Showdomycin acetate, synthesis

These acid-catalyzed C-glycosylations were successfully extended to the D-ribofuranose series by Sorm and coworkers,148 who utilized the reaction in the first reported synthesis of showdomycin. Thus, treatment of 2,3,5-tri-0-benzoyl-/3-D-ribofuranosyl bromide (81) with 1,2,5-trimethoxybenzene in the presence of zinc oxide gave 2,4,6-trimethoxy-l-(2,3,5-tri-0-benzoyl-/3-D-ribofuranosyl)benzene (196). Ozonolysis of the corresponding acetate derivative, followed by esterification, gave the highly functionalized C-/3-I>ribofuranosyl derivative (197), which was used as a key intermediate in the synthesis of showdomycin (see Section III,l,b). 

Phenylselenoetherification. This reaction provides a short synthesis of the C-nucleosides showdomycin (10) and epishowdomycin (11) from D-ribosc (7). Thus the stabilized ylide 8, derived from maleimide, couples with 7 in acetic acid to form 9. Cyclization with QH SeCl in refluxing trimethyl borate gives an unstable product, which on oxidation gives a mixture of 10 and 11. 

A new high-yielding synthesis of showdomycin (14) utilizes the reaction of l,2-bis(trimethylsilyloxy)cyclobutene with a ribofuranosyl acetate derivative as outlined in Scheme 1. A synthesis of (3jR, 5)-3,4-dihydroshowdomycin (15)... 

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