Stereoselective synthesis of substituted ketopyranose subunits of polyketide natural products by intramolecular alkoxycarbonylation of δ-alkynyl alcohols
摘要:
Upon treatment with 5 mol% Pd(MeCN)(2)Cl-2 in methanol containing 1.1-1.5 equiv. of p-benzoquinone under 1 atm of CO, delta-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. (C) 2000 Elsevier Science Ltd. All rights reserved.
A macrolactonisation approach to the cembrane carbocycle of bielschowskysin
摘要:
By judicious choice of a conformationally constraining unit to predispose cyclisation to a 15-membered ring, we present a straightforward strategy to a cembranolide precursor of bielschowskysin by the Sonogashira coupling of two readily prepared fragments (from D-glucose and L-malic acid) followed by a facile beta-acylketene macrolactonisation reaction. (C) 2013 Elsevier Ltd. All rights reserved.