Highly Stereoselective Coupling Reaction of Acrolein or Vinyl Ketone with Aldehydes

Treatment of acrolein with a TiCl₄−<i>n</i>-Bu₄NI mixed reagent in the presence of 2 equiv of aldehydes provided 4-hydroxy-1,3-dioxane derivatives in good yields with high stereoselectivities. The use of vinyl ketones instead of acrolein afforded aldol-type adducts with high syn selectivities.