Stereoselective synthesis of substituted ketopyranose subunits of polyketide natural products by intramolecular alkoxycarbonylation of δ-alkynyl alcohols

Upon treatment with 5 mol% Pd(MeCN)2Cl2 in methanol containing 1.1–1.5 equiv. of p-benzoquinone under 1 atm of CO, δ-hydroxy alkynes are converted to methyl ketopyranosides with excellent stereoselectivity. The reaction proceeds by sequential intramolecular alkoxypalladation of the alkyne followed by CO insertion and methanolysis, then an ensuing Pd+2-catalyzed 1,4-addition of methanol to the intermediate conjugated ester.