Novel platinum-catalyzed ring-opening of 1,2-cyclopropanated sugars with alcohols. Stereoselective synthesis of 2-C-branched glycosides [7]

Full text of DOI:10.1021/ja982964k

J. Am. Chem. Soc. 1998, 120, 12137-12138
12137
Novel Platinum-Catalyzed Ring-Opening of
,2-Cyclopropanated Sugars with Alcohols.
Scheme 1
1
Stereoselective Synthesis of 2-C-Branched Glycosides
J u¨ rgen Beyer and Robert Madsen*
Department of Organic Chemistry
Technical UniVersity of Denmark
DK-2800 Lyngby, Denmark
insertion of platinum into cyclopropanes to give platinacyclo-
butanes12 which are usually fairly stable and can be isolated.
However, for alkoxy and siloxy cyclopropanes platinum-catalyzed
ring-opening of the cyclopropane with rearrangement to olefins
ReceiVed August 18, 1998
has been described.1
3-15
We anticipated that 1,2-cyclopropan-
ated sugars would undergo a similar transformation and treated
cyclopropane 1 with Zeise’s dimer [Pt(C )Cl (2) (Scheme
16
2
H
4
2 2
]
Many C-branched sugars have been found in nature particularly
as glycan portions of antibiotics.1,2 C-Branched sugars have also
1). Unexpectedly, the major product observed was the benzyl
glycoside 4 isolated in 21% yield as a 12/1 R/â mixture.
Presumably, during the reaction some benzyl alcohol is released,
which reacts with platinacyclobutane 3. In fact, when the reaction
was carried out with added benzyl alcohol, the glycoside 4 was
been identified as important subunits in many natural products,3
,4
and especially in macrolides the macrocyclic ring structure is often
comprised of a long-chain C-branched sugar.2 Accordingly, many
total syntheses of natural products have started from a suitable
protected C-branched sugar.3 However, synthesis of C-branched
sugars is not trivial and problems are frequently encountered with
controlling stereochemistry at the C-branching point and the
anomeric center.1 Herein, we report a new glycosylation reaction
1
7
obtained in 95% yield, again as a 12/1 R/â mixture. On scale-
up the amount of Zeise’s dimer could be lowered to 1 mol %
without affecting the yield of 4. Use of deuterated benzyl alcohol
gave the monodeuterated glycoside 5. To further probe the scope
of this transformation, we investigated other cyclopropanes and
nucleophiles (Chart 1) as shown in Table 1.
-5
,6
7
for preparation of 2-C-branched glycosides by employing a
platinum-catalyzed ring-opening of 1,2-cyclopropanated sugars.8
Additionally, this represents to the best of our knowledge the first
example of a platinum-catalyzed ring-opening of a cyclopropane
with an alcohol.
Chart 1
Recently, several efficient methods have been developed for
stereocontrolled synthesis of 1,2-cyclopropanated sugars from
glycals.9 Ring-opening of these cyclopropanes has previously
9b
9c,10
9a,11
been achieved by mercury, strong acid,
or halonium ion
mediated solvolysis. We were, however, attracted to a different
strategy and decided to explore a transition metal-catalyzed ring-
opening. In this context, substantial work has described the
(
1) Chapleur, Y.; Ch e´ tien, F. in PreparatiVe Carbohydrate Chemistry;
Hanessian, S., Ed.; Marcel Dekker: New York, 1997; pp 207-262. Yoshima,
J. AdV. Carbohydr. Chem. Biochem. 1984, 42, 69.
(
2) Celmer, W. D. Pure Appl. Chem. 1971, 28, 413.
(
3) Hanessian, S. Total Synthesis of Natural Products: The Chiron
Approach; Pergamon Press: Oxford, 1983.
A wide variety of alcohols can participate in the ring-opening
reaction, giving C-branched glycosides ranging from simple
methyl glycosides to more complex disaccharides.18 Yields range
from 50 to 97% and very high diastereoselectivity is obtained at
(
4) Fraser-Reid, B. Acc. Chem. Res. 1996, 29, 57.
(
5) For some recent examples, see: Makoto, B.; Nishikawa, T.; Isobe, M.
Tetrahedron 1998, 54, 6639. Chiba, N.; Takeoka, J.; Ando, K.; Tsutsumi, N.;
Ogawa, S. Tetrahedron 1997, 53, 16287. Sasaki, M.; Inoue, M.; Tachibana,
K. J. Org. Chem. 1994, 59, 715. Sato, K.-i.; Bokura, M.; Moriyama, H.;
Igarashi, T. Chem. Lett. 1994, 37. Alonso, R. A.; Burgey, C. S.; Rao, B. V.;
Vite, G. D.; Vollerthun, R.; Zottola, M. A.; Fraser-Reid, B. J. Am. Chem.
Soc. 1993, 115, 6666.
(
(
(
12) Jennings, P. W.; Johnson, L. L. Chem. ReV. 1994, 94, 2241.
13) Doyle, M. P.; van Leusen, D. J. Org. Chem. 1982, 47, 5326.
14) Ikura, K.; Ryu, I.; Kambe, N.; Sonoda, N. J. Am. Chem. Soc. 1992,
(
6) For a recent innovative approach, see: Linker, T.; Sommermann, T.;
Kahlenberg, F. J. Am. Chem. Soc. 1997, 119, 9377.
7) For recent reviews on O-glycoside synthesis, see: Boons, G.-J. Contemp.
Org. Synth. 1996, 3, 173. Boons, G.-J. Tetrahedron 1996, 52, 1095.
1
14, 1520.
15) Pt(II)-catalyzed isomerization of ethoxy cyclopropanes gives alkylated
ketones, see: Hoberg, J. O.; Jennings, P. W. Organometallics 1996, 15, 3902.
(
(
(
8) Previously, efficient glycosylation strategies have been developed by
(
16) When we treated cyclopropane A with Zeise’s dimer we obtained
using 1,2-epoxy and 1,2-aziridino sugars as glycosyl donors, see: Danishefsky,
olefinic product B:
S. J.; Bilodeau, M. T. Angew. Chem., Int. Ed. Engl. 1996, 35, 1380.
(
9) (a) Ramana, C. V.; Murali, R.; Nagarajan, M. J. Org. Chem. 1997, 62,
7
694. (b) Scott, R. W.; Heathcock, C. H. Carbohydr. Res. 1996, 291, 205. (c)
Hoberg, J. O.; Claffey, D. J. Tetrahedron Lett. 1996, 37, 2533. (d) Timmers,
C. M.; Leeuwenburgh, M. A.; Verheijen, J. C.; van der Marel, G.; van Boom,
J. H. Tetrahedron: Asymmetry 1996, 7, 49. (e) Henry, K. J., Jr.; Fraser-Reid,
B. Tetrahedron Lett. 1995, 36, 8901. (f) Hoberg, J. O.; Bozell, J. J. Tetrahedron
Lett. 1995, 36, 6831.
2 2
(17) No reaction occurred in the absence of Zeise’s dimer. PtCl (PhCN)
was less reactive while acids (TsOH, BF
3
‚OEt
2
, TMSOTf) and other platinum
) failed to catalyze the ring-
(
10) Hoberg, J. O. J. Org. Chem. 1997, 62, 6615.
catalysts (Pt(PPh
opening.
3
)
4
, (PPh
3
)
2
Pt(C
2
H
4
), (PPh PtCl
3
)
2
2
(11) Meng, D.; Bertinato, P.; Balog, A.; Su, D.-S.; Kamenecka, T.;
Sorensen, E. J.; Danishefsky, S. J. J. Am. Chem. Soc. 1997, 119, 10073.
Ramana, C. V.; Nagarajan, M. Synlett 1997, 763.
(18) No ring-opening occurred with water as nucleophile under the
conditions in Table 1.
1
0.1021/ja982964k CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/10/1998

12138 J. Am. Chem. Soc., Vol. 120, No. 46, 1998
Communications to the Editor
Table 1. Pt(II)-Catalyzed Ring-Opening of Cyclopropanes
Scheme 2
electron-withdrawing ester substituents undergo the ring-opening
reaction (entries 14 and 15) although some transesterification can
occur. Glycosyl arenes can also be obtained when electron-rich
phenols are used as O-nucleophiles (entry 16). The reaction
probably goes through an intermediate O-aryl glycoside that
1
9
subsequently undergoes a Fries-type rearrangement to the
corresponding glycosyl arene.
A plausible reaction sequence for the ring-opening is depicted
in Scheme 2. Oxidative addition of the cyclopropane to plati-
num(II) would give platinacyclobutane 13. In 13 the polarization
of the platinum(IV)-carbon σ bond20 is further enhanced by
electron donation from the sugar ring oxygen. Accordingly, 13
2
1
is believed to have substantial oxocarbonium ion character.
Nucleophilic attack of the alcohol would give glycoside 14 in
which platinum can be coordinated to either one of the two
oxygens at C-1. Reductive elimination from 14 would then give
the C-branched glycoside and platinum(II).22
In summary, we have developed a novel platinum-catalyzed
ring-opening of carbohydrate-derived cyclopropanes with alcohol
nucleophiles. Further studies on the applications of this new
transformation are currently in progress.
Acknowledgment. We thank the Danish Natural Science Research
Council for financial support.
Supporting Information Available: Experimental procedures and
characterization data for all ring-opening products as well as details of
stereochemical proofs (9 pages, print/PDF). See any current masthead
page for ordering information and Web access instructions.
a
Reactions were conducted with 0.8 mmol of cyclopropane and 1.6
mmol of alcohol in 4 mL of solvent. CH
2 2
Cl at room temperature for
1
°
5 h was used for cyclopropanes 1, 6, 7, and 8 while toluene at 50-70
b
C for 1.5-4 h was used for 9. Isolated yield after column chroma-
JA982964K
c
tography. The product contained 17% of the corresponding methyl
ester.
(
19) Mahling, J.-A.; Jung, K.-H.; Schmidt, R. R. Liebigs Ann. 1995, 461.
20) Ye, Z.; Dimke, M.; Jennings, P. W. Organometallics 1993, 12, 1026.
(
the newly formed C-1 stereocenter. The R-glycoside, favored
by the anomeric effect, is the major product in all O-glycosylations
regardless of the stereochemistry of the starting cyclopropane
(21) Palladium species with oxocarbonium ion character have recently been
identified in Heck arylation of dihydrofuran, see: Hii, K. K.; Claridge, T. D.
W.; Brown, J. M. Angew. Chem., Int. Ed. Engl. 1997, 36, 984.
(
22) For ester-substituted cyclopropanes the involvement of a six-membered
(entries 1-15). Also less reactive cyclopropanes containing
oxaplatinacycle also has to be considered in the catalytic cycle (see ref 13).