Iterative Polyketide Synthesis via a Consecutive Carbonyl-Protecting Strategy

To address the difficulty in protecting a beta-polycarbonyl compound, a method for the sequential protection of elongating carbonyl groups was demonstrated. The iterative chain elongation of a carboxylic acid with malonic acid half thioester followed by the protection of the resulting beta-ketothioester was performed via the stepwise formation of an isoxazole ring using an O-protected oxime functionality. Yangonin and isosakuranetin were synthesized according to this procedure.