A Novel Synthesis of syn and anti (beta)-Hydroxy Dithioacetals, Masked Cross-Aldols between Aldehydes

Ketene dithioacetals readily reacted with aldehydes in the presence of a Lewis acid such as BF3·OEt2 or TMSOTf to generate the cationic adducts, which in turn reacted with NaAlH2(OCH2CH2OCH3)2, leading to the corresponding (beta)-hydroxy dithioacetals, masked cross-aldols between aldehydes. Each diastereomer was selectively obtained by choosing the appropriate Lewis acid and substituents on the sulfur atoms of the ketene dithioacetals.