Stereochemically rich pentaketides from bis(isoxazolines): a general strategy for efficient polyketide synthesis.

[reaction: see text] A strategy based on diastereoselective dipolar cycloaddition reaction of nitrile oxides and allylic alcoholates has been applied to the synthesis of bis(isoxazolines) that are precursors to polyketide fragments. These intermediates can be elaborated into protected polyols by chemoselective reductive opening of each isoxazoline sequentially or, alternatively, both simultaneously, potentially providing access to all stereoisomers of this carbon skeleton.