Iodo furanoside

Following the success of the elimination-allylation and propargylation sequences, Madsen and coworkers investigated the corresponding elimination-vinylation reaction [37]. The vinylation, however, cannot be carried out directly under Barbier conditions because vinyl bromide does not insert zinc under the conditions for the reductive elimination preformed divinyl zinc was used instead [51,52], Treatment of iodo furanoside 55 with zinc dust and divinyl zinc in THF gave diene 56 in a good yield (85%) and excellent diastereoseleetivity (10 1) (Scheme 3.18). 

Benzyl 3-deoxy-3-fluoro-p-D-glucopyranoside, D-89 Benzyl 5-deoxy-3-C-(hydroxymethyl)-a-L-lyxofuranoside, D-230 Benzyl 3-deoxy-3-iodo-p-L-xylopyranoside, D-280 Benzyl l-deoxy-4,5-0-isopropylidene-D-erji/irO hexo-2,3-diulo-3,6-furanoside, D-186... 

For example, Madsen et al. reported a short synthetic strategy for preparation of conduritols, using as a key step a domino zinc-mediated liragmentation/allylation of protected methyl 5-deoxy-5-iodo-D-pentofuranosides followed by ring-closing olefin metathesis [39]. Thus, methyl furanoside 3 and 3-bromopropenyl acetate were treated with zinc in a THF/H2O mixture under sonication at 40°C. This resulted in one major product 14, which was isolated in a 72% yield as a 4 1 mixture of two isomers. Conduritol D (16) was obtained from diene 14 when this compound was subjected to RCM followed by deprotection (Scheme 3.8). 

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