Magnesium bromide-promoted addition of heterosubstituted methylketene silyl acetals to alkoxy aldehydes. Diastereoselective synthesis of 3,4-syn-2-methylene- and 2-(alkoxymethyl)-3-hydroxy-4-alkoxy esters
The catalytic osmylation of electron-poor allylic ethers and alcohols was studied. In the case of γ-alkoxy E-enoates reaction selectivity was found to range from 2:1 to 8:1 in favor of the arabino (2,3-syn - 3,4-anti) product, regardless of the double bond substitution. Lower (if any) selectivity was found for the Z-isomers. On the contrary, 2-Mthylene-3-hydroxy esters were osmylated with virtually
Lewis acid promoted aldol additions of α-thiosilylketeneacetals to α-alkoxy aldehydes: diastereoselective synthesis of -α-methylene-β-hydroxy-∂-alkoxy esters.
MgBr2 mediated addition of Methyl α-methylthio propionate silylketene acetal to α and α,β-alkoxy aldehydes is highly 3,4 syn-selective (18:1). syn-α- methylene-β- hydroxy-∂-alkoxy esters (6) and (8) are synthesized.