Synthetic routes to 2′,3′-cyclopropanated and 2′,3′-unsaturated nucleosides

Abstract

. Can. J. Chem. 55,3996 (1977). Cyclopropyl glycopyranosides which solvolyze via a stabilized cyclopropyl carbinyl-oxocarbonium ion react under neutral conditions with nucleoside bases in nitromethane at 200°C to give good yields of the corresponding cyclopropanated nucleosides. Under similar conditions hex-2-enopyranosides (which solvolyze by allyl-oxocarbonium ions) do not react. However, under catalysis by mercuric bromide or acetic acid, the corresponding 2',3' unsaturated nucleosides are formed although accompanied by appreciable amounts of 1',2'-unsaturated-3'-nucleosides. Formation of the latter may be avoided if the hex-2-enopyranosides are first converted to the hex-2-enopyranosyl acetates by treatment with boron trifluoride and acetic anhydride. The derived acetates react with the nucleoside bases without catalysis to give anomeric mixtures of nucleosides, there being no trace of the unwanted 3'-nucleosides. STEVE YIK-KAI TAM et BERT FRASER-REID. Can. J. Chem. 55,3996 (1977). Les cyclopropyl glycopyrannosides lesquels se solvolysent via un ion cyclopropyl-oxocarbonium stabilise, reagissent dans des conditions de neutralite avec des bases nucleosides dans le nitromethane a 200°C pour conduire avec de bons rendements au nucltoside cyclopropyle correspondant. Dans des conditions similaires, les hexeno-2 pyrannosides (lesquels se solvolysent par un ion allyl-oxocarbonium) ne reagissent pas. Par contre, ces reactions catalysees par le bromure mercurique ou I'acide acetique conduisent aux nucleosides 2',3'-insatures correspondants quoique accompagnks d'une quantite apprbciable de nuclCosides-3' lf,2'-insatures. La formation de ce dernier peut-Ctre Cvitee si on transforme en premier lieu les hexkno-2 pyrannosides en acetate d'hexeno-2 pyrannosyle par action du trifluorure de bore et de I'anhydride acetique. Ces acetates reagissent, sans catalyseur, avec les bases nuclCosides pour conduire a des melanges anomeriques de nuclCosides. On n'observe aucune trace des nucl6osides-3' non desires.[Traduit par le journal]

Unsaturated Sugars: A Rich Platform for Methodological and Synthetic Studies

“…This extreme stability was exploited for the preparation of 2'-3'-cyclopropanated nucleosides, e.g. 20 (Scheme 6), [23] by merely subjecting the cyclopropyl glycoside 16 or its homoallyl relative 17 to boiling nitromethane containing the heterocyclic base. Scheme 6.…”

Glycoscience

“…The study of rearrangement products from d-xylulose (93) with amines and amino acids (Scheme 29) was very important to rationalize the general aspects concerning the tendency of rearrangement of different ketoses [106]. d-Xylulose underwent the rearrangement easily followed by d-fructose and l-sorbose.…”

“…An example of the complexity of the mixture of possible products is the reaction of 2-amino-2-deoxy-d-glucose hydrochloride with ammonia, as conducted by Taha [114] (Scheme 32). He found five main products, which were the unreacted starting material, the cyclization products, 2-methyl-6-d-arabinosylpyrazine (104), 2-methyl-5-d-arabinosyl-3-d-erythrosylpyrazine (105), 2,5-bis-(d-arabinosyl)pyrazine (106), and a dark-brown amorphous substance which consisted of products of further decomposition. From this it can be concluded that careful control of the reaction conditions is very important for the formation of the products.…”

“…In this way compounds 76 [105] and 77 [106] are converted to cyclopropa-furanoid and -pyranoid nucleosides (Schemes 25 and 26, respectively). …”

“…White et al [46] employed the thermal rearrangement of the related vinyl ether 104 to aldehyde 105 for the total synthesis of monic acid C (106). Perspectives…”