Asymmetric Total Synthesis of (11r,12s,13s,9z,15z)-9,12,13-Trihydroxyoctadeca-9,15-Dienoic Acid, a Self-Defensive Agent against Rice-Blast Disease
The Diels-Alder adduct of furan and 1-cyanovinyl (1'R)-camphanate was converted into methyl[(tert-butyl)dimethylsilyl 5-deoxy-2,3-O-isopropylidene-beta-L-ribo-hexofuranosid]uronate ((+)-4). Reduction with diisobutylaluminium hydride gave the corresponding aldehyde which was condensed with the ylide derived from triphenyl(propyl)phosphonium bromide to give (1R,2S,3S,4S)-1-[(tert-butyl)dimethylsilyloxy]tetrahydro-2,3-(isopropyli denedioxy)-4-[(Z)-pent-2'-enyl]furan ((+)-7). Removal of the silyl protective group gave a mixture of the corresponding furanose that underwent Wittig reaction with the ylide derived from [8-(methoxycarbonyl)octyl]triphenylphosphonium bromide to yield methyl (11R,12S,13S,9Z,15Z)-13-hydroxy-11,12-(isopropylidenedioxy)octadeca-9,15 -dienoate ((-)-9). Acidic hydrolysis, then saponification afforded (11R,12S,13S,9Z,15Z)-11,12,13-trihydroxyoctadeca-9, 15-dienoic acid (1).