V. Fournière, I. Cumpstey / Tetrahedron Letters 51 (2010) 2127–2129
2129
the selenoethers 10–12 in excellent yield, using almost stoichiom-
Acknowledgements
etric quantities of the two carbohydrate reaction components, i.e.,
1.2–1.3 equiv of triflate with respect to selenolate. The coupling
reaction appears to work well for the synthesis of primary–sec
and one sec–sec linked systems. One by-product from the reaction
was the reduced compound 13,15 which was seen in all cases. To
investigate the source of this compound, we treated separately
the triflate 3 and selenoether 11 with sodium borohydride in
DMF at 50 °C. The triflate 3 gave significant amounts of the reduced
compound 13 after 3 h,16 whereas the selenoether 11 was not
reduced to 13 under the same conditions (the 1H NMR spectrum
of the crude reaction product showed only clean starting material
and no trace of 13). Hence the formation of 3-deoxysugar 13 during
the selenoetherification reactions is presumably due to the action
of borohydride on the 3-triflate 3, and not due to reduction of
the C–Se bond in the selenoether products.
Financial support from the Carl Trygger Stiftelse för Vetenskap-
lig Forskning, Vetenskapsrådet (the Swedish research council) and
a Stockholm University Ivar Bendixson stipend (to I.C.) is gratefully
acknowledged.
Supplementary data
Supplementary data (Experimental details for all described
reactions, including conversion of the respective alcohols18–20 into
the sulfonates 1–3, characterisation data for new compounds, and
copies of 1H and 13C NMR spectra for all new compounds) associ-
ated with this article can be found, in the online version, at
For the sec–sec linked compound 12, this reduced compound 13
was inseparable from the pseudodisaccharide product. Removal of
the acetonide protection from 12 gave the free selenoether pseudo-
disaccharide 14, which could be purified by column chromatogra-
phy and which was also characterized as its octaacetate 15.
Attempted deprotection of 10 and 11 by treatment with sodium
in liquid ammonia to cleave the benzyl ethers failed. Even when
quenching after very short reaction times (ca. 1 min) at À78 °C,
we found that the starting material had undergone comprehensive
decomposition to give none of the required debenzylated product.
The C–Se bonds are presumably susceptible to reduction under
these conditions.
References and notes
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C-glycosides,
carbasugars
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In a second approach to an unprotected Glc(Se3–6)Glc derivative,
we attempted a synthesis without protection on the glucose C-6-
modified fragment. Hence the 6-deoxy-6-iodosugar 16, available
in one step by Garegg iodination17a of methyl
a-glucoside following
Madsen’s procedure,17b was treated with potassium selenobenzoate
to give the 6-deoxy-6-selenoglucose derivative 17. When excess re-
agent was used, the 4-O-benzoate 18 was formed as a by-product
(1.2 equiv KSeBz; 17, 70%; 18, 21%) or as the major product (3 equiv
KSeBz; 18, 59%). Treatment of the selenobenzoate 17 with sodium
methoxide as before gave the diselenide 19, and reduction followed
by addition of triflate 3 to the reaction vessel gave the coupled prod-
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9. Comparing the bond angles and lengths in dimethyl ether, thioether and
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(C–O 1.42 Å, C–O–C 112°); (C–S 1.81 Å, C–S–C 99°); (C–Se 1.94 Å, C–Se–C 96°).
(Handbook of Chemistry and Physics, 74th edition, 1994, CRC). Crystal
structures of protected ether- and thioether-linked pseudodisaccharides have
values for bond lengths and angles (C–O 1.42 Å, C–O–C 114°);4 (C–S 1.83 Å,
C–S–C 103°)21 similar to those in the simple dimethyl derivatives.
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Non-glycosidically linked selenoether-bridged pseudodisaccha-
rides may be accessed in good yield by reduction of carbohydrate
diselenides in DMF to give selenolates that can displace a carbohy-
drate triflate in situto give selenoethers. Thebehaviour of theseleno-
etherification reactions is similar to the related thioetherification
reactions: primary–sec and sec–sec linked structures are obtained
in the coupling reactions without difficulty, unlike the preparation
of related N-linked structures, where the formation of linkages to
secondary centres is difficult.6 An unprotected selenoether 21 was
stable at rt and open to the air for weeks without appreciable degra-
dation. Thedeprotectionofbenzylethersisproblematic, but(Se3–6)-
linked structures may be formed using a more minimalist protecting
group strategy.
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21. Cumpstey, I.; Eriksson, L. Acta Crystallogr., Sect. E 2007, 63, o4197.