Direct access to furanosidic eight-membered ulosonic esters from cis-α,β-epoxy aldehydes

Direct access to bicyclic precursors of octulosonic acids is achieved by treatment of differentially (or not) protected gamma,delta-bis(silyloxy) cis-alpha,beta-epoxy aldehydes with ethyl 2-(trimethylsilyloxy) -2-propenoate in the presence of boron trifluoride-diethyl ether. An X-ray crystallographic structure of a bicycle (compound 33a) was obtained and used to determine the absolute configurations of the different stereogenic centers and thus the diastereoselective preference of the aldol reaction (syn) and the regioselectivity of the epoxide ring-opening (C-6 atom). Functionalization and opening of the bicyclic compound to afford octulosonic analogues in their furanoside forms was studied. An octulosonic 8-phosphate analogue has been synthesized. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).