On the Absolute Configuration of Penlanfuran and Related Sesquiterpenoids of the Sponge Dysidea fragilis from the North‐Brittany Sea

Abstract

AbstractThe 1,4‐addition of vinylmagnesium bromide/CuBr‐SMe2 to (+)‐(4s)‐cryptone ((+)‐6) in THF in the presence of Me3SiCI gives the silylenol ether 7 which partly undergoes hydrolysis to ketone 8 on aqueous workup; residual 7 is hydrolyzed with pyridinium p‐toluenesulfonate (PyTsOH) to give 8 which is protected in situ with ethylene glycol and then ozonolized to give aldehyde ()‐10. The latter, on addition of 3‐lithiofuran followed by dehydration and deprotection with Py TsOH, gives the unnatural (4S)‐enantiomer (+)‐2 of noroxopenlanfuran. All processes, except 11 → (+)‐2, are of good yield. On the basis of previous chemical transformations, this also establishes the (4R)‐configuration for penlanfuran ((−)‐1) and other sesquiterpenoids of the sponge Dysidea fragilis from the North‐Brittany sea. Non viable routes to (±)‐noroxoperlanfuran ((±)‐2) are also discussed.