MgBr2-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

Article abstract of DOI:10.1021/jo00381a029

The MgBr2-mediated addition of 2- or 3-(methylthio)-substituted ketene silyl acetals 3 and 4 to α-alkoxy and α,β-dialkoxy aldehydes, followed by oxidation and elimination of methanesulfenic acid, gave 3,4-syn 2-methylene-3-hydroxy-4-alkoxy esters 9 and 11 with very high stereoselectivity (up to 100:1) and in good chemical yields.The same diastereofacial selection is at work in the analogous additions of <(benzyloxy)methyl>ketene methyl silyl acetal 5, which affords 3,4-syn 2-<(benzyloxy)methyl>-3-hydroxy-4-alkoxy esters 12-15.