Total synthesis of (-)- and (+)-membrenone C

[GRAPHICS] A synthesis of the polypropionate marine defense substance (+)-membrenone C and its enantiomer that starts from (S)-2-methyl-3-(tert-butyldimethylsilyloxy)propanal is described. Key steps include (1) additions of chiral allenylmetal reagents to effect both chain homologation and the concomitant introduction of four stereo centers, (2) a bis-intramolecular hydrosilylation-oxidation sequence to install beta-hydroxy ketone subunits, and (3) a bis-intramolecular aldol reaction to construct the two dihydropyrone termini.