢀ4.8, 18.1, 25.7, 33.1, 44.8, 72.2, 78.8, 80.6, 127.8, 128.3,
129.4, 130.9, 137.7, 203.4.
4.9. Luche’s intramolecular allylation of 9
To the solution of above crude product in dry acetone (20 ml), dry
NaBr (0.78 g, 7.5 mmol) and a catalytic amount of NaHCO3 was
added and stirred overnight. The reaction mixture was concentrated
under reduced pressure to remove the acetone, washed with dilute
HCl(2%), andextractedwithchloroform.Thecombinedorganiclayer
was washed with brine and dried over Na2SO4. Solvent removal un-
der reduced pressure and column chromatography (silica gel, 0–10%
EtOAc in hexane) of the residue afforded pure 7b (3.06 g, 90.26%) as a
To a well stirred mixture of aldehyde 9 (1 g, 2.5 mmol) and Zn
dust (520 mg, 8 mmol) in THF (30 ml), was added a saturated
aqueous NH4Cl solution (1.5 mL) dropwise over
a period of
20 min. The reaction mixture was then stirred overnight after
which the starting material disappeared completely (TLC). The
mixture was filtered and thoroughly washed with EtOAc. The com-
bined organic layer was washed with 5% HCl to dissolve the sus-
pended turbid material and then with water, brine and dried.
Solvent removal under reduced pressure and column chromatogra-
phy (silica gel, 0–20% EtOAc in Hexane) of the residue afforded
10a/10b (53 mg) as an inseparable mixture of compounds which
eluted first, followed by 10c (127 mg) and 10d (430 mg) which
eluted successively to obtain each in pure form.
colorlessoil. ½a D24
ꢂ
¼ ꢀ11:9 (c 0.95, CHCl3); 1H NMR(200 MHzCDCl3):
d 0.04, 0.06 (2s, 6Heach), 0.94(br s, 18H), 2.33 (t, J = 5.9 Hz 2H), 3.50–
3.62 (m, 3H), 3.80 (dd,J1 = 9.4 Hz, 5.1 Hz 1H), 3.91 (d J = 6.2 Hz, 1H),
4.01 (d, J = 6.2 Hz, 1H), 4.48, 4.62 (AB q, J = 11.58 Hz, 2H), 5.61–5.87
(m, 2H), 7.25–7.31 (m, 5H); 13C NMR (175 MHz CDCl3): ꢀ5.4, ꢀ5.3,
ꢀ4.7, ꢀ4.4, 18.2, 18.3, 25.9, 26.0, 33.0, 45.3, 64.6, 72.3. 74.7, 79.7,
127.5, 127.7, 127.9, 128.2, 133.2, 138.7; Anal. Calcd for C26H47BrO3-
Si2; C, 57.43; H, 8.71; Found: C, 57.66; H, 8.61.
4.10. General procedure for the intramolecular allylation of 9
employing a bimetal redox strategy
4.7. (5S,6R)-1-Bromo-5-O-benzyl-6-O-tert-butyl-dimethylsilyl-
5,6,7-trihydroxy-hept-2E-ene 8
To a cooled (15 °C) solution of aldehyde 9 (1 g, 2.5 mmol) in THF
(30 ml) was added metal salt [FeCl3 (1.29 g, 8.0 mmol) or
SnCl2.2H2O (1.8 g, 8.0 mmol) or CuCl2.2H2O (1.36 g, 8.0 mmol)].
The mixture was stirred for 5 min. To this stirred suspension, Zn
dust (650 mg, 10 mmol) was added in portions over a period of
20 min. The reaction mixture was gradually brought to ambient
temperature and stirred for the period as mentioned in Table 1.
Low valent iron and tin mediated reactions showed the total disap-
pearance of starting material 9 and the formation of product 10
(while monitored by TLC). However, no reaction was found to take
place in the case of low valent copper mediated reactions. Finally,
in both of the successful reactions (iron and tin mediated reac-
tions), the reaction mixture was treated successively with diethyl
ether (50 mL) and water (25 mL) and then stirred for 10 min and
filtered. The filtrate was treated with 2% aqueous HCl to dissolve
a small amount of suspended particles. The organic layer was sep-
arated and the aqueous layer extracted with EtOAc. The combined
organic extract was washed with water, brine and then dried. Sol-
vent removal under reduced pressure and column chromatography
(silica gel, 0-20% EtOAc/Hexane) of the residue gave 10a/10b as an
inseparable mixture of compounds, and 10c and 10d in pure form.
Thus, chromatography of low valent iron mediated reaction gave
57 mg of 10a/10b, 129 mg of 10c, and 370 mg of 10d. Similarly,
low valent tin mediated reaction gave 81 mg of 0a/10b, 447 mg
of 10c, and 185 mg pf 10d.
Compound 7b (2.5 g, 4.59 mmol) was dissolved in acidified
chloroform (15 ml) [prior to its use chloroform had been shaken
with aqueous concentrated HCl (2 ml) and then separated]. The
solution of 7b was stirred at room temperature for 36 h until the
completion of the reaction (confirmed by TLC). The organic layer
was washed successively with water to remove HCl, brine and then
dried over Na2SO4. Solvent removal under reduced pressure and
column chromatography (silica gel, 0–20% EtOAc in hexane) of
the residue afforded pure 8 (1.8 g, 6.44 mmol, 91.2%) as a pale yel-
low oil. ½a 2D4
ꢂ
¼ ꢀ0:7 (c 1.00, CHCl3); 1H NMR (200 MHz CDCl3): d
0.06 (s, 6H), 0.90 (br s, 9H), 1.88 (br s, 1H), 2.35–2.43 (m, 2H),
3.55–3.78 (m, 4H), 4.03 (d, J = 5.9 Hz,2H), 4.62 (bm, 2H), 5.70–
5.82 (m, 2H), 7.25–7.32 (m, 5H); 13C NMR (50 MHz CDCl3): ꢀ4.6,
ꢀ4.4, 18.0, 25.8, 33.7, 45.2, 63.8, 72.8, 73.7, 79.7, 127.8, 128.0,
128.4, 131.9, 137.9; Anal. Calcd for C20H33BrO3Si; C, 55.93; H,
7.75; Found: C, 56.21; H, 7.82.
4.8. (2R,3S)-2-O-tert-Butyl-dimethylsilyl-3-O-benzyl-7-bromo-
2,3-dihydroxy-hept-5E-enal 9
To a cooled (0 °C) solution of 8 (1.5 g, 3.50 mmol) in dry DCM
(35 ml), Dess Martin periodinane (2.23 g, 5.25 mmol) was added
portionwise. The reaction mixture was stirred for 30 min at 0 °C,
and then gradually brought to room temperature and stirred until
completion of the reaction (confirmed from TLC), after which it
was diluted with chloroform (30 ml). The solution was poured into
saturated aqueous NaHCO3 (20 ml) containing a sevenfold excess
of Na2S2O3. The mixture was stirred to dissolve the solid. The or-
4.11. Indium mediated intramolecular allylation of 9 in H2O/
THF
To a magnetically stirred solution of 9 (1 g, 2.5 mmol) in a 1:1
solvent mixture of water and THF (8 mL) was added indium

1428
S. Tripathy, A. Chattopadhyay / Tetrahedron: Asymmetry 23 (2012) 1423–1429
(99.99% pure ingot, Alfa Aesar, 632 mg, 5.5 mmol). The reaction
mixture was stirred for 48 h. No reaction took place (TLC).
(175 MHz CDCl3): 29.2, 39.5, 62.9, 71.7, 78.6, 78.7, 78.8, 127.8,
127.9, 128.5, 137.8; Anal. Calcd for C13H18O4; C, 65.53; H, 7.61;
Found: C, 65.70; H, 7.45.
4.12. (1S,2S,3R,4R)-1-O-Benzyl-2-O-tert-butyldimethylsilyl-4-
vinyl-cyclopentane-1,2,3-triol 10a and (1S,2S,3R,4S)-1-O-benzyl-
2-O-tert-butyldimethylsilyl-4-vinyl-cyclopentane-1,2,3-triol
10b
4.16. (1S,2S,3S,4R)-4-Hydroxymethyl)-cyclopentane-1,2,3-triol
11a [Carba-a-D-xylofuranose I]
A solution of 11 (125 mg) in EtOH (20 ml) was treated with 10%
Pd-C (20 mg). The mixture was stirred under H2 atmosphere for
10hr until the reaction was complete (monitored by TLC). The mix-
ture was filtered through a Celite pad and solvent was removed un-
der reduced pressure. The residue was chromatographed to afford
1H NMR (200 MHz CDCl3): d 0.06 (br s, 6H), 0.93 (br s, 9H), 1.61–
1.64 (m, 1H), 2.1–2.5 (m, 2H, overlapped with a br s, 1H), 3.65–3.70
(m, 1H), 3.81–3.84 (m, 1H), 4.0 (m, 1H), 4.53–4.65 (m, 2H), 4.9–5.1
(m, 2H), 5.73–5.86 (m, 1H), 7.25–7.34 (m, 5H); 13C NMR (50 MHz
CDCl3): ꢀ4.9, ꢀ4.6, 18.3, 25.9, 32.8, 48.1, 71.7, 72.1, 75.1, 75.9,
77.2, 77.6, 78.9, 79.2, 113.9, 127.4, 127.5, 128.2 138.5, 138.6, 140.6.
pure I (73 mg, 93.9%) as a colorless oil. ½a D26
¼ þ12:7 (c 1.0, MeOH)
ꢂ
[lit.,6d
½
a 2D0
ꢂ
¼ þ12:1 (c 0.7, MeOH)]; 1H NMR (600 MHz D2O): d 1.61
(m, 2H), 2.28–2.31 (m, 1H), 3.36 (dd, J = 7.2 Hz, 10.2 Hz, 1H),
3.53(dd, J = 7.2 Hz, 10.2 Hz, 1H), 3.72(m, 1H), 3.99 (m, 2H); 13C
NMR (150 MHz, D2O): 34.7, 41.8, 64.3, 73.3, 78.5, 81.1.
4.13. (1S,2S,3S,4R)-1-O-Benzyl-2-O-tert-butyldimethylsilyl-4-
vinyl-cyclopentane-1,2,3-triol 10c
½
a 2D4
ꢂ
¼ þ3:8 (c 0.51, CHCl3); 1H NMR (200 MHz CDCl3): d 0.09
4.17. (1S,2S,3S,4S)-1-O-Benzyl-4-hydroxymethyl-cyclopentane-
1,2,3-triol 12
(br s, 6H), 0.91 (br s, 9H), 1.6–2.1 (m, 2H, overlapped with a br s,
1H), 3.10 (m, 1H), 3.94–4.06 (m, 3H), 4.53, 4.64 (AB q, J = 12.0 Hz,
2H), 5.1–5.2 (m, 2H), 5.7–5.9 (m, 1H), 7.2–7.4 (m, 5H); 13C NMR
(50 MHz CDCl3): ꢀ4.8, ꢀ4.7, 18.2, 25.8, 32.2, 42.8, 71.7, 78.2,
79.1, 79.2, 116.8, 127.2, 127.5, 127.6 128.1, 129.6, 134.7, 137.7,
138.9 Anal. Calcd for C20H32O3Si; C, 68.92; H, 9.25; Found: C,
68.71; H, 9.15.
Following the same reactions protocol as carried out for the
preparation of 11, compound 10d (348 mg, 1.0 mmol) was trans-
formed into 12 (179 mg, 75.3%) as a colorless oil. ½a D27
¼ þ29:2 (c
ꢂ
2.16, CH2Cl2); 1H NMR (700 MHz CDCl3): d 1.48 (m, 1H), 1.64 (br
s, 1H), 1.92(m, 1H), 2.06 (m, 1H), 3.57 (m, 1H), 3.63–3.70 (m, 1H,
overlapped with a br s, 2H), 3.82(m, 1H), 3.88–3.90 (m, 1H), 3.93
(t, J = 7 Hz, 1H), 4.47 (d, J = 11.9 Hz, 1H), 4.574 (dd, J = 11.9 Hz,
5.6 Hz, 1H), 7.26–7.34 (m, 5H); 13C NMR (175 MHz CDCl3): 29.4,
43.3, 62.6, 71.6, 77.49, 78.6, 79.6, 127.8, 127.9, 128.5, 137.8; Anal.
Calcd for C13H18O4; C, 65.53; H, 7.61; Found: C, 65.41; H, 7.79.
4.14. (1S,2S,3S,4S)-1-O-Benzyl-2-O-tert-butyldimethylsilyl-4-
vinyl-cyclopentane-1,2,3-triol 10d
½
a 2D5
ꢂ
¼ þ12:95 (c 1.39, CHCl3); 1H NMR (200 MHz CDCl3): d 0.10
(br s, 6H), 0.94 (br s, 9H), 1.62–1.69 (m, 1H, overlapped with a br s,
1H), 2.16–2.26 (m, 2H), 3.74–3.93 (m, 3H), 4.59 (d, J = 5.5 Hz, 2H),
4.97–5.11 (m, 2H), 5.72–5.91 (m, 1H), 7.25–7.35 (m, 5H); 13C NMR
(50 MHz CDCl3): ꢀ4.68, ꢀ4.63, 18.2, 25.8, 33.2, 45.2, 71.4, 77.2,
79.6, 80.5, 114.8, 127.3, 127.6, 128.2, 138.7, 140.9; Anal. Calcd for
4.18. (1S,2S,3S,4S)-4-Hydroxymethyl-cyclopentane-1,2,3-triol
[Carba-a-L-arabinofuranose] II
Following the same procedure as carried out for the preparation
C
20H32O3Si;C, 68.92; H, 9.25; Found: C, 68.65; H, 9.08.
of I, 12 (125 mg) was hydrogenated to afford pure II (70 mg, 90%)
as a thick oil. ½a D24
ꢂ
¼ ꢀ8:6 (c 1.4, MeOH) {lit.,6k
½
a 2D0
ꢂ
¼ ꢀ7:9 (c 1.2,
4.15. (1S,2S,3S,4R)-1-O-Benzyl-4-hydroxymethyl-cyclopentane-
1,2,3-triol 11
MeOH)}; 1H NMR (600 MHz D2O): d 1.22–1.26 (m, 1H), 1.73–1.79
(m, 1H), 2.07–2.12 (m, 1H), 3.39–3.42 (m, 1H), 3.54–3.57 (m,
1H), 3.60–3.65 (m, 2H), 3.92–3.95 (m, 1H); 13C NMR (150 MHz
D2O): 34.2, 45.3, 66.7, 72.5, 79.8, 80.9.
To a cooled (ꢀ78 °C) solution of 10c (348 mg, 1.0 mmol) in
CH2Cl2 (25 ml) was bubbled ozone gas until a blue color persisted.
To it was added PPh3 (300 mg, 1.15 mmol), and the blue color dis-
appeared immediately. The solution was brought to room temper-
ature and stirred for 40 min the solvent was removed from the
reaction mixture under reduced pressure. The residue was passed
through a short (200) silica gel column and quickly eluted with 0–
25% EtOAc in hexane to obtain an unstable aldehyde, which was ta-
ken in THF (25 ml). This solution was slowly added to a stirred sus-
pension of LiAlH4 (77 mg, 2.0 mmol) in THF (20 ml) at 10 °C. The
mixture was stirred for 1 h at 10 °C and then at room temperature
overnight. It was then cooled with ice water. The excess hydride
was decomposed by the dropwise addition of a saturated aqueous
solution of Na2SO4. The white precipitate formed was filtered and
washed with dry diethyl ether. The solvent was removed from
the combined washing under reduced pressure and the residue
was passed through a short (200) silica gel column and quickly
eluted with 0–10% MeOH/CHCl3 to obtain 11 (174 mg, 73.1%) as
a colorless oil, which was used as such for the next reaction. A por-
tion of the residue was subjected to spectral analysis for its charac-
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