Direct Access to Furanosidic Eight‐Membered Ulosonic Esters from cis‐α,β‐Epoxy Aldehydes

Abstract

Direct access to bicyclic precursors of octulosonic acids is achieved by treatment of differentially (or not) protected γ,δ‐bis(silyloxy) cis‐α,β‐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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Stereochemistry and Mechanistic Study of Intramolecular PdII‐Catalyzed Oxypalladation and 1,3‐Chirality‐Transfer Reactions

“…Monoprotection of the primary alcohol function of 16 with TBDMSCl followed by the (second) protection of the secondary alcohol with TBDPSCl gave 18 in 77 % yield in two steps. Selective deprotection of the TBDMS ether13 by treatment with BF 3 ⋅OEt 2 afforded 19 in 92 % yield. Swern oxidation and subsequent Horner–Wadsworth–Emmons reaction with triethyl phosphonoacetate gave 21 in 88 % yield in two steps.…”

Synthesis of 3-deoxy-2-uloses via the indium-mediated allylation reaction

“…2,3-O-Isopropylidene-d-glyceraldehyde (17) has been synthesized from d-mannitol via a known isopropylideneprotection procedure [27] and subsequent oxidative diol cleavage [28]. During the indium-mediated allylation, the absolute configuration of the newly formed stereocenter at position C-4 is influenced by the presence or absence of a chelating group in α-position to the reacting carbonyl function.…”

A versatile route to polythiophenes with functional pendant groups using alkyne chemistry

“…The synthesis started from economically available D-mannitol diketal, 1,2:5,6-bis-O-(1-methylethylidene)-D-mannitol which can be obtained via the hydrogenation of common table sugar [32]. Oxidation of this diketal by NaIO 4 led to glyceraldehyde [33], which was transformed into the dibromoolefin 5 by Corey–Fuchs reaction. Dibromoolefin 5 was dehalogenated by adding 2 equivalents of n -butyllithium to produce 4-ethynyl-2,2-dimethyl-1,3-dioxolane 6 , which was deprotected in acid to give ethynyldiol 7 .…”