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

Article abstract of DOI:10.1002/hlca.19900730314

The 1,4-addition of vinylmagnesium bromide/CuBr*SMe2 to (+)-(4S)-cryptone ((+)-6) in THF in the presence of Me3SiCl gives the silyl enol ether 7 which partly undergoes hydrolysis to ketone 8 on aqueous workup; residual 7 is hydrolyzed with pyridinium p-toluenesulfonate (Py*TsOH) 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-Britanny sea.Non viable routes to (+/-)-noroxopenlanfuran ((+/-)-2) are also discussed.