ISSN:
0170-2041
Keywords:
Carbohydrates
;
Monosaccharides
;
Acetalization
;
Hexafluoroacetone
;
Altropyranoses
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Regio- and stereoselective direct acetalizations of chiral vicinal polyols with hexafluoroacetone (HFA) are described. Thus, the reaction of methyl α-D-mannopyranoside (1) and methyl a-L-rhamnopyranoside (5) with HFA affords cyclic 3, 4-Acetals accompanied by simultaneous inversion of configuration at C-3 when N, N′-dicyclohexylcarbodiimide (DCC) is added as a coreagent. Methyl 2-O-(cyclohexylcarbamoyl)-3, 4-O-(hexafluoroisopropylidene)-a-D-altropyranoside (2) and methyl 6-deoxy-3, 4-O-(hexafluoroisopropylidene)-a-L-altropyranoside (6), respectively, have been found to be the major products. The carbamoyl groups found in 2 and moreover in the byproduct 7 may be cleaved by methanolysis giving the Acetals 3 and 6, respectively. All of the products, 2, 3, 6, and 7 adopt a boat conformation as confirmed by NMR data and, additionally, ensured by X-ray analysis in the case of 7. The incorrect structural formula for compound 6, reported as “methyl 2, 3-O-(hexafluoroisopropylidene)-ct-L-rhamnopyranoside” in ref. [2], has to be corrected. The direct Acetalization described in this paper probably includes an intramolecular nucleophilic attack of a hemiacetal oxygen (4-position) on C-3 with substitution of an isourea function.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199419940219
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