Total synthesis and structural elucidation of (-)-maurenone

The total synthesis of (2S,3S)-2,3-dihydro-6-[(YS, 2'R)-2-hydroxy-1-methylbutyl]-3,5-dimethyl-2-[(I Is)1-methylpropyl]-4H-pyran-4-one (3), the (-)enantiomer of the marine polypropionate. maurenone, was achieved in nine linear steps (13% overall yield) from (R)-2-benzylpentaii-3-one ((R)-14) and (R)-2benzoyloxypentan-3-one ((R)-15). Key fragments were synthesized using highly diastereoselective syn and anti boron aldol reactions and were coupled using a lithium-mediated aldol reaction. Trifluoroacetic acid-promoted cyclization/dehydration was then used to install the gamma-dihydropyrone ring. Eight isomers of one enantiomeric series were synthesized by coupling, two ketones with each of four aldehydes. Comparison of the C-13 NMR data for the eight isomers with that reported for maurenone established the relative stereochemistry of the natural product.