Preparation of some carbohydrate pyrazolines by cycloaddition of diazomethane to nitroalkenic sugars
✍ Scribed by Hans H. Baer; Ian Gilron
- Publisher
- Elsevier Science
- Year
- 1987
- Tongue
- English
- Weight
- 474 KB
- Volume
- 164
- Category
- Article
- ISSN
- 0008-6215
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✦ Synopsis
Among the pioneering achievements carbohydrate research owes to H. 0. L. Fischer is the inception and early development of the chemistry of nitro sugars'.
Commencing" in 1944 and continuing'.4 until his death in 1960. Fischer and his associates provided the cornerstones for the important methodologies5 of sugarchain extension by nitroalkane addition, the introduction of nitrogenous functional: ity into sugars and cyclitols by way of dialdehyde cyclization. and the use of nitro carbohydrates as eminently versatile intermediates for many synthetic purposes. One prominent aspect of nitro sugar chemistry, exemplifying its preparative versatility, is the ease with which nitroalkenic sugar derivatives undergo useful addition reactions, especially" of the nucleophilic (Michael) type. Carbohydrate nitroalkenes can also serve as acceptors in 1,3-dipolar cycloadditions. although fewer examples have been reported. Thus, a number of 2,3-dideoxy-3-nitrohex-2-enopyranosides underwent dipolar addition with alkali azidesh and with diazomethane7, leading to the annellation of triazole and pyrazoline rings, respectively, to the pyranosidic structure. Nitrogen extrusion from the pyrazolino derivatives (e.g. 8) so obtained, afforded' pyranoid 2-C-methyl and 2.3-C-methylcne 3-nitro glycosides, and our interest in this subject was recently rekindled when we studied8 different methods for the preparation of nitrocyclopropano carbohydrates from terminal C-nitro alditols. We therefore decided to examine the addition of diazomethane to carbohydrates possessing a terminal nitroalkene grouping.
3-0-Acetyl-S,6-dideoxy-1 ,2-O-isopropylidene-6-nitro-cr-D_xylo-hex-S-eno-furanose9 (1) in ether reacted instantly with ethereal diazomethane at room temperature, and rapidly even at temperatures as low as -60". However, the reaction appeared to be quite complex, as more than 1 mol. equiv. of the reagent was consumed and several product spots occurred in t.1.c. When the amount of diazo-*Dedicated to the memory of Hermann 0. L. Fischer. 'Reactions of Nitro Sugars. part XLV. For part XLIV see ref. 8.