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A series of suitably functionalized C-linked carbohydrate derivatives 9-13 were prepared in good yields from alkenyl glycosides 1-4 by cross-metathesis reaction using Grubbs' catalyst [Cl 2 (PCy 3 ) 2 Ru=CHPh]. The reaction was also applied to 6-O-allyl ether 5 and N-Cbz allylamine 6. C-Linked glycopeptide homologue 15 was prepared in 65% yield by cross-metathesis of perbenzylated b-C-allyl mannopyranoside 1 and allyl glycine derivative 8. Finally, amine-ending C-glycoside 11 was subjected to a sequence of deprotection, amidation with p-iodobenzoic acid (EDC, HOBt, DIPEA, r.t., 12 h), Sonogashira reaction [Pd(PPh 3 ) 2 Cl 2 , Et 3 N, 65 °C, 6 h] and treatment with dicobalt octacarbonyl (60 °C, 6 h) to provide a 'molecular asterisk' 21 in 53% yield.

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A novel isomerization of O-allyl glycosides into prop-1-enyl glycosides was observed instead of cross-metathesis during an olefin metathesis reaction using Grubbs' ruthenium benzylidene catalyst (Cy3P)2RuCl2=CHPh (1), N-allyltritylamine, and N,N-diisopropylethylamine as necessary auxiliary reagents. In the search for a better catalytic system, it has been found that dichlorotris(triphenylphosphine)ruthenium(II), [(C6H5)3P]3RuCl2, (2) was much more efficient for the isomerization of allylic ethers. The labile prop-1-enyl group was easily hydrolyzed using HgCl2-HgO and the hemiacetals (25-32) were isolated in excellent yields (ca. 90%).Key words: allyl ether, carbohydrate, Grubbs' catalyst, isomerization, metathesis, deprotection.