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1-beta-(4-Imidazoyl)- and 1-beta-(5-uracilyl)-1,4-dideoxy-1,4-imino-L-lyxitols were synthesized stereoselectively via a sequential procedure by the addition of the corresponding metal salts of heterocycles, Swern oxidation, reductive aminocyclization, and deprotection. Their structures were determined based on X-ray crystallography. From the NMR measurements of their N-acyl derivatives, two rotational isomers were observed. Their bioassay is also described.

The perbenzylated D-ribofuranosyl fluoride is allowed to react with Grignard reagents of aromatic heterocycles such as thiophene, pyrrole, and indole in THF to afford the corresponding b-C-nucleosides in moderate yields. The present process can be also applied to perbenzylated D-glucopyranosyl fluoride and perbenzylated 2-deoxy-D-ribofuranosyl fluoride as sugar donors.Since the remarkable biological activity of naturally occurring showdomycin was recognized, the synthesis of Cnucleosides has attracted wide interest in the field of organic chemistry. 1 In our study on the use of D-ribofuranosyl fluoride as a sugar donor, 2 we found that aryl Grignard reagents reacted easily with perbenzylated D-ribofuranosyl fluoride without Lewis acids to give the corresponding C-nucleosides in a b-selective manner. Recently, Kool and co-workers reported a procedure to prepare aromatic C-nucleosides using protected D-deoxyribosyl chloride as a sugar donor. 3 We wish to report here a better and practical method for the b-selective synthesis of C-nucleosides by utilizing the sugar fluorides in place of the unstable sugar chlorides (Scheme 1).The reaction of arylmagnesium reagents with the sugar fluoride 1 was also examined. The reaction took place at room temperature to give the desired C-nucleosides with b-selectivity, while the yield of 3 increased at 50°C together with perbenzylated D-ribofuranoid glycals 4 as byproducts (Scheme 1, Table 2). From Entries 2-5 it is clear that the electron-rich benzene derivatives afford more glycals 4. The fact that the reaction with p-methoxyphenylmagnesium bromide gave glycal 4 in 44 % yield without the desired C-nucleoside, and the result of Entry 6 support this result.

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Simple Synthesis of Aromatic β-C-Nucleosides via Coupling of Aryl Grignard Reagents with Sugar Fluorides.-The reactions proceed generally with good β-selectivity. This selectivity is diminished when other metal reagents than Grignards are used. -(YOKOYAMA, M.; TOYOSHIMA, H.; SHIMIZU, M.; MITO, J.; TOGO, H.; Synthesis (1998) 4, 409-412; Dep.