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

Upon treatment with 5 mol% Pd(MeCN)(2)Cl-2 in methanol containing 1.1-1.5 e quiv. of p-benzoquinone under 1 atm of CO, delta-hydroxy alkynes are conver ted to methyl ketopyranosides with excellent stereoselectivity. The reactio n proceeds by sequential intramolecular alkoxypalladation of the alkyne fol lowed by CO insertion and methanolysis, then an ensuing Pd+2-catalyzed 1,4- addition of methanol to the intermediate conjugated ester. (C) 2000 Elsevie r Science Ltd. All rights reserved.