New approach to sugar dienes; Useful building blocks for the synthesis of bicyclic derivatives

Article abstract of DOI:10.1055/s-0033-1339374

A sugar aldehyde with silyl protection at C1, readily prepared from methyl α-d-glucopyranoside, reacted with allylborate or allylchromium reagents to afford the corresponding (anti) adducts, which were selectively converted into either E- or Z-diene. Deprotection of the anomeric position with TBAF proceeded in excellent yield, and further functionalization of the resulting hemiacetal led to the formation of complex bicyclic products such as highly functionalized oxazolidines. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0033-1339374

LETTER
▌1813
lNetteerw Approach to Sugar Dienes; Useful Building Blocks for the Synthesis of
Bicyclic Derivatives
New Approach to Sugar Dienes
Grzegorz Witkowski, Sławomir Jarosz*
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
Fax +48(22)6326681; E-mail: slawomir.jarosz@icho.edu.pl
Received: 23.05.2013; Accepted after revision: 13.06.2013
(Ph3P=CHCO2Me) to give the respective cis-hydrindane 7
Abstract: A sugar aldehyde with silyl protection at C1, readily pre-
(Scheme 2).5b,6
pared from methyl α-D-glucopyranoside, reacted with allylborate or
allylchromium reagents to afford the corresponding (anti) adducts,
only E
which were selectively converted into either E- or Z-diene. Deprot-
ection of the anomeric position with TBAF proceeded in excellent
yield, and further functionalization of the resulting hemiacetal led to
the formation of complex bicyclic products such as highly function-
alized oxazolidines.
SnBu3
O
O
ZnCl2
ref. 5
5
5
BnO
BnO
1
OMe
1
BnO
OBn
BnO
OBn
Key words: carbohydrates, chiral pool, cycloaddition, stereoselec-
tive synthesis, protecting groups
2
1
(E/Z) ~5:1
ref. 5
OBn
H
OBn
OBn
H
Synthesis of complex, optically pure compounds from
readily available starting material, the ‘chiron approach’,1
is a well-established method in synthetic organic chemis-
try. Sugar chirons are particularly useful in the prepara-
tion of polyhydroxylated carbo- and heterocyclic
compounds, which are regarded as sugar mimics;2 be-
cause of their similarity to ‘normal’ sugars, they efficient-
ly block specific enzymes.3 The synthesis and application
of bicyclic derivatives is also a subject of interest.4
BnO
CO2Me
H
H
OBn
R
O
BnO
3
4
Scheme 1 Carbobicyclic compounds from sugar allyltins
S
only Z
SnBu3
We have proposed a general and convenient methodology
for the preparation of enantiomerically pure carbobicyclic
systems from sugar allyltins (Scheme 1).5 Our approach is
based on a controlled fragmentation of these organometal-
lics to dienoaldehydes 2, with exclusively the E-configu-
ration across the internal double bond. Such highly
functionalized dienoaldehydes can be further used as
starting materials for the preparation of cis-decalins and
trans-perhydroindanes derivatives, for example, 3 and 4,
respectively (Scheme 1).5
O
H
O
1
5
140 °C
5
BnO
OMe
BnO
BnO
1
Ph3P=CHCO2Me
BnO
OBn
OBn
5
6
H
glucose
BnO
CO2Me
H
OBn
BnO
7
We faced, however, a significant problem with the effi-
cient preparation of isomeric Z-diene 6, which we wanted
to use to prepare the alternative stereoisomers of 3 and 4:
trans-decalin and cis-hydrindane systems. A partial solu-
tion was found in the thermal degradation of secondary
sugar allyltin 5, which provided the cis-dienoaldehyde,
but this diene was quite unstable and could not be isolated
in pure form, which was a significant limitation of our
method. The only example of the application of this diene
in the synthesis of bicyclic derivatives was demonstrated
by thermal (xylene, 140 °C) degradation of 5 conducted in
the presence of the stabilized phosphorane
Scheme 2 Transformation of secondary sugar allyltins
Here, we would like to report an efficient method of the
synthesis of terminal sugar dienes with either E- or Z-con-
figuration across the internal double. Reaction of alde-
hydes
with
substituted
(E)-allylborones7
or
allylchromium reagents8 provides homoallylic systems
with high syn/anti selectivity in favour of the anti-ad-
ducts. The allyl unit, possessing a trimethylsilyl group, is
converted into the β-hydroxysilane, which can be selec-
tively transformed into the corresponding diene. Elimina-
tion of trimethylsilanol from these adducts under base-
mediated conditions provides Z-diene, whereas elimina-
tion induced by acids leads to the opposite E-olefin
(Scheme 3).
SYNLETT 2013, 24, 1813–1817
Advanced online publication: 26.07.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0033-1339374; Art ID: ST-2013-B0480-L
© Georg Thieme Verlag Stuttgart · New York

1814
G. Witkowski, S. Jarosz
LETTER
yield of the desired process. Catalytic systems such as
those reported by Fürstner13 were not tested due the diffi-
culties of handling anhydrous chromium(II) chloride.
selectively E
CrII and
TMS
H
H2SO4
KH
R
OH
O
R
Br
or
H
H
Treatment of 9 with sodium or potassium hydroxide or so-
dium hydride, even at elevated temperature, did not pro-
vide an elimination product. However, potassium hydride
induced elimination to the diene with Z-configuration
across the internal double bond (10) in a reaction that was
complete in 15 minutes.
R
H
H
H
TMS
H
R
TMS
Bpin
only anti
selectively Z
Scheme 3 Selective synthesis of E- and Z-dienes
Elimination of β-hydroxysilane performed with sulfuric
acid provided the opposite E-diene 11 (Scheme 4); boron
trifluoride etherate gave a complex mixture of products.
The isomeric purity of both sugar dienes (10 and 11) was
very high and exceeded 99:1 (determined by HPLC anal-
ysis).
This strategy was applied for the efficient preparation of
sugar-derived dienes. Glucopyranoside 89 was oxidized to
the corresponding aldehyde 8a, which, upon reaction with
1-bromo-1-(trimethylsilyl)-prop-2-ene10 provided – ac-
cording to a standard Nozaki and Hiyama procedure11
–
Diene 10 or 11 may be used directly to build another
framework with preservation of the original glycosidic
unit, which can be further functionalized to generate more
complex products. However, much more interesting and
promising, would be conversion of these protected dienes
into free sugars 12 or 13 (Scheme 5), which should allow
the desired functionality to be introduced at the C1-posi-
tion. A convenient methodology for removal of methyl
protection from the anomeric position was, therefore,
needed. Such a goal can be very challenging, especially in
the gluco-series, since hydrolysis of the methyl glucopy-
ranoside in partially protected derivatives is usually car-
ried out under rather harsh conditions.14 This was also the
case here. The best results of the hydrolysis at the anomer-
ic position in 10 and, separately, 11, was obtained by
treatment with 2 M triflic acid in glacial acetic acid, but
the yields of the products were very low (ca. 20%). More-
over, the results were not always reproducible. However,
the configuration across the internal double bond re-
mained unchanged (Scheme 5).
adduct 9 as a mixture of two stereoisomers with the antic-
ipated anti-configuration (Scheme 4).
OH
TEMPO
TCICA
O
OMe
OBn
ref. 9
methyl
α-D-gluco
pyranoside
CH2Cl2
r.t., 20 min
BnO
OBn
8
TMS
Bpin
O
TMS
toluene, r.t., 21 d or
O
H
O
CrCl3
LiAlH4
TMS
HO
THF, 0 °C
8a
Br
9 (two anti isomers)
KH, THF
r.t., 10 min
(76% yield
from 8)
H2SO4, THF, r.t., 15 min
(71% yield from 8)
R1
R2
R1
R2
O
OMe
OMe
OBn
O
O
O
OMe
OBn
OH
2 M TfOH, AcOH
BnO
OBn
BnO
1
1
5
5
60 °C, 1,5 h
(10–25% yield)
OBn
OBn
BnO
BnO
OBn
10
11
OBn
OBn
10 (R1 = vinyl, R2 = H)
11 (R1 = H, R2 = vinyl)
12 (R1 = vinyl, R2 = H)
13 (R1 = H, R2 = vinyl)
Scheme 4 Synthesis of dienes 10 and 11 from methyl α-D-glucopy-
ranoside
Scheme 5 Hydrolysis of 10 and 11
The same product was also prepared in the reaction of al-
dehyde 8a with pinacol (E)-1-(trimethylsilyl)prop-1-ene-
3-boronate,12 followed by simple chromatography on sili-
ca. However, although allylboration was much easier to
perform by simple mixing of aldehyde and allylboronic
ester, the reaction was very slow and full conversion was
achieved only after three weeks.
Compounds 12 and 13 may be used as starting materials
for further synthesis of complex products, but the applica-
bility of this method was rather limited because of the
very low yield of deprotection at C1. Changing the group
protecting the anomeric hydroxyl group to another pro-
tecting group that was more easily removable under ‘nor-
mal’ conditions was expected solve the problem. We
therefore decided to replace the methyl moiety with a silyl
group, which are typically easily removed in the presence
of fluoride anions.
Nozaki–Hiyama coupling gave the expected product 9 in
relatively short time (18 h) but this approach requires an-
hydrous solvents and large amounts of anhydrous chromi-
um(III) chloride and lithium aluminium hydride.
Moreover, we also observed the product of the reduction
of aldehyde 8a, glucopyranoside 8, which reduced the
Synlett 2013, 24, 1813–1817
© Georg Thieme Verlag Stuttgart · New York

LETTER
New Approach to Sugar Dienes
1815
Methyl α-D-glucopyranoside was converted into substi- tetrabutylammonium fluoride and acetic acid in THF
tuted glucopyranose 15 according to a known procedure.15 within seven hours.
Protection of the anomeric hydroxyl group in 15 with tert-
butyl-diphenylsilyl chloride, followed by deprotection of
The corresponding dienes with the free anomeric position,
12 (with E-configuration) and 13 (Z), were obtained in
high yield, 86 and 84%, respectively, as a 1:1 mixture of
the terminal 6-OH, provided silyl glucoside 16 as a single
β-anomer (J1,2 = 7.5 Hz)16 in excellent yield (Scheme 6).
α/β anomers (Scheme 7).
Dienes 12 and 13 were used as starting materials for the
preparation of highly functionalized heterocycles
methyl a-D-glucopyranoside
(Scheme 8). Reaction of E-diene 12 with hydroxylamine
ref. 15
afforded the corresponding oxime 20 as an inseparable
(i) TBDPSCl
imidazole,
CH2Cl2, r.t., 2 h
OH
OAc
mixture of syn/anti isomers. The same reaction performed
with Z-diene 13 provided oxime 21 also as an inseparable
mixture of geometrical isomers.
O
OTBDPS
OBn
O
OH
(ii) MeONa
MeOH, r.t., 0.5 h
(76% yield
BnO
BnO
OBn
OBn
OBn
from 15)
16
15
OH
H2NOH⋅HCl
py, r.t., 24 h
O
OH
HO
N
Scheme 6 Synthesis of silyl β-glucopyranoside 16
BnO
OBn
BnO
OBn
(82%)
This molecule was converted into dienes 18 and 19 by us-
ing the same methodology used for 8a (Scheme 7).17
OBn
12
OBn
20
(E/Z oxime mixture)
TEMPO, TCICA
16
CH2Cl2, r.t., 20 min
O
O
H
PIDA, TFA (cat.)
MeOH, r.t., 18 h
H
N
HO
N
+
O
TMS
HO
(60%)
TMS
Bpin
BnO
OBn
24b
O
OBn
24a
H
O
toluene, r.t., 4 d
24a/24b = 81:19
16a
17 (two anti isomers)
OH
KH, THF
r.t., 10 min
(84% yield
from 16)
H2NOH⋅HCl
py, r.t., 24 h
O
OH
HO
N
H2SO4, THF, r.t., 15 min
(80% yield from 16)
BnO
OBn
BnO
OBn
(81%)
OBn
OBn
21
O
R
R
O
13
(E/Z oxime mixture)
BnO
OBn
BnO
OBn
OBn
OBn
TBAF
AcOH
THF
r.t., 7 h
(86%)
TBAF
AcOH
THF
r.t., 7 h
(84%)
O
18 (R = β-OTBDPS)
12 (R = α/β-OH)
19 (R = β-OTBDPS)
O
H
H
PIDA, TFA (cat.)
MeOH, r.t., 18 h
N
HO
N
13 (R = α/β-OH)
+
(62%)
BnO
OBn
Scheme 7 Efficient synthesis of dienes 18 and 19
25b
OBn
25a
25a/25b = 95:5
Oxidation of 16 to the corresponding aldehyde 16a pro-
ceeded smoothly with TEMPO;18 this aldehyde reacted
much faster with the appropriate boronate than 8a (only
four days) and provided β-silyl-alcohol 17 as a mixture of
two stereoisomers (presumably anti as in case of 9). The
synthesis of sugar dienes is, therefore, much easier and
does not require sophisticated synthetic procedures.
Scheme 8 Synthesis of isoxazolines
Both oximes were unusually stable and did not undergo
either hetero-Diels–Alder reaction (even under high tem-
perature and/or high pressure19) or 1,3-dipolar cycloaddi-
tion (olefin/oxime20 cyclization). The latter was very
surprising, since cyclization of the close analogue of such
oximes, compound 22, having one carbon atom less than
20 or 21, occurred readily and afforded the cyclic product
23 in high yield and with very high selectivity (Scheme
9).20b
Removal of the silyl group protecting the anomeric posi-
tion in 18 and 19 was, in contrast to 10 or 11, straightfor-
ward and could be performed conveniently with
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 1813–1817

1816
G. Witkowski, S. Jarosz
LETTER
(2) (a) Arjona, A.; Gomez, A. M.; Lopez, J. C.; Plumet, J. Chem.
Rev. 2007, 107, 1919. (b) Zhou, J.; Wang, G.; Zhang, L.-H.;
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BnO
OH
BnO
BnO
H2NOH⋅HCl
N
O
py
BnO
H
OBn
22
OBn
(3) (a) Ganem, B. Acc. Chem. Res. 1996, 29, 340. (b) Bols, M.
Acc. Chem. Res. 1998, 31, 1. (c) Heightman, T. D.; Vasella,
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H
BnO
O
N
H
BnO
H
OBn
(4) (a) Nowogródzki, M.; Jarosz, S. Curr. Org. Chem. 2010, 14,
533. (b) Nowogródzki, M.; Jarosz, S. Curr. Org. Chem.
2010, 14, 601. (c) Jarosz, S.; Nowogródzki, M.; Magdycz,
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23
Scheme 9 1,3-Dipolar cycloaddition of 22
Conversion of the oximes into highly functionalized het-
erocyclic derivatives was, therefore, realized through an-
other route. Treatment of 20 and, separately, 21 with
(diacetoxy)iodobenzene in the presence of a catalytic
amount of trifluoroacetic acid afforded the corresponding
nitrile oxides, which underwent intramolecular 1,3-dipo-
lar cycloaddition, providing isoxazoline 24a (from E-di-
ene 20) with moderate selectivity (24a/24b, 81:19) and
isoxazoline 25a (from Z-diene 21) with very high selectiv-
ity (25a/25b, 95:5; Scheme 8). In both cases, the products
could be easily separated by column chromatography. The
configurations of the main products 24a and 25a, as well
as the minor sideproducts 24b and 25b, were established
on the basis of NOE experiments (see the Supporting In-
formation).
(6) Jarosz, S.; Szewczyk, K.; Zawisza, A. Tetrahedron:
Asymmetry 2003, 14, 1709.
(7) (a) Roush, W. R.; Grovoer, P. T. Tetrahedron 1992, 48,
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Ber. 1990, 123, 2395. (d) Wang, K. K.; Liu, C.; Gu, Y. G.;
Burnett, F. N.; Sattsangi, P. D. J. Org. Chem. 1991, 56, 1914.
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L.; Correia, I.; Lequin, O. Eur. J. Org. Chem. 2011, 5959.
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In conclusion, we have developed an efficient method of
the synthesis of highly functionalized terminal conjugated
dienes with the D-glucose scaffold in which the anomeric
position is not protected. Such dienes can be prepared
with very high selectivity (>99:1) and both geometrical
isomers, with the E- or Z-configuration across the internal
double bond, are available in high yield. The fact that the
anomeric position is not protected allows suitable func-
tionality to be introduced at C1, which opens a convenient
route to efficient and stereoselective synthesis of bicyclic
products. The availability of isomeric dienes differing in
configuration at the double bond makes this approach to
such complex targets especially attractive.
Acknowledgment
Support from Grant POIG.01.01.02-14-102/09 (partly financed by
the European Union within the European Regional Development
Fund) is acknowledged.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnoIufproig
m
iotSrat
ungIifoop
r
t
(17) Synthesis of Dienes 18 and 19
Oxidation: Silyl pyranoside 16 (2.08 g, 3.02 mmol) and
TEMPO (4.7 mg, 30.2 μmol) were dissolved in anhydrous
CH2Cl2 (30 mL) and placed in a water/ice bath.
Trichloroisocyanuric acid (0.77 g, 3.32 mmol) was added in
one portion and, after 15 min, TLC (hexanes–EtOAc, 7:1)
References and Notes
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references therein.
Synlett 2013, 24, 1813–1817
© Georg Thieme Verlag Stuttgart · New York

LETTER
indicated the disappearance of starting material (Rf = 0.5)
New Approach to Sugar Dienes
1817
THF (70 mL) to which KH (30% in mineral oil, 1.80 g, 13.4
mmol) was added within 5 min. After 5 min, TLC (hexanes–
EtOAc, 7:1) indicated the disappearance of starting material
(Rf = 0.5 and 0.6) and formation of a new product (Rf = 0.7).
Et2O (140 mL) and H2O (70 mL) were added and the
solution was saturated with NaCl. The phases were separated
and the organic layer was dried, concentrated, and the
residue was purified by flash chromatography (hexanes–
Et2O, 11:1→9:1→7:1→5:1) to afford 19 (76% yield from
16) as a colorless oil.
and formation of a new product (Rf = 0.4). The mixture was
filtered through a Celite pad, diluted with Et2O (30 mL), and
washed with 5% Na2S2O3 (10 mL), 1 M NaOH (25 mL), 1 M
H2SO4 (25 mL), H2O (25 mL), and brine (25 mL), and
concentrated. The residue was dissolved in toluene (50 mL)
and evaporated to afford the crude aldehyde.
Allylboronation: Crude aldehyde was dissolved in
anhydrous toluene (30 mL) to which pinacol (E)-1-
(trimethylsilyl)-1-propene-3-boronate (0.75 g, 3.02 mmol)
was added. The mixture was stirred for 4 days, after which
TLC (hexanes–EtOAc, 7:1) indicated the disappearance of
starting material (Rf = 0.4) and formation of a two new
products (Rf = 0.5 and 0.6). The solution was passed through
a column of silica and concentrated to afford the crude
silanol as a mixture of anti diastereomers.
Elimination to (E)-diene 18: Crude silanol was dissolved in
THF (70 mL), then concentrated sulfuric acid (7.2 mL, 134
mmol) was added within 5 min. After 10 min, TLC
(hexanes–EtOAc, 7:1) indicated the disappearance of
starting material (Rf = 0.5 and 0.6) and formation of a new
product (Rf = 0.7). Et2O (140 mL) and H2O (70 mL) were
added and the solution was saturated with NaCl. The phases
were separated and the organic layer was dried and
concentrated. The residue was purified by flash
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chromatography (hexanes–Et2O, 11:1→9:1→7:1→5:1) to
afford 18 (71% yield from 16) as a colorless oil.
Elimination to (Z)-diene 19: Crude silanol was dissolved in
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 1813–1817

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