Stereoselective synthesis of thiochromenes via intramolecular tandem thio-Michael addition of in situ generated α,β-unsaturated aldehydes.

An efficient and highly stereoselective strategy for the synthesis of 2,3-substituted thiochromenes having a complex and easily transformable group at the stereogenic center has been developed via a tandem thio-Michael addition reaction of an in situ generated α,β-unsaturated aldehyde sugar derivative. The protocol is superior to reported protocols in that the carbohydrate-derived substituent at the stereogenic center of the thiochromene is versatile and is amenable for further transformation.

Epoxidation-alcoholysis of cyclic enol ethers catalyzed by Ti(OiPr)4 or Venturello's peroxophosphotungstate complex.

Venturello's peroxophosphotungstate compound and Ti(O(i)Pr)(4) were successfully used as catalysts for the epoxidation-alcoholysis of various dihydropyrans and dihydrofuran using H(2)O(2) as the oxidant. Different alcohols can be used as solvents and nucleophiles, resulting in hydroxy ether products with varying alkoxy groups. The Venturello compound can also be used as catalyst in a biphasic conversion of dihydropyran, in which long chain alcohols or fatty acids are incorporated in the hydroxy ether products with high yield and (stereo)selectivity.

Synthesis of structures corresponding to the capsular polysaccharide of Neisseria meningitidis group A.

Four differently substituted trimers of the CPS repeating unit have been synthesised in order to investigate the dependence on oligosaccharide size, acetylation and mode of phosphorylation of glycoconjugate vaccines against Neisseria meningitidis group A. A spacer-containing starting monomer, a H-phosphonate elongating monomer and a 6-O-phosphorylated H-phosphonate cap monomer have been synthesised and coupled together to afford, after deprotection, the target trimer structures differing in their acetylation and phosphorylation substitution pattern.